|
|
Krasnosvobodtsev, S. I., Shabanova, N., P., Ekimov, E. V., Nozdrin, V. S., & Pechen, E., V. (1995). Critical magnetic field of NbC: new data on clean superconductor films. Zh. Eks. Teor.Fiz., , 534–537.
Abstract: The temperature dependence of the upper critical magnetic fields of exceptionally low-defect-density films of the superconducting compound NbC has been investigated, and previously unknown parameters of this clean superconductor and its electronic characteristics have been evaluated. An electron density of states at the Fermi level equal to 1.3 states/ eV. Nb atom, a Fermi velocity equal to 2.2X lo7 cmls, a plasma frequency equal to 3.6 eV, and a coherence length to 24 nm have been obtained with an electron mean free path exceeding 40 nm. A vortex-free state existing over the entire temperature range below T, which causes a many-fold increase in the critical magnetic field of the films when the field is aligned parallel to their surface, has been discovered in very thin films of superconducting niobium carbide.
|
|
|
|
Shklovskij V.A. (1980). Hot Electrons in Metals at Low Temperatures. J. Low Temp. Phys., 41, 375–396.
Abstract: Hot electrons in metals at helium temperatures under steady conditions can be produced by passing an electric current of moderate density through thin, narrow (-1 μm wide) metallic films in good thermal contact with bulk single-crystal dielectric substrates. This paper is concerned with the theory of hot electrons in normal metals at low temperatures (when θ<< θ(D), where θ is the average electron energy and θ(D) is the Debye temperature). The theory is formulated in terms of realistic electron and phonon dispersion laws, taking into account the experimental possibility of heat removal from the sample. In the case in which the temperature approximation of Kagnov, Lifshitz, and Tanatarov is not satisfied when elastic scattering of electrons is dominant in a steady state electric field, the kinetic equation is derived for the energy-dependent, hot electron distribution function, which determines the associated nonlinear responses. The solution of this equation is discussed for a simple model. It is shown that the experimental information on the electron-phonon interaction in a metal can be obtained in terms of the well-known spectral functions. This is illustrated by experiments determining the nonlinear field dependence of the resistance, by tunnel experiments, and by critical current hysteresis measurements (for superconducting metals). Theoretical estimates which support the observability of the effects underdiscussion are presented.
|
|
|
|
Gousev, Y. P., Semenov, A. D., Pechen, E. V., Varlashkin, A. V., Nebosis, R. S., & Renk K. F. (1996). Coupling of terahertz radiation to a high-Т(с) superconducting hot electron bolometer mixer. Appl. Phys. Lett.,, 69, 691–693.
Abstract: We report on efficient coupling of THz radiation to a high-T(c) superconducting hot electron bolometer that is suitable for heterodyne detection. Our quasioptical system consisted of a planar self-complementary spiral antenna on a dielectric substrate clamped to an extended hyperhemispherical lens. The antenna was integrated into a co-planar line for broadband intermediate frequency matching. Measurements in the homodyne regime at a frequency of 2.5 THz showed a radiation pattern with a beam width of 1° and a coupling efficiency of 0.1. We measured, at an intermediate frequency of 1.5 GHz, an output noise temperature of'160 K and estimated for the device, operated in the heterodyne regime, a system noise temperature of 30 000 K. We also discuss possibilities of significant improvement of the sensitivity.
|
|
|
|
Boogaard, G. R., Verbruggen, A. H., Belzig, W., & Klapwijk T.M. (2004). Resistance of superconducting nanowires connected to normal-metal leads. Phys. Rev. B, 69, 220503(R)(1–4).
Abstract: We study experimentally the low temperature resistance of superconducting nanowires connected to normal metal reservoirs. Wefind that a substantial fraction of the nanowires is resistive, down to the lowest tempera-ture measured, indicative of an intrinsic boundary resistance due to the Andreev-conversion of normal current to supercurrent. The results are successfully analyzed in terms of the kinetic equations for diffusive superconductors.
|
|
|
|
Skocpol', W. J., Beasley, M. R., & Tinkham M. (1974). Self-heating hotspots in superconducting thin film microbridges. J. Appl. Phys., 45, 4054–4066.
Abstract: Heating effects in both long and short superconducting thin-<ef><ac><81>lm rnicrobridges are described and analyzed. Except near T(c), at low voltages where superconducting quantum processes occur, all of our experimental dc I-V characteristics can be satisfactorily understood on the basis of a simple model of a localized normal hotspot maintained by Joule heating. We consider approximations appropriate to the cases of long bridges, short bridges, and bridges coupled to microwave radiation. The analysis leads to analytic expressions for the I-V characteristics which agree well with the experimental data. We show that the formation of such a hotspot is the dominant cause of the hysteresis observed in the I-V characteristics at low temperatures. We also show that the growth of such a hotspot imposes a high-voltage limit on the ac Josephson effect in these devices, and we compare the importance of such heating effects at high voltages in various types of superconducting weak links.
|
|
