Talk by Martin Mourigal, ILL and EPFL – Niels Bohr Institute - University of Copenhagen

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Niels Bohr Institute > Calendar > 2010 > Talk by Martin Mouriga...

Talk by Martin Mourigal, ILL and EPFL

The S = ½ square-lattice Heisenberg antiferromagnet (SLHAF) describes a large variety of Mott insulating materials and has received tremendous attention in the last decades. Spin-Wave Theory (SWT) is a successful paradigm to describe its spin dynamics although the existence of T=0 quantum fluctuations may lead to failures of the spin-wave picture and emergence of new phenomena. Recent experimental efforts focused on the deviations from the linear spin-wave behavior, in zero and finite applied magnetic field, in particular at the magnetic zone boundary points (π,0) and (π/2,π/2).

After a general introduction to the dynamics of low-dimensional quantum magnets and their study by neutron scattering, we will discuss the case of the SLHAF from both the experimental and the theoretical standpoints. In particular, we will present recent inelastic neutron scattering results, in zero and finite field, on the model compounds CFTD [Cu(DCOO)2.4D2O] and CAPCC [(2-amino-5-chloropyridinium)CuCl4] confirming the role of quantum effects already in non-frustrated materials. We will report the observation of multi-magnon continua as well as of spontaneous magnon decays as two signatures of non-linear quantum effects. Our findings will be compared with theoretical and numerical results obtained with SWT, Quantum Monte-Carlo and Exact Diagonalization.

Talk by: Martin Mourigal, Institut Laue-Langevin (ILL), Grenoble, France
& Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland