Heusinger, M. A., Nebosis, R. S., Schatz, W., Renk, K. F., Gol’tsman, G. N., Karasik, B. S., et al. (1993). Temperature dependence of bolometric and non-bolometric photoresponse of a structured YBa2Cu3O7-δ thin film. In M. Meissner, & R. O. Pohl (Eds.), Phonon Scattering in Condensed Matter VII. Springer Series in Solid-State Sciences (Vol. 112, pp. 193–195).
Abstract: We investigated the temperature dependence of the transient voltage photoresponse of a current biased structured YBa2Cu3O7−δ thin film in its transition temperature region, around 79 K. Both, picosecond nonbolometric and nanosecond bolometric response to ultrashort far-infrared laser pulses were found for frequencies between 25 cm−1 and 215 cm−1. We will discuss optimum conditions for radiation detection and present an analysis of the dynamical behaviour of excited high T c thin films.
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Sergeev, A. V., Aksaev, E. E., Gogidze, I. G., Gol’tsman, G. N., Semenov, A. D., & Gershenzon, E. M. (1993). Thermal boundary resistance at YBaCuO film-substrate interface. In M. Meissner, & R. O. Pohl (Eds.), Phonon Scattering in Condensed Matter VII. Springer Series in Solid-State Sciences (Vol. 112, pp. 405–406).
Abstract: The nanosecond voltage response of YBaCuo films on Al2O3, MgO and ZrO2 substrates to electromagnetic radiation of millimeter and visible ranges has been investigated. The analysis of experimental conditions for Al2O3 and MgO substrates shows that the resistance change is monitored by the Kapitza boundary shift of temperature during the temporal interval ~ 100 ns limited by the time of phonon return from a substrate into a film. The observed exponential voltage decay is described by the phonon escape time which is proportional to the film thickness and is weakly temperature dependent.
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Gousev, Y. P., Gol'tsman, G. N., Semenov, A. D., Gershenzon, E. M., Nebosis, R. S., Heusinger, M. A., et al. (1994). Broadband ultrafast superconducting NbN detector for electromagnetic radiation. J. Appl. Phys., 75(7), 3695–3697.
Abstract: An ultrafast detector that is sensitive to radiation in a broad spectral range from submillimeter waves to visible light is reported. It consists of a structured NbN thin film cooled to a temperature below Tc (∼11 K). Using 20 ps pulses of a GaAs laser, we observed signal pulses with both rise and decay time of about 50 ps. From the analysis of a mixing experiment with submillimeter radiation we estimate an intrinsic response time of the detector of ∼12 ps. The sensitivity was found to be similar for the near‐infrared and submillimeter radiation. Broadband sensitivity and short response time are attributed to a quasiparticle heating effect.
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Gol'tsman, G. N., Goghidze, I. G., Kouminov, P. B., Karasik, B. S., Semenov, A. D., & Gershenzon, E. M. (1994). Influence of grain boundary weak links on the nonequilibrium response of YBaCuO thin films to short laser pulses. J. Supercond., 7(4), 751–755.
Abstract: The transient voltage response in both epitaxial and granular YBaCuO thin films to 80 ps pulses of YAG∶Nd laser radiation of wavelength 0.63 and 1.54 μm was studied. In the normal and resistive states both types of films demonstrate two components: a nonequilibrium picosecond component and a bolometric nanosecond one. The normalized amplitudes are almost the same for all films. In the superconducting state we observed a kinetic inductive response and two-component shape after integration. The normalized amplitude of the response in granular films is up to five orders of magnitude larger than in epitaxial films. We interpret the nonequilibrium response in terms of a suppression of the order parameter by the excess of quasiparticles followed by the change of resistance in the normal and resistive states or kinetic inductance in the superconducting state. The sharp rise of inductive response in granular films is explained both by a diminishing of the cross section for current percolation through the disordered network of Josephson weak links and by a decrease of condensate density in neighboring regions.
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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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