Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U35: Focus Session: Search for New Superconductors III |
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Sponsoring Units: DMP Chair: Jochen Mannhart, Max-Planck Institute for Solid State Physics, Stuttgart, Germany Room: 343 |
Thursday, March 21, 2013 11:15AM - 11:51AM |
U35.00001: Designing heterostructures -- a route towards new superconductors Invited Speaker: Thilo Kopp By now it has become technologically feasible to grow controllably transition metal oxides layer by layer. In effect, the achieved progress allows to design heterostructures with optimized electronic properties. The talk will specifically address scenarios for interface superconductivity and the possibility to raise the transition temperature of bulk superconductors by layer design. Heterostructures offer a complexity beyond that of bulk materials. The nature of the superconducting states formed in layered materials and at interfaces is a fascinating topic of recent research which will be in the focus of this presentation. [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U35.00002: Reversible Superconductivity in Electrochromic Indium-Tin Oxide Films Ali Aliev, Miron Salamon Transparent conductive indium tin oxide (ITO) thin films, electrochemically intercalated with sodium or other cations, show tunable superconducting transitions with a maximum $T_{\mathrm{c}}$ at 5 K. The transition temperature and the density of states, $D(E_{F})$ (extracted from the measured Pauli susceptibility $\chi^{\mathrm{p}})$ exhibit the same dome shaped behavior as a function of electron density. Optimally intercalated samples have an upper critical field $\approx $ 4 T and $\Delta $/$k_{\mathrm{B}}T_{\mathrm{c}} \approx $ 2.0. Accompanying the development of superconductivity, the films show a reversible electrochromic change from transparent to colored and are partially transparent (orange) at the peak of the superconducting dome. This reversible intercalation of alkali and alkali earth ions into thin ITO films opens new opportunities for tunable, optically transparent superconductors. [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U35.00003: Molecule/Surface Interactions and the Control of Electronic Structure In Epitaxial Charge Transfer Salts Geoffrey Rojas, P. Ganesh, Simon Kelly, Bobby Sumpter, John Schlueter, Petro Maksymovych The two-dimensionality of the fulvalene-based superconducting charge transfer salts has lead to an increasing interest in the epitaxial growth and local probe analysis of monolayer CTS films. Curiously, these studies have shown remarkable differences in both the electronic structure and topography of the monolayers grown on metals, suggesting that the organic/metal interactions introduced by epitaxial growth strongly influence the resulting structures. Through recent experiments on monolayer films of the CTS (ET)$_2$SF$_5$CH$_2$CF$_2$SO$_3$ and the bare fulvalene ET grown on Ag(111), we illustrate what effect the metal-molecule interaction has on the electronic structure and 2D charge transport of epitaxial CTS and how this differs from the bare fulvalene. Through a comparative analysis of the differences in stoichiometry and topography of these and heretofore published systems, the relative roles of ionic bonding, surface chemisorption, and hybridization for the preparation of this and future compounds are explored. [Preview Abstract] |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U35.00004: Search for Very High-T$_{\mathrm{c}}$ Superconductivity in Modified Compositions of Strontium Ruthenates Armen Gulian, Vahan Nikoghosyan In 2004-2007 we discovered unusual properties in laser-processed crystals of strontium ruthenates (including resistive and magnetic transitions) pointing towards superconductivity at 200K and higher [1]. Being interested in understanding and reproducing their properties we explored their composition further. We obtained, via Auger-analysis, the presence of sulfur in the explored sample. The appearance of iron-based superconductors further enhanced our interest, since compositionally our materials turned out to be close to some of these new materials. If our reported observations [1] have been caused by superconductivity that may mean that one can get T$_{\mathrm{c}}$ as high as 200-250K or even higher with these materials at proper processing. We undertook systematic research of ceramic materials Sr$_{\mathrm{2}}$RuO$_{\mathrm{4}}$ with sulfur and other dopants. Data on resistive, magnetic and other physical properties, as well as preparation techniques are reported. [1] A.M. Gulian, V.R. Nikoghosyan, Unusual properties of laser-processed strontium ruthenates, in: T. Frias, V. Maestas (Eds.), Bulk Materials: Research, Technology and Applications, Nova Science Publishers, Inc., NY, 2010, Ch. 9 (see also arXiv: cond-mat/0509313 and cond-mat/0705.0641). [Preview Abstract] |
Thursday, March 21, 2013 12:27PM - 12:39PM |
U35.00005: Structural instability and superconductivity in (Ir,Pt)Te2: an optical spectroscopic study A.F. Fang, G. Xu, T. Dong, P. Zheng, N.L. Wang Ir$_{1-x}$Pt$_x$Te$_2$ is an interesting system showing competing phenomenon between structural instability and superconductivity. Due to the large atomic numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the system which may lead to nonconventional superconductivity. We grew single crystal samples of this system and investigated their electronic properties. In particular, we performed optical spectroscopic measurements, in combination with density function calculations, on the undoped compound IrTe$_2$ in an effort to elucidate the origin of the structural phase transition at 280 K. The measurement revealed a dramatic reconstruction of band structure and a significant reduction of conducting carriers below the phase transition. We elaborate that the transition is not driven by the density wave type instability but caused by the crystal field effect which further splits/separates the energy levels of Te (p$_x$, p$_y$) and Te p$_z$ bands. [Preview Abstract] |
Thursday, March 21, 2013 12:39PM - 12:51PM |
U35.00006: Superconductivity in electron-doped \emph{Ln}OBiS$_2$ Compounds Duygu Yazici, Kevin Huang, Ben White, Sooyoung Jang, Alan Chang, Aaron Friedman, Brian Maple We present observations of superconductivity in electron-doped \emph{Ln}OBiS$_2$ compounds (\emph{Ln} = La, Ce, Pr, Nd, Yb). Polycrystalline samples were synthesized by a two step solid-state reaction and characterized by x-ray diffraction. The parent compounds, \emph{Ln}OBiS$_2$, exhibit a non-metallic ground state. Superconductivity with $T_c$ in the range 1.9 K - 5.4 K was induced by electron doping these compounds via the substitution of F for O. Prior to the onset of superconductivity, the electrical resistivity of the electron-doped \emph{Ln}OBiS$_2$ compounds exhibit semiconductor like behavior, similar to the behavior observed in the parent compounds. [Preview Abstract] |
Thursday, March 21, 2013 12:51PM - 1:03PM |
U35.00007: Characterization of superconductivity in electron-doped \textit{Ln}OBiS$_2$ compounds with specific heat measurements Benjamin White, Duygu Yazici, Kevin Huang, Alan Chang, Aaron Friedman, M. Brian Maple Superconductivity has been reported recently in Bi$_4$O$_4$S$_3$ and electron-doped \textit{Ln}OBiS$_2$ compounds with \textit{Ln} = La, Ce, Pr, Nd, Yb. These materials share a similar crystal structure composed of superconducting BiS$_2$ layers, which are separated by oxide blocking layers. Early studies have concentrated primarily on the electrical transport properties and magnetic susceptibility measurements of these systems. We present results from specific heat measurements, which were performed in order to study and characterize the superconducting and normal-state properties of several electron-doped \textit{Ln}OBiS$_2$ systems. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U35.00008: Crystal growth of Pt-doped IrTe$_{2}$ Sunseng Pyon, Kazutaka Kudo, Minoru Nohara IrTe$_{2}$, a layered compound with a triangular iridium lattice, exhibits a structural phase transition at approximately 250 K. Electric resistivity and magnetic susceptibility exhibit anomalies at the transition with hysteresis [1]. Charge-orbital density wave or orbitally induced Peierls effect, a crystal field effect are suggested as candidates of the origin of the transition [2-4]. On the other hand, superconducting phase emerges when the structural phase transition is suppressed by chemical substitution or intercalation [2,5]. Analysis of physical property using single crystal should be helpful to clarifying the relation between the ground states of IrTe$_{2}$ and superconductivity. Recently, Fang \textit{et al}. reported the growth of single crystal of parent compound [4]. However, single crystal of superconducting sample had not been reported yet. For these reason, we studied superconductivity and the structural transition in platinum doped IrTe$_{2}$ single crystals. We successfully synthesized several composition of the Ir$_{1-x}$Pt$_{x}$Te$_{2}$ single crystal by flux method. From magnetization and transport measurement, we confirm the suppression of structural phase transition and emergence of superconductivity. Detail of the experiment will be discussed.\\[4pt] [1] N. Matsumoto \textit{et al}., J. Low Temp. Phys. \textbf{117} (1999) 1129.\\[0pt] [2] J. J. Yang \textit{et al}., Phys. Rev. Lett. \textbf{108} (2012) 116402.\\[0pt] [3] D. Ootsuki \textit{et al}., Phys. Rev. B. \textbf{86} (2012) 014519.\\[0pt] [4] A. F. Fang \textit{et al}., arXiv:1203.4061 (2012).\\[0pt] [5] S. Pyon \textit{et al}., J. Phys. Soc. Jpn. \textbf{81}, 053701 (2012). [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U35.00009: Enhanced Upper Critical Fields in a New Quasi-one-dimensional Superconductor Nb$_2$Pd$_{x}$Se$_5$ Seunghyun Khim, Bumsung Lee, Ki-Young Choi, Byung-Gu Jeon, Eun Sang Choi, Kee Hoon Kim We report a discovery of superconductivity with $T_{\mathrm{c}} =$ 5.5 K in Nb$_2$Pd$_{x}$Se$_5$ in which one-dimensional (1D) Nb-Se chains exist along the $b$-direction and each conducting chain is hybridized to form the conducting \textit{bc}* planes. Magnetic susceptibility and heat capacity data in both single- and poly-crystals constitute evidences of bulk superconductivity and BCS-type pairing mechanism. The zero temperature upper critical fields, $H_{\mathrm{c2}}$(0), of a single crystal are found to be 10.5, 35 and 22 T for $a$', $b$ and $c$* directions respectively. $H_{\mathrm{c2}}$(0) is clearly much larger than the expected Pauli limiting field 1.84$T_{\mathrm{c}} \approx $ 9 T along the $b$ and $c$*-direction. We will discuss the possible explanations of such enhancement of $H_{\mathrm{c2}}$ via suppression the Pauli limiting effect, based on the large spin-orbit scattering and the quasi-1D nature of electronic structure in analogy to an organic superconductor (TMTSF)$_{2}X$ ($X =$ PF$_6$, ClO$_4)$ and a purple bronze Li$_{0.9}$Mo$_6$O$_{17}$. [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U35.00010: Quantum Oscillations and Superconductivity in Subband Quantized SrTiO$_3$ Bilayer Delta-Doped Structures Hisashi Inoue, Minu Kim, Christopher Bell, Yasuyuki Hikita, Harold Hwang SrTiO$_3$ delta-doped structures show two-dimensional (2D) Shubnikov de-Haas oscillations (SdH) and 2D superconductivity (SC) [1]. Lightly doped systems, with clear SdH signals are ideal to study the link between 2D single electron states and SC [2]. The subbands (SB) should strongly influence SC: their splitting is larger than the superconducting gap. However, the similar spatial extent of the SB in single delta-layers prohibits the detection of SB modulated SC.
Growing two delta-layers (DL) in parallel with varying interlayer (IL) thickness $d$, we can spatially separate the SB and identify their contributions to SC and SdH. For small $d$, all SB spread over the DL and the IL. For larger $d$ only lower SB are confined around the DL. From the angular-dependence of the main SdH frequency we find a 2D to three-dimensional crossover for $\sim 60 |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U35.00011: Search for new phases in the Praseodymium-Silicon system Jose De La Venta, Ali C. Basaran, Ted Grant, J. Gallardo-Amores, J.G. Ramirez, M.R. Suchomel, M.A. Alario-Franco, Zachary Fisk, Ivan K. Schuller We searched for new superconducting and magnetic phases in the Pr-Si system using high-pressure high-temperature and conventional arc melting syntheses. High pressure synthesis is a unique technique which allows incorporation of elements into compounds which otherwise cannot be synthesized at ambient pressure Both high and low Si concentration areas of the phase diagram were explored. To investigate the high Si concentration compounds, PrSi$_2$ with an excess of Si was subjected to HP-HT synthesis. To explore the high Pr concentration binary compound Pr$_5$Si$_3$, we have synthesized undoped Pr$_5$Si$_3$ as well as different samples doped with C or B. High resolution X-ray powder diffraction, Magnetic Field Modulated Microwave Spectroscopy and magnetic characterization found that the addition of C gave rise to multiple previously-unknown ferromagnetic phases. Furthermore, X-ray refinement of the undoped samples confirmed the existence of the so far unconfirmed Pr$_3$Si$_2$ phase. [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U35.00012: Superconductivity in Bundles of Double-Wall Carbon Nanotubes Zhe Wang, Wu Shi, Qiucen Zhang, Yuan Zheng, Chao Ieong, Mingquan He, Rolf Lortz, Yuan Cai, Ning Wang, Ting Zhang, Haijing Zhang, Zikang Tang, Ping Sheng, Hiroyuki Muramatsu, Yoong Ahm Kim, Morinobu Endo, Paulo T. Araujo, Mildred S. Dresselhaus We will present electrical and thermal specific heat measurements that show superconductivity in double-wall carbon nanotube (DWCNT) bundles. Clear evidence, comprising a resistance drop as a function of temperature, magnetoresistance and differential resistance signature of the supercurrent, suggest an intrinsic superconducting transition below 6.8 K for one particular sample. Additional electrical data not only confirm the existence of superconductivity, but also indicate the Tc distribution that can arise from the diversity in the diameter and chirality of the DWCNTs. A broad superconducting anomaly is observed in the specific heat of a bulk DWCNT sample, which yields a Tc distribution that correlates well with the range of the distribution obtained from the electrical data. As quasi one dimensionality of the DWCNTs dictates the existence of electronic density of state peaks, confirmation of superconductivity in this material system opens the exciting possibility of tuning the Tc through the application of a gate voltage. [Preview Abstract] |
Thursday, March 21, 2013 2:03PM - 2:15PM |
U35.00013: Microwave absorption across phase transitions Juan Gabriel Ramirez, Ali Basaran, J. de la Venta, Juan Pereiro, I.K. Schuller Magnetic Field Modulated Microwave Spectroscopy (MFMMS) is a high-sensitivity technique capable of detecting superconducting phases in volumes as small as 10$^{-11}$ cm$^{3}$ even in discontinuous samples. This method measures the temperature dependence of the reflected microwave power from a sample in an oscillating magnetic field. The signature of superconductivity appears as a peak in the reflected microwave power at the transition temperature. However, the absorption mechanism is still unclear. We present an exhaustive number of measurements of known superconductors as well as other materials that undergo phase transitions to test different microwave absorption mechanisms. MFMMS measurements in micro-patterned superconducting structures were performed in order to determine the detection limit of the superconducting volume. [Preview Abstract] |
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