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.
@article{arxiv.0909.3355,
title = {Excitations from a chiral magnetized state of a frustrated quantum spin liquid},
author = {A. Zheludev and V. O. Garlea and A. Tsvelik and L. -P. Regnault and K. Habicht and K. Kiefer and B. Roessli},
journal= {arXiv preprint arXiv:0909.3355},
year = {2015}
}