Zheludev, A. ; Garlea, V.O. ; Tsvelik, A. ; Regnault, L.-P. ;, Habicht, K. ; Kiefer, K. ; Roessli, B.: Excitations from a chiral magnetized state of a frustrated quantum spin liquid. Physical Review B 80 (2009), p. 214413/1-6
10.1103/PhysRevB.80.214413
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.