## Physics of High Temperature Superconductivity

<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>What\'s the latest in the search to understand the secrets\nof high temperature superconductivity which can\'t be\nexplained by the BCS theory of cooper pairs bonded\nby phonons? What\'s the leading theory or best candidate\nthat has ample scientific and experimental support?\n\nSCy\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">&nbsp;&nbsp;View this Usenet post in original ASCII form </a></div><P></jabberwocky>What's the latest in the search to understand the secrets
of high temperature superconductivity which can't be
explained by the BCS theory of cooper pairs bonded
by phonons? What's the leading theory or best candidate
that has ample scientific and experimental support?

SCy

 PhysOrg.com physics news on PhysOrg.com >> Iron-platinum alloys could be new-generation hard drives>> Lab sets a new record for creating heralded photons>> Breakthrough calls time on bootleg booze


On $2005-06-21,$ SCy wrote: > What's the latest in the search to understand the secrets > of high temperature superconductivity which can't be > explained by the BCS theory of cooper pairs bonded > by phonons? What's the leading theory or best candidate > that has ample scientific and experimental support? The latest is: still searching. One of the main problems is the sheer complexity of the phenomenon and its rich phenomenology. The unit cell of a YBCO crystal, one of the first discovered high-Tc superconductors, contains on the order of 100 atoms. Elementary excitations on top of the superconducting state are well described by BCS-like quasiparticles with a d-wave gap (4-fold rotational symmetry, nodes along the diagonals of the Brillouin zone along wich the gap vanishes). There are important structures in $1D (Cu-O$ chains), $in 2D (Cu-O$ planes, considered most important), and 3D (coupling between $Cu-O$ layers). The presence of superconductivity depends on a certain amount of disorder. The phase diagram of high-Tc materials contains unusual regions such as an antiferromagnetic insulator, the mysterious "pseudogap" state, a non-metallic normal phase, as well as a doped conductor phase. As superconductors, high-Tc materials don't differ much from Type-II superconductors described by BCS theory. So many believe that the superconducting state is due to Cooper-like pairing, except that it is mediated not by phonons, but by as yet an unknown agent. There are many proposals for a microscopic theory of high-Tc superconductivity. But none of them are yet successful. One reason is that the important properties of these materials stem from strong correlations between their electrons. In other words, the electrons cannot be treated $as non-$ or weakly interacting, like in normal metals. This imposes difficulties theoretically since simple models with weak coupling are not expected to be appropriate, and strongly coupled interacting systems are always difficult to work with. Instead, there are many phenomenological theories describing different phases in the phase diagram, with varying degrees of success. But no theory has come close to, say, accurately predicting the transition temperature. A recent review article focusing on the state of the theory is http://www.arxiv.org/abs/cond-mat/0309094 by Yanase et al. Hope this helps. Igor



SCy wrote: > What's the latest in the search to understand the secrets > of high temperature superconductivity which can't be > explained by the BCS theory of cooper pairs bonded > by phonons? What's the leading theory or best candidate > that has ample scientific and experimental support? > > SCy > One possibility: Superconductivity is a Bose Einstein Condensate $h^2/(2 \pi m \lambda^2) =$ kTc in simplicity aided but mostly masked by molecular topology. Richard Saam

## Physics of High Temperature Superconductivity

<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>Richard Saam wrote:\n&gt; SCy wrote:\n&gt; &gt; What\'s the latest in the search to understand the secrets\n&gt; &gt; of high temperature superconductivity which can\'t be\n&gt; &gt; explained by the BCS theory of cooper pairs bonded\n&gt; &gt; by phonons? What\'s the leading theory or best candidate\n&gt; &gt; that has ample scientific and experimental support?\n\n&gt; One possibility:\n\nHardly a leading theory, though.\n\n&gt; Superconductivity is a Bose Einstein Condensate\n\nThe BCS phase is different from the BEC phase. The study of the\ncross-over between the two regimes is a hot topic at the momnent, but\nin cold atomic gases. I don\'t think any superconductors have been found\nto have a BEC as the underlying phase.\n\n&gt; h^2/(2 pi m lambda^2) = kTc\n\nReference?\n\n&gt; in simplicity\n&gt; aided\n&gt; but mostly masked\n&gt; by molecular topology.\n\nThis statement makes little sense, so I can\'t comment on it.\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">&nbsp;&nbsp;View this Usenet post in original ASCII form </a></div><P></jabberwocky>Richard Saam wrote:
> SCy wrote:
> > What's the latest in the search to understand the secrets
> > of high temperature superconductivity which can't be
> > explained by the BCS theory of cooper pairs bonded
> > by phonons? What's the leading theory or best candidate
> > that has ample scientific and experimental support?

> One possibility:

> Superconductivity is a Bose Einstein Condensate

The BCS phase is different from the BEC phase. The study of the
cross-over between the two regimes is a hot topic at the momnent, but
in cold atomic gases. I don't think any superconductors have been found
to have a BEC as the underlying phase.

> $h^2/(2 \pi m \lambda^2) =$ kTc

Reference?

> in simplicity
> aided
> by molecular topology.

This statement makes little sense, so I can't comment on it.

Igor



Igor Khavkine wrote: > Richard Saam wrote: > >>SCy wrote: >> >>>What's the latest in the search to understand the secrets >>>of high temperature superconductivity which can't be >>>explained by the BCS theory of cooper pairs bonded >>>by phonons? What's the leading theory or best candidate >>>that has ample scientific and experimental support? > > >>One possibility: > > > Hardly a leading theory, though. > > >>Superconductivity is a Bose Einstein Condensate > > > The BCS phase is different from the BEC phase. The study of the > cross-over between the two regimes is a hot topic at the momnent, but > in cold atomic gases. I don't think any superconductors have been found > to have a BEC as the underlying phase. > > $>>h^2/(2 \pi m \lambda^2) =$ kTc > > > Reference? > There is some work: http://scienceworld.wolfram.com/phys...densation.html Journal : PHYSICA C: SUPERCONDUCTIVITY ISSN $: 0921-4534$ Vol.$/Iss$. : 301 $/ 3-4$ Bose--Einstein condensation in finite-length channels composed of weakly interacting filaments Eagles , D.M. pp.$: 165-172$ Journal : PHYSICA C: SUPERCONDUCTIVITY ISSN $: 0921-4534$ Vol.$/Iss$. : 305 $/ 1-2$ d-wave Bose--Einstein condensate and tunnelling in superconducting cuprates Alexandrov $, A.S.pp.: 46-56$ Journal: Physica C: Superconductivity ISSN $: 0921-4534$ Volume : 325 Issue $: 1-2$ Date : 26-Nov-1999 $pp 35-40$ D-wave Bose-Einstein condensation and the London penetration depth in superconducting cuprates AS Alexandrov It is not a leading theory, but if room temperature superconductivity is ever to be achieved, a mechanism based on very small (~electron mass) (quasi?) particles must be found/engineered generally aligned with: kTc $= \hbar^2 K^2/(2m)$ m associated with atomic mass will not do the job. Richard Saam