Interplay of the pseudogap and the BCS gap for heteropairs in ⁴⁰K-⁶Li mixture

¹ Faculty of Mathematics and Physics, Charles University - Ke Karlovu 3, 12116 Prague 2, Czech Republic
² Department of Quantum Matter Physics, University of Geneva - 24 quai Ernest-Ansermet, 1211 Geneva, Switzerland

Received: 21 September 2016
Accepted: 24 November 2016

Abstract

The description of heteropairs like ⁴⁰K-⁶Li near and in the superconducting state requires a fully self-consistent theory (see Hanai R. and Ohashi Y., Phys. Rev. A, 90 (2014) 043622). We derive analytic pseudogap Green's functions for the “normal” and superconducting states from the Luttinger-Ward theory with the T-matrix in the static separable approximation. The self-consistency in the closing loop of self-energy has two pronounced effects on the single-particle spectrum. First, the single-particle excitations decay before the asymptotic quasiparticle propagation is established, therefore the normal state is not a Fermi liquid. Second, the pseudogap has a V shape even for s-wave pairing. The V-shaped pseudogap and the U-shaped BCS gap interfere resulting in slope breaks of the gap walls and the in-gap states in the density of states. Various consequences of an incomplete self-consistency are demonstrated.