By means of nuclear spin-lattice relaxation rate 1/T1, we follow the spin dynamics as a function of the applied magnetic field in two gapped one-dimensional quantum antiferromagnets: the anisotropic spin-chain system NiCl2-4SC(NH2)2 and the spin-ladder system (C5H12N)2CuBr4. In both systems, spin excitations are confirmed to evolve from magnons in the gapped state to spinons in the gapples Tomonaga-Luttinger-liquid state. In between, 1/T1 exhibits a pronounced, continuous variation, which is shown to scale in accordance with quantum criticality. We extract the critical exponent for 1/T1, compare it to the theory, and show that this behavior is identical in both studied systems, thus demonstrating the universality of quantum critical behavior.
@article{arxiv.1208.6117,
title = {Quantum-critical spin dynamics in quasi-one-dimensional antiferromagnets},
author = {S. Mukhopadhyay and M. Klanjšek and M. S. Grbić and R. Blinder and H. Mayaffre and C. Berthier and M. Horvatić and M. A. Continentino and A. Paduan-Filho and B. Chiari and O. Piovesana},
journal= {arXiv preprint arXiv:1208.6117},
year = {2014}
}