Effects of Dissipation on a Quantum Critical Point with Disorder

We study the effects of dissipation on a disordered quantum phase transition with $O(N)$ order-parameter symmetry by applying a strong-disorder renormalization group to the Landau-Ginzburg-Wilson field theory of the problem. We find that Ohmic dissipation results in a nonperturbative infinite-randomness critical point with unconventional activated dynamical scaling while super-Ohmic damping leads to conventional behavior. We discuss applications to the superconductor-metal transition in nanowires and to the Hertz theory of the itinerant antiferromagnetic transition.

Figure 1

Temperature-coupling phase diagram for Ohmic dissipation. IRFP denotes the infinite-randomness critical point. The phase boundary (solid) and the crossover line (dashed) between the quantum critical and quantum paramagnetic (QPM) regions take unusual exponential forms leading to a wide quantum critical region. Both phases contain Griffiths regions near the IRFP [10].