Experimentally observed magnetic-field driven quantum phase transition in superconducting nanowires and its striking agreement with critical theory.

We have discovered that a magnetic-field driven quantum phase transition (QPT) in MoGe superconducting nanowires can be fully explained by the pair-breaking critical theory with exponents v≈1 and z≈ 2. We find that in the quantum critical regime, the electrical conductivity is in agreement with a theoretically predicted scaling function and, moreover, that the theory quantitatively describes the nonuniversal dependence of conductivity on the critical temperature, field magnitude and orientation, nanowire cross-sectional area, and microscopic parameters of the nanowire material. Our data analysis is very different from what was used in the past for QPT in superconducting films: (i) we have subtracted contribution of normal electrons, both Drude and quantum corrections, and found that QPT occurs only in the superconducting part of the system, (ii) we also have kept the critical exponents fixed to their theoretical values and not varied them in the scaling procedure. In the second part of the talk, we will briefly comment on reliability of the finite-size scaling analysis and present our work-in-progress on QPT in MoGe films. In these films we have not observed the bosonic “strange metal” phase. However, we have found some evidences of a pair-breaking QPT that occurs at about 0.1 of quantum conductance of Cooper pairs.