Bardeen J, Mattis DC. Theory of the anomalous skin effect in normal and superconducting metals. Phys Rev. 1958;111(2):412–7.
Abstract: Chambers' expression for the current density in a normal metal in which the electric field varies over a mean free path is derived from a quantum approach in which use is made of the density matrix in the presence of scattering centers but in the absence of the field. An approximate expression used for the latter is shown to reduce to one derived by Kohn and Luttinger for the case of weak scattering. A general space-and time-varying electromagnetic interaction is treated by first-order perturbation theory. The method is applied to superconductors, and a general expression derived for the kernel of the Pippard integral for fields of arbitrary frequency. The expressions derived can also be used to discuss absorption of electromagnetic radiation in thin superconducting films.
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Tinkham M, Free JU, Lau CN, Markovic N. Hysteretic I–V curves of superconducting nanowires. Phys. Rev. B. 2003;68:134515(1 to 7).
Abstract: Experimental I–V curves of superconducting MoGe nanowires show hysteresis for the thicker wires and none for the thinner wires. A rather quantitative account of these data for representative wires is obtained by numerically solving the one-dimensional heat flow equation to find a self-consistent distribution of temperature and local resistivity along the wire, using the measured linear resistance R(T) as input. This suggests that the retrapping current in the hysteretic I–V curves is primarily determined by heating effects, and not by the dynamics of phase motion in a tilted washboard potential as often assumed. Heating effects and thermal fluctuations from the low-resistance state to a high-resistance, quasinormal regime appear to set independent upper bounds for the switching current.
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Korneeva YP, Manova NN, Florya IN, Mikhailov MY, Dobrovolskiy OV, Korneev AA, et al. Different single-photon response of wide and narrow superconducting MoxSi1−x strips. Phys Rev Applied. 2020;13(2):024011 (1 to 7).
Abstract: The photon count rate (PCR) of superconducting single-photon detectors made of MoxSi1−x films shaped as a 2-μm-wide strip and a 115-nm-wide meander strip line is studied experimentally as a function of the dc biasing current at different values of the perpendicular magnetic field. For the wide strip, a crossover current Icross is observed, below which the PCR increases with an increasing magnetic field and above which it decreases. This behavior contrasts with the narrow MoxSi1−x meander, for which no crossover current is observed, thus suggesting different photon-detection mechanisms in the wide and narrow strips. Namely, we argue that in the wide strip the absorbed photon destroys superconductivity locally via the vortex-antivortex mechanism for the emergence of resistance, while in the narrow meander superconductivity is destroyed across the whole strip line, forming a hot belt. Accordingly, the different photon-detection mechanisms associated with vortices and the hot belt determine the qualitative difference in the dependence of the PCR on the magnetic field.
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Zhang X, Lita AE, Smirnov K, Liu HL, Zhu D, Verma VB, et al. Strong suppression of the resistivity near the superconducting transition in narrow microbridges in external magnetic fields. Phys Rev B. 2020;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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Heslinga DR, Shafranjuk SE, van Kempen H, Klapwijk TM. Observation of double-gap-edge Andreev reflection at Si/Nb interfaces by point-contact spectroscopy. Phys Rev B. 1994;49(15):10484–94.
Abstract: Andreev reflection point-contact spectroscopy is performed on a bilayer consisting of 50-nm degenerately doped Si backed with Nb. Due to the short mean free path both injection into and transport across the Si layer are diffusive, in contrast to the ballistic conditions prevailing in clean metal layers. Nevertheless a large Andreev signal is observed in the point-contact characteristics, not reduced by elastic scattering in the Si layer or by interface scattering, but only limited by the transmission coefficient of the metal-semiconductor point contact. Two peaks in the Andreev reflection probability are visible, marking the values of the superconducting energy gap at the interface on the Nb and Si sides. This interpretation is supported by a method of solving the Bogolubov equations analytically using a simplified expression for the variation of the order parameter close to the interface. This observation enables a comparison with theoretical predictions of the gap discontinuity in the proximity effect. It is found that the widely used de Gennes model does not agree with the experimental data.
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