Vortex Dynamics and Superconducting Phase Diagrams in Ta x Ge 1-x / Ge Multilayers with Coplanar Defects

<p>The superconducting phase diagrams of amorphous multilayered Ta x Ge 1-x / Ge thin films have been studied over a large range of temperatures and magnetic fields by means of dc electrical transport measurements. These superconducting films belong to the class of extremely type-II superconductors, for which a multitude of superconducting phases has been predicted and experimentally verified. A thorough understanding of these phase diagrams is indispensable for future successful applications of high-temperature superconductors since some of the observed phases severely limit the zero-resistance current-carrying capacity of these materials. The Ta x Ge 1-x / Ge films in this study were prepared by vapour deposition under high vacuum conditions. The Ta-content varied between x = 0.31 and 0.37 and individual layer thicknesses ranged from about 3 to 15 nm. Tilting the sample substrates during the deposition resulted in coplanar defects with variable orientation and structure depending on the tilting angle. This way it was possible to study the interplay between magnetic flux lines and the material structure and defect morphology, respectively. Films with thin insulating Ge layers and thus strong interlayer coupling showed three dimensional behaviour over the complete range of fields and temperatures. The coplanar defect structure was able to extend the zero-resistance phase to significantly higher fields and temperatures for magnetic fields co-aligned with the defects. Strong support for the existence of a low-temperature glass phase was found in the case of aligned and misaligned magnetic fields. Increasing the insulating layer thickness lead to a cross-over to 2D behaviour depending on temperature and field as well as field orientation with respect to the defects. In the 2D phase regions the low-temperature zero-resistance glass phase may have disappeared entirely. Current-voltage characteristics measured in the low-temperature glass phases showed significant differences between the strongly and weakly coupled films. However the detailed temperature and field dependence of these current-voltage curves at low temperatures cannot be explained satisfactorily with existing theoretical models.</p>

Phase fluctuations in conventional superconductors

Within the Bardeen-Cooper-Schrieffer (BCS) theory, superconductivity is entirely governed by the pairing energy scale, which gives rise to the superconducting energy gap, Δ. However, another important energy scale, the superfluid phase stiffness, J, which determines the resilience of the superconductor to phase-fluctuations is normally ignored. The spectacular success of BCS theory owes to the fact that in conventional superconductors J is normally several orders of magnitude larger than Δ and thus an irrelevant energy scale. However, in certain situations such as in the presence of low carrier density, strong disorder, at low-dimensions or in granular superconductors, J can drastically come down and even become smaller than Δ. In such situations, the temperature and magnetic field evolution of superconducting properties is governed by phase fluctuations, which gives rise to novel electronic states where signatures of electronic pairing continue to exist even when the zero resistance state is destroyed. In this article, we will review the recent experimental developments on the study of phase fluctuations in conventional superconductors.

Vortex Dynamics and Superconducting Phase Diagrams in Ta x Ge 1-x / Ge Multilayers with Coplanar Defects

<p>The superconducting phase diagrams of amorphous multilayered Ta x Ge 1-x / Ge thin films have been studied over a large range of temperatures and magnetic fields by means of dc electrical transport measurements. These superconducting films belong to the class of extremely type-II superconductors, for which a multitude of superconducting phases has been predicted and experimentally verified. A thorough understanding of these phase diagrams is indispensable for future successful applications of high-temperature superconductors since some of the observed phases severely limit the zero-resistance current-carrying capacity of these materials. The Ta x Ge 1-x / Ge films in this study were prepared by vapour deposition under high vacuum conditions. The Ta-content varied between x = 0.31 and 0.37 and individual layer thicknesses ranged from about 3 to 15 nm. Tilting the sample substrates during the deposition resulted in coplanar defects with variable orientation and structure depending on the tilting angle. This way it was possible to study the interplay between magnetic flux lines and the material structure and defect morphology, respectively. Films with thin insulating Ge layers and thus strong interlayer coupling showed three dimensional behaviour over the complete range of fields and temperatures. The coplanar defect structure was able to extend the zero-resistance phase to significantly higher fields and temperatures for magnetic fields co-aligned with the defects. Strong support for the existence of a low-temperature glass phase was found in the case of aligned and misaligned magnetic fields. Increasing the insulating layer thickness lead to a cross-over to 2D behaviour depending on temperature and field as well as field orientation with respect to the defects. In the 2D phase regions the low-temperature zero-resistance glass phase may have disappeared entirely. Current-voltage characteristics measured in the low-temperature glass phases showed significant differences between the strongly and weakly coupled films. However the detailed temperature and field dependence of these current-voltage curves at low temperatures cannot be explained satisfactorily with existing theoretical models.</p>

Expansion of the high field-boosted superconductivity in UTe2 under pressure

Magnetic field-induced superconductivity is a fascinating quantum phenomenon, whose origin is yet to be fully understood. The recently discovered spin-triplet superconductor, UTe2, exhibits two such superconducting phases, with the second one reentering in the magnetic field of 45 T and persisting up to 65 T. More surprisingly, in order to induce this superconducting phase, the magnetic field has to be applied in a special angle range, not along any high symmetry crystalline direction. Here we investigated the evolution of this high-field-induced superconducting phase under pressure. Two superconducting phases merge together under pressure, and the zero resistance persists up to 45 T, the field limit of the current study. We also reveal that the high-field-induced superconducting phase is completely decoupled from the first-order field-polarized phase transition, different from the previously known example of field-induced superconductivity in URhGe, indicating superconductivity boosted by a different paring mechanism.

Superconducting diode effect via conformal-mapped nanoholes

A superconducting diode is an electronic device that conducts supercurrent and exhibits zero resistance primarily for one direction of applied current. Such a dissipationless diode is a desirable unit for constructing electronic circuits with ultralow power consumption. However, realizing a superconducting diode is fundamentally and technologically challenging, as it usually requires a material structure without a centre of inversion, which is scarce among superconducting materials. Here, we demonstrate a superconducting diode achieved in a conventional superconducting film patterned with a conformal array of nanoscale holes, which breaks the spatial inversion symmetry. We showcase the superconducting diode effect through switchable and reversible rectification signals, which can be three orders of magnitude larger than that from a flux-quantum diode. The introduction of conformal potential landscapes for creating a superconducting diode is thereby proven as a convenient, tunable, yet vastly advantageous tool for superconducting electronics. This could be readily applicable to any superconducting materials, including cuprates and iron-based superconductors that have higher transition temperatures and are desirable in device applications.

Relationship between the TC of Smart Meta-Superconductor Bi(Pb)SrCaCuO and Inhomogeneous Phase Content

A smart meta-superconductor Bi(Pb)SrCaCuO (B(P)SCCO) may increase the critical transition temperature (TC) of B(P)SCCO by electroluminescence (EL) energy injection of inhomogeneous phases. However, the increase amplitude ΔTC (ΔTC=TC−TC,pure) of TC is relatively small. In this study, a smart meta-superconductor B(P)SCCO with different matrix sizes was designed. Three kinds of raw materials with different particle sizes were used, and different series of Y2O3:Sm3+, Y2O3, Y2O3:Eu3+, and Y2O3:Eu3++Ag-doped samples and pure B(P)SCCO were prepared. Results indicated that the TC of the Y2O3 or Y2O3:Sm3+ non-luminescent dopant doping sample is lower than that of pure B(P)SCCO. However, the TC of the Y2O3:Eu3++Ag or Y2O3:Eu3+ luminescent inhomogeneous phase doping sample is higher than that of pure B(P)SCCO. With the decrease of the raw material particle size from 30 to 5 μm, the particle size of the B(P)SCCO superconducting matrix in the prepared samples decreases, and the doping content of the Y2O3:Eu3++Ag or Y2O3:Eu3+ increases from 0.2% to 0.4%. Meanwhile, the increase of the inhomogeneous phase content enhances the ΔTC. When the particle size of raw material is 5 μm, the doping concentration of the luminescent inhomogeneous phase can be increased to 0.4%. At this time, the zero-resistance temperature and onset transition temperature of the Y2O3:Eu3++Ag doped sample are 4 and 6.3 K higher than those of pure B(P)SCCO, respectively.

Symmetry Conservation of Dirac Fermion With Double Junction and Gauge Field of Weyl Fermion With Single Junction

Majorana fermion and Weyl fermion have matters and antimatters. But Majorana fermion has zero resistance and Weyl fermion has a resistance. It was confirmed that CP symmetry is preserved in the case of Dirac fermion because it only has spin current as the antimatter. Dirac fermion is supercurrent because CP symmetry is preserved by double schottky contact, but the Majorana fermion with ohmic contact has decreased current due to symmetry violation. Parity symmetry conservation was confirmed from the electrical properties of transistors, and charge symmetry conservation was confirmed in diode properties.