Orbital magnetoelectric effect in nanoribbons of transition metal dichalcogenides

TL;DR

This study demonstrates that zigzag-edged transition metal dichalcogenide nanoribbons can exhibit a significant orbital magnetoelectric effect induced by an electric field, with effects depending on layer number and symmetry.

Contribution

It reveals the presence and characteristics of the orbital magnetoelectric effect in TMD nanoribbons, highlighting the influence of edge states, layer number, and symmetry.

Findings

Orbital magnetoelectric effect is prominent near edge-state crossings.

Orbital accumulation from the orbital Hall effect is layer-dependent.

The effect vanishes in bilayer nanoribbons with inversion symmetry.

Abstract

The orbital magnetoelectric effect (OME) generically refers to the appearance of an orbital magnetization induced by an applied electric field. Here, we show that nanoribbons of transition metal dichalcogenides (TMDs) with zigzag (ZZ) edges may exhibit a sizeable OME activated by an electric field applied along the ribbons' axis. We examine nanoribbons extracted from a monolayer (1L) and a bilayer (2L) of MoS$_2$ in the trigonal (H) structural phase. Transverse profiles of the induced orbital angular momentum accumulations are calculated to first order in the longitudinally applied electric field. Our results show that close to the nanoribbon's edge-state crossings energy, the orbital angular momentum accumulations take place mainly around the ribbons' edges. They have two contributions: one arising from the orbital Hall effect (OHE) and the other consists in the OME. The former is transversely anti-symmetric with respect to the principal axis of the nanoribbon, whereas the latter is symmetric, and hence responsible for the resultant orbital magnetization induced in the system. We found that the orbital accumulation originating from the OHE for the 1L-nanoribbon is approximately half that of a 2L-nanoribbon. Furthermore, while the OME can reach fairly high values in 1L-TMD nanoribbons, it vanishes in the 2L ones that preserve spatial inversion symmetry.The microscopic features that justify our findings are also discussed.