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.
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