Character of magnetic excitations in a quasi-one-dimensional antiferromagnet near the quantum critical points: Impact on magneto-acoustic properties

TL;DR

This study investigates how magnetic excitations in a quasi-one-dimensional antiferromagnet influence its magneto-acoustic properties near quantum critical points, revealing a crossover from fermionic to bosonic excitations.

Contribution

It provides experimental evidence of a crossover from fermionic to bosonic magnetic excitations near quantum critical points in a quasi-1D antiferromagnet.

Findings

Pronounced softening of the acoustic $c_{33}$ mode near QCPs

Presence of fermionic magnetic excitations above $T_N$

Crossover from 1D fermionic to 3D bosonic excitations

Abstract

We report results of magneto-acoustic studies in the quantum spin-chain magnet NiCl$_2$-4SC(NH$_2$)$_2$ (DTN) having a field-induced ordered antiferromagnetic (AF) phase. In the vicinity of the quantum critical points (QCPs) the acoustic $c_{33}$ mode manifests a pronounced softening accompanied by energy dissipation of the sound wave. The acoustic anomalies are traced up to $T > T_N$, where the thermodynamic properties are determined by fermionic magnetic excitations, the "hallmark" of one-dimensional (1D) spin chains. On the other hand, as established in earlier studies, the AF phase in DTN is governed by bosonic magnetic excitations. Our results suggest the presence of a crossover from a 1D fermionic to a 3D bosonic character of the magnetic excitations in DTN in the vicinity of the QCPs.