The nature of the low-energy excitations in the short-range-ordered region of Cs2CuCl4 as revealed by 133Cs nuclear magnetic resonance
We report nuclear magnetic resonance (NMR) measurements of the spin-1/2 anisotropic triangular lattice antiferromagnet Cs2CuCl4 as a function of temperature and applied magnetic field. The observed temperature and magnetic field dependence of the NMR relaxation rate suggests that low-energy excitations in the short-range-ordered region stabilized over a wide range of intermediate fields and temperatures of the phase diagram (sketched in figure 1(a)) are gapless or nearly gapless fermionic excitations. An upper bound on the size of the gap of 0.037 meV≈J/10 is established. The magnetization and NMR relaxation rate can be qualitatively described either by a quasi-1D picture of weakly coupled chains or by mean-field theories of specific 2D spin liquids; however, quantitative differences exist between data and theory in both cases. This comparison indicates that 2D interactions are quantitatively important in describing the low-energy physics.