Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L25: Superconductivity: Miscellaneous Experiments |
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Sponsoring Units: DCMP Chair: Eric Palm, High Magnetic Field Laboratory Room: 203B |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L25.00001: Studying Superconductivity and Magnetism in Y$_{9}$Co$_{7}$ with a Tunnel Diode Resonator Circuit R.T. Gordon, M.D. Vannette, J. Strychalska, T. Klimczuk, R.J. Cava, R. Prozorov I will discuss recent tunnel diode resonator (TDR) circuit measurements on a single crystal of the material Y$_{9}$Co$_{7}$. This material displays a superconducting transition at T $=$ 2.5 K and an unusual magnetic state at temperatures just above this transition, up to 8 K. The exact nature of this magnetic state is a point of contention among researchers and one of the goals of this study was to elucidate the details of this magnetism that is proximate to superconductivity. Another goal of this study was to search for signatures of an interaction between the superconducting and magnetic states. The magnetic susceptibility as a function of both temperature and magnetic field was measured using TDR circuits, which are radio frequency oscillators having parts-per-billion sensitivity to measure changes in physical properties of materials. Using both $^{3}$He and $^{4}$He cryostats mounted into superconducting magnet bores, this experiment was able to reach temperatures as low as 500 mK and magnetic fields as high as 9 T. The resulting measurements will be discussed and compared to TDR measurements done on other magnetic materials, especially ZrZn$_{2}$. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L25.00002: Polaronic high-temperature superconductivity in optimally doped bismuthate Ba$_{0.63}$K$_{0.37}$BiO$_3$ Nicholas Derimow, Jacob Labry, Armond Khodagulyan, Jun Wang, Guo-meng Zhao Magnetic measurements have been carried out in the superconducting and normal states of the optimally doped nonmagnetic bismuthate superconductor Ba$_{0.63}$ K$_{0.37}$ BiO$_3$. The magnetic data along with previous $\mu$SR, resistivity, and tunneling data consistently show that there is a large polaronic enhancement in the density of states and effective electron-phonon coupling constant. The first-principle calculation within the density-functional theory indicates a small electron-phonon coupling constant of about 0.3-0.4, which can only lead to about 1 K superconductivity within the conventional phonon-mediated mechanism. Remarkably, the polaronic effect increases the electron-phonon coupling constant to about 1.4, which is large enough to lead to 32 K superconductivity. The present work thus uncovers the mystery of high-temperature superconductivity in bismuthate superconductors, which will also provide important insight into the pairing mechanism of other high-temperature superconductors. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L25.00003: Search for electron-phonon coupling in superconducting BKBO D. Parshall, J.L. Niedziela, S. Barilo, J.W. Lynn Ba0.6K0.4BiO3 is a superconductor with a Tc $=$ 30 K. While generally regarded as a BCS superconductor, previous work searching along the high-symmetry directions did not find characteristic signatures of electron-phonon coupling near the energy gap of $\sim$ 9 meV. Making use of the new Multizone Phonon Refinement technique, we are able to examine the phonon spectrum at all symmetry points and look for signatures of electron-phonon coupling. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L25.00004: Pressure effects on static and dynamic spin properties in CrAs M. Matsuda, M. B. Stone, J.-G. Cheng, W. Wu, F. Lin, J. L. Luo, K. Matsubayashi, Y. Uwatoko CrAs is an antiferromagnetic metal, which shows a helical spin structure accompanied by an abrupt lattice expansion at $T\rm_{N}$$\sim$260 K in ambient pressure. With applying pressure, this material shows superconductivity with a maximum transition temperature of $\sim$2 K. Since Cr has the spin degree of freedom, elucidating the magnetic contribution to the superconductivity is crucial to understand the pairing mechanism. Our neutron diffraction studies have revealed that the static magnetic order as well as the structural anomaly is suppressed with applying external pressure. Chemical pressure effect was also studied by substituting As by P, which is found to be almost the same as the external pressure. We also plan to show the magnetic excitations in undoped and P-doped CrAs measured by inelastic neutron scattering experiments, which will give useful information on a coupling between the magnetism and the superconductivity. [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L25.00005: Chemical doping and pressure effects on the noncentrosymmetric superconductors ZrRe$_{6}$ and BiPd Mojammel Alam Khan, David P. Young, Ahmad Us Saleheen, Amar Karki, Dana Browne, P.W. Adams, Tapas Samanta Polycrystalline samples of ZrRe$_{6}$ doped with Ti, W and Os and BiPd doped with Te and Ni were made using arc melting and RF- induction furnaces. Variation of the superconducting transition temperature with different types of doping was observed. Small suppression of T$_{c}$ was observed for both hole and electron doping in ZrRe$_{6}$ samples. Suppression in T$_{c}$ was also observed for BiPd. The effect of hydrostatic pressure on T$_{c}$ was also determined for both compounds. Effect of Re depreciation on T$_{c}$ for ZrRe$_{6}$ were observed by synthesizing samples, ZrRe$_{5.95 \sim 5.85}$. In addition, small diameter wires (0.0005" $\sim$ 0.004") of BiPd were synthesized for critical current density measurements. The critical temperature of the wires was found to be slightly higher ($\sim$4.07 K) than that reported for bulk samples ($\sim$3.78 K). [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:12AM |
L25.00006: Giant Two-Phonon Raman Signal from NbC Coherent Precipitates in Niobium John Zasadzinski, Chaoyue Cao, Runzhe Tao, Robert Klie, Lance Cooley High purity Nb, subjected to the processing steps used in SRF cavity fabrication, has been shown to reveal nanoscale NbC precipitates near the surface that are coherent with the host Nb matrix. Raman backscattering from such regions reveal spectra similar to the earlier work on bulk NbC but with a strongly enhanced two-phonon signal. The unprecedented strength and sharpness of the two phonon response has allowed a direct comparison to \textit{ab initio} calculations of the phonon dispersion curves of NbC under uniform compression where it is shown directly that the two phonon signal originates in the regions of strong electron-phonon renormalization. The strong two phonon signal may indicate an enhancement of the electron phonon spectral function, $\alpha^{\mathrm{2}}$F($\omega )$ [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L25.00007: Experimental demonstration of superconducting critical temperature increase in electromagnetic metamaterials Vera Smolyaninova, Bradley Yost, Kathryn Zander, Thomas Gresock, Michael Osofsky, Heungsoo Kim, Shanta Saha, Richard Greene, Igor Smolyaninov A recent proposal that the metamaterial approach to dielectric response engineering may increase the critical temperature of a composite superconductor-dielectric metamaterial has been tested in experiments with compressed mixtures of tin and barium titanate nanoparticles of varying composition. An increase of the critical temperature of the order of 0.15 K compared to bulk tin has been observed for 40{\%} volume fraction of barium titanate nanoparticles. Similar results were also obtained with compressed mixtures of tin and strontium titanate nanoparticles. [Preview Abstract] |
Wednesday, March 4, 2015 9:24AM - 9:36AM |
L25.00008: Magneto-transport near a quantum critical point Ian Hayes, Nicholas Breznay, Arkady Shekhter, Ross McDonald, James Analytis The physics of quantum critical phase transitions connects to some of the most difficult problems in condensed matter physics, including metal-insulator transitions, frustrated magnetism and high temperature superconductivity. Near a quantum critical point (QCP) a new kind of metal emerges, whose thermodynamic and transport properties do not fit into the unified phenomenology with which we understand conventional metals - the Landau Fermi liquid (FL) theory - characterized by a low temperature limiting $T$-linear specific heat and a $T^2$ resistivity [1]. Studying the evolution of the $T$ dependence of these observables as a function of a control parameter leads to the identification both of the presence and the nature of the quantum phase transition in candidate systems. In this study we measure the transport properties of basp, at $T < T_c$ by suppressing superconductivity with high magnetic fields. At sufficiently low temperatures, the resistivity of all compositions ($x \geq 0.31$) crosses over from a linear to a quadratic temperature dependence, consistent with a low temperature FL ground state. As compositions with optimal $T_c$ are approached from the overdoped side, this cross-over becomes steeper, consistent with models of quantum criticality where the effective Fermi temperature $T_F$ goes to zero.\\[4pt] [1] Landau, L. The theory of a fermi liquid. Journal of Experimental and Theoretical Physics 6, 920 (1957). [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L25.00009: Low-temperature STM Measurements of Granular Pb films S.A. Moore, J. Fedor, J. Curtis, G. Karapetrov, I. Beloborodov, M. Iavarone Using low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) we have investigated the electronic properties of granular Pb films grown on HOPG at low temperature. Films grown under these conditions form a two-dimensional array of disconnected grains with a similar distribution of sizes. Local spectroscopy measurements as a function of field and temperature reveal a grain size dependent competition between the repulsive electron-electron interaction and the attractive superconducting pairing interaction. Our results show the presence of an increased depletion of states around the Fermi energy for all grain sizes, with a complete suppression of the superconducting state below a critical grain size. We compare these results to those found on 9ML and 100ML continuous films also grown on HOPG, where the superconducting state completely dominates the electronic properties. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L25.00010: Paramagnetic Meissner effect in electrochemically doped Indium-Tin Oxide films Ali Aliev Transparent conductive indium tin oxide (ITO) thin films, electrochemically intercalated with alkali (Li$^{+}$, Na$^{+}$, K$^{+}$, Rb$^{+}$, Cs$^{+})$, alkali earth (Mg$^{+2}$, Ca$^{+2})$, or complex NH$_{4}^{+}$ ions show tunable superconducting transition with dome shape behavior of $T_{c}$ versus electron density around the maximum at 5 K. The zero resistance transition in superconducting state is accompanied with paramagnetic Meissner response to the applied external magnetic field, i.e. the increase of magnetization in field cooling regime. We provide extensive evidences of flax trapping using dc SQUID, ac susceptibility and transport measurements. In particular, we present evidence that the paramagnetic response results from the lower $T_{c}$ on the center of disk samples than on the edges leading to the trapping of magnetic flax in the center, and that change of $T_{c}$ profile to opposite removes the paramagnetic response. The flux trapped state is metastable. An alteration of external magnetic field destroys the giant vortex.. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L25.00011: Novel fabrication process for all-MgB$_{2}$ Josephson junctions and circuits Thomas Melbourne, Elias Galan, Xiaoxing Xi, Ke Chen A novel process for fabricating high-quality MgB$_{2}$/MgO/MgB$_{2}$ Josephson junctions and circuits is reported. A 100 nm-thick bottom electrode of MgB$_{2}$ was grown on SiC (0001) substrate by hybrid physical-chemical vapor deposition (HPCVD) and then coated by a 1 $\sim$ 5 nm-thick MgO junction barrier layer and a 20 nm-thick TiO$_{2}$ protection layer. After the bottom MgB$_{2}$ layer was patterned an 80 nm-thick MgO etch-stop layer was then deposited on the sample with a pattern created by photo- or e-beam lithography and lift-off, followed by reactive ion etching in SF$_{6}$ to remove TiO$_{2}$ from the Josephson junction areas. Finally, a 100 nm-thick MgB$_{2}$ serving as both the top electrode and wiring layer was deposited and patterned by photolithography and ion mill. The advantage over previously reported process is that this process combines the MgB$_{2}$ top electrode and the wiring layer, which simplifies fabrication and allows for an additional layer of MgB$_{2}$ to be dedicated to a ground plane in circuits. Characteristics of all-MgB$_{2}$ Josephson junctions fabricated by this process are shown. [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L25.00012: Electrical transport property of nano carbon superconductors Yuki Matsuda, Satoshi Heguri, Yoichi Tanabe, Katsumi Tanigaki C$_{\mathrm{60}}$-based solids are known as typical nano carbon materials. Superconducting critical temperature ($T_{\mathrm{C}})$ of $A_{\mathrm{3}}$C$_{\mathrm{60}}$ ($A \quad =$ alkali metal) fullerides, with most frequently showing face-centered-cubic (fcc) structure, increases monotonically, and can be controlled by varying the ionic radius of $A$. Recently, $T_{\mathrm{C}}$ raised to 38 K for Cs$_{\mathrm{3}}$C$_{\mathrm{60}}$ under high pressure. All of these compounds are extremely sensitive to the air, and mainly magnetic measurements have been employed as experimental conditions. On the other hand, their transport properties, such as electrical resistivity, Hall effect, and thermoelectric power as a function of temperature or pressure, have not been investigated in spite of much interest in many aspects of physical properties. In order to understand the superconducting mechanism and other electron properties in detail, we will present electrical transport properties for this family. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L25.00013: Confinement of superconducting fluctuations due to emergent electronic inhomogeneities in ultrathin films Cl\'ementine Carbillet, Sergio Caprara, Marco Grilli, Christophe Brun, Tristan Cren, Francois Debontridder, Baptiste Vignolle, Konstantin Ilin, Michael Siegler, Dimitri Roditchev, Brigitte Leridon The question of homogeneity, granularity, or glassiness of materials on the verge of a superconductor/insulator transition is fundamental and hotly debated. Here, by combining macroscopic and nano-scale studies of superconducting ultrathin NbN films, we reveal some nanoscopic electronic inhomogeneity that emerges when the film thickness is reduced. While thicker films display a purely two-dimensional behavior in electrical transport measurements, we demonstrate a seemingly zero-dimensional regime in the superconducting thermal fluctuations for the thinner samples. This regime corresponds to a longer survival and anomalous local diffusion of the Cooper pair fluctuations. Remarkably, the typical length scale, 20-40 nm, extracted from the fluctuation conductivity coincides with the correlation length of the electronic inhomogeneities directly revealed by local scanning tunneling spectroscopy. [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L25.00014: Hall coefficient of ultrathin niobium in Si/Nb/Si trilayers Marta Z. Cieplak, I. Zaytseva, O. Abal'oshev, P. Dluzewski, W. Paszkowicz, L.Y. Zhu, C.L. Chien, M. Konczykowski We study the structural and magnetotransport properties of ultrathin Nb layers in Si/Nb/Si trilayers, grown by magnetron sputtering at room temperature. The thickness of Nb, d, is in the range from 1.1 nm to 50 nm, with a fixed Si thickness of 10 nm. With decreasing d the superconductivity is suppressed for d \textless 1.2 nm, and the structure of the Nb layers evolves, from polycrystalline at d \textgreater 6 nm, to amorphous at d \textless 3.3 nm. The Hall coefficient, positive in thick Nb layers, initially increases with decreasing d, but starts to diminish at d \textless 6 nm, and eventually changes sign into negative at d \textless 2 nm. In the thinnest Nb layers the dependence of the Hall voltage on magnetic field becomes nonlinear at low temperatures, indicating that two types of carriers contribute to transport. The influence of boundary scattering on the relaxation rate of carriers, and band broadening in the amorphous films, may be responsible for this effect. We discuss the correlation between the superconductivity suppression and the appearance of the electron contribution to the conductance, observed in the present films; we also compare our results to the properties of other previously studied ultrathin Nb films. [Preview Abstract] |
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