Excitations from a chiral magnetized state of a frustrated quantum spin liquid

TL;DR

This paper investigates the excitations in a frustrated quantum spin liquid that transitions to a chiral helimagnetic phase under high magnetic fields, revealing unique spectral features and quasiparticle behaviors.

Contribution

It provides the first detailed experimental analysis of excitation spectra in a frustrated quantum spin liquid transitioning to a chiral magnetic phase.

Findings

Observation of a gapless Goldstone mode beyond critical field Hc

Detection of a massive magnon and bound excitation continuum

Distinct spectral differences from frustration-free spin liquids

Abstract

We study excitations in weakly interacting pairs of quantum spin ladders coupled through geometrically frustrated bonds. The ground state is a disordered spin liquid, that at high fields is replaced by an ordered chiral helimagnetic phase. The spectra observed by high-field inelastic neutron scattering experiments on the prototype compound Sul-Cu2Cl4 are qualitatively different from those in the previously studied frustration-free spin liquids. Beyond the critical field Hc=3.7 T, the soft mode that drives the quantum phase transition spawns two separate excitations: a gapless Goldstone mode and a massive magnon. Additional massive quasiparticles are clearly visible below Hc, but are destroyed in the ordered phase. In their place one observes a sharply bound excitation continuum.