Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Q39: Superconductivity: Sr2RuO4 and Related Materials |
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Sponsoring Units: DCMP Chair: Maxim Khodas, University of Iowa Room: Mile High Ballroom 2A-3A |
Wednesday, March 5, 2014 2:30PM - 2:42PM |
Q39.00001: Zero energy bound state at an interface between s-wave superconductor and disordered normal metal with repulsive electron-electron interaction Christopher Reeg, Dmitrii Maslov In recent years there has been a renewed interest in the proximity effect due to its role in the realization of topological superconductivity. In particular, we study a superconductor-normal metal proximity system with a repulsive interaction between electrons in the normal layer. Due to the change in sign of the superconducting pair potential, a zero energy bound state is trapped at the interface [Fauch\`{e}re et al., Phys. Rev. Lett., {\bf 82}, 3336 (1999)]. Using the quasiclassical theory of superconductivity we investigate the behavior of this zero energy state in the presence of finite disorder and an interfacial barrier. We find that as the mean free path is decreased, the peak in the local density of states is broadened and shifted away from zero energy. In the ballistic limit the presence of this bound state eliminates the mini-gap seen in a non-interacting normal layer and a distinct peak is observed. When the mean free path becomes comparable to the normal layer width the low energy peak is strongly suppressed and the mini-gap begins to develop. In the diffusive limit the mini-gap is fully restored and all signatures of the bound state are eliminated. [Preview Abstract] |
Wednesday, March 5, 2014 2:42PM - 2:54PM |
Q39.00002: Satisfaction of Kohler's rule in the pseudogap phase of the high-temperature superconductor HgBa$_2$CuO$_{4+\delta}$ Yang Ge, M. Chan, M. Veit, C. Dorrow, W. Tabis, M. Greven, B. Vignolle, C. Proust, X. Zhao, N. Bari\v{s}i\'{c} We report on the temperature and magnetic field evolution of the planar resistivity in the simple tetragonal high-temperature superconductor HgBa$_2$CuO$_{4+\delta}$ (Hg1201). Counter to the longstanding view that Kohler's rule is universally strongly violated in the cuprates, we find that it is in fact satisfied in the pseudogap state. The magnetoresistance shows a $T^{-4}$ temperature dependence which, in conjunction with previous work demonstrating $\rho\propto T^2$ [1] as well as quadratic temperature and frequency dependence of the dynamical relaxation rate [2], is indicative of a Fermi-liquid quasiparticle scattering in the pseudogap phase of Hg1201. [1] N. Bari\v{s}i\'c et al., Proc. Natl. Acad. Sci. US 110, 12235 (2013). [2] S.I. Mirzaei et al., Proc. Natl. Acad. Sci. US 110, 5774 (2013) [Preview Abstract] |
Wednesday, March 5, 2014 2:54PM - 3:06PM |
Q39.00003: Strong anisotropy in the electromagnetic properties of Na$_{2}$Ti$_{2}X_{2}$O ($X =$ As, Sb) crystals Youguo Shi, Nanlin Wang Na$_{2}$Ti$_{2}X_{2}$O ($X =$ As, Sb) crystals have been grown from the flux method. X-ray diffraction characterization revealed an anti-K$_{2}$NiF$_{4}$-type layered structure (tetragonal, space group $I$4\textit{/mmm}) for both compounds. Magnetic susceptibility ($\chi (T )$) and electrical resistivity ($\rho$($T$) measurements revealed major kinks at 115 K ($T_{s1})$ and 320 K ($T_{s2})$ for Na$_{2}$Ti$_{2}$Sb$_{2}$O and Na$_{2}$Ti$_{2}$As$_{2}$O, respectively, signifying possibly the opening of density wave gaps. Both Na$_{2}$Ti$_{2}$Sb$_{2}$O and Na$_{2}$Ti$_{2}$As$_{2}$O showed remarkably strong anisotropy in their electromagnetic transport properties, and values of $\gamma_{\rho } (\rho_{c}/\rho_{ab})$ even reached 140 and 430, respectively, being much larger than that of iron pnictide BaFe$_{2}$As$_{2}(\gamma_{\rho} =$ 2--5). The $\gamma \rho $of Na$_{2}$Ti$_{2}$Sb$_{2}$O changed slightly with cooling, though a small drop at $T_{s1}$ occurred. In contrast, the $\gamma_{\rho }$ of Na$_{2}$Ti$_{2}$As$_{2}$O changed strikingly by exhibiting not only a small change at $T_{s2}$ but also a sudden decrease of 50 K, reduced nearly 1$/$3. Specific heat measurement indicated that Na$_{2}$Ti$_{2}$Sb$_{2}$O was only partially gapped with $\gamma_{1} =$ 4.1 mJ mol$^{-1}$ K$^{-2}$, though a long-range order was established at $T_{s1}$, while Na$_{2}$Ti$_{2}$As$_{2}$O was fully gapped. The remarkably strong electromagnetic anisotropy revealed in Na$_{2}$Ti$_{2}X_{2}$O suggests the crucial role of the TiO$_{2}X_{4}$ layer for the transport properties of layered titanium oxypnictides. [Preview Abstract] |
Wednesday, March 5, 2014 3:06PM - 3:18PM |
Q39.00004: Anisotropy of transport coefficients in the pseudogap phase of the cuprate superconductor YBCO Olivier Cyr-Choini\`ere, Ga\"el Grissonnanche, Nicolas Doiron-Leyraud, Louis Taillefer, James Day, Ruixing Liang, Doug Bonn, Walter Hardy We recently discovered evidence of a broken rotational symmetry in the pseudogap phase of the cuprate superconductor YBa$_{2}$Cu$_{3}$O$_{y}$ [1]. This broken symmetry was inferred from the onset of a large in-plane anisotropy of the Nernst coefficient $N$ below the pseudogap temperature $T^{\star}$, attributed to an anisotropy in the longitudinal coefficients, i.e. the resistivity $\rho$ and/or the Seebeck coefficient $S$. It was pointed out that an anisotropy in $N$ could also come from an anisotropy of the transverse coefficients, i.e. the Hall and Peltier coefficients, $\sigma_{xy}$ and $\alpha_{xy}$ [2]. We report here a complete study of the anisotropy of all transport coefficients in a YBCO single crystal. The measurements were performed first with the sample oriented along the $b$-axis direction and, then along the $a$-axis direction achieved by rotating the CuO chain direction via detwinning. We therefore extract the anisotropy of the transport coefficients without uncertainty from geometric factors or sample dependence. We discuss the possible implications of these transport anisotropies for the physics of the pseudogap phase. \\[4pt] [1] R. Daou {\it et al.}, {\it Nature} {\bf 463}, 519 (2010).\\[0pt] [2] C. Varma {\it et al.}, {\it arXiv} 1007.1215 (2010). [Preview Abstract] |
Wednesday, March 5, 2014 3:18PM - 3:30PM |
Q39.00005: Anisotropic breakdown of Fermi liquid quasiparticle excitations in overdoped La2$-x$Sr$x$CuO4 Johan Chang, Martin Maansson, Stephane Pailhes, Oliver Lipscompe, Stephen Hayden, Luc Patthey, Oscar Tjernberg, Joel Mesot High-temperature superconductivity emerges from an un-conventional metallic state. This has stimulated strong efforts to understand exactly how Fermi liquids breakdown and evolve into an un-conventional metal [1,2]. A fundamental question is how Fermi liquid quasiparticle excitations break down in momentum space. Here we show, using angle-resolved photoemission spectroscopy, that the Fermi liquid quasiparticle excitations of the overdoped superconducting cuprate La1.77Sr0.23CuO4 is highly anisotropic in momentum space [3]. Fermi liquid excitations are found in the anti-nodal region whereas conventional Fermi liequid excitations are probed around the nodal point [3].\\[4pt] [1] R. A. Copper \textit{et al}., \textit{Science} \textbf{323}, 603--607 (2009).\\[0pt] [2] K. Jin \textit{et al}., \textit{Nature} \textbf{476}, 73--75 (2011).\\[0pt] [3] J. Chang \textit{et al}., \textit{Nature Communications }\textbf{4}, 2559 (2013). [Preview Abstract] |
Wednesday, March 5, 2014 3:30PM - 3:42PM |
Q39.00006: Chiral d-wave superconductivity in SrPtAs: A Weyl superconductor Titus Neupert, Mark Fischer, Christian Platt, Andreas Schnyder, Werner Hanke, Ronny Thomale, Manfred Sigrist, Jun Goryo Recent $\mu$SR measurements suggest that the hexagonal pnictide SrPtAs is a chiral d-wave superconductor that spontaneously breaks time-reversal symmetry in the superconducting state. The $d$-wave order parameter fully gaps all Fermi surfaces, except for point nodes on one Fermi surface sheet near the $K$ and $K'$ points at the Brillouin zone corners. Theses nodal points are Majorana-Weyl fermions in momentum space. We study the topological characteristics of this superconducting phase, which features protected chiral surface states, Majorana-Fermi arcs on the surface and an associated thermal Hall response. [Preview Abstract] |
Wednesday, March 5, 2014 3:42PM - 3:54PM |
Q39.00007: Time-reversal symmetry breaking in superconducting Pr$_{1-x}$Ce$_{x}$Pt$_4$Ge$_{12}$ Lei Shu, Douglas E. MacLaughlin, Kevin Huang, M. Brian Maple Zero-field muon-spin-relaxation ($\mu$SR) experiments were performed on the superconductors Pr$_{1-x}$Ce$_{x}$Pt$_4$Ge$_{12}$ ($x < 0.2$). The results reveal the spontaneous appearance of static internal magnetic fields below the superconducting transition temperature ($T_c$). This observation implies time-reversal symmetry breaking in Pr$_{1-x}$Ce$_{x}$Pt$_4$Ge$_{12}$ ($x < 0.2$) below $T_c$. [Preview Abstract] |
Wednesday, March 5, 2014 3:54PM - 4:06PM |
Q39.00008: Strong Coupling S-wave Superconductivity in Bi$_{4}$O$_{4}$S$_{3}$ - Shruti, Pankaj Srivastava, Satyabrata Patnaik We investigate the superconducting properties and pairing symmetry in recently discovered Bi$_{4}$O$_{4}$S$_{3}$ superconductor. A series of Bi$_{6}$O$_{4}$S$_{4}$(SO$_{4}$)$_{1-x}$ samples were synthesized by solid-state reaction. The optimally doped sample Bi$_{4}$O$_{4}$S$_{3}$ which is 50\% SO$_{4}$ deficient shows maximum T$_{c}$ of 5.3K as confirmed by resistivity and magnetization measurement. The upper critical field at zero temperature is found to be $\sim$ 2.75 T and Ginzburg Landau coherence length is estimated to be $\sim$ 110{\AA}. Hall measurement confirmed the dominant role played by the electrons with charge carrier density of 4.405x10$^{19}$ cm$^{-3}$ at 10 K. The Sommerfeld constant $\gamma$ is calculated to be 1.113 mJ/K$^{2}$mol. Superconducting pairing symmetry and superconducting gap was studied from penetration depth measurement using tunnel diode oscillator technique. It is shown that Bi$_{4}$O$_{4}$S$_{3}$ is a strong coupling s-wave type superconductor with fully developed gap. Below T$_{c}$, superfluid density is best fitted with single gap s wave model with zero-temperature value of the superconducting energy gap $\Delta$$_{0}$= 1.54 meV, corresponding to the ratio 2$\Delta$$_{0}$/k$_{B}$T$_{c}$=7.2 which is much higher than the BCS value of 3.53. [Preview Abstract] |
Wednesday, March 5, 2014 4:06PM - 4:18PM |
Q39.00009: Observation of Time-Reversal Symmetry Breaking in the Non-Centrosymmetric Superconductor Re6Zr Martin R. Lees, Adrian D. Hillier, Bayan Mazidian, James F. Annett, Jorge Quintanilla, Donald McK. Paul, Ravi Singh, Geetha Balakrishnan We have investigated the superconducting state of the non-centrosymmetric compound Re$_{6}$Zr using magnetization, heat capacity, and muon-spin relaxation/rotation ($\mu$SR) measurements. Re$_{6}$Zr has a superconducting transition temperature, $T_c = 6.75\pm0.05$ K. Transverse-field $\mu$SR experiments, used to probe the superfluid density, suggest an $s$-wave character for the superconducting gap. However, zero and longitudinal-field $\mu$SR data reveal the presence of spontaneous static magnetic fields below $T_c$ indicating that time-reversal symmetry is broken in the superconducting state and an unconventional pairing mechanism. An analysis of the pairing symmetries identifies the ground states compatible with time-reversal symmetry breaking. [Preview Abstract] |
Wednesday, March 5, 2014 4:18PM - 4:30PM |
Q39.00010: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 4:30PM - 4:42PM |
Q39.00011: How the insulator and pseudogap states coalesce beneath the superconductor dome Alejandro Cabo Montes de Oca, Victor Martinez, Alejandro Cabo-Bizet The effect of hole doping on La$_{2}$CuO$_{4}$ physical properties is investigated by means of a TB model for the CuO planes proposed in previous works which generalizes the Hubbard model. Thus, its former predictions of the insulator and paramagnetic-pseudogap states at half-filling become natural ones as emerging from a more general analysis. The effects of hole doping on the insulator state and the paramagnetic-pseudogap one are investigated at T$=$0 K$^{0}$. The results predict a quantum phase transition in which the insulator state coalesce at a critical doping $\delta_{\mathrm{c}}=$0.2 with the pseudogap state, to become a paramagnetic-metal at higher hole densities. The evolution with small doping of the Fermi surface in the insulator state, shows that the holes tend to become localized at the middle of the sides of the Brillouin zone. Then, when the hole doping passes through the critical value, the holes move to become situated at the corners of the zone, showing a structural change of the Fermi surface at the phase transition point. These results offer a clear answer to the debated question about the existence and nature of a QPT beneath the superconductor Dome. [Preview Abstract] |
Wednesday, March 5, 2014 4:42PM - 4:54PM |
Q39.00012: ABSTRACT WITHDRAWN |
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