Dissipation-Driven Breakdown of Universality in Two-Dimensional Superconductors

The influence of gapless dissipative degrees of freedom on the superconductor-insulator transition in two dimensions is investigated. We develop a series expansion for the free energy of a (2+1)-dimensional XY model coupled to a bosonic heat bath that can be approximately summed to all orders. The calculation explicitly conserves topological excitations. We derive the zero temperature phase diagram and the free energy critical exponent, and find a transition from universal to non-universal scaling behavior as the coupling to the dissipative environment is increased, implying the existence of a new universality class.