Dresden 2026 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 64: BKT Physics
TT 64.2: Vortrag
Mittwoch, 11. März 2026, 17:00–17:15, HSZ/0103
Finite-size effects in the vicinity of the BKT transition in superconducting NbN thin films — •Lea Pfaffinger1, Alexander Weitzel1, Sven Linzen2, Evgenii Il’ichev2, Ilaria Maccari3, and Christoph Strunk1 — 1Department of Experimental Physics, University Regensburg, Regensburg, Germany — 2Leibniz Institute of Photonic Technology, Jena, Germany — 3ETH, Zurich, Switzerland
For 2D superconducting thin films, Halperin and Nelson predicted a finite resistance between the Berezinskii-Kosterlitz-Thouless temperature TBKT and the mean-field critical temperature Tc0 due to 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 the Pearl length Λp≈2mm>>w=10µ m, we did not observe a size induced smearing of the transition. When further reducing the width to w≤1µ m, we do observe a finite resistance for T<TBKT as expected from the cut-off of the divergence of the correlation length by the finite size. This 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).
Keywords: BKT transition; vortices; superconducting thin film; disordered superconductor