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Register a new userEnhanced superconductivity in hole-doped Nb$_{2}$PdS$_{5}$
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We synthesized a series of Nb$_{2}$Pd$_{1-x}$Ru$_{x}$S$_{5}$ polycrystalline samples by a solid-state reaction method and systematically investigated the Ru-doping effect on superconductivity by transport and magnetic measurements. It is found that superconductivity is enhanced with Ru doping and is quite robust upon disorder. Hall coefficient measurements indicate that the charge transport is dominated by hole-type charge carriers similar to the case of Ir doping, suggesting multi-band superconductivity. Upon Ru or Ir doping, emph H$_{c2}$/$emph T_c$ exhibits a significant enhancement, exceeding the Pauli paramagnetic limit value by a factor of approximately 4. A comparison of $T_c$ and the upper critical field ($H_{c2}$) amongst the different doping elements on Pd site, reveals a significant role of spin--orbit coupling.
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Organic materials are believed to be potential superconductor with high transition temperature (TC). Organic superconductors mainly have two families: the quasi-one dimensional (TMTSF)2X and two dimensional (BEDT-TTF)2X (Ref. 1 and 2), in which TMTSF is tetramethyltetraselenafulvalene (C10H12Se4) and BEDT-TTF or ET is bis(ethylenedithio)tetrathiafulvalene (C10H8S8). One key feature of the organic superconductors is that they have {pi}-molecular orbitals, and the {pi}-electron can delocalize throughout the crystal giving rise to metallic conductivity due to a {pi}-orbital overlap between adjacent molecules. The introduction of charge into C60 solids and graphites with {pi}-electron networks by doping to realize superconductivity has been extensively reported3,4. Very recently, superconductivity in alkali-metal doped picene with {pi}-electron networks was reported5. Here we report the discovery of superconductivity in potassium doped Phenanthrene with TC~5 K. TC increases with increasing pressure, and the pressure of 1 GPa leads to an increase of 20% in TC, suggesting that the potassium doped phenanthrene shows unconventional superconductivity. Both phenanthrene and picene are polycyclic aromatic hydrocarbons, and contain three and five fused benzene rings, respectively. The ribbon of fused benzene rings is part of graphene. Therefore, the discovery of superconductivity in K3Phenanthrene produces a novel broad class of superconductors consisting of fused hydrocarbon benzene rings with {pi}-electron networks. The fact that TC increases from 5 K for KxPhenanthrene with three benzene rings to 18 K for Kxpicene with five benzene rings suggests that such organic hydrocarbons with long benzene rings is potential superconductor with high TC.
SrTiO$_3$ exhibits a superconducting dome upon doping with Nb, with a maximum critical temperature mbox{$T_mathrm{c} approx 0.4$~K}. Using microwave stripline resonators at frequencies from 2 to 23~GHz and temperatures down to 0.02~K, we probe the low-energy optical response of superconducting SrTiO$_3$ with charge carrier concentration from 0.3 to $2.2times 10^{20}$~cm$^{-3}$, covering the majority of the superconducting dome. We find single-gap electrodynamics even though several electronic bands are superconducting. This is explained by a single energy gap $2Delta$ due to gap homogenization over the Fermi surface consistent with the low level of defect scattering in Nb-doped SrTiO$_3$. Furthermore, we determine $T_mathrm{c}$, $2Delta$, and the superfluid density as a function of charge carrier concentration, and all three quantities exhibit the characteristic dome shape.
Polycrystalline Eu0.5La0.5BiS2F was synthesized by solid state reaction which crystallizes in the tetragonal CeOBiS2 structure (P4/nmm). We report here enhancement of Tc to 2.2 K in Eu0.5La0.5BiS2F (by electron doping in EuBiS2F with Tc ~ 0.3 K). Eu0.5La0.5BiS2F is semiconducting down to 3 K and an onset of superconductivity is seen at 2.2 K at ambient pressure. Upon application of pressure the Tc could be enhanced upto 10 K. Step like features are seen in the resistivity curves at intermediate pressures (0.5 - 1 GPa) which hints towards the possible existence of two phases with different Tc. At a pressure above 1.38GPa, the Tconset remains invariant at 10 K but the Tc(r{ho}=0) is increased to above 8.2 K. There is a possible transformation from a low Tc phase to a high Tc phase by application of pressure.
The layered lithium borocarbide LiBC, isovalent with and structurally similar to the superconductor MgB2, is an insulator due to the modulation within the hexagonal layers (BC vs. B2). We show that hole-doping of LiBC results in Fermi surfaces of B-C p sigma character that couple very strongly to B-C bond stretching modes, precisely the features that lead to superconductivity at Tc = 40 K in MgB2. Comparison of Li{0.5}BC with MgB2 indicates the former to be a prime candidate for electron-phonon coupled superconductivity at substantially higher temperature than in MgB2.
We successfully synthesized the nickel-based compound GdONiBi with superconducting transition temperature about 4.5 K. By partially substituting the element Gd with Sr to introduce holes into the material, we got new superconductor Gd0.9Sr0.1ONiBi with critical temperature about 4.7 K. The normal state resistivity in nickel-based samples shows a metallic behavior. The magnetoresistance measurements show a different behavior compared to those in iron-based compounds which indicates that the mechanism in the two kinds of superconductors maybe different.
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