Machine learning guided discovery of stable, spin-resolved topological insulators

Abstract

Identification of a non-trivial ${\mathbb{Z}}_2$ index in a spinful two dimensional insulator indicates the presence of an odd, quantized (pseudo)spin-resolved Chern number, $C_s=(C_{\uparrow }-C_{\downarrow })/2$. However, the statement is not biconditional. An odd spin-Chern number can survive when the familiar ${\mathbb{Z}}_2$ index vanishes. Identification of solid-state systems hosting an odd, quantized $C_s$ and trivial ${\mathbb{Z}}_2$ index is a pressing issue due to the potential for such insulators to admit band gaps optimal for experiments and quantum devices. Nevertheless, they have proven elusive due to the computational expense associated with their discovery. In this work, a neural network capable of identifying the spin-Chern number is developed and used to identify the first solid-state systems hosting a trivial ${\mathbb{Z}}_2$ index and odd $C_s$. We demonstrate the potential of one such system, Ti${}_2$CO${}_2$, to support Majorana corner modes via the superconducting proximity effect.

9 + 8 pages, 5+5 figures, To appear in Phys. Rev. Res