Orbital Hall effect in spin-3/2 hole-doped semiconductors and its implications for orbitronics

Abstract

State-of-the-art magnetic devices rely on faster, more efficient memory elements. A major recent advance is the discovery of orbital torques, which use the orbital angular momentum of Bloch electrons to switch the magnetisation of an adjacent ferromagnet, motivating the search for orbitronic materials with strong orbital responses, exemplified by the orbital Hall effect (OHE). Here we propose $p$-type semiconductors, with a focus on Ge, as orbitronic platforms. We demonstrate that bulk holes in five common semiconductors exhibit a large orbital Hall conductivity of order $10^3 (\hbar/e)Ω^{-1}$cm$^{-1}$, exceeding the spin-Hall effect by 2-3 orders of magnitude. The calculation is performed within the framework of the modern theory of orbital magnetisation, while incorporating recently-discovered quantum corrections to the OHE. Moreover, we argue that bulk $p$-type Ge and Si serve as ideal testbeds for the orbital torque resulting from a charge current, since the spin- and orbital-Edelstein effects are forbidden by symmetry. Our results provide a blueprint for producing strong orbital torques in magnetic devices with $p$-type semiconductors, guiding experimental work in this direction.