Violation of the isotropic-ℓ\ell approximation in overdoped La_{2-x}Sr_xCuO_4

Magnetotransport measurements on the overdoped cuprate La_{1.7}Sr_{0.3}CuO_4 are fitted using the Ong construction and band parameters inferred from angle-resolved photoemission. Within a band picture, the low temperature Hall data can only be fitted satisfactorily by invoking strong basal-plane anisotropy in the mean-free-path $\ell$. This violation of the isotropic-$\ell$ approximation supports a picture of dominant small-angle elastic scattering in cuprates due to out-of-plane substitutional disorder. We show that both band anisotropy and anisotropy in the elastic scattering channel strongly renormalize the Hall coefficient in overdoped La_{2-x}Sr_xCuO_4 over a wide doping and temperature range.Comment: 4 pages, 4 figure

Josephson effect in a weak link between borocarbides

A stationary Josephson effect is analyzed theoretically for a weak link between borocarbide superconductors. It is shown that different models of the order parameter result in qualitatively different current-phase relations

Spins in the Vortices of a High Temperature Superconductor

Neutron scattering is used to characterise the magnetism of the vortices for the optimally doped high-temperature superconductor La(2-x)Sr(x)CuO(4) (x=0.163) in an applied magnetic field. As temperature is reduced, low frequency spin fluctuations first disappear with the loss of vortex mobility, but then reappear. We find that the vortex state can be regarded as an inhomogeneous mixture of a superconducting spin fluid and a material containing a nearly ordered antiferromagnet. These experiments show that as for many other properties of cuprate superconductors, the important underlying microscopic forces are magnetic

Orbital Degeneracy and Peierls Instability in Triangular Lattice Superconductor Ir1−x_{1-x}Ptx_xTe2_2

We have studied electronic structure of triangular lattice Ir$_{1-x}$Pt$_x$Te$_2$ superconductor using photoemission spectroscopy and model calculations. Ir $4f$ core-level photoemission spectra show that Ir $5d$ $t_{2g}$ charge modulation established in the low temperature phase of IrTe$_2$ is suppressed by Pt doping. This observation indicates that the suppression of charge modulation is related to the emergence of superconductivity. Valence-band photoemission spectra of IrTe$_2$ suggest that the Ir $5d$ charge modulation is accompanied by Ir $5d$ orbital reconstruction. Based on the photoemission results and model calculations, we argue that the orbitally-induced Peierls effect governs the charge and orbital instability in the Ir$_{1-x}$Pt$_x$Te$_2$.Comment: 5 pages,4 figure

Coexistence of Bloch electrons and glassy electrons in Ca10(Ir4As8)(Fe2_xIrxAs2)5 revealed by angle-resolved photoemission spectroscopy

Angle-resolved photoemission spectroscopy of Ca10(Ir4As8)(Fe2_xIrxAs2)5 shows that the Fe 3d electrons in the FeAs layer form the hole-like Fermi pocket at the zone center and the electron-like Fermi pockets at the zone corners as commonly seen in various Fe-based superconductors. The FeAs layer is heavily electron doped and has relatively good two dimensionality. On the other hand, the Ir 5d electrons are metallic and glassy probably due to atomic disorder related to the Ir 5d orbital instability. Ca10(Ir4As8)(Fe2_xIrxAs2)5 exhibits a unique electronic state where the Bloch electrons in the FeAs layer coexist with the glassy electrons in the Ir4As8 layer.Comment: 4 pages, 3 figure

Reentrant vortex lattice transformation in four-fold symmetric superconductors

The physics behind the rhombic$\to$square$\to$rhombic flux line lattice transformation in increasing fields is clarified on the basis of Eilenberger theory. We demonstrate that this reentrance observed in LuNi$_2$B$_2$C is due to intrinsic competition between superconducting gap and Fermi surface anisotropies. The calculations reproduce not only it but also predict yet not found lock-in transition to a square lattice with different orientation in higher field. In view of physical origin given, this sequence of transitions is rather generic to occur in four-fold symmetric superconductors.Comment: 5 pages, 4 figures,submitted to Phys. Rev. Let

On the Ginzburg-Landau Analysis of the Upper Critical Field Hc2 in MgB2

Temperature dependence of the upper critical field Hc2 (T) for the superconducting magnesium diboride, MgB2, is studied in the vicinity of Tc by using a two-band Ginzburg-Landau (G-L) theory. The temperature dependence of Hc2 (T) near Tc exhibits a positive curvature. In addition, the calculated temperature dependence and its higher order derivatives are also shown to be in a good agreement with the experimental data. In analogy with the multi-band character of Eliashberg microscopic theory, the positive curvature of Hc2 (T) is described reasonably by solving the two-band of G-L theory.Comment: 14 pages, 2 figures, submitted to SUST November 200