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Zhang, X., Lita, A. E., Smirnov, K., Liu, H. L., Zhu, D., Verma, V. B., et al. (2020). Strong suppression of the resistivity near the superconducting transition in narrow microbridges in external magnetic fields. Phys. Rev. B, 101(6), 060508 (1 to 6).
Abstract: We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 to 1000μm and film thicknesses d∼4−6 and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature T∗(B) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1/w, which may suggest either the presence of a highly conducting region that is dominating the electric transport, or a change in the vortex dynamics in narrow enough bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning.
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Sidorova, M., Semenov, A., Hübers, H. - W., Kuzmin, A., Doerner, S., Ilin, K., et al. (2018). Timing jitter in photon detection by straight superconducting nanowires: Effect of magnetic field and photon flux. Phys. Rev. B, 98(13), 134504 (1 to 14).
Abstract: We studied the effects of the external magnetic field and photon flux on timing jitter in photon detection by straight superconducting NbN nanowires. At two wavelengths 800 and 1560 nm, statistical distribution in the appearance times of photon counts exhibits Gaussian shape at small times and an exponential tail at large times. The characteristic exponential time is larger for photons with smaller energy and increases with external magnetic field while variations in the Gaussian part of the distribution are less pronounced. Increasing photon flux drives the nanowire from the discrete quantum detection regime to the uniform bolometric regime that averages out fluctuations of the total number of nonequilibrium electrons created by the photon and drastically reduces jitter. The difference between standard deviations of Gaussian parts of distributions for these two regimes provides the measure for the strength of electron-number fluctuations; it increases with the photon energy. We show that the two-dimensional hot-spot detection model explains qualitatively the effect of magnetic field.
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Sergeev, A., Karasik, B. S., Ptitsina, N. G., Chulkova, G. M., Il'in, K. S., & Gershenzon, E. M. (1999). Electron–phonon interaction in disordered conductors. Phys. Rev. B Condens. Matter, 263-264, 190–192.
Abstract: The electron–phonon interaction is strongly modified in conductors with a small value of the electron mean free path (impure metals, thin films). As a result, the temperature dependencies of both the inelastic electron scattering rate and resistivity differ significantly from those for pure bulk materials. Recent complex measurements have shown that modified dependencies are well described at K by the electron interaction with transverse phonons. At helium temperatures, available data are conflicting, and cannot be described by an universal model.
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Verevkin, A. A., Ptitsina, N. G., Chulcova, G. M., Gol'Tsman, G. N., Gershenzon, E. M., & Yngvesson, K. S. (1996). Determination of the limiting mobility of a two-dimensional electron gas in AlxGa1-xAs/GaAs heterostructures and direct measurement of the energy relaxation time. Phys. Rev. B Condens. Matter., 53(12), R7592–R7595.
Abstract: We present results for a method to measure directly the energy relaxation time (τe) for electrons in a single AlxGa1−xAs/GaAs heterojunction; measurements were performed from 1.6 to 15 K under quasiequilibrium conditions. We find τeαT−1 below 4 K, and τe independent of T above 4 K. We have also measured the energy-loss rate, ⟨Q⟩, by the Shubnikov-de Haas technique, and find ⟨Q⟩α(T3e−T3) for T<~4.2 K; Te is the electron temperature. The values and temperature dependence of τe and ⟨Q⟩ for T<4 K agree with calculations based on piezoelectric and deformation potential acoustic phonon scattering. At 4.2 K, we can also estimate the momentum relaxation time, τm, from our measured τe. This leads to a preliminary estimate of the phonon-limited mobility at 4.2 K of μ=3×107 cm2/Vs (ns=4.2×1011 cm−2), which agrees well with published numerical calculations, as well as with an earlier indirect estimate based on measurements on a sample with much higher mobility.
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Sergeev, A. V., Semenov, A. D., Kouminov, P., Trifonov, V., Goghidze, I. G., Karasik, B. S., et al. (1994). Transparency of a YBa2Cu3O7-film/substrate interface for thermal phonons measured by means of voltage response to radiation. Phys. Rev. B Condens. Matter., 49(13), 9091–9096.
Abstract: The transparency of a film/substrate interface for thermal phonons was investigated for YBa2Cu3O7 thin films deposited on MgO, Al2O3, LaAlO3, NdGaO3, and ZrO2 substrates. Both voltage response to pulsed-visible and to continuously modulated far-infrared radiation show two regimes of heat escape from the film to the substrate. That one dominated by the thermal boundary resistance at the film/substrate interface provides an initial exponential decay of the response. The other one prevailing at longer times or smaller modulation frequencies causes much slower decay and is governed by phonon diffusion in the substrate. The transparency of the boundary for phonons incident from the film on the substrate and also from the substrate on the film was determined separately from the characteristic time of the exponential decay and from the time at which one regime was changed to the other. Taking into account the specific heat of optical phonons and the temperature dependence of the group velocity of acoustic phonons, we show that the body of experimental data agrees with acoustic mismatch theory rather than with the model that assumes strong diffusive scattering of phonons at the interface.
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Sergeev, A., & Mitin, V. (2000). Electron-phonon interaction in disordered conductors: Static and vibrating scattering potentials. Phys. Rev. B., 61(9), 6041–6047.
Abstract: Employing the Keldysh diagram technique, we calculate the electron-phonon energy relaxation rate in a conductor with the vibrating and static δ-correlated random electron-scattering potentials. If the scattering potential is completely dragged by phonons, this model yields the Schmid’s result for the inelastic electron-scattering rate τ−1e−ph. At low temperatures the effective interaction decreases due to disorder, and τ−1e−ph∝T4l (l is the electron mean-free path). In the presense of the static potential, quantum interference of numerous scattering processes drastically changes the effective electron-phonon interaction. In particular, at low temperatures the interaction increases, and τ−1e−ph∝T2/l. Along with an enhancement of the interaction, which is observed in disordered metallic films and semiconducting structures at low temperatures, the suggested model allows us to explain the strong sensitivity of the electron relaxation rate to the microscopic quality of a particular film.
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Beck, M., Klammer, M., Lang, S., Leiderer, P., Kabanov, V. V., Gol'tsman, G. N., et al. (2011). Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy. Phys. Rev. Lett., 107(17), 4.
Abstract: Using time-domain terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare quasiparticle recombination rate, the Cooper pair-breaking rate and the electron-phonon coupling constant, λ=1.1±0.1, which is in excellent agreement with theoretical estimates.
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Beck, M., Rousseau, I., Klammer, M., Leiderer, P., Mittendorff, M., Winnerl, S., et al. (2013). Transient increase of the energy gap of superconducting NbN thin films excited by resonant narrow-band terahertz pulses. Phys. Rev. Lett., 110(26), 267003 (1 to 5).
Abstract: Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2Delta/h. Utilizing intense, narrow-band, picosecond, terahertz pulses, tuned to just below and above 2Delta/h of a BCS superconductor NbN, we demonstrate that the superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced nonthermal electron distribution persisting on a 100 ps time scale.
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Shein, K. V., Zarudneva, A. A., Emel’yanova, V. O., Logunova, M. A., Chichkov, V. I., Sobolev, A. S., et al. (2020). Superconducting microstructures with high impedance. Phys. Solid State, 62(9), 1539–1542.
Abstract: The transport properties of two types of quasi-one-dimensional superconducting microstructures were investigated at ultra-low temperatures: the narrow channels close-packed in the shape of meander, and the chains of tunneling contacts “superconductor-insulator-superconductor.” Both types of the microstructures demonstrated high value of high-frequency impedance and-or the dynamic resistance. The study opens up potential for using of such structures as current stabilizing elements with zero dissipation.
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Gol'tsman, G. N., Korneev, A., Rubtsova, I., Milostnaya, I., Chulkova, G., Minaeva, O., et al. (2005). Ultrafast superconducting single-photon detectors for near-infrared-wavelength quantum communications. Phys. Stat. Sol. (C), 2(5), 1480–1488.
Abstract: We present our progress on the research and development of NbN superconducting single‐photon detectors (SSPD's) for ultrafast counting of near‐infrared photons for secure quantum communications. Our SSPD's operate in the quantum detection mode based on the photon‐induced hotspot formation and subsequent development of a transient resistive barrier across an ultrathin and submicron‐width superconducting stripe. The devices are fabricated from 4‐nm‐thick NbN films and kept in the 4.2‐ to 2‐K temperature range. The detector experimental quantum efficiency in the photon‐counting mode reaches above 40% for the visible light and up to 30% in the 1.3‐ to 1.55‐µm wavelength range with dark counts below 0.01 per second. The experimental real‐time counting rate is above 2 GHz and is limited by our readout electronics. The SSPD's timing jitter is below 18 ps, and the best‐measured value of the noise‐equivalent power (NEP) is 5 × 10–21 W/Hz1/2 at 1.3 µm. In terms of quantum efficiency, timing jitter, and maximum counting rate, our NbN SSPD's significantly outperform semiconductor avalanche photodiodes and photomultipliers in the 1.3‐ to 1.55‐µm range.
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Fedorov, G., Gayduchenko, I., Titova, N., Gazaliev, A., Moskotin, M., Kaurova, N., et al. (2018). Carbon nanotube based schottky diodes as uncooled terahertz radiation detectors. Phys. Status Solidi B, 255(1), 1700227 (1 to 6).
Abstract: Despite the intensive development of the terahertz technologies in the last decade, there is still a shortage of efficient room‐temperature radiation detectors. Carbon nanotubes (CNTs) are considered as a very promising material possessing many of the features peculiar for graphene (suppression of backscattering, high mobility, etc.) combined with a bandgap in the carrier spectrum. In this paper, we investigate the possibility to incorporate individual CNTs into devices that are similar to Schottky diodes. The latter is currently used to detect radiation with a frequency up to 50 GHz. We report results obtained with semiconducting (bandgap of about 0.5 eV) and quasi‐metallic (bandgap of few meV) single‐walled carbon nanotubes (SWNTs). Semiconducting CNTs show better performance up to 300 GHz with responsivity up to 100 V W−1, while quasi‐metallic CNTs are shown to operate up to 2.5 THz.
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Tretyakov, I., Shurakov, A., Perepelitsa, A., Kaurova, N., Svyatodukh, S., Zilberley, T., et al. (2019). Room temperature silicon detector for IR range coated with Ag2S quantum dots. Phys. Status Solidi RRL, 13(9), 1900187–(1–6).
Abstract: For decades, silicon has been the chief technological semiconducting material of modern microelectronics and has a strong influence on all aspects of the society. Applications of Si-based optoelectronic devices are limited to the visible and near infrared (IR) ranges. For photons with an energy less than 1.12 eV, silicon is almost transparent. The expansion of the Si absorption to shorter wavelengths of the IR range is of considerable interest for optoelectronic applications. By creating impurity states in Si, it is possible to cause sub-bandgap photon absorption. Herein, an elegant and effective technology of extending the photo-response of Si toward the IR range is presented. This approach is based on the use of Ag 2 S quantum dots (QDs) planted on the surface of Si to create impurity states in the Si bandgap. The specific sensitivity of the room temperature zero-bias Si_Ag 2 Sp detector is 10 11 cm Hz W 1 at 1.55 μm. Given the variety of available QDs and the ease of extending the photo-response of Si toward the IR range, these findings open a path toward future studies and development of Si detectors for technological applications. The current research at the interface of physics and chemistry is also of fundamental importance to the development of Si optoelectronics.
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Peltonen, J. T., Peng, Z. H., Korneeva, Y. P., Voronov, B. M., Korneev, A. A., Semenov, A. V., et al. (2016). Coherent dynamics and decoherence in a superconducting weak link. Physic. Rev. B,, 94, 180508.
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Antipov, S. V., Svechnikov, S. I., Smirnov, K. V., Vakhtomin, Y. B., Finkel, M. I., Goltsman, G. N., et al. (2001). Noise temperature of quasioptical NbN hot electron bolometer mixers at 900 GHz. Physics of Vibrations, 9(4), 242–245.
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Svechnikov, S. I., Antipov, S. V., Vakhtomin, Y. B., Goltsman, G. N., Gershenzon, E. M., Cherednichenko, S. I., et al. (2001). Conversion and noise bandwidths of terahertz NbN hot-electron bolometer mixers. Physics of Vibrations, 9(3), 205–210.
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