Going beyond the BCS level in the superfluid path integral: A consistent treatment of electrodynamics and thermodynamics

Brandon M. Anderson, Rufus Boyack, Chien-Te Wu, K. Levin

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

In this Rapid Communication we derive the full gauge-invariant electromagnetic response beyond the BCS level using the fermionic superfluid path integral. In the process we identify and redress a failure to satisfy the compressibility sum rule; this shortcoming is associated with the conventional path-integral formulation of BCS-level electrodynamics. The approach in this paper builds on an alternative saddle point scheme. At the mean field level, this leads to the well known gauge-invariant electrodynamics of BCS theory and to the satisfaction of the compressibility sum rule. Moreover, this scheme can be readily extended to address arbitrary higher order fluctuation theories (for example, at the Gaussian level.) At any level this approach will lead to a gauge invariant and compressibility sum rule consistent treatment of electrodynamics and thermodynamics.

Original languageEnglish
Article number180504
JournalPhysical Review B
Volume93
Issue number18
DOIs
StatePublished - 12 May 2016

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