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.
@article{arxiv.1803.08922,
title = {Majorana Corner Modes in a Second-Order Kitaev Spin Liquid},
author = {Vatsal Dwivedi and Ciarán Hickey and Tim Eschmann and Simon Trebst},
journal= {arXiv preprint arXiv:1803.08922},
year = {2018}
}