Tatiana G. Rappoport: Orbital Hall effect in 2D Materials

The field of spintronics blossomed in the last decade, as a consequence of the use of spin-orbit coupling to efficiently generate and manipulate spin currents in non-magnetic materials. In these systems, the efficient conversion between charge and spin currents is mediated by the spin-orbit coupling.

Great progress in the manipulation of the orbital angular momentum of light has also been achieved in the last decades, leading to many relevant applications. Still, electron orbitals in solids were less exploited, even though they are known to be essential in several underlying physical processes in materials science. The orbital Hall effect (OHE), similarly to the spin Hall effect (SHE), refers to the creation of a transverse flow of orbital angular momentum that is induced by a longitudinally applied electric field. Recently, a renewed interest in orbital magnetism and other orbital effects in solids gave origin to various theoretical studies on the OHE and related phenomena, raising expectations that orbital angular degrees of freedom may be eventually employed to process information in logic and memory devices.

I will discuss different aspects of the OHE in 2D materials. In particular, I will show that monolayers and bilayers of transition metal dichalcogenides (TMDs) like MoS2 and WSe2, exhibit OHE in its insulating phase. The orbital Hall conductivity presents a plateau in the semiconductor gap of these materials that can be associated with a topological phase characterized by an orbital Chern number. Our results offer the possibility of using TMDs for orbital current injection and orbital torque transfer that surpass their spin equivalents.