Microscopic origin of broad ESR resonance widths

Determine the microscopic origin of the broad electron-spin-resonance linewidths and correspondingly short spin-relaxation times observed in high-Fermi-energy monolayer graphene and WSe₂/graphene heterostructures, including whether the broadening arises from inhomogeneous dephasing or other mechanisms inherent to resonance measurements.

Background

The paper reports ESR-driven photogalvanic resonances in monolayer graphene and WSe₂/graphene heterostructures with full widths at half maximum of approximately 0.05–0.6 T, corresponding to spin-relaxation times of roughly 18–130 ps. These lifetimes are substantially shorter than those commonly reported in modern graphene spin-transport measurements, which can reach 1–10 ns even at room temperature.

The authors note that the measured linewidths show no pronounced dependence on sample mobility, making conventional disorder-based explanations insufficient. They suggest that additional dephasing mechanisms, including inhomogeneous broadening associated with resonance measurements, may contribute, but they do not identify the microscopic mechanism. Establishing the origin of the linewidths is therefore left unresolved.