Berezinskii-Kosterlitz-Thouless to BCS-like superconducting transition crossover driven by weak magnetic fields in ultra-thin NbN films

Meenakshi Sharma; Sergio Caprara; Andrea Perali; Surinder P. Singh; Sandeep Singh; Matteo Fretto; Natascia De Leo; Nicola Pinto

arXiv · 2403.11685

Berezinskii-Kosterlitz-Thouless to BCS-like superconducting transition crossover driven by weak magnetic fields in ultra-thin NbN films

Meenakshi Sharma·Sergio Caprara·Andrea Perali·Surinder P. Singh·Sandeep Singh·Matteo Fretto·Natascia De Leo·Nicola Pinto

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Abstract

The Berezinskii-Kosterlitz-Thouless (BKT) transition in ultra-thin NbN films is investigated in the presence of weak perpendicular magnetic fields. A jump in the phase stiffness at the BKT transition is detected up to 5 G, while the BKT features are smeared between 5 G and 50 G, disappearing altogether at 100 G, where conventional current-voltage behaviour is observed. Our findings demonstrate that weak magnetic fields, insignificant in bulk systems, deeply affect our ultra-thin system, promoting a crossover from Halperin-Nelson fluctuations to a BCS-like state with Ginzburg-Landau fluctuations, as the field increases. This behavior is related to field-induced free vortices that screen the vortex-antivortex interaction and smear the BKT transition.

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Meenakshi Sharma, Sergio Caprara, Andrea Perali, Surinder P. Singh, Sandeep Singh, Matteo Fretto, Natascia De Leo, Nicola Pinto. 2024-03-18. Berezinskii-Kosterlitz-Thouless to BCS-like superconducting transition crossover driven by weak magnetic fields in ultra-thin NbN films. https://arxiv.org/abs/2403.11685

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