Quantum magnetism and quantum phase transitions

Abstract:

We explore the magnetic excitations as a function of applied field in the quasi 1D s=12 XY-like magnet Cs2CoCl4. A transition from spin-flop antiferromagnetic order to a quantum paramagnet occurs at the critical field BC=2.15 T and fields higher than 2.5 T fully align the spins along the field. In the spin-flop phase gapped scattering continua dominate, identified with the creation of pairs of quantum domain walls. In the saturated phase sharp peaks are observed, as expected for magnons in a ferromagnetically ordered ground state. © 2003 Elsevier B.V. All rights reserved.

Abstract:

High-resolution inelastic neutron scattering is used to explore the magnetic excitations in Cs2CuCl4, a quasi-2D spin-5 frustrated Heisenberg antiferromagnet on an anisotropic triangular lattice. In the spin liquid phase above the 3D ordering transition a broad continuum of excited states is observed, characteristic of excitations of pairs of spin-1/2 spinons of a resonating-valence-bond state. In the ordered phase stabilized at low temperatures by the weak inter-layer couplings a sharp spin-wave mode emerges below the continuum lower boundary. © 2004 Published by Elsevier B.V.