some superfluid questions [Archive]

aSkeptic

Apr7-04, 03:13 PM

Douglas Natelson

Apr8-04, 02:27 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>aSkeptic wrote:\n> 1. Is helium the only known material to have a super fluid state?\n\nNo; there is evidence that Bose-condensed cold atomic gases\nalso exhibit superfluidity. See\nhttp://cua.mit.edu/ketterle_group/Research_topics/Superfluidity.htm\n\nIt\'s also worth noting that both stable isotopes of helium can be\nsuperfluids. In fact, 3He has more than one superfluid phase (!).\nThe phases are distinguished by their magnetic properties\n(what their nuclear magnetic moments are doing).\n\n> 2. Is super fluid helium a superconductor of electricity?\n\nNo. Superfluid helium is neutral.\n\n> 3. When was super fluidity discovered?\n\nWhile superfluidity was achieved experimentally as early as\n1910 (Onnes liquified 4He in 1909), it was not observed\nas such until the late 1920s. Rather, what was noticed\nfirst was the diverging specific heat of 4He at the\ntransition. The specific heat vs. temperature curve looks\nlike the letter lambda; hence the transition is often\ncalled the "lambda point". Physics Today has a nice article\nabout this here:\n\nhttp://www.physicstoday.com/pt/vol-54/iss-2/pdf/vol48no7p30-36(part1).pdf\n\n--DN\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>aSkeptic wrote:
> 1. Is helium the only known material to have a super fluid state?

No; there is evidence that Bose-condensed cold atomic gases
also exhibit superfluidity. See
http://cua.mit.edu/ketterle_group/Research_topics/Superfluidity.htm

It's also worth noting that both stable isotopes of helium can be
superfluids. In fact, 3He has more than one superfluid phase (!).
The phases are distinguished by their magnetic properties
(what their nuclear magnetic moments are doing).

> 2. Is super fluid helium a superconductor of electricity?

No. Superfluid helium is neutral.

> 3. When was super fluidity discovered?

While superfluidity was achieved experimentally as early as
1910 (Onnes liquified 4He in 1909), it was not observed
as such until the late 1920s. Rather, what was noticed
first was the diverging specific heat of 4He at the
transition. The specific heat vs. temperature curve looks
like the letter \lambda; hence the transition is often
called the "\lambda point". Physics Today has a nice article
about this here:

http://www.physicstoday.com/pt/vol-54/iss-2/pdf/vol48no7p30-36(part1).pdf

--DN