Upper critical field measurement and penetration depth determination for superconducting NbCN films

Abstract

High T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> , low resistivity NbCN films were prepared by rf sputtering in a reactive gas mixture of Ar, N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and cyanogen. Upper critical field for parallel and perpendicular orientation of the films to the applied field were measured systematically from T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> down to 1.5 K. The critical field anisotropy is anomalous i.e., <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H\min{c2}\max{\perp} &gt; H\min{c2}\max{\parallel}</tex> for films sputtered at lower substrate temperature, whereas it shows normal behavior for films deposited at T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> ∼ 1100°C. This behavior is similar to that in sputtered NbN. The measured critical current in the presence of an applied magnetic field is lower than that in NbN of comparable properties. The penetration depth, λ(0), was determined by measuring the self inductance of these NbCN films using it as an inductor in an LC oscillator circuit driven by a tunnel diode. It appears that NbCN films have lower λ(0) than sputtered NbN films. The fact that NbCN films have higher T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> , lower ρ and lower λ(0) makes this a somewhat better superconductor for superconducting electronics applications.