Dissipation in strongly disordered quantum magnets
Heiko Rieger
Theoretische Physik, Universitaet d. Saarlandes, 66041 Saarbruecken, Germany
The presence of quenched disorder in a quantum mechanical system may have drastic effects in particular close to and at a quantum critical point. The appearance of Griffiths-McCoy singularities, leading to the divergence of various quantities like the susceptibility at zero temperature even far away from a quantum critical point, has received considerable attention recently. This quantum Griffiths behavior is characteristic for quantum phase transitions described by an infinite randomness fixed point (IRFP), which is relevant for many disordered quantum systems. Here we study the effect of a dissipative environment, as for instance present in metals due to the conduction electrons, on such a scenario in a magnetic system with a strong disorder renormalization group scheme. We find that at the coupling of disordered magnet to a dissipative Ohmic bath transforms the sharp quantum transition into a smeared one and produces a crossover from singular quantum-Griffiths behavior to classic Curie behavior at low temperatures.