Field induced spontaneous quasiparticle decay and renormalization of quasiparticle dispersion in a quantum antiferromagnet

TL;DR

This study investigates how high magnetic fields induce quasiparticle decay and alter magnon dispersion in a quantum antiferromagnet, revealing complex many-body effects through neutron scattering experiments.

Contribution

It provides detailed experimental evidence of field-induced magnon decay, dispersion renormalization, and spectral weight transfer in a quantum antiferromagnet, expanding understanding of quantum many-body phenomena.

Findings

Field-induced magnon decay observed via linewidth broadening

Renormalization of magnon dispersion in high magnetic fields

Spectral weight shifts from one-magnon to multi-magnon states

Abstract

The notion of a quasiparticle, such as a phonon, a roton, or a magnon, is used in modern condensed matter physics to describe an elementary collective excitation. The intrinsic zero-temperature magnon damping in quantum spin systems can be driven by the interaction of the one-magnon states and multi-magnon continuum. However, detailed experimental studies on this quantum many-body effect induced by an applied magnetic field are rare. Here we present a high-resolution neutron scattering study in high fields on an S=1/2 antiferromagnet C9H18N2CuBr4. Compared with the non-interacting linear spin-wave theory, our results demonstrate a variety of phenomena including field-induced renormalization of one-magnon dispersion, spontaneous magnon decay observed via intrinsic linewidth broadening, unusual non-Lorentzian two-peak structure in the excitation spectra, and a dramatic shift of spectral weight from one-magnon state to the two-magnon continuum.