Quantum magnetism and quantum phase transitions

Abstract:

The spin excitation spectrum in the 2D square lattice Heisenberg antiferromagnet CFTD has been investigated using time-of-flight neutron scattering. The magnon dispersion and intensities have been determined as a function of wavevector Q in the full Brillouin zone. Both quantities are found to deviate significantly from the predictions of linear spin wave theory for wavevectors in the vicinity of Q=(π,0), whereas good agreement is found near Q=(π/2,π/2). © 2004 Published by Elsevier B.V.

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.