Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session T11: Superconductivity: Heavy Elements and Spin-Orbit Effects |
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Sponsoring Units: DCMP Chair: Valentin Taufour, Ames Laboratory Room: 007B |
Thursday, March 5, 2015 11:15AM - 11:27AM |
T11.00001: Fermi-surface instabilities in the presence of spin-orbit coupling Christian Platt, Mario Fink, Werner Hanke, Ronny Thomale Besides its relevance in the formation of topological insulators, the effect of spin-orbit coupling also gives rise to novel types of superconductivity and unprecedented spin- and charge orders. Due to the progress in the fabrication of tailored materials and surfaces, these novel states-of-matter now become accessible and can be investigated by different experimental probes. Within the theoretical framework of functional renormalization group, we study the effect of spin-orbit coupling on the emergence of Fermi-surface instabilities. Starting from an ab-initio model input, we compare our results with recent experiments performed on the metallic surface states of half-Heusler compounds. [Preview Abstract] |
Thursday, March 5, 2015 11:27AM - 11:39AM |
T11.00002: Far-from-equilibrium dynamics of spin-orbit coupled superfluids Mubarak AlQahtani, Maxim Dzero We present the results of the theoretical study for the collisionless dynamics of the pairing amplitude in two-dimensional superfluid with strong spin-orbit coupling. We consider the cases when the dynamics is initiated by a sudden change of the coupling constant or an external magnetic field. Depending on the initial conditions and an amplitude of a quench, at long times the pairing amplitude dynamically vanishes, reaches a constant or periodically oscillates with time. We determine the corresponding steady state phase diagram exactly for generic quenches of the coupling constant and specific quenches of the magnetic field. We also study topological Floquet superfluidity which can be generated by the periodic oscillations of the pairing amplitude. [Preview Abstract] |
Thursday, March 5, 2015 11:39AM - 11:51AM |
T11.00003: Superconducting hyper-honeycomb lattice Adrien Bouhon, Annica Black-Schaffer Motivated by the recent discovery of the hyper-honeycomb $\beta $-Li2IrO3 studied in the context of Kitaev spin liquids, we investigate the possibility to realize superconductivity in the hyper-honeycomb lattice. Based on a t-J model we discuss the effect of the band structure and spin-orbit coupling on the most stable superconducting state. [Preview Abstract] |
Thursday, March 5, 2015 11:51AM - 12:03PM |
T11.00004: Superconductivity in R$_{3}$T$_{4}$Ge$_{13}$ (R $=$ Y, Lu and T $=$ Rh, Co, Os) single crystals Binod Rai, Iain Oswald, Jiakui Wang, Gregory McCandless, Julia Chan, Emilia Morosan Single crystals of R$_{3}$T$_{4}$Ge$_{13}$ (R $=$ Y, Lu and T $=$ Rh, Co, Os) have been grown by flux methods and have been found to adopt the Pr$_{3}$Rh$_{4}$Sn$_{13}$ structure type. Magnetization and specific heat measurements confirm that all four compounds are bulk superconductors. Reduced superconducting gaps observed in the specific heat suggest that these may be multi-band superconductors. We observe an unusual increase of the electrical resistivity and a decrease of the charge carrier density on cooling in the normal state in all four reported compounds. However, band structure calculations reveal a metallic ground state in all four compounds, consistent with the emergence of superconductivity at low temperatures. We empirically show that large atomic displacement parameter ratios in R$_{3}$T$_{4}$Ge$_{13}$ compounds are correlated with the semiconduc tor-like behavior, resolving the contradiction between the experiment and the calculations. [Preview Abstract] |
Thursday, March 5, 2015 12:03PM - 12:15PM |
T11.00005: Unconventional superconductivity in U$_2$PtC$_2$ Nick Wakeham, Andy Mounce, Ni Ni, Mingu Kang, Sangyun Lee, Roman Movshovich, Jianxin Zhu, Tuson Park, Eric Bauer, Joe Thompson, Filip Ronning U$_2$PtC$_2$ has long been known to be a moderately heavy-fermion superconductor with transition temperature $T_c\sim 1.5$\,K. However, until recently little was known about the nature of the superconductivity. We will present a summary of our recent investigation into the superconductivity in this material through structural, transport, thermodynamic, and nuclear magnetic resonance measurements. Evidence for an unconventional gap structure comes from power law dependencies of the specific heat as a function of field and temperature $T$, as well as $T^2$ temperature dependence of the spin-lattice relaxation rate. The upper critical field exceeds the Pauli limit and there is no change in the Knight shift through $T_c$, which is suggestive of spin-triplet superconductivity. Based on DFT calculations the Fermi surface consists of 2 complex sheets. In pure U$_2$PtC$_2$ as well as the doped samples there is evidence for competing ferromagnetic interactions, which may be relevant to the superconductivity. [Preview Abstract] |
Thursday, March 5, 2015 12:15PM - 12:27PM |
T11.00006: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 12:27PM - 12:39PM |
T11.00007: Superconducting and normal state properties in Uranium-based materials from thermal and thermoelectric measurements J.-Ph. Reid, J. Barraclough, O. Entwisle, C. Lithgow, D. Sokolov, W. Whitley, E. Yelland, Andrew Huxley Although it is clear that the interplay between superconductivity and magnetic or charge orders has a crucial role to the origin of superconductivity, it is not yet understood how and why that is. One of the best ways to shed light on this question is by measuring thermal conductivity and thermoelectricity. The former probes the zero-energy ($T\to 0$) quasiparticles and is very sensitive to the superconducting gap structure, whereas the latter is ideal to detect any change in the Fermi surface due to competitive orders. In this talk, a thermal and thermoelectric study will be presented and will focus on the ferromagnetic superconductor URhGe. [Preview Abstract] |
Thursday, March 5, 2015 12:39PM - 12:51PM |
T11.00008: Possible mechanism for $s$-wave superconductivity in heavy-fermion systems: Variational cluster study Keisuke Masuda, Daisuke Yamamoto We study $s$-wave superconductivity in heavy-fermion systems, which cannot be easily understood due to the existence of the strong Coulomb repulsion between $f$ electrons. The key idea of our proposal is to consider the interorbital Cooper pairing between conduction electrons ($c$ electrons) and localized $f$ electrons, which we refer to as the ``$c$-$f$ pairing.'' We analyze the periodic Anderson model by means of the variational cluster approach, in which all the three types of on-site pairing, namely intraorbital pairings between $c$ electrons and between $f$ electrons and the $c$-$f$ pairing, are taken into account. At half filling, the system exhibits the Kondo insulating or antiferromagnetic state, depending on the strength of the Coulomb repulsion. When electrons or holes are doped to the antiferromagnetic state, $s$-wave superconductivity appears coexisting with the antiferromagnetic long-range order. We also find that the magnetic order vanishes for further doping, and a pure $s$-wave superconducting state is formed for a certain range of doping concentration. We suggest the $c$-$f$ pairing as a possible mechanism for $s$-wave superconductivity in heavy-fermion systems. [Preview Abstract] |
Thursday, March 5, 2015 12:51PM - 1:03PM |
T11.00009: A comprehensive study of chemical substitution effects on superconductivity in LaPt4Ge12 Kevin Huang, Duygu Yazici, Benjamin White, Alexander Breindel, Naveen Pouse, Lei Shu, Brian Maple The compound PrPt$_4$Ge$_{12}$ has attracted significant attention following observations of signatures of unconventional superconductivity such as time reversal symmetry breaking from $\mu$SR measurements. In contrast, LaPt$_4$Ge$_{12}$ is a conventional BCS-type superconductor, interestingly, with the same superconducting transition temperature, $T_c$, as PrPt$_4$Ge$_{12}$ ($T_c$ = 8 K). To elucidate the properties of superconductivity in PrPt$_4$Ge$_{12}$, the system La$_{1-x}$Ce$_x$Pt$_4$Ge$_{12}$ was investigated and the results are compared to our previous work on Pr$_{1-x}$Ce$_x$Pt$_4$Ge$_{12}$. Measurements of magnetic susceptibility, electrical resistivity, and specific heat were performed demonstrating that $T_c$ is suppressed more rapidly in La$_{1-x}$Ce$_x$Pt$_4$Ge$_{12}$ than in Pr$_{1-x}$Ce$_x$Pt$_4$Ge$_{12}$. Specific heat measurements reveal a crossover in the temperature dependence of the superconducting state of La$_{1-x}$Ce$_x$Pt$_4$Ge$_{12}$, changing from a power law for $x$ = 0 to an exponential for the Ce-substituted samples, possible evidence of a transition from a multiband to a single-band superconducting energy gap. Th substitution for La did not produce the crossover. [Preview Abstract] |
Thursday, March 5, 2015 1:03PM - 1:15PM |
T11.00010: Superconductivity at 600 mK in a novel ternary platinum phosphide $\mathbf{SrPt_6P_2}$ BenMaan Jawdat, Bing Lv, Zheng Wu, Melissa Gooch, Kui Zhao, Liangzi Deng, Yuyi Xue, Bernd Lorenz, Arnold Guloy, Ching-wu Chu In the course of our search for new superconducting materials, we have synthesized a novel, metal-rich ternary platinum phosphide superconductor with a unique structure type and an onset $\mathrm{T_c}$ of 600 mK, $\mathrm{SrPt_6P_2}$. The crystal structure was determined by single crystal X-ray diffraction, and features a unique three-dimensional anionic network of vertex-shared $\mathrm{Pt_6P}$ trigonal prisms. Furthermore, we have investigated the superconductivity in this material resistively, magnetically, and calorimetrically. The results of these studies will be presented and discussed. [Preview Abstract] |
Thursday, March 5, 2015 1:15PM - 1:27PM |
T11.00011: Penetration depth and point-contact spectroscopy studies of exotic superconductivity in noncentrosymmetric half-Heusler YPtBi Hyunsoo Kim, Steven Ziemak, Kefeng Wang, Yasuyuki Nakajima, Johnpierre Paglione, Makariy Tanatar, Ruslan Prozorov Strong asymmetric spin-orbit coupling in a noncentrosymmetric superconductor allows mixing of even and odd parity of the pairing interactions. Such an exotic pairing interaction has been suggested in some Pt-based noncentrosymmetric superconductors such as CePt$_3$Si and Li$_2$Pt$_3$B. More recently, we reported superconductivity below 0.8 K in YPtBi, a half-Heusler compound that lacks inversion symmetry. Here we present our studies of the superconducting energy gap in YPtBi using soft point contact spectroscopy and superconducting penetration depth measurements via tunnel diode resonator technique as a function of temperature and applied magnetic field. We will compare the morphology of our dI/dV energy gap spectra to previous theoretical and experimental results for triplet $p$-wave materials, and review our analysis of normalized superfluid density and theoretical current density and compare to various possible superconducting energy gap symmetries. [Preview Abstract] |
Thursday, March 5, 2015 1:27PM - 1:39PM |
T11.00012: Origins of charge density wave in novel Pt-based superconductors: SrPt$_{2}$As$_{2}$ and LaPt$_{2}$Si$_{2}$ Sooran Kim, Kyoo Kim, B.I. Min The intriguing coexistence of the charge density wave (CDW) and superconductivity in SrPt$_{2}$As$_{2}$ and LaPt$_{2}$Si$_{2}$ has been investigated by using the ab initio density functional theory band structure and phonon calculations. We have found that the local split distortions in the [As-Pt-As] layers play an essential role in driving the five-fold supercell CDW instability as well as the phonon softening instability in SrPt$_{2}$As$_{2}$. In contrast to SrPt$_{2}$As$_{2}$, the CDW and phonon softening instabilities in LaPt$_{2}$Si$_{2}$ occur without split positions of Pt, indicating that the driving mechanisms of the CDW in SrPt$_{2}$As$_{2}$ and LaPt$_{2}$Si$_{2}$ are different. The phonon calculations, however, suggest that the CDW and the superconductivity coexist in [X-Pt-X] layers (X = As or Si) in both cases. [Preview Abstract] |
Thursday, March 5, 2015 1:39PM - 1:51PM |
T11.00013: Superconductivity in AuBe D.J. Rebar, J.F. DiTusa, P. Adams, D. Browne, I. Vekhter, D. Young, J. Prestigiacomo Metallic AuBe, which forms with the chiral B20 crystal structure, is a superconductor (SC) with a T$_{\mathrm{c\thinspace }}$of approximately 3.2 K. Recent research on materials with this structure has revealed Skyrmion lattices, a topologically interesting magnetic state. We investigate the role the Dzyaloshinsky-Moriya interaction and spin-orbit coupling play in the superconductivity and normal state properties of this material. Samples were arc-melted in Ar atmosphere and characterized for structure and elemental composition. Magnetic susceptibility measurements revealed a full Meissner effect while the specific heat showed a sharp step at the transition temperature whose size is characteristic of a weakly-coupled SC. Measurements of the electrical resistivity at 1.8 K revealed a critical field that is five to six times that seen in the magnetization, far above the enhancement expected from a simple superconducting surface layer. In addition, we observed de Haas-van Alphen (dHvA) oscillations in these polycrystalline samples with two dominant frequencies indicating small spin-orbit split Fermi surfaces. We interpret the dHvA oscillations as emanating from a Dirac point approximately 0.4 eV below the Fermi level. [Preview Abstract] |
Thursday, March 5, 2015 1:51PM - 2:03PM |
T11.00014: Characterization of the Heavy Metal Pyrochlore Lattice Superconductor CaIr2 Neel Haldolaarachchige, Quinn Gibson, Leslie Schoop, Huixia Luo, Robert Cava Compounds based on 5d transition metals are of recent interest because electron correlations and spin-orbit interactions play an important role in determining their electronic properties. Iridium oxides with the pyrochlore lattice, in particular, are predicted to host exotic electronic states, but these materials have not yet been shown to host superconductivity. A handful of Ir compounds are known to be superconducting, some more likely showing this property due to the presence of rare earths, but in other cases the superconductivity is derived from Ir states at the Fermi Energy. Here we report the synthesis, experimental electronic characterization, and calculated electronic band structure of the cubic Laves phase superconductor CaIr2. The inferred electron-phonon coupling constant show that CaIr2 is a weakly coupled BCS-type superconductor. The electronic band structure calculations indicate that the Ir d states are dominant through the Fermi level. Given the profound effect of spin-orbit coupling on the electronic structure, it can be argued that the value of Tc, and possibly even the existence of superconductivity at all, is due to the heavy element character imparted to this material by the Ir pyrochlore lattice. [Preview Abstract] |
Thursday, March 5, 2015 2:03PM - 2:15PM |
T11.00015: The electron-phonon coupling and superconductivity for light-actinides on fcc structure: a first principles study Omar De La Pe\~na-Seaman, Paola Gonz\'alez-Castelazo, Rolf Heid, Klaus-Peter Bohnen We have studied the electronic structure, lattice dynamical properties, electron-phonon (e-ph) coupling and superconducting properties of the light-actinides (Ac, Th, Pa, U) on fcc structure. These systems have been studied within the framework of density functional perturbation theory, using a mixed-basis pseudopotential method. The electronic density of states (DOS), full-phonon dispersion as well as the Eliashberg spectral function ($\alpha^2F(\omega)$) and the electron-phonon coupling ($\lambda$) parameter have been calculated with and without the inclusion of spin-orbit coupling (SOC). The observed effects of SOC on $\alpha^2F(\omega)$ for the light-actindes under study have its roots on the changes of two quatities: the full phonon dispersion and the e-ph coupling matrix elements. The observed influence of these two ingredients is different depending of the actinide, and it is analyzed together with the contribution of the different states on the DOS at the Fermi level. The superconducting critical temperature ($T_c$) has been analyzed solving numerically the Eliashberg gap equations on the strong-coupling regime with the information provided from $\alpha^2F(\omega)$ for the entire series, analyzing the superconducting behavior of the light-actinides. [Preview Abstract] |
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