Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C31: Superconductivity in Chalcogenides and Related Compounds |
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Sponsoring Units: DCMP Chair: Dirk van der Marel, University of Geneva Room: LACC 407 |
Monday, March 5, 2018 2:30PM - 2:42PM |
C31.00001: Hole-driven Superconductivity and Non-Fermi Liquid Transport in Layered Nb2Se3 Kyungrok Kang, Heejun Yang Layered transition metal chalcogenides have attracted scientific interests to investigate intriguing physics such as topological insulating states, reversible structural phase transition, large magnetoresistance in semimetallic states, and non-Fermi liquid behaviors. Such features mostly originate from their low dimensionality (2D geometry) combined with strong spin-orbit coupling and electron-electron interaction. In particular, Nb2Se3 has been reported as a superconductor with its possible quasi 1D transport characteristics, resulting in an electrical anisotropy, but the interpretation of the results remains limited considering only electron carriers. We have conducted systematic Hall measurements and magnetoresistance studies at various temperatures. We discovered that the Nb2Se3 is a semimetal where more holes exist than electrons at low temperature. This implies that the superconductivity is governed by the hole carriers. Moreover, the temperature-resistance characteristics showed a non-Fermi liquid transport. Carrier type- and density-driven superconductivity and the possible origin of the non-Fermi liquid transport will be discussed in this presentation. |
Monday, March 5, 2018 2:42PM - 2:54PM |
C31.00002: Exploring Potential Charge Density Waves in the One-dimensional Superconductor Ta4Pd3Te16 Stephen Kuhn, Zhenzhong Shi, Toni Helm, Felix Flicker, Jooseop Lee, Brodie Popovic, David Graf, Jacob Ruff, Joerg Strempfer, Daniel Haskel, Sara Haravifard The coexistence of superconductivity with competing ground states continues to be a useful field for exploring novel quantum behavior. The monoclinic crystal Ta4Pd3Te16 is a one-dimensional superconductor with critical temperature 4.2 K. Previous Scanning Tunneling Microscopy (STM) measurements suggest a Charge Density Wave (CDW) existing at and below 4 K. Additionally, an anomaly in the resistivity occurs around 18 K, suggesting a thermodynamic phase transition. Further studies are required to understand the relationship between this thermodynamic transition, the charge density waves, and superconductivity. We discuss quantum oscillation and synchrotron X-ray studies of charge density waves in this novel superconductor. |
Monday, March 5, 2018 2:54PM - 3:06PM |
C31.00003: Unexpected Enhancement of Superconductivity in CeO0.5F0.5BiS2 at 10 GPa Zackary Rehfuss, Christian Wolowiec, Yuankan Fang, Colin McElroy, Duygu Yazici, Kevin Huang, Inho Jeon, Kalyan Sasmal, Jason Jeffries, Ryan Stillwell, Samuel Weir, Yogesh Vohra, M Brian Maple We report measurements of electrical resistivity as a function of temperature, at pressures up to 20 GPa, on the layered BiS2-based superconducting system LnO0.5F0.5BiS2 (Ln = La, Ce). Under pressure, compounds with Ln = La, Ce, Pr, Nd or Yb exhibit a rapid and pronounced increase in the superconducting transition temperature (Tc) from a low-Tc phase to a higher-Tc phase, followed by a gradual decrease in Tc as pressure is increased. LaO0.5F0.5BiS2 shows an enhancement of Tc from 3.3 K at 0 GPa to 10.1 K at 1.1 GPa followed by a monotonic decrease up to 15 GPa. CeO0.5F0.5BiS2 displays an increase of Tc from 2.3 K at 0 GPa to 6.7 K at 2 GPa. Preliminary results indicate a subsequent enhancement of Tc from 4.7 K at 5.5 GPa to 7.2 K at 10 GPa. This may be associated with a pressure-induced increase in the valence of Ce that electron dopes the BiS2 planes. This is consistent with a previous report on the effect of substituting tetravalent Th, Hf, Zr, or Ti for trivalent La in inducing superconductivity in LaOBiS2. We are performing further measurements to substantiate these results. |
Monday, March 5, 2018 3:06PM - 3:18PM |
C31.00004: Upper critical field study of LaO0.5F0.5BiS2 single crystals Yuet Ching Chan, King Yau Yip, Yiu Wing Cheung, Yuk Tai Chan, Niu Qun, Joe Kajitani, Ryuji Higashinaka, T. D. Matsuda, Youichi Yanase, Yuji Aoki, Kwing To Lai, Swee Kuan Goh The anisotropy between the in-plane upper critical field Hc2//ab and the out-of-plane upper critical field Hc2⊥ab in as-grown LaO0.5F0.5BiS2 has been investigated in polycrystalline samples for years, but studies on single crystals, which are more ideal, are absent. Here the upper critical field investigations of LaO0.5F0.5BiS2 single crystals under various field angles via transport measurements are presented. The anisotropic factor Hc2//ab/Hc2⊥ab reaches ~16 at zero-temperature limit. The temperature dependence of Hc2//ab(T) shows a pronounced upward curvature near the critical temperature Tc, which can be described by a two-gap model in dirty limit. These features suggest that LaO0.5F0.5BiS2 is a highly anisotropic two-gap superconductor. Furthermore, Hc2//ab(0) exceeds Pauli paramagnetic limit. The strong spin-orbit coupling associated with Bi and the breaking of the local inversion symmetry at the electronically active BiS2 bilayers are proposed to explain this behavior. |
Monday, March 5, 2018 3:18PM - 3:30PM |
C31.00005: Superconductivity in BaNbS3 and BaNb2S5 John Neumeier, Michael G. Smith BaNbS3 and BaNb2S5 were synthesized using BaCO3 and Nb2O5 in a nitrogen stream laden with CS2. In some cases, samples were synthesized from the elements. BaNbS3 has a hexagonal crystal structure characterized by quasi-one-dimensional Nb-Nb chains. The crystal structure of BaNb2S5 is hexagonal, but otherwise not fully characterized. We observed superconductivity at 0.89 K in BaNbS3 and 0.95 K in BaNb2S5. Electrical resistivity, specific heat, magnetic susceptibility, and Hall effect were measured on the samples to determine their basic physical properties, including parameters that characterize the superconductiviy (e.g. energy gap and upper critical magnetic field). Our findings will be presented along with comparisons of the two compounds. |
Monday, March 5, 2018 3:30PM - 3:42PM |
C31.00006: Pressure-induced superconductivity in palladium sulfide Liu-Cheng Chen, Hao Yu, Hongjie Pang, Binbin Jiang, Shi Xun, Lidong Chen, Xiao-Jia Chen An extend study on PdS is carried out with the measurements of the resistivity, Hall coefficient, Raman scattering, and X-ray diffraction at high pressures up to 42.3 GPa. With increasing pressure, superconductivity is observed accompanying with a metallic phase emerging above 19.5 GPa. The coexistence of semiconducting and metallic phases observed at normal state is confirmed by the Raman scattering and X-ray diffraction between 19.5 and 29.5 GPa. After that, only the metallic normal state phase maintains with an almost constant superconducting transition temperature. These results highlight that the important role of pressure played in inducing superconductivity in these narrow band-gap semiconductors. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C31.00007: Abstract Withdrawn
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Monday, March 5, 2018 3:54PM - 4:06PM |
C31.00008: Modelling the Superconducting Proximity Effect in Bi2Se3 James Eckstein, Yang Bai, Can Zhang, David Flötotto, Xiangyu Song, Alexey Bezryadin, Tai-Chang Chiang We analyze data from two recent experiments we carried out, studying the superconducting proximity effect in Bi2Se3, using the quasiclassical Green’s function formulation of the Usadel equations. One experiment studied the resistive transition on Bi2Se3 films covered with niobium islands, while the other used ARPES to measure E(k) at low temperatures in Bi2Se3 films of different thicknesses formed on niobium substrates to determine the dependence of the density of states on temperature and depth. We extract the pair amplitude as a function of energy and depth and use the Usadel equation to describe how this varies in space. This provides a prediction of the Berezinskii-Kosterlitz-Thouless transition temperature in the island arrays. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C31.00009: Local and Non-local Transport Measurements in Bi2Se3-Nb-Bi2Se3 Heterostructures Erik Huemiller, Can Zhang, Maryam Salehi, Nikesh Koirala, Seongshik Oh, Dale Van Harlingen
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Monday, March 5, 2018 4:18PM - 4:30PM |
C31.00010: Superconductivity in Bi2Se3 coupled with niobium islands Yang Bai, Can Zhang, Brian Mulcahy, David Flötotto, Xiangyu Song, Alexey Bezryadin, Tai-Chang Chiang, James Eckstein To study how the superconductivity works in topological insulator, we performed a transport experiment to measure the proximity effect in devices consisting of an array of many niobium islands on a Bi2Se3 film. We extract parameters describing the Berezinskii-Kosterlitz-Thouless (BKT) phase stiffening transition in the resistance-temperature dependence. We have also measured nonlinear transport in the array and find that the BKT relationship between these two measurements holds. ARPES measurements were also done on another set of Nb/Bi2Se3 samples to study how deep Cooper pair penetrate into Bi2Se3. This allows us to determine how surface state carriers and bulk carriers participate in proximity induced superconductivity in Bi2Se3. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C31.00011: Nb Intercalated/Substituted Bismuth Selenide Superconductor Kaya Kobayashi, Teppei Ueno, Hirokazu Fujiwara, Takayoshi Yokoya, Jun Akimitsu The compound (NbxBi2Se3) is reported to have ferromagnetic order coexistence with superconductivity. To study how superconductivity changes in NbxBi2Se3, we synthesized for x=0 to 1. The superconductivity appears in all compound except x=0 but no ferromagnetic behavior. This implies that the superconductivity is stable in various Nb-doping. This contrasts the behavior of SrxBi2Se3 of which superconductivity appears in very little amount of Sr intercalation. In increasing Nb(x), the structure gradually changes from Bi2Se3 to BiSe. BiSe structure is one of the infinite layer structures in Bi-Se compounds discussed for their structural stability in various Bi-Se ratio. We observed BiSe structure to be stable beyond x=0.3 indicating that the superconductivity is stable in BiSe and the possibility of new doping mechanism achieved in the material family. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C31.00012: Signatures of finite momentum Cooper pairing in the Fraunhofer pattern of superconductor-Bi2Se3 Josephson junctions Angela Chen, Moon Jip Park, Greg MacDougall, Matthew Gilbert, Nadya Mason Unconventional superconductivity is predicted to arise at the intersection of magnetism and superconductivity. One such form of unconventional superconductivity has been proposed to occur when Cooper pairs acquire a finite momentum shift due to a magnetic exchange coupling. 3D topological insulators, which have strong spin-orbit coupling and surface states that consist of nondegenerate Dirac cones, are a prime candidate for observing a finite momentum shift. We study superconducting (S)-Bi2Se3-S Josephson junctions subjected to out-of-plane and in-plane magnetic fields by looking at the evolution of the Fraunhofer patterns. The Fraunhofer pattern evolves from a conventional pattern to an anomalous one as an in-plane field is applied, which is suggestive of a phase modulation in the superconducting order parameter. The phase accumulation in the junction due to in-plane and out-of-plane fields is simulated based on a finite momentum pair model, and the simulations match well with the observed transport signal. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C31.00013: Scattering Mechanisms of Near Surface Two Dimensional Electron Gas in Epitaxial InAs-Al Structures KAUSHINI WICKRAMASINGHE, Joseph Yuan, William Mayer, Tri Nguyen, Klea Dhimitri, Vladimir Manucharyan, Javad Shabani Increasing interest in superconducting proximity effect in semiconductors is driven by the recent proposal to realize hybrid topological materials for quantum information. The quality of the superconductor-semiconductor interface is crucial for these applications since the interface controls how the superconducting properties are imparted on the semiconductor. In this study, we grow epitaxial Al on InAs surface quantum well [1] using molecular beam epitaxy followed by structural and electrical characterization. In Hall bar geometry, the low temperature magnetotransport data exhibits high visibility of Shubnikov de-Haas oscillations and electron mobility near 40,000 cm2/Vs. Further transport studies are done with gated Hall bars and superconductor-semiconductor-superconductor (SNS) junctions. We analyze transport scattering mechanisms present in our heterostructures in detail and show the limiting factor in the mobility of our surface quantum wells are surface and ionized scattering. SNS junctions based on these structures exhibit high transparency and large supercurrent with product of critical current and normal resistance reaching the superconducting gap. [1] J. Shabani et al. PRB 2016 |
Monday, March 5, 2018 5:06PM - 5:18PM |
C31.00014: Gate-defined Quantum Wires with Superconducting Contacts in Epitaxial Al/InAs Heterostructures William Mayer, Joseph Yuan, KAUSHINI WICKRAMASINGHE, Javad Shabani Hybrid semiconductor-superconductor devices offer the exciting opportunity of gate-tunability for Josephson junctions and the search for toplogical superconductivity. We systematically study switching current and Fraunhofer oscillations in gate-tunable Josephson junctions on our epitaxially grown Al/InAs material heterostructure. We study in and out of the gap features of these junctions where we tune the density or area using gate bias. These studies are extended to the case of 1D transport using a gate-defined quantum point contact placed within the Josephson junction, and the nature of proximitized superconductivity in 1D is explored. |
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