Strong and Tunable Spin–Orbit Coupling in a Two-Dimensional Hole Gas in Ionic-Liquid Gated Diamond Devices

Hydrogen-terminated diamond possesses due to transfer doping a quasi-two-dimensional (2D) hole accumulation layer at the surface with a strong, Rashba-type spin–orbit coupling that arises from the highly asymmetric confinement potential. By modulating the hole concentration and thus the potential using an electrostatic gate with an ionic-liquid dielectric architecture the spin–orbit splitting can be tuned from 4.6–24.5 meV with a concurrent spin relaxation length of 33–16 nm and hole sheet densities of up to 7.23 × 1013 cm–2. This demonstrates a spin–orbit interaction of unprecedented strength and tunability for a 2D hole system at the surface of a wide band gap semiconductor. With a spin relaxation length that is experimentally accessible using existing nanofabrication techniques, this result suggests that hydrogen-terminated diamond has great potential for the study and application of spin transport phenomena.