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A novel material is obtained by modifying pristine YBCO superconductor via simultaneous partial substitution of Sr for Ba and Se for O. The intended stoichiometry was YBa 2 − x SrxCu3 O 7 − x Sex with x = 0. 5 , 0.75 and 1; and x ≈ 1 yielded the most interesting results considered in detail. We confirmed that Se atoms indeed enter the superconductor lattice cell. The obtained polycrystalline material contains five phases, with the major phase (> 4 4 wt.%) being YBa 1. 4 Sr 0. 6 Cu3O6 Se 0. 5 . The synthesized superconductor demonstrates unique properties, including (i) two superconducting transitions with T c 1 ≈ 3 6 K and T c 2 ≈ 1 3 K yielding the Wohlleben effect; (ii) strong-coupling d-wave superconductivity (with 2 Δ / (k B T c) ≈ 5); (iii) Schottky anomaly in the heat capacity; and, most importantly, (iv) a very unusual anomaly in the heat capacity which can be associated with the quantum criticality typically observable at much higher fields. The fact that the quantum criticality is visible in weaker fields (∼ 7 T) may open opportunities for exploration of the interplay between superconductivity and pair density waves by wide research community particularly when its pure phase is available. To facilitate this, the stability of single-phase YBa 1. 4 Sr 0. 6 Cu3O6 Se 0. 5 is analyzed using machine learning methods. [ABSTRACT FROM AUTHOR]

Here, we demonstrate superconducting Dayem-bridge weak-links made of different stoichiometric compositions of NbRe. Our devices possess a relatively high critical temperature, normal-state resistance, and kinetic inductance. In particular, the high kinetic inductance makes this material a good alternative to more conventional niobium-based superconductors (e.g., NbN or NbTiN) for the realization of superinductors and high-quality factor resonators, whereas the high normal-state resistance yields a large output voltage in superconducting switches and logic elements realized upon this compound. Moreover, out-of-plane critical magnetic fields exceeding 2 T ensure that possible applications requiring high magnetic fields can also be envisaged. Altogether, these features make this material appealing for a number of applications in the framework of quantum technologies. [ABSTRACT FROM AUTHOR]

A highly anisotropic superconducting gap is found in single crystals of FeSe by studying the London penetration depth Δλ measured down to 50 mK in samples before and after 2.5 MeV electron irradiation. The gap minimum increases with introduced pointlike disorder, indicating the absence of symmetry-imposed nodes. Surprisingly, the superconducting transition temperature Tc increases by 0.4 K from Tc0≈8.8 K while the structural transition temperature Ts decreases by 0.9 K from Ts0≈91.2 K after electron irradiation. We discuss several explanations for the Tc enhancement and propose that local strengthening of the pair interaction by irradiation-induced Frenkel defects most likely explains the phenomenon. [ABSTRACT FROM AUTHOR]

Measurements of the London penetration depth Δλ(T) and tunneling conductance in single crystals of the recently discovered stoichiometric iron-based superconductor CaKFe4As4 (CaK1144) show nodeless, two-effective-gap superconductivity with a larger gap of about 6-10 meV and a smaller gap of about 1-4 meV. Having a critical temperature Tc,onset≈35.8 K, this material behaves similar to slightly overdoped (Ba1-xKx)Fe2As2 (e.g., x=0.54,Tc≈34 K), a known multigap s± superconductor. We conclude that the superconducting behavior of stoichiometric CaK1144 demonstrates that two-gap s± superconductivity is an essential property of high-temperature superconductivity in iron-based superconductors, independent of the degree of substitutional disorder. [ABSTRACT FROM AUTHOR]

The London penetration depth λ(T) was measured in single crystals of a SrFe2(As1-xPx)2 (x = 0.35) iron-based superconductor. The influence of disorder on the transition temperature Tc and on λ(T) was investigated. The effects of scattering controlled by the annealing of as-grown crystals was compared with the effects of artificial disorder introduced by 2.5 MeV electron irradiation. The low-temperature behavior of λ(T) can be described by a power-law function Δ λ(T) = ATn, with the exponents close to one in pristine annealed samples, as expected for a superconducting gap with line nodes. Upon electron irradiation with a dose of 1.2 × 1019 e /cm2, the exponent n increases rapidly, exceeding a dirty limit value of n = 2, implying that the nodes in the superconducting gap are accidental and can be lifted by the disorder. The variation of the exponent n with Tc is much stronger in the irradiated crystals compared to the crystals in which disorder was controlled by the annealing of the growth defects. We discuss the results in terms of different influence of different types of disorder on intraband and interband scattering. [ABSTRACT FROM AUTHOR]

We report the electronic structure, synthesis, and measurements of the magnetic, transport, and thermal properties of the polycrystalline noncentrosymmetric compound Re6Zr. We observed a bulk superconducting transition at temperature Tc~6.7 K, and measured the resistivity, heat capacity, thermal conductivity, and the London penetration depth below the transition, as well as performed doping and pressure studies. From these measurements we extracted the critical field and the superconducting parameters of Re6Zr. Our measurements indicate a relatively weak to moderate contribution from a triplet component to the order parameter, and favor a full superconducting gap, although we cannot exclude the existence of point nodes based on our data. [ABSTRACT FROM AUTHOR]