Dynamics of a bond-disordered $S=1$ quantum magnet near $z=1$ criticality

Abstract

Neutron scattering is used to study NiCl${}_{2-2x}$Br${}_{2x}\cdot$4SC(NH${}_2$)${}_2$, $x=0.06$, a bond-disordered modification of the well-known gapped $S=1$ antiferromagnetic quantum spin system NiCl${}_2\cdot$4SC(NH${}_2$)${}_2$. The magnetic excitation spectrum throughout Brillouin zone is mapped out at $T=60$ mK using high-resolution time-of-flight spectroscopy. It is found that the dispersion of spin excitation is renormalized, as compared to that in the parent compound. The lifetime of excitations near the bottom of the band is substantially decreased. No localized states are found below the gap energy $\Delta \simeq 0.2$ meV. At the same time, localized zero wave vector states are detected above the top of the band. The results are consistent with a more or less continuous random distribution of bond strengths, and a discrete, possibly bimodal, distribution of single-ion anisotropies in the disordered material.

11 pages, 10 figures, 3 tables

References in corpus (7)

• Quantum magnetism and criticality
• Rare region effects at classical, quantum, and non-equilibrium phase transitions
• A direct measurement of the Bose-Einstein Condensation universality class in NiCl${}_2$-4SC(NH${}_2$)${}_2$ at ultra-low temperatures
• Characterizing the Haldane phase in quasi-one-dimensional spin-1 Heisenberg antiferromagnets
• Spin Dynamics of $NiC{l}_2-4SC(N{H}_2{)}_2$ in the Field-Induced Ordered Phase
• Critical exponents and intrinsic broadening of the field-induced transition in NiCl${}_2$$\cdot$4SC(NH${}_2$)${}_2$
• Localized and propagating excitations in gapped phases of spin systems with bond disorder

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