Cooper-pair size and binding energy for unconventional superconducting systems

TL;DR

This paper investigates how hybridization and mass imbalance affect Cooper-pair size and binding energy in unconventional superconductors, revealing phase transitions and dependencies across the BCS-BEC crossover.

Contribution

It introduces a model analyzing inter-band pairing with hybridization and mass imbalance, highlighting phase transitions and pair properties in unconventional superconducting systems.

Findings

Hybridization can induce first-order phase transitions breaking Cooper pairs.

Cooper-pair size varies with hybridization at zero temperature.

Binding energy structure depends on two-band quasiparticle energies.

Abstract

The main proposal of this paper is to analyze the size of the Cooper pairs composed by unbalanced mass fermions from different electronic bands along the BCS-BEC crossover and study the binding energy of the pairs. We are considering an interaction between fermions with different masses leading to an inter-band pairing. In addiction to the attractive interaction we have an hybridization term to couple both bands, which in general acts unfavorable for the pairing between the electrons. We get first order phase transitions as the hybridization break the Cooper pairs for the the $s$-wave symmetry of the gap amplitude. The results show the dependence of the Cooper-pair size as a function of the hybridization for $T=0$. We also propose the structure of the binding energy of the inter-band system as a function of the two-bands quasi-particle energies.