Direct Observation of Magnon Fractionalization in the Quantum Spin Ladder

Authors :: 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.
Source :: Phys. Rev. Lett. 102, 107204 (2009)
Publication Year :: 2008
Abstract: We measure by inelastic neutron scattering the spin excitation spectra as a function of applied magnetic field in the quantum spin-ladder material (C5H12N)2CuBr4. 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.<br />Comment: 4 pages, 4 figures