Instabilities at [110] Surfaces of d_{x^2-y^2} Superconductors

TL;DR

This paper investigates various mechanisms causing zero-energy peak splitting at (110) surfaces of d_{x^2-y^2} superconductors, revealing surface phase transitions involving time-reversal symmetry breaking, s+id-wave states, and magnetic order due to electron correlations.

Contribution

It compares different theoretical scenarios for surface phase transitions in d_{x^2-y^2} superconductors using a tight binding Bogolyubov-de Gennes model, highlighting new possible states.

Findings

Surface phase transition to time-reversal symmetry breaking state with spontaneous currents

Emergence of an s+id-wave surface state under certain conditions

Electron correlations induce a magnetic surface phase with local spin density wave order

Abstract

We compare different scenarios for the low temperature splitting of the zero-energy peak in the local density of states at (110) surfaces of d_{x^2-y^2}-wave superconductors, observed by Covington et al. (Phys.Rev.Lett.79 (1997), 277). Using a tight binding model in the Bogolyubov-de Gennes treatment we find a surface phase transition towards a time-reversal symmetry breaking surface state carrying spontaneous currents and an s+id-wave state. Alternatively, we show that electron correlation leads to a surface phase transition towards a magnetic state corresponding to a local spin density wave state.