Enhanced thermoelectric properties by Ir doping of PtSb2 with pyrite structure

The effects of Ir doping on the thermoelectric properties of Pt1-xIrxSb2 (x = 0, 0.01, 0.03, and 0.1) with pyrite structure were studied. Measurements of electrical resistivity rho, Seebeck coefficient S, and thermal conductivity kappa were conducted. The results showed an abrupt change from semiconducting behavior without Ir (x = 0) to metallic behavior at x = 0.01. The sample with x = 0.01 exhibited large S and low rho, resulting in a maximum power factor (S^2/rho) of 43 muW/cmK^2 at 400 K. The peculiar "pudding mold"-type electronic band dispersion could explain the enhanced thermoelectric properties in the metallic state.Comment: 3 pages, 2 figure

Directional tunnelling spectroscopy of a normal metal-s+gs+g-wave superconductor junction

We calculate the normal metal-$s+g$-wave superconductor tunnelling spectrum for various junction orientations and for two forms of the superconducting gap, one which allows for point nodes and the other which allows for line nodes. For a junction oriented with its normal parallel to the ab plane of the tetragonal superconductor, we find that the tunnelling spectrum is strongly dependent on orientation in the plane. The spectrum contains two peaks at energies equivalent to the magnitudes of the gap function in the direction parallel to the interface normal and in the direction making a $\pi/4$ angle with the normal. These two peaks appear in both superconductors with point nodes and line nodes, but are more prominent in the latter. For the tunnelling along the c axis, we find a sharp peak at the gap maximum in the conductance spectrum of the superconductor with line nodes, whereas with point nodes we find a peak occurring at the value of the gap function along the c axis. We discuss the relevance of our result to borocarbide systems.Comment: 16 pages, 10 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

Fulde-Ferrell-Larkin-Ovchinnikov state in a perpendicular field of quasi two-dimensional CeCoIn5

A Fulde-Ferrell-Larkin-Ovchinnkov (FFLO) state was previously reported in the quasi-2D heavy fermion CeCoIn5 when a magnetic field was applied parallel to the ab-plane. Here, we conduct 115^In NMR studies of this material in a PERPENDICULAR field, and provide strong evidence for FFLO in this case as well. Although the topology of the phase transition lines in the H-T phase diagram is identical for both configurations, there are several remarkable differences between them. Compared to H//ab, the FFLO region for H perpendicular to the ab-plane shows a sizable decrease, and the critical field separating the FFLO and non-FFLO superconducting states almost ceases to have a temperature dependence. Moreover, directing H perpendicular to the ab-plane results in a notable change in the quasiparticle excitation spectrum within the planar node associated with the FFLO transition.Comment: 5 pages, 3 figure

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