Topological Quantum Phase Transitions in Metallic Shiba Lattices

TL;DR

This paper theoretically predicts a new type of gapless topological Shiba metal in magnetic impurity lattices on superconductors, characterized by Lifshitz transitions and large nonquantized thermal Hall conductance.

Contribution

It introduces the concept of topological Shiba metals and reveals mechanisms protecting quantum phase transitions in such systems.

Findings

Existence of topological Shiba metals with gapless bands.

Lifshitz phase transitions lead to changes in thermal Hall conductance.

Large nonquantized thermal Hall conductance observed.

Abstract

Shiba bands formed by overlapping Yu-Shiba-Rusinov subgap states in magnetic impurities on a superconductor play an important role in topological superconductors. Here, we theoretically demonstrate the existence of a new type of Shiba bands (dubbed topological Shiba metal) on a magnetically doped $s$-wave superconducting surface with Rashba spin-orbit coupling in the presence of a weak in-plane magnetic field. Such topological gapless Shiba bands develop from gapped Shiba bands through Lifshitz phase transitions accompanied by second-order quantum phase transitions for the intrinsic thermal Hall conductance. We also find a mechanism in Shiba lattices that protects the first-order quantum phase transitions for the intrinsic thermal Hall conductance. Due to the long-range hopping in Shiba lattices, the topological Shiba metal exhibits intrinsic thermal Hall conductance with large nonquantized values. As a consequence, there emerge a large number of second-order quantum phase transitions.