Pair-breaking quantum phase transition in superconducting nanowires
Résumé
A quantum phase transitions (QPT) between distinct ground states of matter is a wide-spread phenomenon in nature, yet there are only a few real systems where the microscopic mechanism of the transition can be tested and understood. These systems are unique and form the experimentally established foundation for our understanding of quantum critical phenomena. Here we report the discovery that a magnetic-field-driven QPT in superconducting nanowires, a prototypical 1d-system, can be fully explained by the critical theory of pair-breaking transitions. The theory quantitatively describes the dependence of conductivity on the critical temperature, field magnitude and orientation, nanowire cross sectional area, and microscopic parameters of the nanowire material. The QPT is characterized by a dynamic critical exponent, $z=2$ due to a dissipative coupling between Cooper pairs and electronic degrees of freedom. At the critical field, the conductivity follows a $T^{(d-2)/z}$ dependence predicted by phenomenological scaling theories and more recently obtained within a holographic framework.