# Condensed-Matter Physics & Materials Science Seminar

## "Pair-breaking quantum phase transition in superconducting nanowires"

#### Presented by Andrey Rogachev, University of Utah

Friday, September 7, 2018, 11:00 am — ISB Bldg. 734 Conference Room 201 (upstairs)

Quantum phase transitions (QPT) between distinct ground states of matter are widespread phenomena, yet there are only a few experimentally accessible systems where the microscopic mechanism of the transition can be tested and understood. In this talk we will report on discovery that a magnetic-field driven quantum phase transition in MoGe superconducting nanowires can be fully explained by the critical theory of pair-breaking transitions characterized by a correlation length exponent v≈1 and dynamic critical exponent 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 dependence of conductivity on the critical temperature, field magnitude and orientation, nanowire cross-sectional area, and microscopic parameters of the nanowire material. 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. Our work uncovers the microscopic processes governing the transition: the pair-breaking effect of the magnetic field on interacting Cooper pairs overdamped by their coupling to electronic degrees of freedom. It also reveals the universal character of continuous quantum phase transitions. In the talk we will also briefly comment on reliability of the finite-size scaling analysis, origin of zero-bias anomaly in wires and implication of our finding for QPT in superconducting films.

Hosted by: Ivan Bozovic

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