Extended universal finite-T renormalization of excitations in a class of one-dimensional quantum magnets

Temperature dependencies of gap energies and magnon lifetimes are measured in the quasi-one-dimensional S=1/2 gapped quantum magnets (CH3)2CHNH3CuCL3 (IPA-CuCl3, where IPA denotes isopropyl ammonium) and Cu2Cl4•D8C4SO2 (Sul-Cu2Cl4) using inelastic neutron scattering. The results are compared to those found in literature for S=1 Haldane spin chain materials and to theoretical calculations for the O(3)- and O(N)- quantum nonlinear σ-models. It is found that when the T=0 energy gap Δ is used as the temperature scale, all experimental and theoretical curves are identical to within system-dependent but temperature-independent scaling factors of the order of unity. This quasi-universality extends over a surprising broad T range, at least up to κT∼1.5Δ.