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The application of a gate voltage to control the superconducting current flowing through a nanoscale superconducting constriction, named as gate-controlled supercurrent (GCS), has raised great interest for fundamental and technological reasons. To gain a deeper understanding of this effect and develop superconducting technologies based on it, the material and physical parameters crucial for GCS must be identified. Top-down fabrication protocols should be also optimized to increase device scalability, although studies suggest that top-down fabricated devices are more resilient to show GCS. Here, we investigate gated superconducting nanobridges made with a top-down fabrication process from thin films of the non-centrosymmetric superconductor NbRe. Unlike other devices previously reported, our NbRe devices systematically exhibit GCS, when made in specific conditions, which paves the way for higher device scalability. Our results also suggest that surface properties of NbRe nanobridges and their modification during fabrication are key for GCS., Comment: 14 pages, 4 figures

We report on magnetron deposition of thin superconducting rhenium films on sapphire substrates. During the deposition, substrates were held at ambient temperature. Critical temperature of the films is Tc~3.6 K. Films have polycrystalline structure, and grazing incidence X-ray diffractometry indicates that crystalline lattice parameters are somewhat larger compared to the bulk ones. Magnetoresistive and AC/DC susceptibilities allowed us to determine $H_{c1}$ and $H_{c2}$ of these films, as well as estimate coherence length $\xi$(0) and magnetic penetration depth $\lambda_L$(0). We also provide information on surface morphology of these films., Comment: arXiv admin note: text overlap with arXiv:2307.16313

We report on magnetron deposition and superconducting properties of a novel superconducting material: rhenium-lutetium films on sapphire substrates. Different compositions of Re$_{x}$Lu binary are explored from $x\approx 3.8$ to close to pure Re stoichiometry. The highest critical temperature, up to $T_{c}\approx $ 6.95 K, is obtained for $x\approx 10.5$. Depending on the deposition conditions, polycrystalline or amorphous films are obtainable, both of which are interesting for practice. Crystalline structure of polycrystalline phase is identified using grazing incidence X-ray diffractometry as a non-centrosymmetric superconductor. Superconducting properties were characterized both resistively and magnetically. Demonstration of superconductivity in this material justifies the point of view that Lu plays a role of group 3 transition metal in period 6 of the Periodic table of elements. In analogy with Re$_{0.82}$Nb$_{0.18}$, Re$_{6}$Ti, Re$_{6}$Hf and Re$_{6}$Zr, one can expect that crystalline Re--Lu is also breaking the time-reversal symmetry (this still waits confirmation). Magnetoresistivity and AC/DC susceptibility measurements allowed us to determine H$_{c1}$ and H$_{c2}$ of these films, as well as estimate coherence length $\xi (0)$ and magnetic penetration depth $\lambda _{L}(0)$. We also provide information on surface morphology of these films.

We designed and experimentally demonstrated a four-terminal superconducting device which can function as a non-latching (reversible) superconducting switch from the diode regime to the resistive state by applying a control current much smaller than the main transport current. The device utilizes a vortex-based superconducting diode mechanism which is switched back and forth via the injection of flux quanta through auxiliary current leads. Various applications in superconducting electronics can be foreseen.

The superconducting diode effect has been recently reported in a variety of systems and different symmetry breaking mechanisms have been examined. However, the frequency range of these potentially important devices still remains obscure. We investigated superconducting micro-bridges of Nb$_{3}$Sn in out-of-plane magnetic fields; optimum magnetic fields of $\sim$10 mT generate $\sim $10% diode efficiency, while higher fields of $\sim$15-20 mT quench the effect. The diode changes its polarity with magnetic field reversal. We documented superconductive diode rectification at frequencies up to 100 kHz, the highest reported as of today. Interestingly, the bridge resistance during diode operation reaches a value that is a factor of two smaller than in its normal state, which is compatible with the vortex-caused mechanism of resistivity. This is confirmed by finite element modeling based on time-dependent Ginzburg-Landau equations. To explain experimental findings, no assumption of lattice thermal inequilibrium was required. Dissimilar edges of the superconductor strip can be responsible for the inversion symmetry breaking by vortex penetration barrier; visual evidence of this opportunity was revealed by scanning electron microscopy. Estimates are in favor of much higher (GHz) range of frequencies for this type of diode.

Based on a time-dependent Ginzburg-Landau system of equations and finite element modeling, we present novel results related with the physics of phase-slippage in superconducting wires surrounded by a non-superconductive environment. These results are obtained within our previously reported approach related to superconducting rings and superconductive gravitational wave detector transducers. It is shown that the phase-slip centers (PSCs) can be effective in originating not only positive but also negative thermal fluxes. With an appropriate design utilizing thermal diodes, PSCs can serve as cryocooling engines. Operating at $T\sim 1$ K cryostat cold-finger, they can achieve sub-Kelvin temperatures without using $^3$He.

The results on the behavior of phase-slip centers in thin superconducting wires based on finite-element modeling and time-dependent Ginzburg-Landau (TDGL) equations are discussed. For closer relationship with experiments, we used finite-gap formulation of the TDGL system. Both the dynamic equation for the Cooper-pair condensate wave-function and the expression for the electric current are more complex than in the gapless case. On this basis, the influence of nonequilibrium phonons is explored. These phonons can essentially change the location of geometrical points in which the phase slippage takes place. They also affect the frequency of phase-slip oscillations. The reported effects are experimentally detectable and can be used in practical devices.

Strontium ruthenates have many similarities with copper oxide superconductors and are of particular interest for the investigation of the mechanisms and conditions which lead to high-temperature superconductivity. We report here on multiple experimental indications of superconductivity with onset at 40 K in strontium ruthenate doped by rhenium and selenium with chlorine used as the flux. The main experimental evidence arises from terahertz spectroscopy of this material followed by AC and DC magnetization, as well as measurements of its heat capacity and magnetoresistance. Structural and morphological studies revealed the heterophase nature of this polycrystalline material as well as the changes of lattice parameters relative to the original phases. Experimental data show a higher critical temperature on the surface compared to that of the bulk of the sample.

Study of the Abrikosov vortex motion in superconductors based on time-dependent Ginzburg-Landau equations reveals an opportunity to locally detect the values of the Aharonov-Bohm type curl-less vector potentials., Comment: The content of this article is presented at the APS March Meeting (New Orleans, 2017)

Theoretical explanation of the Meissner effect involves proportionality between current density and vector potential [1], which has many deep consequences. Amongst them, one can speculate that superconductors in a magnetic field "find an equilibrium state where the sum of kinetic and magnetic energies is minimum" and this state "corresponds to the expulsion of the magnetic field" [2]. This statement still leaves an open question: from which source is superconducting current acquiring its kinetic energy? A na\"ive answer, perhaps, is from the energy of the magnetic field. However, one can consider situations (Aharonov-Bohm effect), where the classical magnetic field is absent in the space area where the current is being set up. Experiments demonstrate [3] that despite the local absence of magnetic field, current is, nevertheless, building up. From what source is it acquiring its energy then? Locally, only a vector potential is present. How does the vector potential facilitate the formation of the current? Is the current formation a result of truly non-local quantum action, or does the local action of the vector potential have experimental consequences, which are measurable quasi-locally? We discuss possible experiments with a hybrid normal-metal superconductor circuitry, which can clarify this puzzling situation. Experimental answers would be important for further theoretical developments., Comment: Reported at the conference M2S, August 1, 2012

Ceramic samples of Sr2RuO(4-y)Sy (y=0.03-1.2) with intended isovalent substitution of oxygen by sulfur have been synthesized and explored in the temperature range 4-300K. It is found that at a range of optimum sulfur substitution the magnetic response of ceramic samples reveals large diamagnetic signal with amplitudes approaching comparability with that of the YBCO-superconductors. Contrary to a pure ceramic Sr2RuO4, if properly optimized, the resistivity of sulfur-substituted samples has a metallic behavior except at lower temperatures where an upturn occurs. Both synthesis conditions and results of measurements are reported. The Meissner effect may point to high-temperature superconductivity., Comment: 4 pages, 2 figures

We propose to use the Bragg interference filter technology for fabrication of microrefrigerators. The idea of using superconductor-insulator-superconductor (SIS) or normal metal-insulator-superconductor (SIN) tunnel junctions as cooling elements in micro-refrigerators is attractive because of the absence of (micro-) refrigerators operating below 150 K. The microscopic approach to cooling is based on the "phonon deficit effect" in nonequilibrium regime of tunnel junctions. This effect can be improved by use of phonon filters placed between the tunnel junction and the heath-bath. Such a filter can be the Bragg interference superlattice (Bragg's grating) which is well studied for problems of optical communications. Bragg interference filters are used also for detection of phonons emitted by tunnel junctions. To enhance the refrigeration process one needs filters with very broad spectral transmission properties or a large transmission band with one or two narrow stop bands. The type of the needed filter will depend on the types of the used tunnel junction. Corresponding discussion is presented., Comment: 9 pages, International Conference of Applied Photonic Technologies (ICAPT), Quebec, 2000

We discuss possibilities of utilizing superconductors with Cooper condensates in triplet pairing states (where the spin of condensate pairs is S=1) for practical realization of quantum computers. Superconductors with triplet pairing condensates have features that are unique and cannot be found in the usual (singlet pairing, S=0) superconductors. The symmetry of the order parameter in some triplet superconductors (e.g., ruthenates) corresponds to doubly-degenerate chiral states. These states can serve as qubit base states for quantum computing., Comment: 4 pages, 5 figures, will be presented at ASC-2002 and submitted to IEEE Trans. Appl. Supercond

Symmetry of the order parameter in some triplet superconductors corresponds to doubly-degenerate chiral states. We predict that in a sufficiently small sample this degeneracy can be lifted via macroscopic quantum tunneling. Moreover, if the initial state is prepared correspondingly, 'instanton'-like quantum behavior is possible in a single-domain sample. In this case coherent oscillations of magnetic momentum should take place, as well as the sign alternations of the boundary currents. In particular, spontaneous Hall-effect recently predicted for ruthenates should posses the oscillating voltage feature., Comment: 6 pages, 1 figure, submitted to Phys. Rev. Lett

We consider tunnel microrefrigerators at low temperature. There is a number of experimental studies performed on microrefrigeration in tunneling superconductor--normal metal (SN) structures. Related to these experiments, only the electron subsystem has been considered theoretically. Independently, the phonon deficit effect has been studied a while ago in superconductor-superconductor tunnel junctions. It can be regarded as a possible prototype scheme for superconducting microrefrigerators. We try to provide the missing link between experiments on the SN tunnel junction refrigerators and the theory which includes microscopically phonons in combination with the mechanism of the phonon deficit effect., Comment: 2 pages, 1 figure