Experimental Realization of a 2D Fractional Quantum Spin Liquid

Abstract

The ground-state ordering and dynamics of the two-dimensional $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ frustrated Heisenberg antiferromagnet ${\mathrm{Cs}}_{2}{\mathrm{CuCl}}_{4}$ are explored using neutron scattering in high magnetic fields. We find that the dynamic correlations show a highly dispersive continuum of excited states, characteristic of the resonating valence bond state, arising from pairs of $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ spinons. Quantum renormalization factors for the excitation energies (1.65) and incommensuration (0.56) are large.