Hybrid-Order Topological Phase And Transition in 1H Transition Metal Compounds

TL;DR

This paper predicts and characterizes hybrid-order topological insulators in 1H transition metal compounds, revealing a tunable phase transition with potential spintronic applications, based on first-principles calculations and experimental parallels.

Contribution

It introduces the concept of hybrid-order topological phases in 1H TMCs and demonstrates their tunability and properties through theoretical modeling and material examples.

Findings

Hybrid-order topological phase exists in 1H TMCs.

Phase transition can be tuned via crystal field effects.

Strong spin Hall effect observed in the hybrid topological insulator.

Abstract

Inspired by recent experimental observations of hybrid topological states [Hossain et al. Nature 628, 527 (2024)], we predict hybrid-order topological insulators in 1H transition metal compounds (TMCs), where both second-order and first-order topological (FOT) states coexist near the Fermi level. Initially, 1H-TMCs exhibit a second-order topological phase due to the d orbital bandgap. Upon coupling of p and d orbitals through the crystal field effect, first-order topological characteristics emerge. This hybrid-order topological phase transition can be tuned via crystal field effects. Combined with first-principles calculations, we illustrate the phase transition with WTe2 and NbSe2. The WTe2 exhibits hybrid-order under ambient conditions, while NbSe2 transitions to hybrid-order under pressure. Additionally, the first-order topological bandgap in the HyOTI demonstrates a strong spin Hall effect. Our findings reveal a hybrid-order topological phase in two-dimensional electron materials and underscore spintronic applications.