Monday, April 22, 2013

1304.5419 (Jie Yong et al.)

Robustness of the Berezinskii-Kosterlitz-Thouless Transition in
Ultrathin NbN Films near the Superconductor-Insulator Transition

Jie Yong, T. Lemberger, L. Benfatto, K. Ilin, M. Siegel
Occurrence of the Berezinskii-Kosterlitz-Thouless (BKT) transition is investigated by superfluid density measurements for two-dimensional (2D) disordered NbN films with disorder level very close to a superconductor-insulator transition (SIT). Our data show a robust BKT transition even near this 2D disorder-tuned quantum critical point (QCP). This observation is in direct contrast with previous data on deeply underdoped quasi-2D cuprates near the SIT. As our NbN films approach the QCP, the vortex-core energy, an important energy scale in the BKT transition, scales with the superconducting gap, not with the superfluid density, as expected within the standard 2D-XY model description of BKT physics.
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