Pairing Constraint on the Real Space Formalism of the Theory of Superconductivity

TL;DR

This paper reviews a new real-space formalism for impure superconductors, emphasizing the importance of pairing constraints on the Green's functions and ground state, which could impact the understanding of inhomogeneous superconductors.

Contribution

It introduces the necessity of pairing constraints on the kernel and ground state in Gor'kov's equations, advancing the theory of inhomogeneous and impure superconductors.

Findings

Pairing constraints are essential for the correct vacuum state in Gor'kov's formalism.

Clarification of the relation between pair potential and gap parameter.

Opens new avenues for studying inhomogeneous superconductors.

Abstract

We review the new theory of impure superconductors constructed by Kim and Overhauser, and further developed by Kim. It was shown that Gor'kov's self-consistency equation needs a pairing constraint derived from the Anomalous Green's function. Whereas earlier studies have applied a constraint only on the pair potential, we show that the kernel also should be fixed by the ground state. The Bogoliubov-de Gennes equations need a pairing constraint in order to obtain the proper vacuum state by the corresponding unitary transformation. The relation between the pair potential and the gap parameter is clarified. This new study opens up a reinvestigation of inhomogeneous superconductors. We will discuss (i) strong coupling theory of dirty superconductors, (ii) suppression of magnetic impurity effect by ordinary impurities, (iii) weak localization correction to the phonon-mediated interaction, and (iv) other inhomogeneous superconductors.