paper

Scaling and data collapse from local moments in frustrated disordered quantum spin systems

arXiv:1803.00013 · doi:10.1038/s41467-018-06800-2

Abstract

Recently measurements on various spin-1/2 quantum magnets such as HLiIrO, LiZnMoO, ZnCu(OH)Cl and 1T-TaS -- all described by magnetic frustration and quenched disorder but with no other common relation -- nevertheless showed apparently universal scaling features at low temperature. In particular the heat capacity C[H,T] in temperature T and magnetic field H exhibits T/H data collapse reminiscent of scaling near a critical point. Here we propose a theory for this scaling collapse based on an emergent random-singlet regime extended to include spin-orbit coupling and antisymmetric Dzyaloshinskii-Moriya (DM) interactions. We derive the scaling with at small , with (0,1,2) an integer exponent whose value depends on spatial symmetries. The agreement with experiments indicates that a fraction of spins form random valence bonds and that these are surrounded by a quantum paramagnetic phase. We also discuss distinct scaling for magnetization with a -dependent subdominant term enforced by Maxwell's relations.

v2. Expanded argument in Appendix 2 and revised for clarity. v3. Fixed typo in Fig 3 caption. Main text 4 pages 4 figures, Appendix 6 pages 1 figure

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