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

Science cafés. Cross-cultural adaptation and educational applications

Tokyo Institute of Technology (TokyoTech) has been developing a number of methodologies to teach graduate students the theory and practice of science communication since 2005. One of the tools used is the science café, where students are taught about the background based primarily on theoretical models developed in the UK. They then apply that knowledge and adapt it the Japanese cultural context and plan, execute and review outcomes as part of their course. In this paper we review 4 years of experience in using science cafés in this educational context; we review the background to the students’ decision-making and consensus-building process towards deciding on the style and subject to be used, and the value this has in illuminating the cultural influences on the science café design and implementation. We also review the value of the science café as an educational tool and conclude that it has contributed to a number of teaching goals related to both knowledge and the personal skills required to function effectively in an international environment

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

Quasiparticle spectrum of the hybrid s+g-wave superconductors YNi_2B_2C and LuNi_2B_2C

Recent experiments on single crystals of YNi$_2$B$_2$C have revealed the presence of point nodes in the superconducting energy gap Delta(k} at k = (1,0,0), (0,1,0), (-1,0,0), and (0,-1,0). In this paper we investigate the effects of impurity scattering on the quasiparticle spectrum in the vortex state of s+g-wave superconductors, which is found to be strongly modified in the presence of disorder. In particular, a gap in the quasiparticle energy spectrum is found to open even for infinitesimal impurity scattering, giving rise to exponentially activated thermodynamic response functions, such as the specific heat, the spin susceptibility, the superfluid density, and the nuclear spin lattice relaxation. Predictions derived from this study can be verified by measurements of the angular dependent magnetospecific heat and the magnetothermal conductivity.Comment: 8 pages, RevTex, 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