Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Q11: Chalcogenide Superconductors |
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Chair: Houlong Zhuang, Oak Ridge National Laboratory Room: 007B |
Wednesday, March 4, 2015 2:30PM - 2:42PM |
Q11.00001: Phonon-driven superconductivity in the vicinity of ferroelectric and charge density wave ordering in La(O,F)BiX$_2$ (X=S, Se, O) Taner Yildirim Examples of layered superconductors include cuprates, MgB$_2$, CaC$_6$, and recent iron-pnictides. Recently a new family of layered materials containing BiS$_2$ planes, was discovered to be superconducting at temperatures up to 10 K. In order to reveal the mechanism of superconductivity, here we present results from first-principles calculations with many surprising findings for La(O,F) Bi X$_2$ for X=S, Se, and O. The parent compound LaOBiS$_2$ possesses anharmonic ferroelectric soft phonons at the zone center with a rather large polarization of P $\approx$ 10 $\mu$C/cm$^2$. Upon electron doping, new unstable phonon branches appear along the entire line Q=(q,q,0), causing Bi/S atoms to order in a one-dimensional charge density wave (CDW). We find that BiS$_2$ is a strong electron-phonon coupled superconductor in the vicinity of competing ferroelectric and CDW phases. We discuss similar results for X=Se and hypothetical compound X=0. These results will be compared with another interesting system, namely Ba$_{1-x}$K$_x$BiO$_3$, which exhibits several phases, including CDW, an incommensurate pseudo ferroelectric, and superconductivity at 31 K. Our results suggest new directions to tune the balance between these phases and increase T$_c$ in this new class of materials. [Preview Abstract] |
Wednesday, March 4, 2015 2:42PM - 2:54PM |
Q11.00002: Coexistence of ferromagnetism and superconductivity in CeO0.3F0.7BiS2 Jooseop Lee, Satoshi Demura, Matthew Stone, Kazuki Iida, Georg Ehlers, Clarina dela Cruz, Masaaki Matsuda, Keita Deguchi, Yoshihiko Takano, Yoshikazu Mizuguchi, Osuke Miura, Despina Louca, Seunghun Lee Bulk magnetization, transport and neutron scattering measurements were performed to investigate the electronic and magnetic properties of a polycrystalline sample of the newly discovered ferromagnetic superconductor, CeO0.3F0.7BiS2. Ferromagnetism develops below T\textunderscore \textbraceleft FM\textbraceright $=$ 6.54(8) K and superconductivity is found to coexist with the ferromagnetic state below T\textunderscore \textbraceleft SC\textbraceright $=$ 4.5 K. Inelastic neutron scattering measurements reveal a very weakly dispersive magnetic excitation at 1.8 meV that can be explained by an Ising-like spin Hamiltonian. Under application of an external magnetic field, the direction of the magnetic moment changes from the c-axis to the ab-plane and the 1.8 meV excitation splits into two modes. A possible mechanism for the unusual magnetism and its relation to superconductivity is discussed. [Preview Abstract] |
Wednesday, March 4, 2015 2:54PM - 3:06PM |
Q11.00003: Observation of anomalous temperature dependence of spectrum on small Fermi surfaces in a BiS$_2$-based superconductor L.K. Zeng, X.B. Wang, J. Ma, P. Richard, S.M. Nie, H.M. Weng, N.L. Wang, Z. Wang, T. Qian, H. Ding We have performed an angle-resolved photoemission spectroscopy study of the BiS2-based superconductor Nd(O,F)BiS$_2$. Two small electron-like Fermi surfaces around X ($\pi$, 0) are observed, which enclose 2.4\% and 1.1\% of the Brillouin zone area, respectively, corresponding to an electron doping of 7\% per Bi site. The low- energy spectrum consists of a weakly-dispersing broad hump and a dispersive branch, which follows well the calculated band dispersion. This hump is drastically suppressed with increasing temperature, while the dispersive branch is essentially unaffected. The anomalous thermal effect indicates a highly interacting electronic state, in which the superconducting pairing develops [Preview Abstract] |
Wednesday, March 4, 2015 3:06PM - 3:18PM |
Q11.00004: Single crystal growth and superconducting properties of the Bi(S,Se)2-based superconductor Takuma Yamaki, Yoshihiko Takano Introduction After the discovery of superconductivity in Bi4O4S3 [1], much attention has been paid to synthesizing a new superconductors. The BiS2-based compounds have a layered structure similar to those of cuprates or Fe-based superconductors. In these compounds, superconducting layers and blocking layers are stacked alternatively. Many BiS2-based superconductors have been found by arranging the blocking layer so far. The modification in superconducting layer is important to clarify the superconducting mechanism of BiS2-based superconductor and the single crystal preparation is necessary to discuss such a intrinsic properties. In this study, we perform the single crystal growth of La(O,F)Bi(S,Se)2 and investigate the substitution effect for the superconducting properties by replacing S with Se. Results and discussion Single crystals of LaO1-xFxBiS2-ySey (0?y?2) were synthesized by CsCl flux method. The single crystals was plate-like shape with approximately 1 mm2 in size, which is enough to perform various characteristic measurements, such as single crystal X-ray analysis and electrical resistivity measurement, and so on. We will discuss the crystal structure, electrical resistivity and magnetic properties in detail. [1] Y. Mizuguchi et al.,Phys. Rev. B 86,220510(2012) [Preview Abstract] |
Wednesday, March 4, 2015 3:18PM - 3:30PM |
Q11.00005: Superconductivity in PdxBi2Se3 by anneal doping Grace McClintock, J. T. Mlack, Nina Markovic We show that superconductivity can be induced in Bi2Se3 by palladium doping via annealing. Thin films of palladium are deposited on prefabricated Bi2Se3 nanodevices and annealed at temperatures in excess of 100 Celsius. We find that Bi2Se3 absorbs Pd under these conditions and that the absorption of Pd results in superconductivity, as evidenced by resistance and magnetoresistance measurements below 1K. [Preview Abstract] |
Wednesday, March 4, 2015 3:30PM - 3:42PM |
Q11.00006: Charge fluctuations in a disordered superconductor, LaO$_{1-x}$F$_{x}$BiS$_{2}$ Anushika Athauda, Seunghun Lee, Despina Louca, Yoshikazu Mizuguchi LaO1-xFxBiS2 is a disordered, non-magnetic superconductor with a transition temperature of 10.8 K at x $=$ 0.5. The parent compound, LaOBiS2, is a band insulator with a layered tetragonal structure. The evolution of the crystal structure and nano-scale atomic fluctuations are investigated as a function of temperature and composition using neutron scattering. Even though the symmetry remains unchanged with doping, lattice strain develops along the c-axis and buckling of the BiS2 plane changes orientation. In addition, strong local distortions are observed around the Bi ion that are in response to charge fluctuations. Two distinct Bi-S plaquettes are present due to atomic displacement of in-plane sulfur because the Bi ion undergoes a charge disproportionation. The charge fluctuations along with spin-orbit coupling most likely play important roles in the mechanism of superconductivity in this system. [Preview Abstract] |
Wednesday, March 4, 2015 3:42PM - 3:54PM |
Q11.00007: Anisotropic spin-singlet pairings in CuxBi2Se3 and Bi2Te3 Wei-Feng Tsai, Lei Hao, Gui-Ling Wang, Ting-Kuo Lee, Jun Wang, Yong-Hong Yang We report possible anisotropic spin-singlet pairings in Bi2X3 (X \quad is Se or Te). Among six pairings compatible with the crystal symmetry, two novel pairings show nontrivial surface Andreev bound states, which form flat bands and could produce zero-bias conductance peak in measurements such as point-contact spectroscopy. By considering purely repulsive short-range Coulomb interaction as the pairing mechanism, the dominant super-exchange terms are all antiferromagnetic, which would usually favor spin-singlet pairing in Bi2$X$3. Mean-field analyses show that the inter-orbital pairing interaction favors a mixed spatial-parity anisotropic pairing state, and one pairing channel with zero-energy surface states has a sizable component. The results provide important information for future experiments. [Preview Abstract] |
Wednesday, March 4, 2015 3:54PM - 4:06PM |
Q11.00008: Structural role of the pressure-dependent charge-density-wave to superconductor transition in $ZrTe_{3}$: an inelastic light scattering study Yewon Gim, Sam Gleason, Taylor Byrum, Astha Sethi, C. Petrovic, S.L. Cooper One of the most exciting areas of condensed matter research involves the study of how superconductivity evolves from magnetic- or charge-ordered phases in strongly correlated systems. We present a Raman scattering study of the temperature- and pressure-induced structural changes leading to the transition between charge-density wave (CDW) and superconducting phase regimes in $ZrTe_{3}$. We show that the internal deformation modes associated with the Te-Te chains--which support the CDW in this material--exhibit anomalous linewidth changes as a function of temperature, indicating strong electron-phonon coupling associated with these modes. Additionally, the pressure-dependence of these modes suggests that dissociation of the Te-Te chain bonds may be responsible for the suppression of the CDW phase as a function of pressure. These studies provide insight into the structural changes responsible for CDW collapse in this material. [Preview Abstract] |
Wednesday, March 4, 2015 4:06PM - 4:18PM |
Q11.00009: A DFT study of electron-phonon coupling in proxy rocksalt CuX (X $=$ S, Se, Te) structures and its relationship to possible manifestation of superconductivity Paul Grant, Robert Hammond We have previously reported our computational studies on idealized copper monochalcogenide rocksalt structures, both cubic and tetragonal, focusing on their possible antiferromagnetic properties as determined within a Van Vleck-Mott-Anderson-Hubbard framework [1]. For all values of Hubbard U in the range 0-7 eV, only copper monoxide exhibits a Mott-Hubbard electronic structure [2-3], the remainder (S, Se, Te) yielding metallic states characterized by nesting Fermi surfaces arising from Jahn-Teller degenerate s-p overlap. These results suggest exploring possible manifestation of superconductivity via electron-phonon mediated Cooper pairing. We will disclose our results to date applying the Eliashberg-McMillan-Allen-Dynes strong coupling framework to the DFT --derived electronic and vibrational states of CuS, CuSe and CuTe.\\[4pt] [1] P. M. Grant and R. H. Hammond, BAPS 59, Y47.00008 (2014).\\[0pt] [2] W. Siemons, et al., PRB 79, 195122 (2009), DOI: 10.1103/PhysRevB.79.195122.\\[0pt] [3] P. M. Grant, J. of Physics: CS 129, 012042 (2008), DOI: 10.1088/1742-6596/129/1/012042. [Preview Abstract] |
Wednesday, March 4, 2015 4:18PM - 4:30PM |
Q11.00010: Competition between Weak Localization and Superconductivity in $Ta_{1-x}Pt_{x}Se_{2}$ Single Crystal Jinyu Liu, Ali Radmanesh, Jin Hu, Leonard Spinu, Zhiqiang Mao Exotic properties such as superconductivity and charge density wave (CDW) in transition metal diachalcogenides (TMDCs) have attracted a great deal of interest in past decades. Research in this area is focused on understanding the interplay between CDW, structure instability and superconductivity in doped/intercalated TMDCs. We have recently studied the Pt doping effect on electronic properties of $2H-TaSe_{2}$. With only $\sim 2\%$ Pt doping, we observed dramatic changes in its electronic properties. Firstly, Pt doping leads to an evolution from an anisotropic, three-dimensional (3D) metal to a quasi-2D metal. Secondly, while Pt doping suppresses the CDW of $TaSe_{2}$ only to some extent, its superconducting transition temperature is remarkably increased, from 0.2K to 2.1 K. Moreover, Pt doping induces quantum transport behavior prior to the superconducting transition, i.e. weak localization (WL) and strong competition between WL and superconducting pairing was probed in angle-resolved magnetoresistivity measurements. We will discuss the origin of the evolution of such exotic phenomena. [Preview Abstract] |
Wednesday, March 4, 2015 4:30PM - 4:42PM |
Q11.00011: STM study on single crystal of noncentrosymmetric superconductor PbTaSe$_{2}$ Rui Wu, Zhiyang Ye, Jihui Wang, Xuejin Liang, Hanqing Mao, Lingxiao Zhao, Genfu Chen, Shuheng Pan We use low temperature scanning tunneling microscopy (STM) to study the single crystal of noncentrosymmetric superconductor PbTaSe$_{2}$. Two types of atomically resolved topographic image have been observed on the surfaces exposed by low temperature in situ cleaving. One of the topographic images clearly displays the noncentrosymmetric crystal structure, which we identify as the Se terminated surface. With the help of lattice symmetry and the step between two terraces, we also identify that the other topographic image belongs to the Pb terminated surface, which is the complementary exposure of the Se termination. In addition to the lattice symmetry and the surface reconstruction, there is a super modulation with a period of about 10.5 unit cells. This super modulation persists through the superconducting transition (Tc $=$ 3.7K), but is energy dependent, indicating its electronic nature. We will show how this super modulation relates to the normal state tunneling spectrum. [Preview Abstract] |
Wednesday, March 4, 2015 4:42PM - 4:54PM |
Q11.00012: STS study on single crystal of noncentrosymmetric superconductor PbTaSe2 Zhiyang Ye, Rui Wu, Jihui Wang, Xuejin Liang, Hanqing Mao, Lingxiao Zhao, Genfu Chen, Shuheng Pan We report our low temperature scanning tunneling spectroscopic study on single crystals of noncentrosymmetric superconductor PbTaSe2. On the background of the normal state tunneling spectrum, a superconducting energy gap opens at a temperature below the bulk Tc $=$ 3.7K. At t $=$ 1.4K, the gap magnitude is estimated to be about 1meV. This energy gap is particle-hole symmetry and is homogeneous in space. Extrapolating the low energy part of the spectrum, we find that the low energy part of the gap spectrum is linear like ``V'' shape. We will present the results of the numerical fit with various gap functions of proposed possible pairing symmetry. We will also present our preliminary results of the magnetic field dependence measurement and discuss the implications of these observations. [Preview Abstract] |
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