Theory of the pair-breaking quantum phase transition in superconducting nanowires*

We present a theoretical description of a zero temperature phase transition between superconducting and diffusive metallic states in ultra thin wires induced by Cooper pair-breaking perturbations. Fluctuation corrections to BCS theory motivate a dissipative field theory that can be used to compute the universal scaling of the electrical and thermal conductivity in the quantum critical regime. In the large-N limit, we obtain predictions for transport in striking agreement with recent experimental measurements of the fluctuation conductivity of metallic nanowires in parallel and transverse magnetic fields. The ability to quantitatively describe the experiment goes beyond the usual scaling approach and validates the underlying pair-breaking mechanisms near the quantum phase transition. Extensions of the theory including the effects of disorder and higher dimensions are considered, with implications for the interpretation of transport measurements in superconducting films.