Finite temperature behavior of strongly disordered quantum magnets coupled to a dissipative bath

We study the effect of dissipation on the infinite randomness fixed point and the Griffiths–McCoy singularities of random transverse Ising systems in chains, ladders and in two dimensions. A strong disorder renormalization group scheme is presented that allows the computation of the finite temperature behavior of the magnetic susceptibility and the spin specific heat. In the case of ohmic dissipation the susceptibility displays a crossover from Griffiths–McCoy behavior (with a continuously varying dynamical exponent) to classical Curie behavior at some temperature T ∗. The specific heat displays Griffiths–McCoy singularities over the whole temperature range. For super-ohmic dissipation we find an infinite randomness fixed point within the same universality class as the transverse Ising system without dissipation. In this case the phase diagram and the parameter dependence of the dynamical exponent in the Griffiths–McCoy phase can be determined analytically.