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Abstract

Using Schwinger-boson mean-field theory, we calculate the dynamic spin structure factor at low temperatures 0 < T << J for the spin-1/2 antiferromagnetic Heisenberg kagome model, within the gapped Z(2) spin liquid phase Ansatz. We find that the spectral gap rapidly fills with temperature, with robust low-energy spectral weight developing by a temperature of Delta/3, where the spin gap is 2 Delta (i.e., Delta is the spinon gap), before any appreciable rise in spinon density or change in zero-temperature mean-field parameters. This is due to deconfinement of spinons which leads to terms suppressed only by exp(-Delta/T). At still higher temperatures, the spinon density increases rapidly leading to a breakdown of the Schwinger-boson mean-field approach. We suggest that if the impurity-free spectral functions can be obtained through neutron scattering experiments on kagome herbertsmithites, temperature dependence of the subgap weight can provide distinct signatures of a Z(2) quantum spin liquid.