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

Monolayers of transition metal dichalcogenides (TMDs) in the 2H structural phase have been recently classified as higher-order topological insulators (HOTIs), protected by C-3 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 Z(4) 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 orbitronics and spin orbitronics.

Automated summary

Monolayers of transition metal dichalcogenides (TMDs) in the 2H structural phase have been classified as higher-order topological insulators (HOTIs), protected by C-3 rotation symmetry. The insulating gap of TMDs also exhibits an orbital Hall plateau characterized by an orbital Chern number. By using density functional theory, the correlation between these two phenomena in TMD monolayers in two structural phases (2H and 1T) is explored. The findings show that the HOTI phase is accompanied by an orbital Hall effect, which has potential implications for orbitronics and spin orbitronics.