Floet D. W., Gao J. R., Klapwijk T. M., de Korte P. A. J. Bias Dependence of the Thermal Time Constant in Nb Superconducting Diffusion-Cooled HEB Mixers. Appl Phys Lett. 2000;77:1719.
Abstract: We present an experimental study of the intermediate frequency bandwidth of a Nb diffusion-cooled hot-electron bolometer mixer for different bias voltages. The measurements show that the bandwidth increases with increasing voltage. Analysis of the data reveals that this effect is mainly caused by a decrease of the intrinsic thermal time of the mixer and that the effect of electrothermal feedback through the intermediate frequency circuit is small. The results are understood using a qualitative model, which takes into account the different effective diffusion constants in the normal and superconducting domains.
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Il'in KS, Lindgren M, Currie MA, Semenov D, Gol'tsman GN, Sobolewski R, et al. Picosecond hot-electron energy relaxation in NbN superconducting photodetectors. Appl Phys Lett. 2000;76(19):2752–4.
Abstract: We report time-resolved characterization of superconducting NbN hot-electron photodetectors using an electro-optic sampling method. Our samples were patterned into micron-size microbridges from 3.5-nm-thick NbN films deposited on sapphire substrates. The devices were illuminated with 100 fs optical pulses, and the photoresponse was measured in the ambient temperature range between 2.15 and 10.6 K (superconducting temperature transition TC). The experimental data agreed very well with the nonequilibrium hot-electron, two-temperature model. The quasiparticle thermalization time was ambient temperature independent and was measured to be 6.5 ps. The inelastic electron–phonon scattering time Ï„e–ph tended to decrease with the temperature increase, although its change remained within the experimental error, while the phonon escape time Ï„es decreased almost by a factor of two when the sample was put in direct contact with superfluid helium. Specifically, Ï„e–ph and Ï„es, fitted by the two-temperature model, were equal to 11.6 and 21 ps at 2.15 K, and 10(±2) and 38 ps at 10.5 K, respectively. The obtained value of Ï„e–ph shows that the maximum intermediate frequency bandwidth of NbN hot-electron phonon-cooled mixers operating at TC can reach 16(+4/–3) GHz if one eliminates the bolometric phonon-heating effect.
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Smirnov KV, Ptitsina NG, Vakhtomin YB, Verevkin AA, Gol’tsman GN, Gershenzon EM. Energy relaxation of two-dimensional electrons in the quantum Hall effect regime. JETP Lett. 2000;71(1):31–4.
Abstract: The mm-wave spectroscopy with high temporal resolution is used to measure the energy relaxation times τe of 2D electrons in GaAs/AlGaAs heterostructures in magnetic fields B=0–4 T under quasi-equilibrium conditions at T=4.2 K. With increasing B, a considerable increase in τe from 0.9 to 25 ns is observed. For high B and low values of the filling factor ν, the energy relaxation rate τ −1e oscillates. The depth of these oscillations and the positions of maxima depend on the filling factor ν. For ν>5, the relaxation rate τ −1e is maximum when the Fermi level lies in the region of the localized states between the Landau levels. For lower values of ν, the relaxation rate is maximum at half-integer values of τ −1e when the Fermi level is coincident with the Landau level. The characteristic features of the dependence τ −1e (B) are explained by different contributions of the intralevel and interlevel electron-phonon transitions to the process of the energy relaxation of 2D electrons.
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Sergeev A, Mitin V. Electron-phonon interaction in disordered conductors: Static and vibrating scattering potentials. Phys Rev B. 2000;61(9):6041–7.
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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Kawamura J, Blundell R, Tong C-YE, Papa DC, Hunter TR, Paine St. N, et al. Superconductive hot-electron bolometer mixer receiver for 800 GHz operation. Vol 48.; 2000.
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