Condensed Matter Seminar Series

Dissipative Effects in Quantum Phase Transitions of Disordered Magnets

Jose A. Hoyos Neto

Duke University

Thursday November 8,  11:30 am,  Room 298,  Physics Building

Abstract:  We will discuss the interplay between dissipation, symmetry, and quenched disorder in quantum phase transitions. We will mainly focus on a randomly diluted transverse-field Ising magnet close to the percolation threshold in which each spin is coupled to a bosonic bath corresponding to Landau damping. For weak transverse fields, a novel percolation quantum phase transition separates a superparamagnetic cluster phase from an inhomogeneously ordered ferromagnetic phase. The properties of this transition are dominated by large frozen and slowly fluctuating percolation clusters. This leads to a discontinuous magnetization-field curve and exotic hysteresis phenomena as well as highly singular behavior of magnetic susceptibility and specific heat. We compare our results to the smeared transition in generic dissipative random quantum Ising magnets. We point out the role of the symmetry by comparing these scenarios with that one concerning O(N) quantum rotors with N>1. Finally, we discuss the relation to metallic quantum magnets and other experimental realizations.