'Pi State' Induced by Impurities with a Repulsive Interaction

TL;DR

This paper investigates how a repulsive impurity affects the local electronic properties and phase behavior of a superconductor modeled by the negative U Hubbard model, revealing conditions for pi-like phase differences.

Contribution

It demonstrates the emergence of pi-like behavior in a superconductor with a repulsive impurity, combining attractive and repulsive interactions at the impurity site.

Findings

Identification of pi-like phase behavior due to impurity interactions

Analysis of local density of states and electron pairing modifications

Conditions for phase difference of pi in the system

Abstract

We study the properties of a quantum impurity embedded in a superconducting host. The superconductor is described by the negative U Hubbard model while the impurity introduces a repulsive interaction to the system. We discuss the influence of this `on-impurity' Coulomb repulsion on the local properties (density of states, electron pairing) of the superconductor. We show the condition of pi - like behaviour, defined as two subsystems having a phase difference of pi, in the system by using a proper combination of attractive pairing interaction and repulsive one located at impurity site.