Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session G36: Superconductivity: Transport Properties |
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Sponsoring Units: DCMP Chair: Zhuan Xu, Zhejiang University, China Room: 344 |
Tuesday, March 19, 2013 11:15AM - 11:27AM |
G36.00001: c-axis resistivity, pseudogap, superconductivity and Widom line in doped Mott insulators Giovanni Sordi, Patrick Semon, K. Haule, A.-M. S. Tremblay Layered doped Mott insulators, such as the cuprates, show unusual temperature dependence of the resistivity. We calculate the c-axis resistivity $\rho_c$ for the two-dimensional Hubbard model within plaquette cellular dynamical mean-field theory. The temperature and doping dependencies of $\rho_c$ are controlled by the first-order transition between pseudogap and correlated metal phases from which superconductivity can emerge. On the large doping side of the transition $\rho_c(T)$ is metallic, while on the low-doping side $\rho_c(T)$ changes from metallic to semi-conducting behavior with decreasing $T$. As a function of doping, the jump in $\rho_c$ across the first-order transition evolves into a sharp crossover at higher temperatures. This crossover coincides with the pseudogap temperature $T^*$ in the single-particle density of states, the spin susceptibility and other observables. Such coincidence in crossovers is expected along the continuation of the first-order transition into the supercritical regime, called the Widom line. This implies that not only the dynamic and the thermodynamic properties but also the DC transport in the normal state are governed by the hidden first-order transition. Refs: G. Sordi et al, Sci. Rep. 2, 547 (2012); G.Sordi et al, arXiv:1211.1702 (2012) [Preview Abstract] |
Tuesday, March 19, 2013 11:27AM - 11:39AM |
G36.00002: C-Axis Conductivity of a Layered Superconductor in a Transverse Magnetic Field Shimul Akhanjee, Robert Konik We study the temperature and field dependence of Josephson pair tunneling between parallel superconducting films in the presence of a transverse magnetic field, modeled as a 2+1 dimensional XY model, transformed under the Villain duality. The magnetic field-induced diamagnetism is treated using a variational scheme developed by Benfatto et. al (2007) and the conductivity is described in terms of correlations between quantum phase slip events. We find that the universal point contact conductivity is modified by characteristic power laws. [Preview Abstract] |
Tuesday, March 19, 2013 11:39AM - 11:51AM |
G36.00003: Low-frequency Electronic Transport Noise in La$_{2-x}$Ba$_x$CuO$_4$ Nanowires Adam Weis, Yizhou Xin, Dale Van Harlingen In the pseudogap regime, high temperature superconductors often exhibit electronic structure, such as charge stripes. Charge stripes pinned to disorder have been predicted to contribute to low-frequency resistance fluctuations when sample dimensions are comparable to the size of stripe domains (Carlson, 2006). We are extending our previous studies of resistance fluctuations in YBa$_2$Cu$_3$O$_{7-\delta}$ (Bonetti, 2004; Caplan, 2010) to thin films of La-based cuprates expected to have a more stable stripe phase, particularly in the regime near 1/8-filling. We present measurements of the low-frequency electronic transport in La$_{2-x}$Ba$_x$CuO$_4$ nanowires fabricated by pulsed laser deposition and lithographic techniques. We discuss temperature dependence of the power spectral density and its relevance to correlated electron phases above T$_c$. [Preview Abstract] |
Tuesday, March 19, 2013 11:51AM - 12:03PM |
G36.00004: Hall effect and ghost critical field in disordered superconducting films Nicholas Breznay, Aharon Kapitulnik abstract-We observe a peak in the Hall resistance ocurring at a magnetic field H* in superconducting disordered thin films. Below the zero-field transition temperature Tc0, H* exactly tracks the upper critical field, Hc2, all the way to zero temperature. Near Tc0, H* becomes vanishingly small, while above Tc0 the peak again scales to higher fields as the temperature is further increased. Companion measurements of the fluctuation magnetoconductivity at temperatures above Tc0 allow precise and indpendent determination of the 'ghost critical field' Hgc, the field scale for suppression of superconducting fluctuations above Tc0. We find that H* and Hgc are distinct quantities but show similar scaling above Tc0, and compare these results to similar findings in studies of the Nernst effect in thin films [A. Pourret et al. Phys. Rev. B 76, 214504, (2007)] and high-temperature superconductors [J. Chang et al. Nature Physics 8, 751 (2012)]. [Preview Abstract] |
Tuesday, March 19, 2013 12:03PM - 12:15PM |
G36.00005: Comparing the specific heat to the cyclotron mass in two dopings of YBCO in the underdoped regime Jonathon Kemper, Scott C. Riggs, O. Vafek, A. Migliori, J.B. Betts, B.J. Ramshaw, R.D. McDonald, F.F. Balakirev, R. Liang, D.A. Bonn, G.S. Boebinger Two underdoped High T$_{\mathrm{c}}$ superconductors, YBa$_{2}$Cu$_{3}$O$_{6.51}$ and YBa$_{2}$Cu$_{3}$O$_{6.56}$, show finite electronic specific heat even in vanishing magnetic field and temperature as well as quantum magneto-oscillations at high magnetic~ fields. Previous results show the high-field electronic specific heat up to 45 T to be a sum of contributions from superconducting vortices and quantum magneto-oscillations, the latter a signature of an un-gapped Fermi surface. The vortex contribution appears as a smooth square-root field dependence of the Sommerfeld coefficient that shows no sign of diminished superconductivity up to 45 T. We present new results which allow a comparison between the cyclotron mass from high field experiments to the zero field Sommerfeld coefficient in the same crystal. The discussion will include implications of the new results on the interpretation of the previous data. [Preview Abstract] |
Tuesday, March 19, 2013 12:15PM - 12:27PM |
G36.00006: Exfoliated Bi2Sr2CaCu2O8+x thin flakes for electronic transport experiments Menyoung Lee, Michael Neumann, David Goldhaber-Gordon, Luke Sandilands, Kenneth Burch, Zhijun Xu, Alina Yang, Genda Gu Bismuth-based cuprates are the model high-temperature superconductor of choice for experimental probes that are spectroscopic and sensitive to the surface (STM, ARPES), while studies of transport properties have typically focused on rare-earth element-based compounds. We will first discuss preparation methods for and characterization of tape-exfoliated single crystal thin (few to tens nm) flakes of the Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ compound, in particular focusing on protocols designed to produce exposed conducting surfaces that are atomically smooth over several microns, and addressing the factors that influence the surface morphology and Raman scattering properties of BSCCO thin flakes. In addition, data from electronic transport measurements, aimed at observing a modulation of critical temperature and an insulator to superconductor transition as a function of hole density in the compound, will be presented. [Preview Abstract] |
Tuesday, March 19, 2013 12:27PM - 12:39PM |
G36.00007: Nonlinear transport properties of La$_2$CuO$_4$/ La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$ CuO$_4$ heterostructures in the resistive state Bo Wen, Roman Yakobov, M.P. Sarachik, Sergey Vitkalov, A. Bollinger, I. Bozovic, A. Sergeev We report measurements of the nonlinear transport properties of oxide heterojunctions La$_{2}$CuO$_{4}$/La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$CuO$_{4}$ in the vicinity of the superconducting transition. The transition occurs over a wide temperature range (7-15K) and shifts to lower temperatures in the presence of a magnetic field, as expected. Strongly nonlinear behavior is observed for the $V-I $characteristic. At low bias currents the nonlinearity has a non-thermal origin close to the transition temperature and is strongly sensitive to magnetic fields. Above the middle of the superconducting transition the nonlinear behavior is consistent instead with electron heating with a value of electron-phonon thermal conductance of $\sim$ 10$^{-6}$ W/K per square micron, which is significantly smaller than the thermal conductance of Nb and NbN ultrathin superconducting films. Our results indicate that this novel low-dimensional superconducting material shows great promise for substantial enhancement of direct detection and wide band mixing of radiation. [Preview Abstract] |
Tuesday, March 19, 2013 12:39PM - 12:51PM |
G36.00008: Tuning the static spin stripe phase and supercoductivity in La$_{2-x}$Ba$_{x}$CuO$_{4}$ ($x$ = 1/8) by hydrostatic pressure Zurab Guguchia, Alexander Shengelaya, Alexander Maisuradze, Giorgi Ghambashidze, Ekaterina Pomjakushina, Kazimierz Conder, Hugo Keller Muon spin rotation (${\mu}$SR) and magnetization measurements were performed in stripe-stabilized La$_{1.875}$Ba$_{0.125}$CuO$_{4}$ as a function of pressure up to $p$ ${\simeq}$ 2.25 GPa. At ambient pressure this system exhibits static spin stripe order below $T{\rm so}$ ${\approx}$ 30 K. Zero-field ${\mu}$SR experiments indicate that the volume fraction ${\omega}$ of static spin-stripe order significantly decreases with increasing $p$, while the size of the ordered moment and the ordering temperature remain constant. The magnetization measurements show that the sample exhibits a tiny superconducting (SC) volume fraction at ambient pressure. However, by the application of pressure the SC phase volume increases proportionally to the non-magnetic volume fraction (1-${\omega}$). These results indicate that in La$_{1.875}$Ba$_{0.125}$CuO$_{4}$ magnetism and superconductivity occur in mutually exclusive spatial regions. [Preview Abstract] |
Tuesday, March 19, 2013 12:51PM - 1:03PM |
G36.00009: Spin fluctuations on the verge of Mott localization Himadri Barman, N.S. Vidhyadhiraja We investigate the effects of local, transverse spin fluctuations on transport and thermodynamic quantities in the proximity of a paramagnetic Mott transition. Low temperature Fermi liquid coherence is seen to cross over to universal power laws in resistivity, optical conductivity and specific heat at higher temperatures and frequencies. Striking agreement with the normal phase properties of LSCO and BSSCO series of high temperature superconductors (HTS) is found. We conclude that the anomalous properties of HTS above the superconducting dome originate from spin fluctuation scattering concomitant to Mott localization. [Preview Abstract] |
Tuesday, March 19, 2013 1:03PM - 1:15PM |
G36.00010: Resistivity of Sr$_2$ RuO$_4$ under uniaxial stress Daniel Brodsky, Clifford Hicks, Andrew P. Mackenzie We report high precision resistivity measurements on single crystals of Sr$_2$RuO$_4$ under in-plane uniaxial stress. A specially built probe enables the stress to be varied continuously whilst the sample is at low temperature. The needle-like shape of the samples ensures that the strain is homogeneous in the region probed. We compare results for different directions of applied stress relative to the crystal axes. [Preview Abstract] |
Tuesday, March 19, 2013 1:15PM - 1:27PM |
G36.00011: Circuit influence on electron transport in hybrid superconductor---normal-metal nanostructures Vladimir Bubanja, Shuichi Iwabuchi We study the effects of the circuit impedance on transport properties of hybrid structures consisting of a superconductor tunnel-coupled to two normal-metal electrodes. At subgap conditions (i.e. at low voltages and temperatures with respect to the superconducting energy gap) the dominant transport mechanism of Cooper pairs is by Andreev reflection. We derive the analytic expressions for the direct and crossed Andreev current, and the elastic cotunneling current. The results can be used for improving the accuracy of hybrid devices employed in electrical metrology and for noise measurements in quantum information processing. [Preview Abstract] |
Tuesday, March 19, 2013 1:27PM - 1:39PM |
G36.00012: Micro-mechanical and Structural Properties and Activation Energy Calculation of Nd$_{2}$O$_{3}$ Added Bi$_{2}$Sr$_{2}$Ca$_{1}$Cu$_{2}$O$_{y}$ Superconducting System Ozgur Ozturk, Elif Asikuzun, Murat Coskunyurek, Seydanur Kaya, Mustafa Yilmazlar, Gurcan Yildirim, Cabir Terzioglu Nd added Bi-2212 superconducting samples with x$=$0, 0.001, 0.005, 0.01, 0.05 and 0.1 were prepared by conventional solid state reaction method and annealed at 840$^{\circ}$C for 72 h. For the comparison, an undoped sample was produced to the same conditions. The effects of Nd addition on structural and micromechanical properties were systematically investigated. The volume fraction, lattice parameters, crystal structure and grain size of the samples were characterized using the X-ray diffractometer and Scanning Electron Microscope. In addition, this study includes determination of the activation energy of Nd in the Bi-2212 system using the magnetoresistivity measurements. And also, we were investigated the mechanical properties for all samples using the Vickers microhardness measurements. Microhardness values of the samples decrease with increasing adding and applied load. The Vickers hardness of the samples studied, exhibits the typical indentation size effect (ISE). [Preview Abstract] |
Tuesday, March 19, 2013 1:39PM - 1:51PM |
G36.00013: Analysis of Indentation Size Effect (ISE) Behavior in Low-Load Vickers Microhardness Testing of (Sm123)$_{\mathbf{1-x}}$(Nd123)$_{\mathbf{x}}$ Superconductor System Sukru Celik, Ozgur Ozturk, Elvan Co\c{s}kun, Elif Asikuzu, Kemal Ozturk, Cabir Terzioglu Indentation size effect (\textit{ISE}) for (Sm123)$_{1-x}$(Nd123)$_{x}$ superconducting samples which were fabricated by the solid state reaction technique for values of x$=$0.00, 0.05, 0.10, 0.20, and 0.30 was investigated by analyzing the theoretical models. When the experimental data of a number of single crystals which have the different crystal structure and different chemical bonding inside the polycrystallined samples were analyzed with the \textit{ISE} models, the sample encountering with resistance and elastic deformation was observed as well as plastic deformation. The microhardness values on different surfaces of materials were calculated by using Meyer Law, \textit{PSR} model, MPSR model, \textit{EDP} (Elastic / Plastic Deformation model) model and the Hays-Kendall (\textit{HK}) approach. The results showed that the Hays- Kendall approach was determined as the most successful model. Furthermore, XRD and SEM measurements were analyzed for superconducting properties of (Sm123)$_{1-x}$(Nd123)$_{x}$ superconductor system. The results showed that while Nd123 concentration is increasing, microhardness values at the minimum load and averaged plateau region of load. [Preview Abstract] |
Tuesday, March 19, 2013 1:51PM - 2:03PM |
G36.00014: Investigation of Indentation Size Effect (ISE) of Bi$_2$Sr$_2$CaNd$_{\mathrm{x}}$Cu$_2$O$_{\mathrm{y}}$ Superconducting System using Vickers Microhardness Test Method Elif Asikuzun, Ozgur Ozturk, Seydanur Kaya, Murat Coskunyurek, Nevin Soylu, Ahmet Varilci, Cabir Terzioglu In this work, the effects of Nd doping on the structural and mechanical properties of the samples were analyzed. Nd$_{2}$O$_{3}$ doped Bi-2212 superconductors were obtained using solid state reaction method. Microhardness measurements were made to analyze the mechanical properties. XRD and SEM measurements were done for determination of crystal structure and surface morphology and calculation of the lattice parameters. The Vickers microhardness was calculated for undoped and doped samples. The experimental results of the microhardness measurements were analyzed using Kick's Law, PSR (proportional specimen resistance), modified PRS (MPSR) and Hays--Kendall (HK) approach. The microhardness values of the samples decreased with increasing Nd doping and applied load. Finally, the Hays-Kendall \textit{(HK)} approach was determined as the most successful model describing the mechanical properties of our samples. [Preview Abstract] |
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