Modes of magnetic resonance in the spin liquid phase of Cs2CuCl4

We report the observation of a frequency shift and splitting of the electron spin resonance (ESR) mode of the low-dimensional S=1/2 frustrated antiferromagnet Cs2CuCl4 in the spin-correlated state below the Curie-Weiss temperature 4 K but above the ordering temperature 0.62 K. The shift and splitting exhibit strong anisotropy with respect to the direction of the applied magnetic field and do not vanish in zero field. The low-temperature evolution of spin resonance response is a result of the specific modification of one-dimensional spinon continuum under the action of the uniform Dzyaloshinskii-Moriya interaction (DM) within the spin chains. Parameters of the uniform DM interaction are derived from the experiment.