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Baeva, E. M., Titova, N. A., Veyrat, L., Sacépé, B., Semenov, A. V., Goltsman, G. N., et al. (2021). Thermal relaxation in metal films bottlenecked by diffuson lattice excitations of amorphous substrates. arXiv:2101.07071v1 [cond-mat.mtrl-sci]. Retrieved June 30, 2024, from https://arxiv.org/abs/2101.07071v1
Abstract: Here we examine the role of the amorphous insulating substrate in the thermal relaxation in thin NbN, InOx, and Au/Ni films at temperatures above 5 K. The studied samples are made up of metal bridges on an amorphous insulating layer lying on or suspended above a crystalline substrate. Noise thermometry was used to measure the electron temperature Te of the films as a function of Joule power per unit of area P2D. In all samples, we observe the dependence P2D∝Tne with the exponent n≃2, which is inconsistent with both electron-phonon coupling and Kapitza thermal resistance. In suspended samples, the functional dependence of P2D(Te) on the length of the amorphous insulating layer is consistent with the linear T-dependence of the thermal conductivity, which is related to lattice excitations (diffusons) for the phonon mean free path smaller than the dominant phonon wavelength. Our findings are important for understanding the operation of devices embedded in amorphous dielectrics.
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Saveskul, N. A., Titova, N. A., Baeva, E. M., Semenov, A. V., Lubenchenko, A. V., Saha, S., et al. (2019). Superconductivity behavior in epitaxial TiN films points at surface magnetic disorder. arXiv:1903.05009v3 [cond-mat.mtrl-sci]. Retrieved June 30, 2024, from https://arxiv.org/abs/1903.05009v3
Abstract: We analyze the evolution of the normal and superconducting electronic properties in epitaxial TiN films, characterized by high Ioffe-Regel parameter values, as a function of the film thickness. As the film thickness decreases, we observe an increase of in the residual resistivity, which becomes dominated by diffusive surface scattering for d≤20nm. At the same time, a substantial thickness-dependent reduction of the superconducting critical temperature is observed compared to the bulk TiN value. In such a high quality material films, this effect can be explained by a weak magnetic disorder residing in the surface layer with a characteristic magnetic defect density of ∼1012cm−2. Our results suggest that surface magnetic disorder is generally present in oxidized TiN films.
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Baeva, E., Sidorova, M., Korneev, A., & Goltsman, G. (2018). Precise measurement of the thermal conductivity of superconductor. In Proc. AIP Conf. (Vol. 1936, 020003 (1 to 4)).
Abstract: Measuring the thermal properties such as the heat capacity provide information about intrinsic mechanisms operated inside. In general, the ratio between electron and phonon specific heat Ce/Cp shows how the absorbed energy shared between electron and phonon subsystems. In this work we make estimations for amplitude-modulated absorption of THz radiation technique for investigation of the ratio Ce/Cp in superconducting Niobium Nitride (NbN) at T = Tc. Our results indicates that experimentally the frequency of modulation has to be extra large to extract the quantity. We perform a new technique allowed to work at low frequency with accurately measurement of absorbed power.
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Korneeva, Y. P., Vodolazov, D. Y., Semenov, A. V., Florya, I. N., Simonov, N., Baeva, E., et al. (2018). Optical single photon detection in micron-scaled NbN bridges. arXiv:1802.02881v1 [cond-mat.supr-con]. Retrieved June 30, 2024, from https://arxiv.org/abs/1802.02881v1
Abstract: We demonstrate experimentally that single photon detection can be achieved in micron-wide NbN bridges, with widths ranging from 0.53 μm to 5.15 μm and for photon-wavelengths from 408 nm to 1550 nm. The microbridges are biased with a dc current close to the experimental critical current, which is estimated to be about 50 % of the theoretically expected depairing current. These results offer an alternative to the standard superconducting single-photon detectors (SSPDs), based on nanometer scale nanowires implemented in a long meandering structure. The results are consistent with improved theoretical modelling based on the theory of non-equilibrium superconductivity including the vortex-assisted mechanism of initial dissipation.
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Baeva, E. M., Titova, N. A., Kardakova, A. I., Piatrusha, S. U., & Khrapai, V. S. (2020). Universal bottleneck for thermal relaxation in disordered metallic films. Jetp Lett., 111(2), 104–108.
Abstract: We study the heat relaxation in current biased metallic films in the regime of strong electron–phonon coupling. A thermal gradient in the direction normal to the film is predicted, with a spatial temperature profile determined by the temperature-dependent heat conduction. In the case of strong phonon scattering, the heat conduction occurs predominantly via the electronic system and the profile is parabolic. This regime leads to the linear dependence of the noise temperature as a function of bias voltage, in spite of the fact that all the dimensions of the film are large compared to the electron–phonon relaxation length. This is in stark contrast to the conventional scenario of relaxation limited by the electron–phonon scattering rate. A preliminary experimental study of a 200-nm-thick NbN film indicates the relevance of our model for materials used in superconducting nanowire single-photon detectors.
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