Skip to main content
Physics

You are not logged in. Your edit will be placed in a queue until it is peer reviewed.

We welcome edits that make the post easier to understand and more valuable for readers. Because community members review edits, please try to make the post substantially better than how you found it, for example, by fixing grammar or adding additional resources and hyperlinks.

4
  • $\begingroup$ But the question is really about why the same BCS Hamiltonian (by BCS I mean a non-relativistic electron system with an attractive quartic interaction ) used to describe a neautral fermi system undergoing BCS transition and a charged system has different spectrum in the 2 cases. $\endgroup$
    – cx1114
    Commented yesterday
  • $\begingroup$ The question of the difference between charged and neutral superfluids is just one of classical electrodynamics. Any charged compressible fluid, super or normal, has its sound modes pushed up to above the plasma-frequency gap. In addition, for a superfluid of charge $e$ particles you have the London relation $m{\boldsymbol \omega}+ e {\bf B}=0$ and plugging this into Maxwell gives you the Meissner effect as well. BCS is not involved. $\endgroup$
    – mike stone
    Commented yesterday
  • $\begingroup$ The sound/phase modes being pushed up to plasma frequency seem to be deduced from applying an external field, as Anderson in his paper already pointed out. But if the fields are to fluctuate quantum mechanically, and no external field is applied. How would the argument go? $\endgroup$
    – cx1114
    Commented yesterday
  • $\begingroup$ So intuitively imagine cool down an atomic fermi gas to be a superfluid, and then we may observe some sound wave propagation. Now we cool down a piece of metal to undergo a BCS, but appliying no fields to excite current. Then why there will not be gapless modes as in the netral fermi superfluid case? $\endgroup$
    – cx1114
    Commented yesterday