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- ItemQuasi one dimensional dirac electrons on the surface of Ru2 Sn3(London : Nature Publishing Group, 2014) Gibson, Q.D.; Evtushinsky, D.; Yaresko, A.N.; Zabolotnyy, V.B.; Ali, Mazhar N.; Fuccillo, M.K.; Van den Brink, J.; Büchner, B.; Cava, R.J.; Borisenko, S.V.We present an ARPES study of the surface states of Ru2Sn3, a new type of a strong 3D topological insulator (TI). In contrast to currently known 3D TIs, which display two-dimensional Dirac cones with linear isotropic dispersions crossing through one point in the surface Brillouin Zone (SBZ), the surface states on Ru2Sn3 are highly anisotropic, displaying an almost flat dispersion along certain high-symmetry directions. This results in quasi-one dimensional (1D) Dirac electronic states throughout the SBZ that we argue are inherited from features in the bulk electronic structure of Ru2Sn3 where the bulk conduction bands are highly anisotropic. Unlike previous experimentally characterized TIs, the topological surface states of Ru2Sn3 are the result of a d-p band inversion rather than an s-p band inversion. The observed surface states are the topological equivalent to a single 2D Dirac cone at the surface Brillouin zone.
- ItemIsotropic multi-gap superconductivity in BaFe1.9Pt0.1As2 from thermal transport and spectroscopic measurements(Bristol : IOP Publishing, 2014) Ziemak, Steven; Kirshenbaum, K.; Saha, S.R.; Hu, R.; Reid, J.-Ph.; Gordon, R.; Taillefer, L.; Evtushinsky, D.; Thirupathaiah, S.; Büchner, B.; Borisenko, S.V.; Ignatov, A.; Kolchmeyer, D.; Blumberg, G.; Paglione, J.Thermal conductivity, point contact spectroscopy, angle-resolved photoemission and Raman spectroscopy measurements were performed on BaFe1.9Pt0.1As2 single crystals obtained from the same synthesis batch in order to investigate the superconducting energy gap structure using multiple techniques. Low temperature thermal conductivity was measured in the superconducting state as a function of temperature and magnetic field, revealing an absence of quasiparticle excitations in the $T\to 0$ limit up to 15 T applied magnetic fields. Point-contact Andreev reflection spectroscopy measurements were performed as a function of temperature using the needle-anvil technique, yielding features in the conductance spectra at both 2.5 meV and 7.0 meV scales consistent with a multi-gap scenario. Angle-resolved photoemission spectroscopy probed the electronic band structure above and below the superconducting transition temperature of Tc = 23 K, revealing an isotropic gap of magnitude $\sim 3$ meV on both electron and hole pockets. Finally, Raman spectroscopy was used to probe quasiparticle excitations in multiple channels, showing a threshold energy scale of 3 meV below Tc. Overall, we find strong evidence for an isotropic gap structure with no nodes or deep minima in this system, with a 3 meV magnitude gap consistently observed and a second, larger gap suggested by point-contact spectroscopy measurements. We discuss the implications that the combination of these results reveal about the superconducting order parameter in the BaFe2−xPtxAs2 doping system and how this relates to similar substituted iron pnictides.