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تسجيل مستخدم جديدSite Selectivity on Chalcogen Atoms in Superconducting La(O,F)BiSSe
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Single crystals of La(O,F)BiSSe were successfully grown by a CsCl flux method. Single crystal X-ray structural analysis revealed that the crystal structure is isostructural with BiS$_2$- or BiSe$_2$-based compounds with space group $P4/nmm$ (lattice parameters $a$ = 4.1110(2) {AA}, $c$ = 13.6010(7) {AA}). However, the S atoms are selectively occupied at the apical site of the Bi-SSe pyramids in the superconducting layer. The single crystals show a superconducting transition at 4.2 K in the magnetic susceptibility and resistivity measurement. The superconducting anisotropic parameter is determined to be 34 from its upper critical magnetic field. The anisotropy is in the same range with that of other members of the La(O,F)BiCh$_2$ ($Ch$ = S, Se) family under ambient pressure.
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Ce(O,F)Sb(S,Se)2 single crystals were successfully grown using a CsCl/KCl flux method. The obtained crystals have a plate-like shape with the typical size of 1-2 mm and well-developed ab-plane, which enables X-ray single crystal structural analysis.
The Ce(O,F)Sb(S,Se)2 crystallizes in a monoclinic space group, P21/m, with lattice parameters of a = 4.121(7) A, b = 4.109(7) A, c = 13.233(15) A, beta = 97.94(7) deg. It is composed of alternate stacking of Ce-(O,F) and Sb-SSe layers, and the Sb-SSe layer includes selective occupation of Se atoms in its in-plane site. The valence state of Ce is estimated to be Ce3+ by X-ray absorption fine spectroscopy analysis. The single crystals show an insulating behavior, and a magnetic ordering around 6 K.
The newly discovered superconductor La(O,F)FeAs (Tc = 26 K) was investigated using the neutron scattering technique. No spin-density-wave (SDW) order was observed in the normal state nor in the superconducting state, both with and without an applied
magnetic field of 9 T, consistent with the proposal that SDW and superconductivity are competing in the laminar materials. While our inelastic measurements offer no constraints on the spin dynamic response from d-wave pairing, an upper limit for the magnetic resonance peak predicted from an extended s-wave pairing mechanism is provided. Our measurements also support the energy scale of the calculated phonon spectrum which is used in electron-phonon coupling theory, and fails to produce the high observed Tc.
We report the electrical resistivity measurements under pressure for the recently discovered BiS2-based layered superconductors Bi4O4S3 and La(O,F)BiS2. In Bi4O4S3, the transition temperature Tc decreases monotonically without a distinct change in th
e metallic behavior in the normal state. In La(O,F)BiS2, on the other hand, Tc initially increases with increasing pressure and then decreases above ? 1 GPa. The semiconducting behavior in the normal state is suppressed markedly and monotonically, whereas the evolution of Tc is nonlinear. The strong suppression of the semiconducting behavior without doping in La(O,F)BiS2 suggests that the Fermi surface is located in the vicinity of some instability. In the present study, we elucidate that the superconductivity in the BiS2 layer favors the Fermi surface at the boundary between the semiconducting and metallic behaviors.
We present the effect of yttrium substitution on superconductivity in the La$_{1-textit{x}}$Y$_{textit{x}}$O$_{0.5}$F$_{0.5}$BiS$_{2}$ system. Polycrystalline samples with nominal Y concentrations up to 40% were synthesized and characterized via elec
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