Spin-Dependent Photovoltage and Tunable Zero-Field Splitting in Graphene Transistors

Highly sensitive photovoltage detection in gigahertz/terahertz (THz) graphene sensors enables direct probing of electron spin resonances (ESRs) and provides access to the intrinsic spin–orbit coupling (SOC) and sublattice-potential gaps in graphene-based systems. In this work, we employ a sub-THz photoconductivity-based technique to investigate spin-flip transitions in bilayer graphene and graphene/MoS 2 heterostructures at low temperatures. In both systems, three spin resonances are observed corresponding to Zeeman, intrinsic SOC, and sublattice-potential splittings. The resonance frequencies and extracted [Formula: see text]-factors and spin relaxation times are nearly identical in the two structures, indicating that the proximity of MoS 2 does not significantly enhance graphene’s SOC under the present conditions. The energy gaps show a pronounced temperature dependence, increasing steadily as the temperature decreases and suggesting a contribution from thermally induced strain or electron–phonon coupling. Notably, all resonances are accompanied by a characteristic drop in photovoltage, consistent with spin-dependent recombination of photoexcited carriers. These findings establish THz photovoltage spectroscopy as a powerful, contact-free, and on-chip method for probing spin-dependent electronic structure and relaxation phenomena in the material forming the detector.