Fizika Nizkikh Temperatur: Volume 44, Number 6 (June 2018), p. 684-690    ( to contents , go back )

Evolution of the dynamics of neutral superconductors between BCS and BEC regimes: the variational approach

Andrey V. Chubukov

Department of Physics, University of Minnesota, Minneapolis MN 55455, USA
E-mail: achubuko@umn.edu

Dmitry Mozyrsky

Theoretical Division (T-4), Los Alamos National Laboratory, Los Alamos NM 87545, USA
E-mail: mozyrsky@lanl.gov

Received January 24, 2018

Abstract

We use variational approach to analyze the evolution of the dynamics of a neutral s-wave superconductor between BCS and BEC regimes. We consider 2D case, when BCS–BEC crossover occurs already at weak coupling and is governed by the ratio of the two scales — the Fermi energy EF and the bound state energy for two fermions in a vacuum, E0. BCS and BEC regimes correspond to EF >> E0 and EF << E0, respectively. We compute the spectrum of low-energy bosonic excitations and show that the velocity of phase fluctuations remains υF / 2 through BCS–BEC crossover. We also discuss the topological Aφ ̇ term in the effective action.

PACS: 74.20.Fg Nanotubes;
PACS: 74.25.Вt Thermodynamic properties;
PACS: 74.78.–w Superconducting films and low-dimensional structures.

Key words: s-wave, superconductor, Berry phase.

Published online: April 25, 2018

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