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Blagosklonskaya, L. E., Gershenzon, E. M., Gol'tsman, G. N., & Elant'ev, A. I. (1977). Effect of a high magnetic field on the spectrum of donors in InSb. Fizika i Tekhnika Poluprovodnikov, 11(12), 2373–2375.
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Bespalov, A. V., Gol'tsman, G. N., Semenov, A. D., & Renk, K. F. (1991). Determination of the far-infrared emission characteristic of a cyclotron p-germanium laser by use of a superconducting Nb detector. Solid State Communications, 80(7), 503–506.
Abstract: We studied the far-infrared emission characteristics of a cyclotron p-germanium laser using a broad-band superconducting Nb film detector. For magnetic fields between ∼25 kOe and ∼50 kOe, emission in a frequency range from ∼50 cm-1 to ∼100 cm-1 with maximum intensity around 90 cm-1 was obtained. We determined, for fixed magnetic fields, electric field dependences of the emission intensity taking into account that the total electric field is a sum of the applied and the Hall electric field. An analysis of the emission intensity characteristic gives evidence that transitions between the two lowest Landau levels of light holes are responsible for the laser action.
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Bell, M., Sergeev, A., Mitin, V., Bird, J., Verevkin, A., & Gol’tsman, G. (2007). One-dimensional resistive states in quasi-two-dimensional superconductors: Experiment and theory. Phys. Rev. B, 76(9), 094521 (1 to 5).
Abstract: We investigate competition between one- and two-dimensional topological excitations—phase slips and vortices—in the formation of resistive states in quasi-two-dimensional superconductors in a wide temperature range below the mean-field transition temperature TC0. The widths w=100nm of our ultrathin NbN samples are substantially larger than the Ginzburg-Landau coherence length ξ=4nm, and the fluctuation resistivity above TC0 has a two-dimensional character. However, our data show that the resistivity below TC0 is produced by one-dimensional excitations—thermally activated phase slip strips (PSSs) overlapping the sample cross section. We also determine the scaling phase diagram, which shows that even in wider samples the PSS contribution dominates over vortices in a substantial region of current and/or temperature variations. Measuring the resistivity within 7 orders of magnitude, we find that the quantum phase slips can only be essential below this level.
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Bell, M., Sergeev, A., Mitin, V., Bird, J., Verevkin, A., & Gol'tsman, G. (2007). One-dimensional resistive states in quasi-two-dimensional superconductors. arXiv:0709.0709v1 [cond-mat.supr-con], , 1–11.
Abstract: We investigate competition between one- and two-dimensional topological excitations – phase slips and vortices – in formation of resistive states in quasi-two-dimensional superconductors in a wide temperature range below the mean-field transition temperature T(C0). The widths w = 100 nm of our ultrathin NbN samples is substantially larger than the Ginzburg-Landau coherence length ξ = 4nm and the fluctuation resistivity above T(C0) has a two-dimensional character. However, our data shows that the resistivity below T(C0) is produced by one-dimensional excitations, – thermally activated phase slip strips (PSSs) overlapping the sample cross-section. We also determine the scaling phase diagram, which shows that even in wider samples the PSS contribution dominates over vortices in a substantial region of current/temperature variations. Measuring the resistivity within seven orders of magnitude, we find that the quantum phase slips can only be essential below this level.
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Bell, M., Kaurova, N., Divochiy, A., Gol'tsman, G., Bird, J., Sergeev, A., et al. (2007). On the nature of resistive transition in disordered superconducting nanowires. IEEE Trans. Appl. Supercond., 17(2), 267–270.
Abstract: Hot-electron single-photon counters based on long superconducting nanowires are starting to become popular in optical and infrared technologies due to their ultimately high sensitivity and very high response speed. We investigate intrinsic fluctuations in long NbN nanowires in the temperature range of 4.2 K-20 K, i.e. above and below the superconducting transition. These fluctuations are responsible for fluctuation resistivity and also determine the noise in practical devices. Measurements of the fluctuation resistivity were performed at low current densities and also in external magnetic fields up to 5 T. Above the BCS critical temperature T co the resistivity is well described by the Aslamazov-Larkin (AL) theory for two-dimensional samples. Below T co the measured resistivity is in excellent agreement with the Langer-Ambegaokar-McCumber-Halperin (LAMH) theory developed for one-dimensional superconductors. Despite that our nanowires of 100 nm width are two-dimensional with respect to the coherence length, our analysis shows that at relatively low current densities the one-dimensional LAMH mechanism based on thermally induced phase slip centers dominates over the two-dimensional mechanism related to unbinding of vortex-antivortex pairs below the Berezinskii-Kosterlitz-Thouless transition.
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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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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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Baubert, J., Salez, M., Merkel, H., Pons, P., Cherednichenko, S., Lecomte, B., et al. (2005). IF gain bandwidth of membrane-based NbN hot electron bolometers for SHAHIRA. IEEE Trans. Appl. Supercond., 15(2), 507–510.
Abstract: SHAHIRA (Submm Heterodyne Array for HIgh-speed Radio Astronomy) is a project supported by the European Space Agency (ESA) and is designed to fly on the SOFIA observatory. A quasi-optic design has been chosen for 2.5/2.7 THz and 4.7 THz, for hydroxyde radical OH, deuterated hydrogen HD and neutral atomic oxygen OI lines observations. Hot electron bolometers (HEBs) have been processed on 1 /spl mu/m thick SiO/sub 2//Si/sub 3/N/sub 4/ stress-less membranes. In this paper we analyse the intermediate frequency (IF) gain bandwidth from the theoretical point of view, and compare it to measurements.
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Baselmans, J. J. A., Hajenius, M., Gao, J. R., Baryshev, A., Kooi, J., Klapwijk, T. M., et al. (2005). NbN hot electron bolometer mixers: sensitivity, LO power, direct detection and stability. IEEE Trans. Appl. Supercond., 15(2), 484–489.
Abstract: We demonstrate that the performance of NbN lattice cooled hot electron bolometer mixers depends strongly on the interface quality between the bolometer and the contact structure. Both the receiver noise temperature and the gain bandwidth can be improved by a factor of 2 by cleaning the interface and adding an additional superconducting interlayer to the contact pad. Using this we obtain a double sideband receiver noise temperature of 950 K at 2.5 THz and 4.3 K, using a 0.4/spl times/4 /spl mu/m HEB mixer with a spiral antenna. At the same bias point, we obtain an IF gain bandwidth of 6 GHz. To comply with current demands on THz mixers for use in space based receivers we reduce the device size to 0.15/spl times/1 /spl mu/m and use a twin slot antenna. We report measurements of the noise temperature, LO power requirement, stability and the direct detection effect, using a mixer with a 1.6 THz twin slot antenna and a 1.462 THz solid state LO source with calibrated output power.
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Baselmans, J. J. A., Baryshev, A., Reker, S. F., Hajenius, M., Gao, J. R., Klapwijk, T. M., et al. (2006). Influence of the direct response on the heterodyne sensitivity of hot electron bolometer mixers. J. Appl. Phys., 100(8), 084510 (1 to 7).
Abstract: We present a detailed experimental study of the direct detection effect in a small volume (0.15μm×1μm×3.5nm) quasioptical NbN phonon cooled hot electron bolometer mixer at 673GHz. We find that the small signal noise temperature, relevant for an astronomical observation, is 20% lower than the noise temperature obtained using 300 and 77K calibration loads. In a separate set of experiments we show that the direct detection effect is caused by a combination of bias current reduction when switching from the 77 to the 300K
load in combination with the bias current dependence of the receiver gain. The bias current dependence of the receiver gain is shown to be mainly caused by the current dependence of the mixer gain.
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