Orateur
Description
For 2D superconducting thin films, Halperin and Nelson predicted a finite resistance above the Berezinskii-Kosterlitz-Thouless temperature TBKT caused by the unbinding of thermally excited vortex-antivortex pairs. Recently, we observed a sharp BKT-transition in homogeneously disordered 3nm NbN films grown by ALD, which is in very good agreement with these theoretical predictions [1]. Although the sample width was much smaller than the Pearl length Λ ≃ 2mm ≫ w = 10µm, we did not observe a size induced smearing of the transition down to our detection limit. When further reducing the width to w ≤ 1µm, we do observe a finite resistance for T < T_BKT as expected from the cut-off of the divergence of the correlation length by the finite size. The resistance is thermally activated with an activation energy that depends logarithmically on the width. We present a systematic study of the resistance in this regime combined with an analysis based on the work of [2] and [3].
[1] A. Weitzel et al., Phys. Rev. Lett. 131, 186002 (2023).
[2] L. Benfatto et al., Phys. Rev. B 80, 214506 (2009).
[3] V.G. Kogan et al., Phys. Rev. B 83, 144526 (2011).