Natural width of the superconducting transition in epitaxial TiN films

• Main Authors: Baeva, E. M, Kolbatova, A. I, Titova, N. A, Saha, S, Boltasseva, A, Bogdanov, S, Shalaev, V. M, Semenov, A. V, Goltsman, G. N, Khrapai, V. S
• Format: Journal Article
• Language: English
• Published: 02-10-2024
• Subjects: Physics - Mesoscale and Nanoscale Physics; Physics - Superconductivity
• DOI: 10.48550/arxiv.2202.06310

Supercond. Sci. Technol. 37, 105017 (2024) We investigate the effect of various fluctuation mechanisms on the DC
resistance in superconducting devices based on epitaxial titanium nitride (TiN)
films. The samples we studied show a relatively steep resistive transition
(RT), with a transition width $\Delta T/T_\mathrm{c} \sim 0.002-0.025$,
depending on the film thickness (20 nm, 9 nm, and 5 nm) and device dimensions.
This value is significantly broader than expected due to conventional
superconducting fluctuations ($\Delta T/T_\mathrm{c} \ll 10^{-3}$). The shape
and width of the RT can be perfectly described by the well-known effective
medium theory, which allows us to understand the origin of the inhomogeneity in
the superconducting properties of TiN films. We propose that this inhomogeneity
can have both dynamic and static origins. The dynamic mechanism is associated
with spontaneous fluctuations in electron temperature (T-fluctuations), while
the static mechanism is due to a random spatial distribution of surface
magnetic disorder (MD). Our analysis has revealed clear correlations between
the transition width and material parameters as well as device size for both
proposed mechanisms. While T-fluctuations may contribute significantly to the
observed transition width, our findings suggest that the dominant contribution
comes from the MD mechanism. Our results provide new insights into the
microscopic origin of broadening of the superconducting transition and
inhomogeneity in thin superconducting films.