Majorana Corner Modes in a Second-Order Kitaev Spin Liquid

TL;DR

This paper introduces a new second-order topological phase in a frustrated quantum magnet modeled after the Kitaev honeycomb, featuring stable Majorana corner modes protected by mirror symmetries, with implications for topological quantum states.

Contribution

It presents an exactly-solvable model of a second-order topological insulator in a quantum magnet with Majorana corner modes, extending Kitaev's model to a new lattice and demonstrating stability at finite temperatures.

Findings

Existence of Majorana corner modes protected by mirror symmetries.

Model remains stable under thermal fluctuations.

Finite-temperature phase transition observed in simulations.

Abstract

Higher-order topological insulators are distinguished by the existence of topologically protected modes with codimension two or higher. Here, we report the manifestation of a second-order topological insulator in a two dimensional frustrated quantum magnet, which exhibits topological corner modes. Our exactly-solvable model is a generalization of the Kitaev honeycomb model to the Shastry-Sutherland lattice that, besides a chiral spin liquid phase, exhibits a gapped spin liquid with Majorana corner modes, which are protected by two mirror symmetries. This second-order Kitaev spin liquid remains stable in the presence of thermal fluctuations and undergoes a finite-temperature phase transition evidenced in large-scale quantum Monte Carlo simulations.