Monday, January 14, 2013
Our measurements of the ac conductivity of disordered thin films near the field-tuned superconductor-insulator transition show a sudden drop in the superfluid response with either increased temperature or with applied magnetic field. Surprisingly, this abrupt drop, seen in two different material systems, has the same universal value as that expected for a Berezinskii-Kosterlitz-Thouless (vortex-antivortex unbinding) transition in zero field, despite the presence of a net vorticity. What's more, we find that the characteristic temperature where the phase rigidity of superconducting order is suddenly lost can be tuned to zero at a critical magnetic field smaller than that measured using traditional electrical transport measurements, suggesting the possibility that there is an intermediate metallic phase which appears once phase coherence is suddenly lost in the field-tuned transition out of the superconducting state.
Published in Physical Review Letters, "Evidence for a universal minimum superfluid response in field-tuned disordered superconducting films," Shashank Misra, Lukas Urban, Minsoo Kim, Ganapathy Sambandamurthy and Ali Yazdani, Phys. Rev. Lett. 110, 037002 (2013). (Letter)