arXiv subjects

A. I. Kolbatova

Publications and source records attributed to A. I. Kolbatova.

6 recordsLinked to original sources

arXiv2025

Low-temperature electron dephasing rates indicate magnetic disorder in superconducting TiN films

We investigate electron transport and phase-breaking processes in thin titanium nitride (TiN) films of epitaxial quality. Previous studies show that a minute surface magnetic disorder significantly reduces the critical temperature ($T_\mathrm{c}$) and broadens the superconducting transition as the film thickness and device size decrease. We measure electron dephasing rates via magnetoresistance from $T_\mathrm{c}$ to $\sim 4T_\mathrm{c}$ in various-thickness TiN films. Electron dephasing occurs on the picosecond timescale and is nearly independent of temperature, differing from the expected inelastic scattering due to the electron-phonon and electron-electron interactions near $T_\mathrm{c}$, which occur over a nanosecond timescale. We propose spin-flip scattering as a possible additional phase-breaking mechanism. The significant increase in the dephasing rate for the thinnest film indicates that magnetic disorder resides near the surface of naturally oxidized films. Our research suggests that magnetic disorder may be a significant contributor to RF dissipation in superconducting devices based on TiN.

cond-mat.supr-con↗

arXiv2025

Accurate measurement of energy relaxation via flux-flow instability

In this paper, we investigate flux-flow instability (FFI) in a superconducting single-crystal titanium nitride (TiN) film with negligible volume pinning. By studying the critical current density in 12-nm thick TiN strips of varying widths, we accurately identify the experimental parameters at which the FFI regime occurs. A comprehensive analysis of critical velocity measurements allows us to determine the quasiparticle energy relaxation time, $τ_E$. By comparing our results with the $τ_E$ values obtained from other experimental methods, we gain insight into the dominant microscopic process that governs quasiparticle relaxation within the vortex core in TiN. This mechanism is driven by an increase in quasiparticle temperature relative to phonons, rather than by quasiparticles leaving the core. Our findings indicate that $τ_E$ can be accurately determined through FFI measurements.

cond-mat.supr-con↗

arXiv2024

Natural width of the superconducting transition in epitaxial TiN films

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 $ΔT/T_\mathrm{c} \sim 0.002-0.025$, 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 ($ΔT/T_\mathrm{c} \ll 10^{-3}$). 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.

cond-mat.supr-con↗

arXiv2024

Slow electron-phonon relaxation controls the dynamics of the superconducting resistive transition

We investigate the temporal and spatial scales of resistance fluctuations ($R$-fluctuations) at the superconducting resistive transition accessed through voltage fluctuations measurements in thin epitaxial TiN films. This material is characterized by a slow electron-phonon relaxation, which puts it far beyond the applicability range of the textbook scenario of superconducting fluctuations. The measured Lorentzian spectrum of the $R$-fluctuations identifies their correlation time, which is nearly constant across the transition region and has no relation to the conventional Ginzburg-Landau time scale. Instead, the correlation time coincides with the energy relaxation time determined by a combination of the electron-phonon relaxation and the relaxation via diffusion into reservoirs. Our data is quantitatively consistent with the model of spontaneous temperature fluctuations and highlight the lack of understanding of the resistive transition in materials with slow electron-phonon relaxation.

cond-mat.supr-con↗

arXiv2023

Fundamental limits of few-layer NbSe$_2$ microbolometers at terahertz frequencies

The rapid development of infrared spectroscopy, observational astronomy, and scanning near-field microscopy has been enabled by the emergence of sensitive mid- and far-infrared photodetectors. Owing to their exceptional signal-to-noise ratio and fast photoresponse, superconducting hot-electron bolometers (HEBs) have become a critical component in these applications. While superconducting HEBs are traditionally made from sputtered superconducting thin films like Nb or NbN, the potential of layered van der Waals (vdW) superconductors is untapped at THz frequencies. Here, we report the fabrication of superconducting HEBs out of few-layer NbSe$_2$ microwires. By improving the interface between NbSe$_2$ and metal leads connected to a broadband antenna, we overcome the impedance mismatch between this vdW superconductor and the radio frequency (RF) readout circuitry that allowed us to achieve large responsivity THz detection over the range from 0.13 to 2.5 THz with minimum noise equivalent power of 7~pW$\sqrt{Hz}$. Using the heterodyne sub-THz mixing technique, we reveal that NbSe$_2$ superconducting HEBs are relatively fast and feature a characteristic response time in the nanosecond range limited by the slow heat escape to the bath through a SiO$_2$ layer, on which they are assembled, in agreement with energy relaxation model. Our work expands the family of materials for superconducting HEBs technology, reveals NbSe$_2$ as a promising platform, and offers a reliable protocol for the in-lab production of custom bolometers using the vdW assembly technique.

cond-mat.supr-con↗

arXiv2022

Evidence of the disorder-independent electron-phonon scattering time in thin NbN films

We report on experimental study of the effect of disorder on electronic parameters and inelastic scattering mechanisms in ultrathin superconducting NbN films, which are commonly used in single-photon detectors. An increase in disorder in the studied 2.5 nm thick NbN films characterized by Ioffe-Regel parameter from 6.3 to 1.6 is accompanied by a decrease in the critical temperature $T_c$ from 11.5 K to 3.4 K. By measuring magnetoconductance in the range from $T_c$ to $\sim3T_c$, we extract the inelastic scattering rates of electrons, including electron-phonon (e-ph) scattering rates $τ_{e-ph}^{-1}$. We observe that $τ_{e-ph}^{-1}$ and their temperature dependencies are insensitive to disorder that is not described by the existing models of the e-ph scattering in disordered metals and can be due to the presence of weakly disordered metal grains. As the temperature decreases the temperature dependence $τ_{e-ph}^{-1}$ changes from $T^3$ to $T^2$, which can be result of a decrease in the dimension of the phonons involved in the e-ph scattering. The obtained values of material parameters of ultrathin NbN films can be useful for optimization of performance of NbN-based electronic devices.

cond-mat.supr-con↗