Magnon pairing in quantum spin nematic
Service de Physique Statistique, Magnétisme et Supraconductivité, UMR-E9001 CEA-INAC/UJF 17 rue des Martyrs, F-38054 Grenoble cedex 9, France
2 Institute for Solid State Physics, University of Tokyo - Kashiwanoha, 5-1-5, Chiba 277-8581 Japan
3 Max-Planck-Institut für Physik Komplexer Systeme - Nöthnitzer str. 38, D-01187 Dresden, Germany
Accepted: 25 October 2010
Competing ferro- and antiferromagnetic exchange interactions may lead to the formation of bound magnon pairs in the high-field phase of a frustrated quantum magnet. With decreasing field, magnon pairs undergo a Bose-condensation prior to the onset of a conventional one-magnon instability. We develop an analytical approach to study the zero-temperature properties of the magnon-pair condensate, which is a bosonic analog of the BCS superconductors. The representation of the condensate wave function in terms of the coherent bosonic states reveals the spin-nematic symmetry of the ground state and allows one to calculate various static properties. Sharp quasiparticle excitations are found in the nematic state with a small finite gap. We also predict the existence of a long-range–ordered spin-nematic phase in the frustrated chain material LiCuVO4 at high fields.
PACS: 75.10.Jm – Quantized spin models, including quantum spin frustration / 75.10.Kt – Quantum spin liquids, valence bond phases and related phenomena / 75.10.Pq – Spin chain models
© EPLA, 2010