Regensburg 2007 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 30: Poster II

DY 30.33: Poster

Donnerstag, 29. März 2007, 16:00–18:00, Poster D

Effects of dissipation in random quantum magnets — •Heiko Rieger¹ and Gregory Schehr² — ¹Theoretische Physik, Universität des Saarlandes, PF 151150, D-66041 Saarbrücken — ²Laboratoire de Physique Théorique, Université de Paris-Sud, F-91405 Orsay

Quantum phase transitions in a large class of one-dimensional and some higher-dimensional quantum magnets with quenched disorder are described by an infinite randomness fixed point. Unusual scaling laws and the occurence of Griffiths-McCoy singularities away from the critical point characterize theses universality classes, which have been studied with a strong disorder renormalization group (SDRG), exact diagonalization and quantum Mone-Carlo methods. A coupling of the spin degrees of freedom to a dissipative bosonic bath alters this scenario significantly: The sharp quantum phase transition is smeared and the Griffiths-McCoy singularities become dominated by a classical behavior of the susceptibility and specific heat below a crossover temperature T*. By combining the SDRG with a renormalization scheme for the spin-boson-system it became possible to describe this crossover quantitatively in random transverse field Ising systems and possibly also in other quantum spin systems.