Presentation Title: Destructive regime, superconducting fluctuations, Little-Parks-de Gennes effect in doubly connected mesoscopic superconductors

When: 10:00 on July 17, 2015

Where: 502 Conference Hall, CHMFL

Host: Prof. Mingliang Tian

Abstract

Sample topology plays an important role in determining the properties of mesoscopic superconductors.  The Little-Parks effect, the quantum oscillations of the superconducting transition temperature with the applied flux, was observed long ago in doubly connected superconducting cylinders. Its limiting behavior, the loss of the global superconducting phase coherence near the half-flux quanta found in ultrasmall doubly connected rings or cylinders with a diameter smaller than the superconducting coherence length, referred to originally by de Gennes as the destructive regime, was found more recently. Here the superconductivity is destroyed because of the doubly connected sample topology that leads to a competition between the kinetic and the condensation energies. Moreover, de Gennes predicted that the global phase coherence in such doubly connected samples could be tuned by the addition of a side branch, referred to as the Little-Parks-de Gennes effect, which was confirmed experimentally recently.  I will present measurements on ultrathin doubly connected cylinders and ultrasmall loops of Al that led to the observation of the destructive regime and the Little-Parks-de Gennes effect and the exploration of depairing tuned superconducting quantum fluctuations near the onset of the destructive regime.