Collective Spin Dynamics in the Coherence Window for Quantum Nanomagnets.pdf

Collective Spin Dynamics in the ”Coherence Window” for Quantum Nanomagnets I. S. Tupitsyn1,2 1 Pacific Institute for Theoretical Physics, University of British Columbia, 6224 Agricultural Rd., Vancouver, B.C. V6T 1Z1, Canada 2 Theoretical Division of the Institute of Superconductivity and Solid State Physics, 5 Russian Research Centre ”Kurchatov Institute”, Kurchatov Sq.1, Moscow 123182, Russia 0 0 The spin coherence phenomena and the possibility of their observation in nanomagnetic insulators 2 attract more and more attention in the last several years. Recently it has been shown that in these systems in large transverse magnetic field there can be a fairly narrow ”coherence window” for n phonon and nuclear spin-mediated decoherence. What kind of spin dynamics can then be expected a in this window in a crystal of magnetic nanomolecules coupled to phonons, to nuclear spin bath J and to each other via dipole-dipole interactions? Studying multispin correlations, we determine the 3 region of parameters where ”coherent clusters” of collective spin excitations can appear. Although two particular systems, namely crystals of F e -triazacyclonane and Mn -acetate molecules, are 8 12 ] used in this work to illustrate the results, here we are not trying to predict an existence of collective l l coherent dynamics in some particular system. Instead, we discu