Interplay of spin-orbit coupling and Zeeman splitting in the absorption lineshape of 2D fermions

We suggest that electron spin resonance (ESR) experiment can be used as a probe of spinon excitations of hypothetical spin-liquid state of frustrated antiferromagnet in the presence of asymmetric Dzyaloshinskii-Moriya (DM) interaction. We describe assumptions under which the ESR response is reduced to the response of 2D electron gas with Rashba spin-orbit coupling. Unlike previous treatments, the spin-orbit coupling, \Delta_{SO}, is not assumed small compared to the Zeeman splitting, \Delta_Z. We demonstrate that ESR response diverges at the edges of the absorption spectrum for ac magnetic field perpendicular to the static field. At the compensation point, \Delta_{SO}\approx \Delta_Z, the broad absorption spectrum exhibits features that evolve with temperature, T, even when T is comparable to the Fermi energy.