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Abstract The superconductivity in systems containing dispersionless (flat) bands is seemingly paradoxical, as traditional Bardeen-Cooper-Schrieffer theory requires an infinite enhancement of the carrier masses. However, the combination of flat and steep (dispersive) bands within the multiple band scenario might boost superconducting responses, potentially explaining high-temperature superconductivity in cuprates and metal hydrides. Here, we report on the magnetic penetration depths, the upper critical field, and the specific heat measurements, together with the first-principles calculations for the Mo5Si3−x P x superconducting family. The band structure features a flat band that gradually approaches the Fermi level as a function of phosphorus doping x, reaching the Fermi level at x ≃ 1.3. This leads to an abrupt change in nearly all superconducting quantities. The superfluid density data placed on the ’Uemura plot‘ results in two separated branches, thus indicating that the emergence of a flat band enhances correlations between conducting electrons.

We report the synthesis and characterization of a new ternary molybdenum pnictide superconductor, Cs2Mo3As3. The powder x-ray diffraction analysis reveals the quasi-one-dimensional (Q1D) hexagonal crystal structure formed by Cs+ and infinite (Mo3As3)2− chains as indicated by the wire-like grain morphology. Electrical resistivity and magnetic susceptibility characterizations exhibit superconductivity with the onset transition temperature at 11.5 K, which is the highest in all Q1D superconductors reported so far. An upper critical magnetic field of about 61.7 T at zero temperature was extrapolated from the resistivity measurement under a magnetic field, which is much higher than the Pauli paramagnetic limit, and the reason for such a high upper critical field may lie in its unconventional nature of superconducting pairing symmetry. The discovery of Cs2Mo3As3 inspires the search for new superconductors for future high field applications.

Here we report the preparation and superconductivity of the 133-type Cr-based quasi–one-dimensional (Q1D) RbCr3As3 single crystals. The samples were prepared by the deintercalation of Rb+ ions from the 233-type Rb2Cr3As3 crystals which were grown from a high-temperature solution growth method. The RbCr3As3 compound crystallizes in a centrosymmetric structure with the space group P63/m (No. 176) different from its non-centrosymmetric Rb2Cr3As3 superconducting precursor, and the refined lattice parameters are and . Electrical resistivity and magnetic susceptibility characterizations reveal the occurrence of superconductivity with an interestingly higher onset Tc of 7.3 K than other Cr-based superconductors, and an estimated high upper critical field Hc2(0) about 72.4 T in this 133-type RbCr3As3 crystals. [ABSTRACT FROM AUTHOR]

Recently a new family of Cr-based A2Cr3As3 (A=K, Rb, Cs) superconductors was reported, which own a rare quasi-one-dimensional (Q1D) crystal structure with infinite (Cr3As3)2- chains and exhibit intriguing superconducting characteristics possibly derived from spin-triplet electron pairing. The crystal structure of A2Cr3As3 is actually a slight variation of the hexagonal TlFe3Te3 prototype, although they have different lattice symmetry. Here we report superconductivity in a 133-type KCr3As3 compound that belongs to the latter structure. The single crystals of KCr3As3 were prepared by the deintercalation of K ions from K2Cr3As3 crystals which were grown from a high-temperature solution growth method, and it owns a centrosymmetric lattice in contrast to the noncentrosymmetric K2Cr3As3. After annealing at a moderate temperature, the KCr3As3 crystals show superconductivity at 5 K revealed by electrical resistivity, magnetic susceptibility, and heat capacity measurements. The discovery of this KCr3As3 superconductor provides a different structural instance to study the exotic superconductivity in these Q1D Cr-based superconductors. [ABSTRACT FROM AUTHOR]

Here we report the synthesis and discovery of superconductivity in a novel ternary iridium–arsenide compound BaIr2As2. The polycrystalline BaIr2As2 sample was first synthesized by a high temperature and high pressure method. Crystal structural analysis indicates that BaIr2As2 crystallizes in the ThCr2Si2-type layered tetragonal structure with space group I4/mmm (No. 139), and the lattice parameters were refined to be a = 4.052(9) Å and c = 12.787(8) Å. By the electrical resistivity and magnetic susceptibility measurements we found type-II superconductivity in the new BaIr2As2 compound with a Tc (critical temperature) of 2.45 K, and an upper critical field μ0Hc2(0) about 0.2 T. Low temperature specific heat measurements gave a Debye temperature of about 202 K and a distinct specific jump with ΔCe/γTc = 1.36, which is close to the value of BCS weak coupling limit and confirms the bulk superconductivity in this new BaIr2As2 compound. [ABSTRACT FROM AUTHOR]

We report the synthesis, crystal structure, superconductivity and physical property characterizations of the ternary equiatomic compound ScRuSi. Polycrystalline samples of ScRuSi were prepared by an arc-melting method. The as-prepared samples were identified as the orthorhombic Co2P-type o-ScRuSi by powder x-ray diffraction analysis. Electrical resistivity measurements show o-ScRuSi to be a metal which superconducts below a Tc of 3.1 K; the upper critical field μ0Hc2(0) is estimated to be 0.87 T. The magnetization and specific heat measurements confirm the bulk type-II superconductivity in o-ScRuSi, with a specific heat jump within the BCS weak coupling limit. o-ScRuSi is the first Co2P-type superconductor to contain scandium. After annealing at 1273 K for a week, o-ScRuSi transforms into hexagonal Fe2P-type h-ScRuSi, which is a Pauli-paramagnetic metal with no superconductivity observed above 1.8 K. [ABSTRACT FROM AUTHOR]

In this article, the Sm-doping single crystals Ca1 − xSmxFe2As2 (x = 0 ∼ 0.2) were prepared by the CaAs flux method, and followed by a rapid quenching treatment after the high temperature growth. The samples were characterized by structural, resistive, and magnetic measurements. The successful Sm-substitution was revealed by the reduction of the lattice parameter c, due to the smaller ionic radius of Sm3+ than Ca2+. Superconductivity was observed in all samples with onset Tc varying from 27 K to 44 K upon Sm-doping. The coexistence of a collapsed phase transition and the superconducting transition was found for the lower Sm-doping samples. Zero resistivity and substantial superconducting volume fraction only happen in higher Sm-doping crystals with the nominal x > 0.10. The doping dependences of the c-axis length and onset Tc were summarized. The high-Tc observed in these quenched crystals may be attributed to simultaneous tuning of electron carriers doping and strain effect caused by lattice reduction of Sm-substitution. [ABSTRACT FROM AUTHOR]

Single crystals of undoped CaFe2As2 are grown by an FeAs self-flux method, and the crystals are quenched in ice-water rapidly after high-temperature growth. The quenched crystal undergoes a collapsed tetragonal structural phase transition around 80 K revealed by the temperature-dependent x-ray diffraction measurements. Superconductivity below 25 K is observed in the collapsed phase by resistivity and magnetization measurements. The isothermal magnetization curve measured at 2 K indicates that this is a typical type-II superconductor. For comparison, we systematically characterize the properties of the furnace-cooled, quenched, and post-annealed single crystals, and find strong internal crystallographic strain existing in the quenched samples, which is the key for the occurrence of superconductivity in the undoped CaFe2As2 single crystals. [ABSTRACT FROM AUTHOR]

The single crystal of ThCr2Si2-type BaPd2As2 was successfully prepared by a self-flux method, and the crystal structure was characterized by X-ray diffraction method with the lattice parameters and (space group , No. 139). Bulk superconductivity below a Tc (critical temperature) of 3.85 K was revealed in this compound by the measurements of resistivity, magnetic susceptibility and specific heat, and this Tc is much higher than those of other isostructural Pd-based superconductors. [ABSTRACT FROM AUTHOR]