Thielemann, B.; Rüegg, Ch.; Rønnow, H.M.; Läuchli, A.M.; Caux J.-S.; Normand, B.; Biner, D.; Krämer, K.W.; Güdel, H.-U.; Stahn, J.; Habicht, K.; Kiefer, K.; Boehm, M.; McMorrow, D.F.; Mesot, J.: Direct Observation of Magnon Fractionalization in the Quantum Spin Ladder. Physical Review Letters 102 (2009), p. 107204/1-5
10.1103/PhysRevLett.102.107204
Abstract:
We measure by inelastic neutron scattering the spin excitation spectra as a function of applied magnetic field in the quantum spin-ladder material ðC5H12NÞ2CuBr4. Discrete magnon modes at low fields in the quantum disordered phase and at high fields in the saturated phase contrast sharply with a spinon continuum at intermediate fields characteristic of the Luttinger-liquid phase. By tuning the magnetic field, we drive the fractionalization of magnons into spinons and, in this deconfined regime, observe both commensurate and incommensurate continua.