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When a non-equilibrium excitation (a non-paired electron) is injected into a superconductor, it can travel fairly large distance before forming an equilibrium Copper pair. Here, we fabricated and experimentally studied electron transport in a solid-state analogue of a two-slit optical interferometer: T-shaped normal metal electrode (copper) — dielectric tunnel layer (aluminum oxide) — superconducting fork (aluminum). If the perimeter of the interferometer loop is sufficiently small, the phase of the non-equilibrium quasiparticle wave function is preserved and can be adjusted utilizing the Aharonov-Bohm effect. The coherent contribution manifests itself as non-monotonic dependence of the tunnel current on perpendicular magnetic field. [ABSTRACT FROM AUTHOR]

We measured the temporal voltage response of NbTi superconducting filaments with varied nanoscale thicknesses to step current pulses that induce non-equilibrium superconducting states governed by a hot spot mechanism. Such detected voltage emerges after a delay time  t d , which is intimately connected to the gap relaxation and heat escape times. By employing time-dependent Ginzburg–Landau theory to link the delay time to the applied current, we determined that the gap relaxation time depends linearly on film thickness, aligning with the acoustic mismatch theory for phonon transmission at the superconductor–substrate interface. We thereby find a gap relaxation time of 104 ps per nm of thickness for NbTi films on polished sapphire. We further show that interfacial interaction with the substrate significantly impacts the gap relaxation time, with observed values of 9 ns on Si O x , 6.8 ns on fused silica, and 5.2 ns on sapphire for a 50 nm thick NbTi strip at  T = 5.75  K. These insights are valuable for optimizing superconducting sensing technologies, particularly the single-photon detectors that operate in the transient regime of nanothin superconducting bridges and filaments. [ABSTRACT FROM AUTHOR]

The electron transport of non-equilibrium quasiparticles injected into superconducting aluminum from a normal metal has been experimentally studied at ultralow temperatures. We studied hybrid nanostructures in the form of a T-shaped normal metal electrode (copper)—a dielectric tunnel layer (aluminum oxide)—a superconducting fork (aluminum), which can be considered as a solid-state analogue of a double-slit optical interferometer. At fixed bias voltages larger than the superconducting gap, a non-monotonic dependence of the tunnel current on perpendicular magnetic field has been observed. The effect is interpreted as the presence of a coherent component of the quasiparticle current. [ABSTRACT FROM AUTHOR]

Development of ultrafast lasers and nonlinear optical techniques over the last two decades provides tools to access real-time dynamics of low energy excitations in superconductors. For example, time-resolved THz spectroscopy and time- and angular-resolved photoemission spectroscopy provide access to the real-time dynamics of the superconducting gap amplitude. Such studies enable determination of microscopic parameters like quasi-particle recombination rates, pair-breaking rates and electron–boson coupling constants. Recently, intense THz pulses have been used to probe the nonlinear dynamics, including observation of collective modes. Moreover, using low-frequency electromagnetic pulses, there are several reports of amplification of superconductivity in both conventional and unconventional superconductors. Starting with a brief historical overview of the pioneering work, where non-equilibrium phenomena in superconductors were investigated using quasi-continuous excitation, we review some of the insights that are provided by using real-time approaches. We focus on conventional BCS superconductors, whose ground state is reasonably well understood, and address similarities and open questions related to the corresponding studies in high- T c superconductors. [ABSTRACT FROM AUTHOR]

Polarons and percolation were mentioned as guiding concepts in the paper by Bednorz and Müller in their report on the discovery of superconductivity in Ba–La–Cu–O. Both of these concepts seem to have survived, but their role in high-temperature superconductivity is somewhat different than originally envisaged. Optical and time-resolved experiments have been extremely useful for understanding the roles and dynamical interplay of polaronic and itinerant charge carriers in the different states of matter that appear in the cuprate phase diagram. The present article outlines some of the connections between the original concepts, systematics and apparent dichotomies, and discusses them in the light of more recent experimental observations, leading to some important theoretical considerations on the mechanism for superconductivity. • The role of polarons in the mechanism for high T c superconductivity is presented. • Ultrafast quasiparticle dynamics and non-equilibrium superconductivity are discussed. • The coexistence of itinerant and localized states coincides with optimal T c. [ABSTRACT FROM AUTHOR]

The phenomenological Ginzburg–Landau theory and the charge conservation directly lead to the finite Higgs-mode generation and vanishing charge-density fluctuation in the second-order optical response of superconductors at clean limit. Nevertheless, recent microscopic theoretical studies of the second-order optical response, apart from the one through the gauge-invariant kinetic equation (Yang and Wu, 2019), have derived a vanishing Higgs-mode generation but finite charge-density fluctuation at clean limit. We resolve this controversy by re-examining the previous derivations with the vector potential alone within the path-integral and Eilenberger-equation approaches, and show that both previous derivations contain flaws. After fixing these flaws, a finite Higgs-mode generation through the drive effect of vector potential is derived at clean limit, exactly recovering the previous result from the gauge-invariant kinetic equation as well as Ginzburg–Landau theory. By further extending the path-integral approach to include electromagnetic effects from the scalar potential and phase mode, in the second-order response, a finite contribution from the drive effect of scalar potential to the Higgs-mode generation at clean limit as well as the vanishing charge-density fluctuation are derived, also recovering the results from the gauge-invariant kinetic equation. Particularly, we show that the phase mode is excited in the second-order response, and exactly cancels the previously reported unphysical excitation of the charge-density fluctuation, guaranteeing the charge conservation. [ABSTRACT FROM AUTHOR]

Abstract: From the point of view of time-dependent Ginzburg Landau (TDGL) theory, a Josephson-like relation is derived for an Abrikosov vortex lattice accelerated and deformed by applied fields. Beginning with a review of the Josephson Relation derived from the two ingredients of a lattice-kinematics assumption in TDGL theory and gauge invariance, we extend the construction to accommodate a time-dependent applied magnetic field, a Floating-Kernel formulation of normal current, and finally lattice deformation due to the electric field and inertial effects of vortex-lattice motion. The resulting Josephson-like relation, which we call an Extended Josephson Relation, applies to a much wider set of experimental conditions than the original Josephson Relation, and is explicitly compatible with the considerations of TDGL theory. [Copyright &y& Elsevier]

Abstract: The peculiarities of electron transport trough the tunnel half-metallic ferromagnet(Co2CrAl)/insulator/superconductor(Pb) (HMF/I/S) junctions have been investigated. It was experimentally shown that the effective life-time of the spin-polarized quasi-particles ensemble in superconductor before their recombination into singlet cooper pairs is much longer than that for non-polarized ones. It was also found that the tunnel injection of spin-polarized current from HMF into S in HMF/I/S junction in its superconductive state the effect of “giant blocking” of the tunnel current is appeared. In this case at bias voltage, , close to zero a very significant increase in differential resistance of the HMF/I/S junction in comparison with that of the N/I/S one is observed (where N is normal metal). Additionally, it was also established that at the ratio of differential resistance in superconductive state to that of in the normal state for the Co2CrAl/I/Pb junction is much bigger than corresponding ratio for N/I/S junctions obtained experimentally as well as in the frame of Bardeen, Cooper and Schrieffer theory. [Copyright &y& Elsevier]

An analysis of different strategies for increasing the maximum count rate of superconducting single photon detectors using parallel nanowires is performed with particular emphasis on the expected behaviour when the detector area is increased. We find that for a serial connection of blocks of parallel nanowires, the maximum count rate decreases with the square root of the detector area, whereas it decreases proportional to the detector area for current meandered detectors. Using this design we estimate that a signal pulse falltime of 7.8 ns for a 84 × 84 µm2 parallel detector based on current material parameters should be obtainable. We argue that the slow decrease of count rate with detector area might permit detectors based on parallel nanowires to fully exploit the available cooling power. [ABSTRACT FROM AUTHOR]

Abstract: We present a phenomenological model that qualitatively explains negative magnetoresistance in quasi-one-dimensional superconducting channels in the resistive state. The model is based on the assumption that fluctuations of the order parameter (phase slips) are responsible for the finite effective resistance of a narrow superconducting wire sufficiently close to the critical temperature. Each fluctuation is accompanied by an instantaneous formation of a quasi-normal region, of the order of the non-equilibrium quasiparticle relaxation length, ‘pinned’ to the core of the phase slip. The effective time-averaged voltage measured in experiments is a sum of two terms. The first is the conventional contribution associated with the rate of the fluctuations via the Josephson relation. The second term is the Ohmic contribution of this quasi-normal region. Depending on the material properties of the wire, there might be a range of magnetic fields where the first term is not significantly affected, while the second term is effectively suppressed, contributing to the experimentally observed negative magnetoresistance. [Copyright &y& Elsevier]

Abstract: Epitaxial superlattices of half-metal, colossal magnetoresistive La2/3Ca1/3MnO3 (HM-CMR) and high-T c superconducting YBa2Cu3O7−δ (HTSC) are prepared on single-crystalline substrate by pulsed laser deposition. Transport measurements R(T) at a superconducting layer of these hybrids exhibit features of both of the constituents of the superlattice. Additionally, below T =35K, far below the superconducting transition temperature a reentrance into a resistive state can be observed. [Copyright &y& Elsevier]

Superconducting tunnel junction (STJ) detectors can be characterized by ultra-high-energy resolution, high count rate capability, and stability against temperature fluctuation. This tutorial article briefly introduces some principles of STJ detectors and also reviews their recent developments. [Copyright &y& Elsevier]

We present studies of superconducting state recovery dynamics in superconductors probed by time-resolved optical-pump terahertz-probe spectroscopy. In these experiments femtosecond optical pulses excite the superconductor out of equilibrium, while the condensate and quasiparticle dynamics are probed by measuring the associated changes in the far-infrared conductivity as a function of time delay with respect to the excitation pulse. Recent results on MgB2 and YBa2Cu3O7 are presented, with main differences and similarities between the two pointed out and discussed. [ABSTRACT FROM AUTHOR]

Scanning tunneling spectroscopic studies of cuprate superconductors revealed that the most eminent phenomena of hole-doped (p-type) cuprates, including the predominant dx2−y2 pairing symmetry, spin fluctuations and pseudogap, are absent in the infinite-layer electron-doped (n-type) cuprates Sr1−xLaxCuO2. The optimally doped Sr0.9La0.1CuO2 exhibits s-wave pairing symmetry, with a superconducting transition temperature Tc=43.0 K, a large energy gap Δ=13.0±1.0 meV, and no pseudogap in the normal state. The response of Sr0.9La0.1CuO2 to quantum impurities is also conventional, being less sensitive to non-magnetic impurities than to magnetic impurities, in sharp contrast to the strong effects induced by static non-magnetic impurities in the p-type cuprates. The dynamic injection of spin-polarized quasiparticles into the p-type cuprates is found to incur significant suppression of superconductivity, probably due to the strong influence on the spin fluctuations. [Copyright &y& Elsevier]

Abstract: A relation between the velocity of Abrikosov vortices and the electric field in type-II superconductors is derived from the point of view of time-dependent Ginzburg–Landau theory. The analysis confirms a well-known result from 1965 of Abrikosov, Kemoklidze and Khalatnikov, which is an extension of the Josephson relation by an inertial term as in the London theory. [Copyright &y& Elsevier]

The development of a superconductive detector for simultaneous measurement of energy and arrival time is reported. The detector consists of two superconducting tunnel junctions coupled through a passive network. The first junction operates in the quasi-particle regime and measures the energy absorbed by counting the total charge that tunnels. The second junction uses the DC Josephson effect to act as a fast discriminator for the onset of surplus current in the first junction. The feasibility of the detector is demonstrated through simultaneous time and energy measurements of 6 keV X-rays. A model of the detector is presented and numerical simulations show good correspondence with experimental data. [Copyright &y& Elsevier]

Abstract: Non-equilibrium phase transitions are studied theoretically for the two-dimensional Hubbard model subject to bias voltages from the electrodes coupled to the system. By combining the fluctuation exchange approximation with the Keldysh method for non-equilibrium, we have studied the properties of the non-equilibrium Fermi liquid phase and determined the phase diagram with transition to non-equilibrium magnetic and superconducting phases. [ABSTRACT FROM AUTHOR]

Abstract: We have studied relaxation of charge imbalance of non-equilibrium superconductivity in magnetic field. We found that excess current due to charge imbalance showed striking dependence on magnitude of magnetic field and its orientation. We discussed origin of the relaxation. [ABSTRACT FROM AUTHOR]