Ferroelectric polarization controlled orbital Hall conductivity in a higher-order topological insulator: \textit{d1T}-phase monolayer MoS$_2$

TL;DR

This paper predicts that monolayer d1T-MoS2 is a higher-order topological insulator with ferroelectric properties, exhibiting a tunable orbital Hall effect that can be controlled by electric polarization.

Contribution

It introduces monolayer d1T-MoS2 as a ferroelectric higher-order topological insulator with a controllable orbital Hall conductivity, expanding the understanding of topological materials.

Findings

Identification of nontrivial topological index and corner states in d1T-MoS2.

Discovery of a nonzero orbital Hall conductivity plateau within the energy gap.

Demonstration that ferroelectric polarization direction modulates orbital Hall conductivity.

Abstract

The higher-order topological insulator is an extended concept of the conventional topological insulator, which obeys the generalization of the standard bulk-boundary correspondence. In our paper, we predict the monolayer \textit{d1T}-phase transition metal dichalcogenide MoS$_2$ to be a higher-order topological insulator, while also possessing intriguing ferroelectric characteristics. We explicitly demonstrate the nontrivial topological index and reveal the hallmark corner states with quantized fractional charge within the bulk band gap. Second, we show the existence of a nonzero orbital Hall conductivity plateau within the energy gap which is a signature to identify higher-order topology system. Additionally, we investigate the relationship between the ferroelectricity and the orbital Hall conductivity of \textit{d1T} MoS$_2$ and find that the direction of ferroelectric polarization can modulate the positive and negative values of the orbital Hall conductivity $\sigma_{\rm{OH}}^x$. Our findings provide the theory and material candidate for ferroelectricity tunable orbital Hall effect which is promising to realize the external electric field controllable orbitronics.