Connecting Higher-Order Topology with the Orbital Hall Effect in Monolayers of Transition Metal Dichalcogenides

Abstract

Monolayers of transition metal dichalcogenides (TMDs) in the 2H structural phase have been recently classified as higher-order topological insulators (HOTI), protected by C3 rotation symmetry. In addition, theoretical calculations show an orbital Hall plateau in the insulating gap of TMDs, characterized by an orbital Chern number. We explore the correlation between these two phenomena in TMD monolayers in two structural phases: the noncentrosymmetric 2H and the centrosymmetric 1T. Using density functional theory, we confirm the characteristics of 2H-TMDs and reveal that 1T-TMDs are identified by a Z4 topological invariant. As a result, when cut along appropriate directions, they host conducting edge-states, which cross their bulk energy-band gaps and can transport orbital angular momentum. Our linear response calculations thus indicate that the HOTI phase is accompanied by an orbital Hall effect. Using general symmetry arguments, we establish a connection between the two phenomena with potential implications for spin-orbitronics.

Orbital magnetoelectric effect in nanoribbons of transition metal dichalcogenides

“…MoS 2 is topologically trivial with respect to Z 2 index and its nanoribbon edge states are not protected by Kramer's degeneracy [57]. Notwithstanding, MoS 2 has a nontrivial topology related to OAM [35][36][37], which may be categorized by an orbital Chern number [24][25][26] that indicates the presence of orbital-polarized edge states, as those shown in Fig. 12.…”

“…In particular, transition metal dichalcogenides (TMDs) comprise prospective candidates for applications in orbitronics. These materials exhibit orbital textures that underlie the OHE even in its insulating phase [24][25][26][32][33][34], where nontrivial topology associated with the OAM is beginning to be unveiled [25,[35][36][37].…”