Berlin 2008 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 29: Spin Structures / Magnetic Phase Transitions
MA 29.4: Vortrag
Donnerstag, 28. Februar 2008, 18:30–18:45, H 1012
Quantum Phase Transition of a Magnet in a Spinbath — •Conradin Kraemer1,2, Henrik M. Ronnow1, Joel Mesot2, Peter Link3, Astrid Schneidewind4, Tobias Unruh3, Thomas F. Rosenbaum5, Gabriel Aeppli6, and Jens Jensen7 — 1Laboratory for Quantum Magnetism EPFL, CH-1015 Lausanne — 2Laboratory for Neutron Scattering ETHZ PSI, CH-5232 Villigen — 3Forschungsneutronenquelle FRM II, D-85747 Garching — 4Institut für Festkoerperphysik, TU Dresden, D-01062 Dresden — 5Department of Physics, University of Chicago, Chicago, IL 60637 — 6London Centre for Nanotechnology, UCL, London WC1E 6BT — 7Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen
As a physical realisation of the ferromagnetic Ising model with a quantum phase transition in a transverse field of 5T, LiHoF4 is a widely celebrated model system with a thoroughly characterized Hamiltonian. However, the innocently weak hyperfine coupling to the nuclear spins dramatically influence the quantum critical point. Below 600 mK the critical field is extended slightly upwards. More spectacularly, is softening of the principal electronic excitation - the hall mark of a quantum phase transition - forestalled by hybridization, which transfers true softening to the mixed nuclear electronic states at much lower energies. The electronic system thus remain sub-critical with finite quantum coherence. We report the counterintuitive observation that maximum electronic quantum criticality is achieved not as expected at T=0 K but rather at a finite intermediate temperature 0<T<Tc.