View Full Version : [SOLVED] High temperature superconductors
Hans Aberg
May3-04, 01:32 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nWhat is the highest known temperature of superconductors these days?\n\nHans Aberg\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>What is the highest known temperature of superconductors these days?
Hans Aberg
Igor Khavkine
May4-04, 03:05 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>haberg.not.this@matematik.su.se (Hans Aberg) wrote in message news:<haberg.not.this-0305041935390001@du129-86.ppp.su-anst.tninet.se>...\n> What is the highest known temperature of superconductors these days?\n\nThe ambient pressure record is 138K. It is held by\nHg_{1-x} Tl_x Ba_2 Ca_2 Cu_3 O_{8.33}, also referred to\nas Hg-1223. Under pressures of about 300 000 atm, the transition\ntemperature goes up to 160K. This is the current world record.\n\nhttp://www.ceramics.nist.gov/srd/hts/A00373.htm\n\nHope this helps,\n\nIgor\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>haberg.not.this@matematik.su.se (Hans Aberg) wrote in message news:<haberg.not.this-0305041935390001@du129-86.ppp.su-anst.tninet.se>...
> What is the highest known temperature of superconductors these days?
The ambient pressure record is 138K. It is held by
Hg_{1-x} Tl_x Ba_2 Ca_2 Cu_3 O_{8.33}, also referred to
as Hg-1223. Under pressures of about 300 000 atm, the transition
temperature goes up to 160K. This is the current world record.
http://www.ceramics.nist.gov/srd/hts/A00373.htm
Hope this helps,
Igor
Dirk Bruere at Neopax
May6-04, 10:46 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Hans Aberg wrote:\n\n> What is the highest known temperature of superconductors these days?\n>\n> Hans Aberg\n\n135K\n\n--\nDirk\n\nThe Consensus:-\nThe political party for the new millenium\nhttp://www.theconsensus.org\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Hans Aberg wrote:
> What is the highest known temperature of superconductors these days?
>
> Hans Aberg
135K
--
Dirk
The Consensus:-
The political party for the new millenium
http://www.theconsensus.org
alistair
May10-04, 05:02 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n\nWhy does increasing the pressure increase the temperature at which materials\ncan be superconductors? And could sound waves passed through\na superconductor raise the temperature at which it superconducts\ngiven that sound causes regions of high pressure in solids?\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Why does increasing the pressure increase the temperature at which materials
can be superconductors? And could sound waves passed through
a superconductor raise the temperature at which it superconducts
given that sound causes regions of high pressure in solids?
Igor Khavkine
May11-04, 07:04 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nalistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405061532.3d60059b@posting.google. com>...\n> Why does increasing the pressure increase the temperature at which materials\n> can be superconductors? And could sound waves passed through\n> a superconductor raise the temperature at which it superconducts\n> given that sound causes regions of high pressure in solids?\n\nI think a naive argument would go as follows. In the standard theory of\nsuperconductivity (BCS theory), the transition temperature is proportional\nto exp(-1/g), where g is a dimensionless constant proportional to both\nthe density of states of the electrons at the Fermi surface and to the\nstrength of the electron-phonon coupling. Simply speaking, putting pressure\non a solid decreases its volume and thus increases the density of states,\nwhich in turn increases g, which in turn increases the transition temperature.\n\nIn high temperature superconductors, the BCS electron-phonon theory does\nnot seem to appy directly. However, many people believe that electron pairing\ninto Cooper pairs still takes place, although phonons may not be responsible\nfor the attractive interaction between them. In this case the constant\ng should still be proportional to the charge carrier density of states\nat the Fermi surface, hence pressure can still increase the transition\ntemperature.\n\nAs for the effect of sound, I doubut it would affect the properties of\nthe material much. I would guess that pressure produced by sound waves\nin solids are is tiny compared to the amount of hydrostatic pressure\nneeded to change the transition temperature. And if you could inject\na sound wave with a great enough amplitude, the crystal would most\nprobably not be able to sustain it.\n\nThis argument is a product of a moment\'s reflection and I don\'t\nhave solid references to back it up. So I hope someone corrects me\nif I\'m wrong.\n\nHope this helps.\n\nIgor\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405061532.3d60059b@posting.google.com>...
> Why does increasing the pressure increase the temperature at which materials
> can be superconductors? And could sound waves passed through
> a superconductor raise the temperature at which it superconducts
> given that sound causes regions of high pressure in solids?
I think a naive argument would go as follows. In the standard theory of
superconductivity (BCS theory), the transition temperature is proportional
to \exp(-1/g), where g is a dimensionless constant proportional to both
the density of states of the electrons at the Fermi surface and to the
strength of the electron-phonon coupling. Simply speaking, putting pressure
on a solid decreases its volume and thus increases the density of states,
which in turn increases g, which in turn increases the transition temperature.
In high temperature superconductors, the BCS electron-phonon theory does
not seem to appy directly. However, many people believe that electron pairing
into Cooper pairs still takes place, although phonons may not be responsible
for the attractive interaction between them. In this case the constant
g should still be proportional to the charge carrier density of states
at the Fermi surface, hence pressure can still increase the transition
temperature.
As for the effect of sound, I doubut it would affect the properties of
the material much. I would guess that pressure produced by sound waves
in solids are is tiny compared to the amount of hydrostatic pressure
needed to change the transition temperature. And if you could inject
a sound wave with a great enough amplitude, the crystal would most
probably not be able to sustain it.
This argument is a product of a moment's reflection and I don't
have solid references to back it up. So I hope someone corrects me
if I'm wrong.
Hope this helps.
Igor
alistair
May12-04, 05:05 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nThanks Igor -your post was very helpful.\n\nPresumably, if positrons were fed into a superconductor,\ntheir positive electric charge could hold electron pairs together\nat higher temperatures?\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Thanks Igor -your post was very helpful.
Presumably, if positrons were fed into a superconductor,
their positive electric charge could hold electron pairs together
at higher temperatures?
Igor Khavkine
May12-04, 05:28 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405111151.1d88a2ce@posting.google. com>...\n> Thanks Igor -your post was very helpful.\n>\n> Presumably, if positrons were fed into a superconductor,\n> their positive electric charge could hold electron pairs together\n> at higher temperatures?\n\nIf positrons were to be injected into any material, all they would\ndo is annihilate some electrons and produce some photons. Believe\nit or not, this technique is actually useful for styding the distribution\nof electron states inside a material. But it has nothing to do with\nsuperconductivity.\n\nIgor\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405111151.1d88a2ce@posting.google.com>...
> Thanks Igor -your post was very helpful.
>
> Presumably, if positrons were fed into a superconductor,
> their positive electric charge could hold electron pairs together
> at higher temperatures?
If positrons were to be injected into any material, all they would
do is annihilate some electrons and produce some photons. Believe
it or not, this technique is actually useful for styding the distribution
of electron states inside a material. But it has nothing to do with
superconductivity.
Igor
Uncle Al
May12-04, 05:28 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>alistair wrote:\n>\n> Thanks Igor -your post was very helpful.\n>\n> Presumably, if positrons were fed into a superconductor,\n> their positive electric charge could hold electron pairs together\n> at higher temperatures?\n\nPresumably, positrons injectd into a superconductor will annihilate\nwith electrons to give 511 keV photons, within nanoseconds. If they\npair to positronium, the singlet has a half-life of 10(-10) seconds\nand the triplet 10^(-7) seconds.\n\nhttp://rockpile.phys.virginia.edu/mod23.pdf\n\n--\nUncle Al\nhttp://www.mazepath.com/uncleal/qz.pdf\nhttp://www.mazepath.com/uncleal/eotvos.htm\n(Do something naughty to physics)\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair wrote:
>
> Thanks Igor -your post was very helpful.
>
> Presumably, if positrons were fed into a superconductor,
> their positive electric charge could hold electron pairs together
> at higher temperatures?
Presumably, positrons injectd into a superconductor will annihilate
with electrons to give 511 keV photons, within nanoseconds. If they
pair to positronium, the singlet has a half-life of 10(-10) seconds
and the triplet 10^(-7) seconds.
http://rockpile.phys.virginia.edu/mod23.pdf
--
Uncle Al
http://www.mazepath.com/uncleal/qz.pdf
http://www.mazepath.com/uncleal/eotvos.htm
(Do something naughty to physics)
Igor Khavkine
May14-04, 04:08 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>k_igor_k@lycos.com (Igor Khavkine) wrote in message news:<f1ac2e6e.0405102119.46fb470f@posting.google. com>...\n> alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405061532.3d60059b@posting.google. com>...\n> > Why does increasing the pressure increase the temperature at which materials\n> > can be superconductors? And could sound waves passed through\n> > a superconductor raise the temperature at which it superconducts\n> > given that sound causes regions of high pressure in solids?\n>\n> I think a naive argument would go as follows. In the standard theory of\n> superconductivity (BCS theory), the transition temperature is proportional\n> to exp(-1/g), where g is a dimensionless constant proportional to both\n> the density of states of the electrons at the Fermi surface and to the\n> strength of the electron-phonon coupling. Simply speaking, putting pressure\n> on a solid decreases its volume and thus increases the density of states,\n> which in turn increases g, which in turn increases the transition temperature.\n>\n> In high temperature superconductors, the BCS electron-phonon theory does\n> not seem to appy directly. However, many people believe that electron pairing\n> into Cooper pairs still takes place, although phonons may not be responsible\n> for the attractive interaction between them. In this case the constant\n> g should still be proportional to the charge carrier density of states\n> at the Fermi surface, hence pressure can still increase the transition\n> temperature.\n\n> This argument is a product of a moment\'s reflection and I don\'t\n> have solid references to back it up. So I hope someone corrects me\n> if I\'m wrong.\n\nAlas, as most of such arguments go, it\'s not entirely correct. I should\nhave also mentioned that in BCS theory, the transition temperature is\nproportional to the so-called Debye temperature. Both it and the value\nof g depend on the phonon spectrum and structural properties of the\nmaterial. High pressure can change structural properties and even\ninduce structural transitions (change from one crystal lattice type\nto another), so it definitely affects the superconducting transition\ntemperature. However, the effect itself is difficult to predict a priori.\nFor example, this experiment reports decreasing transition temperature\nwith increasing pressure cond-mat/0105475.\n\nAs for high temperature superconductors, people don\'t actually know\nwhat makes the transition temperature increase under pressure. But\nit is belived that the layered nature of these materials is important,\nespecially when pressure is applied to bring the layers closer together.\n\nIgor\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>k_{igor_k}@lycos.com (Igor Khavkine) wrote in message news:<f1ac2e6e.0405102119.46fb470f@posting.google.com>...
> alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405061532.3d60059b@posting.google.com>...
> > Why does increasing the pressure increase the temperature at which materials
> > can be superconductors? And could sound waves passed through
> > a superconductor raise the temperature at which it superconducts
> > given that sound causes regions of high pressure in solids?
>
> I think a naive argument would go as follows. In the standard theory of
> superconductivity (BCS theory), the transition temperature is proportional
> to \exp(-1/g), where g is a dimensionless constant proportional to both
> the density of states of the electrons at the Fermi surface and to the
> strength of the electron-phonon coupling. Simply speaking, putting pressure
> on a solid decreases its volume and thus increases the density of states,
> which in turn increases g, which in turn increases the transition temperature.
>
> In high temperature superconductors, the BCS electron-phonon theory does
> not seem to appy directly. However, many people believe that electron pairing
> into Cooper pairs still takes place, although phonons may not be responsible
> for the attractive interaction between them. In this case the constant
> g should still be proportional to the charge carrier density of states
> at the Fermi surface, hence pressure can still increase the transition
> temperature.
> This argument is a product of a moment's reflection and I don't
> have solid references to back it up. So I hope someone corrects me
> if I'm wrong.
Alas, as most of such arguments go, it's not entirely correct. I should
have also mentioned that in BCS theory, the transition temperature is
proportional to the so-called Debye temperature. Both it and the value
of g depend on the phonon spectrum and structural properties of the
material. High pressure can change structural properties and even
induce structural transitions (change from one crystal lattice type
to another), so it definitely affects the superconducting transition
temperature. However, the effect itself is difficult to predict a priori.
For example, this experiment reports decreasing transition temperature
with increasing pressure http://www.arxiv.org/abs/cond-mat/0105475.
As for high temperature superconductors, people don't actually know
what makes the transition temperature increase under pressure. But
it is belived that the layered nature of these materials is important,
especially when pressure is applied to bring the layers closer together.
Igor
alistair
May17-04, 08:18 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Graphite conducts well because of layers of hexagonally arranged\ncarbon atoms with overlapping p orbitals. Maybe p orbitals overlap\nmore\nwhen pressure is applied to superconducting materials. I\'ve also read\nthat in some high temperature superconductors there are cooper pairs\nin existence even before the transition temperature is reached.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Graphite conducts well because of layers of hexagonally arranged
carbon atoms with overlapping p orbitals. Maybe p orbitals overlap
more
when pressure is applied to superconducting materials. I've also read
that in some high temperature superconductors there are cooper pairs
in existence even before the transition temperature is reached.
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>An article about one interesting work on superconductors can be found\nhere http://www.physorg.com/news60.html\nIt\'s about YBa2Cu3O6.9 and it\'s superconductivity mechanism.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>An article about one interesting work on superconductors can be found
here http://www.physorg.com/news60.html
It's about YBa2Cu3O6.9 and it's superconductivity mechanism.
Igor Khavkine
May20-04, 11:51 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405170315.568054bb@posting.google. com>...\n> Graphite conducts well because of layers of hexagonally arranged\n> carbon atoms with overlapping p orbitals. Maybe p orbitals overlap\n> more\n> when pressure is applied to superconducting materials.\n\nI\'m afraid the crystal structure of most high Tc superconductors is\nmore complicated than that of graphite (dozens of atoms per site in some\ncases, plus disorder through doping). The copper-oxygen planes that\nare believed to be responsible for superconductivity are separated by\nmany insulating layers layers. So there might not be much overlap between\natomic orbitals between separated Cu-O planes. However, electrons can\nstill tunnel through the insulating layers. This tunneling is believed\nto affect superconductivity, but it is not well understood how.\n\n> I\'ve also read\n> that in some high temperature superconductors there are cooper pairs\n> in existence even before the transition temperature is reached.\n\nThis is the so-called preformed pairs hypothesis. In this scenario,\nelectrons bind into cooper pairs at one temperature, and condense\na la BEC at a lower temperature, thus creating a superconductor.\nSome people believe that this scenario is responsible for the presence\nof the mysterious pseudogap region in the phase diagram of cuprate\n(Cu-O based) superconductors, but so far evidence is inconclusive.\n\nIgor\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405170315.568054bb@posting.google.com>...
> Graphite conducts well because of layers of hexagonally arranged
> carbon atoms with overlapping p orbitals. Maybe p orbitals overlap
> more
> when pressure is applied to superconducting materials.
I'm afraid the crystal structure of most high Tc superconductors is
more complicated than that of graphite (dozens of atoms per site in some
cases, plus disorder through doping). The copper-oxygen planes that
are believed to be responsible for superconductivity are separated by
many insulating layers layers. So there might not be much overlap between
atomic orbitals between separated Cu-O planes. However, electrons can
still tunnel through the insulating layers. This tunneling is believed
to affect superconductivity, but it is not well understood how.
> I've also read
> that in some high temperature superconductors there are cooper pairs
> in existence even before the transition temperature is reached.
This is the so-called preformed pairs hypothesis. In this scenario,
electrons bind into cooper pairs at one temperature, and condense
a la BEC at a lower temperature, thus creating a superconductor.
Some people believe that this scenario is responsible for the presence
of the mysterious pseudogap region in the phase diagram of cuprate
(Cu-O based) superconductors, but so far evidence is inconclusive.
Igor
alistair
May20-04, 03:42 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>This is a great site for superconductors - must be one of the best\nscience sites on the web: www.superconductors.org\n\nApparently even a normally good insulator like a diamond shows\nevidence of\nsuperconductivity at high pressure.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>This is a great site for superconductors - must be one of the best
science sites on the web: www.superconductors.org
Apparently even a normally good insulator like a diamond shows
evidence of
superconductivity at high pressure.
alistair
May22-04, 04:48 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>The copper-oxygen planes that\nare believed to be responsible for superconductivity are separated by\nmany insulating layers layers. So there might not be much overlap\nbetween\natomic orbitals between separated Cu-O planes. However, electrons can\nstill tunnel through the insulating layers. This tunneling is believed\nto affect superconductivity, but it is not well understood how.\n\n\n\nIn type 1 superconductors cooper pairs suddenly form as the transition\ntemperature is reached and there is a rapid change in\nconductivity.Type 2 superconductors show a gradual change from normal\nto super conductivity .Perhaps type 2 superconductors conduct\nincreasingly better as the temperature changes because electron\nmovement through a lattice causes the formation of "groups" of atoms\nin the lattice which at a slightly lower temperature can then cause\nfurther electron movements in such a way as to increase the formation\nof yet more "groups" and so on.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>The copper-oxygen planes that
are believed to be responsible for superconductivity are separated by
many insulating layers layers. So there might not be much overlap
between
atomic orbitals between separated Cu-O planes. However, electrons can
still tunnel through the insulating layers. This tunneling is believed
to affect superconductivity, but it is not well understood how.
In type 1 superconductors cooper pairs suddenly form as the transition
temperature is reached and there is a rapid change in
conductivity.Type 2 superconductors show a gradual change from normal
to super conductivity .Perhaps type 2 superconductors conduct
increasingly better as the temperature changes because electron
movement through a lattice causes the formation of "groups" of atoms
in the lattice which at a slightly lower temperature can then cause
further electron movements in such a way as to increase the formation
of yet more "groups" and so on.
Igor Khavkine
May23-04, 03:14 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405201457.765b7191@posting.google. com>...\n\n> In type 1 superconductors cooper pairs suddenly form as the transition\n> temperature is reached and there is a rapid change in\n> conductivity.Type 2 superconductors show a gradual change from normal\n> to super conductivity .Perhaps type 2 superconductors conduct\n> increasingly better as the temperature changes because electron\n> movement through a lattice causes the formation of "groups" of atoms\n> in the lattice which at a slightly lower temperature can then cause\n> further electron movements in such a way as to increase the formation\n> of yet more "groups" and so on.\n\nThis kind of formation of clusters of particles that are in one phase\nwhile they are surrounded by a sea of particles in another phase is\ncharacteristic of first order phase transitions, such as the water-vapor\ntransition. This behavior is due to the thermodynamic stability (or rather\nmetastability) of both phases near the critical point.\n\nHowever, transition into the superconducting state is second order,\nmeaning that at the critical pint the sample changes completely into\nthe new phase. This happens because thermodynamically, only the new\nphase is stable while the old one is not.\n\nI am not aware of any cases where the normal state-superconductor transition\nis first order, so neither type I nor II superconductors show a slow\nand gradual transition. Perhaps you are referring to the transition\nfrom superconductor to normal state when a magnetic field is applied.\nFor type II superconductors, there exists an intermediate state\nwhere the supercunducting bulk is pierced by tubes of normal metal\nthat allow through magnetic flux. The transitions between superconducting\nand intermediate as well as intermediate and normal states are still\nsecond order.\n\nHope this helps.\n\nIgor\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405201457.765b7191@posting.google.com>...
> In type 1 superconductors cooper pairs suddenly form as the transition
> temperature is reached and there is a rapid change in
> conductivity.Type 2 superconductors show a gradual change from normal
> to super conductivity .Perhaps type 2 superconductors conduct
> increasingly better as the temperature changes because electron
> movement through a lattice causes the formation of "groups" of atoms
> in the lattice which at a slightly lower temperature can then cause
> further electron movements in such a way as to increase the formation
> of yet more "groups" and so on.
This kind of formation of clusters of particles that are in one phase
while they are surrounded by a sea of particles in another phase is
characteristic of first order phase transitions, such as the water-vapor
transition. This behavior is due to the thermodynamic stability (or rather
metastability) of both phases near the critical point.
However, transition into the superconducting state is second order,
meaning that at the critical pint the sample changes completely into
the new phase. This happens because thermodynamically, only the new
phase is stable while the old one is not.
I am not aware of any cases where the normal state-superconductor transition
is first order, so neither type I nor II superconductors show a slow
and gradual transition. Perhaps you are referring to the transition
from superconductor to normal state when a magnetic field is applied.
For type II superconductors, there exists an intermediate state
where the supercunducting bulk is pierced by tubes of normal metal
that allow through magnetic flux. The transitions between superconducting
and intermediate as well as intermediate and normal states are still
second order.
Hope this helps.
Igor
Dirk Bruere at Neopax
May24-04, 04:31 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n\nalistair wrote:\n\n> This is a great site for superconductors - must be one of the best\n> science sites on the web: www.superconductors.org\n>\n> Apparently even a normally good insulator like a diamond shows\n> evidence of\n> superconductivity at high pressure.\n\nWhat I did not know, and found fascinating, is the class of materials known as\nultraconductors, with conductivities up to a million times better than copper at\nroom temp.\nhttp://www.superconductors.org/ultra.htm\n\nIf only I could get some of that in bulk wire form, cheaply...\n\n--\nDirk\n\nThe Consensus:-\nThe political party for the new millenium\nhttp://www.theconsensus.org\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair wrote:
> This is a great site for superconductors - must be one of the best
> science sites on the web: www.superconductors.org
>
> Apparently even a normally good insulator like a diamond shows
> evidence of
> superconductivity at high pressure.
What I did not know, and found fascinating, is the class of materials known as
ultraconductors, with conductivities up to a million times better than copper at
room temp.
http://www.superconductors.org/ultra.htm
If only I could get some of that in bulk wire form, cheaply...
--
Dirk
The Consensus:-
The political party for the new millenium
http://www.theconsensus.org
alistair
May24-04, 04:31 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n\n\nelectrons can\nstill tunnel through the insulating layers. This tunneling is believed\nto affect superconductivity, but it is not well understood how\n\nIf electrons start tunnelling at one end of a conducting layer and\nthey spend time between conducting layers then they are leaving a\ndefecit of negative charge in the conducting layers and creating a\ndiffusion gradient that can make a current move across the conducting\nlayer.As the temperature is lowered\nand the insulating layers increase their density,would the number of\ntunneling\nelectrons increase- perhaps the insulators lower their resistance with\ndecreasing temperature - and increase the current?\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>electrons can
still tunnel through the insulating layers. This tunneling is believed
to affect superconductivity, but it is not well understood how
If electrons start tunnelling at one end of a conducting layer and
they spend time between conducting layers then they are leaving a
defecit of negative charge in the conducting layers and creating a
diffusion gradient that can make a current move across the conducting
layer.As the temperature is lowered
and the insulating layers increase their density,would the number of
tunneling
electrons increase- perhaps the insulators lower their resistance with
decreasing temperature - and increase the current?
alistair
May24-04, 04:31 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nIs there a difference in temperature between the conducting and\ninsulating layers of type 2 superconductors like the cuprates that\ncould lead to one type of layer being put in a state of tension or\ncompression compared to the other.This would distort orbitals and\nmight result in electrons moving through the insulating layer and\nhelping to form "holes" in the conducting layer for cooper pairs and\neven enable electrons to pass from one layer to another to form cooper\npairs.Presumably as the temperature is lowered the effect would get\nmagnified.If high pressure was applied to a type 2 superconductor this\ncould increase the tension/compression in the layers and cause the\nsame effects.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Is there a difference in temperature between the conducting and
insulating layers of type 2 superconductors like the cuprates that
could lead to one type of layer being put in a state of tension or
compression compared to the other.This would distort orbitals and
might result in electrons moving through the insulating layer and
helping to form "holes" in the conducting layer for cooper pairs and
even enable electrons to pass from one layer to another to form cooper
pairs.Presumably as the temperature is lowered the effect would get
magnified.If high pressure was applied to a type 2 superconductor this
could increase the tension/compression in the layers and cause the
same effects.
Joseph.D.Warner
May25-04, 01:31 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>alistair wrote:\n> Is there a difference in temperature between the conducting and\n> insulating layers of type 2 superconductors like the cuprates <snip>\n\nNo. If you look up papers on the fermi surface of the cuprate compounds\nyou\'ll see why the critical current along the basal plane is higher than\nthat perpendicular to it. Some of the measurement have the fermi surface\nbarely touching ( or may have a very slight bandgap) and be elongated\nsurfaces in the basal plane of k-space.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair wrote:
> Is there a difference in temperature between the conducting and
> insulating layers of type 2 superconductors like the cuprates <snip>
No. If you look up papers on the fermi surface of the cuprate compounds
you'll see why the critical current along the basal plane is higher than
that perpendicular to it. Some of the measurement have the fermi surface
barely touching ( or may have a very slight bandgap) and be elongated
surfaces in the basal plane of k-space.
Joseph.D.Warner
May25-04, 01:31 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Igor Khavkine wrote:\n> alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405201457.765b7191@posting.google. com>...\n>\n\n>\n> This kind of formation of clusters of particles that are in one phase\n> while they are surrounded by a sea of particles in another phase is\n> characteristic of first order phase transitions, such as the water-vapor\n> transition. This behavior is due to the thermodynamic stability (or rather\n> metastability) of both phases near the critical point.\n\nIn second order phase transistions as you approach the transistion from\nhigher temperature the order parameter versus position begins to\nflucuate rapidly and the regions of order grows as 1/(T-Tc)^x where T is\nthe temperature and Tc is the transistion temperature and x is an\nuniversal exponent that depends on the dimensionality of the material.\n\nThis is manifested in physical measurements such as heat capacity and\nmagneti susceptibility (for magnetic systems).\n\nIn first order phase transistion the region of order above Tc remains of\nzero volume until you get to Tc. Then the crystal oders and the order\nparameter is 1 everywhere. This discontinuous behaviour is seen again in\nheat capacity, volume and such. For heat capacity you see a delta\nfunction at Tc and the derivative of the volume with temperature.\n\nOf course as one measures the properties of the material these functions\nare spead out due to noise in the measurement system and temperature\ngradients in the sample.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Igor Khavkine wrote:
> alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405201457.765b7191@posting.google.com>...
>
>
> This kind of formation of clusters of particles that are in one phase
> while they are surrounded by a sea of particles in another phase is
> characteristic of first order phase transitions, such as the water-vapor
> transition. This behavior is due to the thermodynamic stability (or rather
> metastability) of both phases near the critical point.
In second order phase transistions as you approach the transistion from
higher temperature the order parameter versus position begins to
flucuate rapidly and the regions of order grows as 1/(T-Tc)^x where T is
the temperature and Tc is the transistion temperature and x is an
universal exponent that depends on the dimensionality of the material.
This is manifested in physical measurements such as heat capacity and
magneti susceptibility (for magnetic systems).
In first order phase transistion the region of order above Tc remains of
zero volume until you get to Tc. Then the crystal oders and the order
parameter is 1 everywhere. This discontinuous behaviour is seen again in
heat capacity, volume and such. For heat capacity you see a \delta
function at Tc and the derivative of the volume with temperature.
Of course as one measures the properties of the material these functions
are spead out due to noise in the measurement system and temperature
gradients in the sample.
Igor Khavkine
May25-04, 03:56 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nalistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405221103.766aa7e1@posting.google. com>...\n> electrons can\n> still tunnel through the insulating layers. This tunneling is believed\n> to affect superconductivity, but it is not well understood how\n\nPlease try to make quoted text obvious and include an attribution.\n\n> If electrons start tunnelling at one end of a conducting layer and\n> they spend time between conducting layers then they are leaving a\n> defecit of negative charge in the conducting layers and creating a\n> diffusion gradient that can make a current move across the conducting\n> layer.As the temperature is lowered\n> and the insulating layers increase their density,would the number of\n> tunneling\n> electrons increase- perhaps the insulators lower their resistance with\n> decreasing temperature - and increase the current?\n\nalistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405221448.3717f27a@posting.google. com>...\n> Is there a difference in temperature between the conducting and\n> insulating layers of type 2 superconductors like the cuprates that\n> could lead to one type of layer being put in a state of tension or\n> compression compared to the other.This would distort orbitals and\n> might result in electrons moving through the insulating layer and\n> helping to form "holes" in the conducting layer for cooper pairs and\n> even enable electrons to pass from one layer to another to form cooper\n> pairs.Presumably as the temperature is lowered the effect would get\n> magnified.If high pressure was applied to a type 2 superconductor this\n> could increase the tension/compression in the layers and cause the\n> same effects.\n\nIt is a good rule of thumb to cover basic subjects before jumping to\nmore complex ones. So before trying to make guesses about the inner\nworkings of superconductors, you might want to get a bit more informed\nabout topics such as equilibrium thermodynamics, elementary quantum\nmechanics, crystal structure, band theory, etc.\n\nIf do not need more than a passing familiarity, I highly recommend\nthis site http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html\n\nNow, let me make some comments that will hopefully answer your questions:\n\n* In thermal equilibrium, there cannot be charge, thermal or other\ngradients without external fields. As for thermal gradients, even\nif they do exist, a moment\'s reflection will tell you that they\nwill not be apparent on the inter-atomic scale.\n\n* In equilibrium or steady state quantum mechanics, tunneling results\nin the electron wave functions extending into regions where they\nare classically forbidden. Think about the ground state of a single\nparticle in a double potential well. Moreover, the amplitude of the\nelectron wave function is exponentially suppressed in these regions\nas a function of the width and height of the barrier.\n\n* Applying pressure to a crystal may change the material\'s properties.\nHowever, the results are difficult to predict without involving the\ncrystal structure and some other factors in the reasoning. However,\npressure does not change the particle content and as such cannot\ncreate electrons or holes in the solid.\n\n* Insulators (or at least band insulators) do not conduct well because\nit is very costly to excite their valence electrons into motion. THis\ndoes not change even at zero temperature, so they remain insulators.\n\n* I\'m not sure why you brought up type II superconductors. It is true\nthat all high temperature superconductors are type II, but the\nconverse is not true. Type II refers to the sample\'s response to\nan external magnetic field. Type I superconductors return to the\nnormal state at a given critical magnetic field. On the other hand\ntype II materials go into a mixed state at one critical field and\nback to normal state at a second higher critical field.\n\nHope this helps.\n\nIgor\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405221103.766aa7e1@posting.google.com>...
> electrons can
> still tunnel through the insulating layers. This tunneling is believed
> to affect superconductivity, but it is not well understood how
Please try to make quoted text obvious and include an attribution.
> If electrons start tunnelling at one end of a conducting layer and
> they spend time between conducting layers then they are leaving a
> defecit of negative charge in the conducting layers and creating a
> diffusion gradient that can make a current move across the conducting
> layer.As the temperature is lowered
> and the insulating layers increase their density,would the number of
> tunneling
> electrons increase- perhaps the insulators lower their resistance with
> decreasing temperature - and increase the current?
alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405221448.3717f27a@posting.google.com>...
> Is there a difference in temperature between the conducting and
> insulating layers of type 2 superconductors like the cuprates that
> could lead to one type of layer being put in a state of tension or
> compression compared to the other.This would distort orbitals and
> might result in electrons moving through the insulating layer and
> helping to form "holes" in the conducting layer for cooper pairs and
> even enable electrons to pass from one layer to another to form cooper
> pairs.Presumably as the temperature is lowered the effect would get
> magnified.If high pressure was applied to a type 2 superconductor this
> could increase the tension/compression in the layers and cause the
> same effects.
It is a good rule of thumb to cover basic subjects before jumping to
more complex ones. So before trying to make guesses about the inner
workings of superconductors, you might want to get a bit more informed
about topics such as equilibrium thermodynamics, elementary quantum
mechanics, crystal structure, band theory, etc.
If do not need more than a passing familiarity, I highly recommend
this site http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
Now, let me make some comments that will hopefully answer your questions:
* In thermal equilibrium, there cannot be charge, thermal or other
gradients without external fields. As for thermal gradients, even
if they do exist, a moment's reflection will tell you that they
will not be apparent on the inter-atomic scale.
* In equilibrium or steady state quantum mechanics, tunneling results
in the electron wave functions extending into regions where they
are classically forbidden. Think about the ground state of a single
particle in a double potential well. Moreover, the amplitude of the
electron wave function is exponentially suppressed in these regions
as a function of the width and height of the barrier.
* Applying pressure to a crystal may change the material's properties.
However, the results are difficult to predict without involving the
crystal structure and some other factors in the reasoning. However,
pressure does not change the particle content and as such cannot
create electrons or holes in the solid.
* Insulators (or at least band insulators) do not conduct well because
it is very costly to excite their valence electrons into motion. THis
does not change even at zero temperature, so they remain insulators.
* I'm not sure why you brought up type II superconductors. It is true
that all high temperature superconductors are type II, but the
converse is not true. Type II refers to the sample's response to
an external magnetic field. Type I superconductors return to the
normal state at a given critical magnetic field. On the other hand
type II materials go into a mixed state at one critical field and
back to normal state at a second higher critical field.
Hope this helps.
Igor
alistair
May25-04, 10:01 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n\nIn thermal equilibrium, there cannot be charge, thermal or other\ngradients without external fields. As for thermal gradients, even\nif they do exist, a moment\'s reflection will tell you that they\nwill not be apparent on the inter-atomic scale.\n\n* In equilibrium or steady state quantum mechanics, tunneling results\nin the electron wave functions extending into regions where they\nare classically forbidden. Think about the ground state of a single\nparticle in a double potential well. Moreover, the amplitude of the\nelectron wave function is exponentially suppressed in these regions\nas a function of the width and height of the barrier.\n\n* Applying pressure to a crystal may change the material\'s properties.\nHowever, the results are difficult to predict without involving the\ncrystal structure and some other factors in the reasoning. However,\npressure does not change the particle content and as such cannot\ncreate electrons or holes in the solid.\n\n* Insulators (or at least band insulators) do not conduct well because\nit is very costly to excite their valence electrons into motion.\nTHis\ndoes not change even at zero temperature, so they remain insulators.\n\n* I\'m not sure why you brought up type II superconductors. It is true\nthat all high temperature superconductors are type II, but the\nconverse is not true. Type II refers to the sample\'s response to\nan external magnetic field. Type I superconductors return to the\nnormal state at a given critical magnetic field. On the other hand\ntype II materials go into a mixed state at one critical field and\nback to normal state at a second higher critical field.\n\nHope this helps.\n\nI asked the questions about superconductors to find out how different\nsuperconductors are from other materials.The web is not as informative\nas someone who knows the subject well! I understand quantum mechanics\nand\nthermodynamics etc but I never assume that they are entirely right in\ntheir current formulations because history has shown that most things\nin science change.Thanks for your answers.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>In thermal equilibrium, there cannot be charge, thermal or other
gradients without external fields. As for thermal gradients, even
if they do exist, a moment's reflection will tell you that they
will not be apparent on the inter-atomic scale.
* In equilibrium or steady state quantum mechanics, tunneling results
in the electron wave functions extending into regions where they
are classically forbidden. Think about the ground state of a single
particle in a double potential well. Moreover, the amplitude of the
electron wave function is exponentially suppressed in these regions
as a function of the width and height of the barrier.
* Applying pressure to a crystal may change the material's properties.
However, the results are difficult to predict without involving the
crystal structure and some other factors in the reasoning. However,
pressure does not change the particle content and as such cannot
create electrons or holes in the solid.
* Insulators (or at least band insulators) do not conduct well because
it is very costly to excite their valence electrons into motion.
THis
does not change even at zero temperature, so they remain insulators.
* I'm not sure why you brought up type II superconductors. It is true
that all high temperature superconductors are type II, but the
converse is not true. Type II refers to the sample's response to
an external magnetic field. Type I superconductors return to the
normal state at a given critical magnetic field. On the other hand
type II materials go into a mixed state at one critical field and
back to normal state at a second higher critical field.
Hope this helps.
I asked the questions about superconductors to find out how different
superconductors are from other materials.The web is not as informative
as someone who knows the subject well! I understand quantum mechanics
and
thermodynamics etc but I never assume that they are entirely right in
their current formulations because history has shown that most things
in science change.Thanks for your answers.
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nalistair@goforit64.fsnet.co.uk (alistair) wrote in message\n> I never assume that they are entirely right in\n> their current formulations because history has shown that most things\n> in science change.Thanks for your answers.\n\n\nThey are exactly right and history shows no such thing (at least in\nthe hard sciences). What history shows are every more encompassing and\npredictive theories.\n\nNews theories must, as a rule, contain everything in the old theory.\nMeaning; old theories are never proven wrong or changed by new\ntheories, new theories just build on old theories to expand the scope\nof our understanding.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair@goforit64.fsnet.co.uk (alistair) wrote in message
> I never assume that they are entirely right in
> their current formulations because history has shown that most things
> in science change.Thanks for your answers.
They are exactly right and history shows no such thing (at least in
the hard sciences). What history shows are every more encompassing and
predictive theories.
News theories must, as a rule, contain everything in the old theory.
Meaning; old theories are never proven wrong or changed by new
theories, new theories just build on old theories to expand the scope
of our understanding.
Dirk Bruere at Neopax
May26-04, 10:51 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nksh95 wrote:\n\n> alistair@goforit64.fsnet.co.uk (alistair) wrote in message\n>\n>>I never assume that they are entirely right in\n>>their current formulations because history has shown that most things\n>>in science change.Thanks for your answers.\n>\n>\n>\n> They are exactly right and history shows no such thing (at least in\n> the hard sciences). What history shows are every more encompassing and\n> predictive theories.\n>\n> News theories must, as a rule, contain everything in the old theory.\n> Meaning; old theories are never proven wrong or changed by new\n> theories, new theories just build on old theories to expand the scope\n> of our understanding.\n\nPtolemaic v Copernican?\nhardly one building on the other.\n\n--\nDirk\n\nThe Consensus:-\nThe political party for the new millenium\nhttp://www.theconsensus.org\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>ksh95 wrote:
> alistair@goforit64.fsnet.co.uk (alistair) wrote in message
>
>>I never assume that they are entirely right in
>>their current formulations because history has shown that most things
>>in science change.Thanks for your answers.
>
>
>
> They are exactly right and history shows no such thing (at least in
> the hard sciences). What history shows are every more encompassing and
> predictive theories.
>
> News theories must, as a rule, contain everything in the old theory.
> Meaning; old theories are never proven wrong or changed by new
> theories, new theories just build on old theories to expand the scope
> of our understanding.
Ptolemaic v Copernican?
hardly one building on the other.
--
Dirk
The Consensus:-
The political party for the new millenium
http://www.theconsensus.org
Roman Werpachowski
May29-04, 11:51 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On the Tue, 25 May 2004 06:31:59 +0000 (UTC), Joseph.D.Warner wrote:\n\n> In second order phase transistions as you approach the transistion from\n> higher temperature the order parameter versus position begins to\n> flucuate rapidly and the regions of order grows as 1/(T-Tc)^x where T is\n> the temperature and Tc is the transistion temperature and x is an\n> universal exponent that depends on the dimensionality of the material.\n>\n> This is manifested in physical measurements such as heat capacity and\n> magneti susceptibility (for magnetic systems).\n>\n> In first order phase transistion the region of order above Tc remains of\n> zero volume until you get to Tc. Then the crystal oders and the order\n> parameter is 1 everywhere. This discontinuous behaviour is seen again in\n> heat capacity, volume and such. For heat capacity you see a delta\n> function at Tc and the derivative of the volume with temperature.\n>\n> Of course as one measures the properties of the material these functions\n> are spead out due to noise in the measurement system and temperature\n> gradients in the sample.\n\nIsn\'t it also because the behaviour described above applies to\nthermodynamical limit only?\n\n\n\n--\n\nRoman Werpachowski\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On the Tue, 25 May 2004 06:31:59 +0000 (UTC), Joseph.D.Warner wrote:
> In second order phase transistions as you approach the transistion from
> higher temperature the order parameter versus position begins to
> flucuate rapidly and the regions of order grows as 1/(T-Tc)^x where T is
> the temperature and Tc is the transistion temperature and x is an
> universal exponent that depends on the dimensionality of the material.
>
> This is manifested in physical measurements such as heat capacity and
> magneti susceptibility (for magnetic systems).
>
> In first order phase transistion the region of order above Tc remains of
> zero volume until you get to Tc. Then the crystal oders and the order
> parameter is 1 everywhere. This discontinuous behaviour is seen again in
> heat capacity, volume and such. For heat capacity you see a \delta
> function at Tc and the derivative of the volume with temperature.
>
> Of course as one measures the properties of the material these functions
> are spead out due to noise in the measurement system and temperature
> gradients in the sample.
Isn't it also because the behaviour described above applies to
thermodynamical limit only?
--
Roman Werpachowski
Igor Khavkine
May29-04, 11:53 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405250530.7caa5957@posting.google. com>...\n\n> I asked the questions about superconductors to find out how different\n> superconductors are from other materials.The web is not as informative\n> as someone who knows the subject well!\n\nTrue, unfortunately the web is not yet as universal a source of information\nas one would wish. That is why books are still around. As I\'ve mentioned,\nsuperconductivity is not an easy topic to just jump into. But if you wish,\nyou could follow this stair case:\n\nBackground information and experimental facts:\nMost modern intro solid state books, such as:\nAshcroft & Mermin, Solid State Physics, Chapter 34\nMarder, Condensed Matter Physics, Chapter 27\nKittel, Introduction to Solid State Physics, Chapter 12\nFirst few chapters of more specialized books:\nSchrieffer, Theory of Superconductivity\nTinkham, Introduction to Superconductivity\n\nSecond Quntization:\nAn advanced QM or intro to QFT book\nFor the curious and dilligent student:\nP.A.M. Dirac, The Principles of Quantum Mechanics, Chapter X,\nespecially Sections 59, 60, and 65\nSecond Quantization and Green Functions in condensed matter theory:\nMahan, Many-Particle Physics, Chapters 1-3, very readable\nFetter & Walecka, Quantum Theory of Many-Particle Systems\nSchrieffer, Theory of Superconductivity, Chapter 5\nAbrikosov et al., QFT Methods in Statistical Physics, Chapters II and III\nLandau & Lifshitz, Statistical Physics Part II (vol 9), Chapters II and IV\n\nBCS theofy of superconductivity and quantitative predictions:\nSchrieffer, Fetter & Walecka, Abrikosov et al., Mahan, Landau & Lifshitz\nWeinberg, The Quantum Theory of Fields II, Section 21.6, cond-mat/9306055\n(hard to swallow without a solid background in QFT)\n\nOverall reference, but dated and not very intductory:\nParks, Superconductivity (vols 1 & 2)\n\n\n> I understand quantum mechanics\n> and\n> thermodynamics etc but I never assume that they are entirely right in\n> their current formulations because history has shown that most things\n> in science change.Thanks for your answers.\n\nIt is very good to keep an open mind and realize that even established\ntheories may be changed if there are phenomena they cannot explain.\nHowever, history has also shown that thermodynamics and quantum mechanics\nare among the best verified theories we have.\n\nI realize that climbing this ladder is difficult, and I haven\'t climbed\nall the way myself yet. However, taking the first step is not too hard\nand is quite englightening.\n\nIgor\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0405250530.7caa5957@posting.google.com>...
> I asked the questions about superconductors to find out how different
> superconductors are from other materials.The web is not as informative
> as someone who knows the subject well!
True, unfortunately the web is not yet as universal a source of information
as one would wish. That is why books are still around. As I've mentioned,
superconductivity is not an easy topic to just jump into. But if you wish,
you could follow this stair case:
Background information and experimental facts:
Most modern intro solid state books, such as:
Ashcroft & Mermin, Solid State Physics, Chapter 34
Marder, Condensed Matter Physics, Chapter 27
Kittel, Introduction to Solid State Physics, Chapter 12
First few chapters of more specialized books:
Schrieffer, Theory of Superconductivity
Tinkham, Introduction to Superconductivity
Second Quntization:
An advanced QM or intro to QFT book
For the curious and dilligent student:
P.A.M. Dirac, The Principles of Quantum Mechanics, Chapter X,
especially Sections 59, 60, and 65
Second Quantization and Green Functions in condensed matter theory:
Mahan, Many-Particle Physics, Chapters 1-3, very readable
Fetter & Walecka, Quantum Theory of Many-Particle Systems
Schrieffer, Theory of Superconductivity, Chapter 5
Abrikosov et al., QFT Methods in Statistical Physics, Chapters II and III
Landau & Lifshitz, Statistical Physics Part II (vol 9), Chapters II and IV
BCS theofy of superconductivity and quantitative predictions:
Schrieffer, Fetter & Walecka, Abrikosov et al., Mahan, Landau & Lifshitz
Weinberg, The Quantum Theory of Fields II, Section 21.6, http://www.arxiv.org/abs/cond-mat/9306055
(hard to swallow without a solid background in QFT)
Overall reference, but dated and not very intductory:
Parks, Superconductivity (vols 1 & 2)
> I understand quantum mechanics
> and
> thermodynamics etc but I never assume that they are entirely right in
> their current formulations because history has shown that most things
> in science change.Thanks for your answers.
It is very good to keep an open mind and realize that even established
theories may be changed if there are phenomena they cannot explain.
However, history has also shown that thermodynamics and quantum mechanics
are among the best verified theories we have.
I realize that climbing this ladder is difficult, and I haven't climbed
all the way myself yet. However, taking the first step is not too hard
and is quite englightening.
Igor
alistair
May29-04, 11:56 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>If I rotated a superconducting disc, that has superconducting vortices\ninterspersed with normal conducting regions, I would expect the\nvortices to stay separated at a higher temperature because groups of\natoms in the disc would be more widely separated than when it is at\nrest.I would expect the disc to superconduct at a higher\ntemperature.Am I right about this?\nMany superconductors are brittle materials.Perhaps this would put a\nlimit on the speed of rotation?\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>If I rotated a superconducting disc, that has superconducting vortices
interspersed with normal conducting regions, I would expect the
vortices to stay separated at a higher temperature because groups of
atoms in the disc would be more widely separated than when it is at
rest.I would expect the disc to superconduct at a higher
temperature.Am I right about this?
Many superconductors are brittle materials.Perhaps this would put a
limit on the speed of rotation?
Joseph.D.Warner
May31-04, 06:26 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nRoman Werpachowski wrote:\n> On the Tue, 25 May 2004 06:31:59 +0000 (UTC), Joseph.D.Warner wrote:\n>\n>\n>\n>>\n>>Of course as one measures the properties of the material these functions\n>>are spead out due to noise in the measurement system and temperature\n>>gradients in the sample.\n>\n>\n> Isn\'t it also because the behaviour described above applies to\n> thermodynamical limit only?\n\nYes it does. Superconductivity is a cooperative affect. When the volume\nbecomes "small" one should expect shifting of energy levels to occur and\nthe re-organization of atoms at the surface could influence a very large\npercentage of the remaining energy band near rest of the atoms.\n\nBut one does approach the thermodynamic limit quickly. Once you have\nabout 1,000,000 unit cells you will be "near" the thermodynamic limit.\nDepends on the material 1,000,000 atoms could form a cube with sides\nwith a length of 5 nm to 80 nm. Since the pentration depth of a magnetic\nfield in a "good" cuprate superconductor is on the order of 120 nm you\ncan see that you should begin to see deviations from bulk behaviour for\nthin films with thickness of ~ 240 nm or less. This is observed by\nmeasuring the "Q" of thin film HTS microwave resonators versus\nthickness. One sees "Q" go up and reach a maximun and hold constant\nabove 200 nm until the film becomes too thick and A-axis growth begins\nto occur and "Q" begins to fall off.\n\nThe spread in the functions are not due to the material being in a\nthermodynamic limit but in the set-up of the measurement system, time\none waits for thermogradients to stablize, and the measurement\nequipment. Not in HTS but I\'ve seen old papers measuring the universal\nconstants of various thermodynamic quantities where Tc/(T-Tc) approached\n1000. Others here may be able to give you references and clearer data as\nmy memory of these papers are ~25 to 30 years old and I am no longer\ndoing basic measurements of thermodynamic quantities.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Roman Werpachowski wrote:
> On the Tue, 25 May 2004 06:31:59 +0000 (UTC), Joseph.D.Warner wrote:
>
>
>
>>
>>Of course as one measures the properties of the material these functions
>>are spead out due to noise in the measurement system and temperature
>>gradients in the sample.
>
>
> Isn't it also because the behaviour described above applies to
> thermodynamical limit only?
Yes it does. Superconductivity is a cooperative affect. When the volume
becomes "small" one should expect shifting of energy levels to occur and
the re-organization of atoms at the surface could influence a very large
percentage of the remaining energy band near rest of the atoms.
But one does approach the thermodynamic limit quickly. Once you have
about 1,000,000 unit cells you will be "near" the thermodynamic limit.
Depends on the material 1,000,000 atoms could form a cube with sides
with a length of 5 nm to 80 nm. Since the pentration depth of a magnetic
field in a "good" cuprate superconductor is on the order of 120 nm you
can see that you should begin to see deviations from bulk behaviour for
thin films with thickness of ~ 240 nm or less. This is observed by
measuring the "Q" of thin film HTS microwave resonators versus
thickness. One sees "Q" go up and reach a maximun and hold constant
above 200 nm until the film becomes too thick and A-axis growth begins
to occur and "Q" begins to fall off.
The spread in the functions are not due to the material being in a
thermodynamic limit but in the set-up of the measurement system, time
one waits for thermogradients to stablize, and the measurement
equipment. Not in HTS but I've seen old papers measuring the universal
constants of various thermodynamic quantities where Tc/(T-Tc) approached
1000. Others here may be able to give you references and clearer data as
my memory of these papers are ~25 to 30 years old and I am no longer
doing basic measurements of thermodynamic quantities.
Doug Sweetser
May31-04, 06:26 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nHello Dirk:\n\n> Ptolemaic v Copernican?\n> hardly one building on the other.\n\nThis is probably the best example, not a counter example :-) Copernicus\nknew how to use the Ptolemaic system with all its epicycles. There is\nno contraint on the relative sizes of cycles and epicycles. One can\nthen choose to make all the epicycles the same size. That same size\nepicycle is now the orbit of the Earth around the Sun. In a history of\nscience class, the professor even drew it up on the board, quite\nimpressive. This transformation is not known by many, not often taught\n- too technical perhaps. It is one reason Copernicus stuck with\nperfect circles instead of ellipses. In effect, he was saying closs to\nthe Ptolemaic approach for calculations.\n\nWhat bugged Copernicus the most was something called the equant. This\nwas something required to account for the apparent difference in the\nspeed the Sun moves about in summer (slower) versus winter (faster).\nThe Copernican system does not need the bug fix.\n\nI would definitely agree that the this bit of science is usually\n_taught_ as being a radical break from anything done in the past, but\nthat may be due to sloppy history repeatly told, an urban myth of\nscience.\n\n\ndoug\nquaternions.com\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Hello Dirk:
> Ptolemaic v Copernican?
> hardly one building on the other.
This is probably the best example, not a counter example :-) Copernicus
knew how to use the Ptolemaic system with all its epicycles. There is
no contraint on the relative sizes of cycles and epicycles. One can
then choose to make all the epicycles the same size. That same size
epicycle is now the orbit of the Earth around the Sun. In a history of
science class, the professor even drew it up on the board, quite
impressive. This transformation is not known by many, not often taught
- too technical perhaps. It is one reason Copernicus stuck with
perfect circles instead of ellipses. In effect, he was saying closs to
the Ptolemaic approach for calculations.
What bugged Copernicus the most was something called the equant. This
was something required to account for the apparent difference in the
speed the Sun moves about in summer (slower) versus winter (faster).
The Copernican system does not need the bug fix.
I would definitely agree that the this bit of science is usually
_taught_ as being a radical break from anything done in the past, but
that may be due to sloppy history repeatly told, an urban myth of
science.
doug
quaternions.com
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