Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session P13: Superconducting Thin Films and Transport |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Paola Barbara, Georgetown University Room: LACC 402B |
Wednesday, March 23, 2005 11:15AM - 11:27AM |
P13.00001: Electrical properties of epitaxial junctions between Nb:SrTiO$_{3}$ and optimally doped, underdoped and Zn-doped YBa$_{2}$Cu$_{3}$O$_{7-\delta }$ Wegdan Ramadan, S.B. Ogale, S. Dhar, S.R. Shinde, M.S.R Rao, T. Venkatesan Epitaxial thin films of optimally doped, underdoped and Zn-doped YBa$_{2}$Cu$_{3}$O$_{7-\delta }$ were grown on single crystal (001) Nb:SrTiO$_{3}$ substrates by pulsed laser deposition (PLD) and the electrical properties of the corresponding interface junctions were examined. The growth conditions were optimized in each case to get the appropriate crystalline quality of the films as well as the desired normal state and superconducting properties. The films/heterointerfaces were characterized by x-ray diffraction, Rutherford backscattering channeling (RBSC) spectrometry in normal and oxygen resonance modes, magnetic susceptibility, four probe in-plane resistivity, and the temperature dependent junction current-voltage (I-V) characteristics. Non-linear I-V curves (forward and reverse) were obtained in all the cases, revealing some characteristic differences and interesting temperature evolution. These data were analyzed within the framework of a standard description of the transport across the metal-semiconductor (Schottky) interface and the curve fitting parameters were extracted in each case. An attempt is made to relate the observed parametric differences to the existing knowledge about the normal state and superconducting properties of the films. [Preview Abstract] |
Wednesday, March 23, 2005 11:27AM - 11:39AM |
P13.00002: Ce doping in T-La2CuO4 films: Broken electron-hole symmetry in high-Tc superconductivity Akio Tsukada, Hideki Yamamoto, Michio Naito We attempted Ce doping in La$_{2}$CuO$_{4}$ with the K$_{2} $NiF$_{4}$ ($T)$ structure by molecular beam epitaxy. With low growth temperature and appropriate substrate choice, we found that Ce can be incorporated into the K$_{2}$NiF$_{4}$ lattice up to $x \quad \sim $ 0.06, which has not yet been realized in bulk synthesis. The doping of Ce made $T$-La$_{2-x}$Ce$_{x}$CuO$_{4}$ more insulating, which is in sharp contrast to Ce doping in La$_{2}$CuO$_{4}$ with the Nd$_{2}$CuO$_{4}$ structure, which made the compounds superconducting. The observed smooth increase in resistivity from hole-doped side ($T$-La$_{2-x}$Sr$_{x}$CuO$_ {4})$ to electron-doped side ($T$-La$_{2-x}$Ce$_{x}$CuO$_{4})$ indicates that electron-hole symmetry is broken in the $T$-phase materials. We propose that the nature of the insulating state in $T$-La$_{2-x}$Ce$_{x} $CuO$_{4}$ is of a Kondo insulator instead of a Mott insulator. The insulating mechanism based on Kondo interaction between Cu3d spins and O2p holes explains the global evolution of the resistivity and also the pseudo gap phenomenon from hole-doping to electron doping. [Preview Abstract] |
Wednesday, March 23, 2005 11:39AM - 11:51AM |
P13.00003: Magnetic impurity doping effect of Bi2201 superconducting thin films Xiaofang Zhai, Maitri Warusawithana, James Eckstein We have studied the effect of doping Mn into Cu-O planes of Bi$_{2}$Sr$_{2}$CuO$_{6}$ thin films grown by atomic layer-by-layer Molecular Beam Epitaxy in an ozone environment of 8E-6 Torr. These films were grown on SrTiO$_{3 }$substrates at 680$^{o}$C. The in-situ Reflection-High-Energy-Electron-Diffraction showed two-dimensional atomically flat surfaces during the whole growth. As Mn concentration on Cu site is varied, we see significant changes in transport. Bi2201 films with no Mn are superconducting with Tc of about 12.5K. By substituting 3.5{\%} of the Cu sites with Mn, we observed insulating behavior characterized by a variable range hopping mechanism with dimensionality between 2 and 3. [Preview Abstract] |
Wednesday, March 23, 2005 11:51AM - 12:03PM |
P13.00004: Complex Conductance Measurements of Ultra-thin MoGe films near the Superconductor-Insulator Transition Lukas Urban, Michael Callahan, Ali Yazdani The application of a magnetic field destroys the superconducting state and gives rise to unusual conducting or insulating states in two-dimensional samples. [1,2] This field-tuned transition has been extensively studied using conventional electrical transport measurements and analyzed within the context of critical behavior near a quantum phase transition. We report on a new approach to study the magnetic field-tuned transition using a two-coil mutual inductance technique, which has been integrated into a top-loading dilution refrigerator. Using this experimental setup, we have measured the complex conductance of Mo$_{43}$Ge$_{57}$ thin films as function of temperature and magnetic field. These measurements are used to determine the behavior of the superconducting electron density in the vicinity of the field-tuned transition. $^{1}$ A Yazdani and A. Kapitulnik \textit{Phys. Rev. Lett.} \textbf{74}, 3037(1995). $^{2}$ N. Mason and A. Kapitulnik.,\textit{ Phys Rev.} B \textbf{64}, 60504-1 (2001). [Preview Abstract] |
Wednesday, March 23, 2005 12:03PM - 12:15PM |
P13.00005: Crossover from 2D-XY to 3D-XY superconducting fluctuations with hole-doping in dynamical conductivity of La$_{2-x}$Sr$_x$CuO$_4$ thin films by broadnband technique A. Maeda, H. Kitano, T. Ohashi, I. Tsukada We report the systematic study of dynamical complex ac conductivity, $\sigma(\omega)=\sigma_1(\omega)+i\sigma_2(\omega)$, of high-quality La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) ($x$=0.07 to 0.24) thin films ate temperatures ($T$s) just above the superconducting transition temperature, $T_c$, by using a broadband microwave technique, where both components of the complex conductivity can be obtained as a detailed function of frequency by sweeping the microwave frequency continuously (0.1 to 12~GHz). For all superconducting films, we observed a definite contribution of the superconducting fluctuation to $\sigma(\omega, T)$, which could not be described by the conventional Aslamazov- Larkin term. Detailed analyses using a dynamic scaling theory clearly indicated that the fluctuation can be well described by the 2D-$XY$ critical behavior for the underdoped LSCO samples, whereas it changes into the 3D-XY critical behavior in the optimally doped samples. We are now fixing the fluctuation behavior in the overdoped samples, which is very important to judge whether or not the quantum-criticality picture proposed in some theories is appropriate for the description of the electronic state of the high-$T_c$ cuprate supercondutors. [Preview Abstract] |
Wednesday, March 23, 2005 12:15PM - 12:27PM |
P13.00006: Vortices and the superconductor-insulator transition D. Shahar, G. Sambandamurthy, A. Johansson, E. Peled, P.G. Bjornsson, K.A. Moler We present results from a study of the temperature ($T$) and magnetic field ($B$) dependence of disordered, superconducting, amorphous indium-oxide thin-films. Application of a perpendicular $B$ weakens superconductivity until, at a well- defined critical $B$, the system is driven into an insulating state. We find that our samples follow a simple power-law dependence on $B$ that holds over a wide range of $T$ and resistance. Surprisingly, this power-law dependence continues, uninterrupted, into the $B$-driven insulating state. These results indicate that vortices play a central role in determining the transport properties of our films. [Preview Abstract] |
Wednesday, March 23, 2005 12:27PM - 12:39PM |
P13.00007: Fractional-exponent behavior of magnetization near $T_c$ in ${\rm Bi_2Sr_2CaCu_2O_8}$ Lu Li, Yayu Wang, M.J. Naughton, S. Ono, Y. Ando, N.P. Ong Using high-resolution torque magnetometry, we have investigated in detail how long-range phase coherence develops as the critical temperature $T_c$ (88.7 K) is approached in optimally-doped $\rm Bi_2Sr_2CaCuO_{8+\delta}$ with field $\bf H||c$. Three distinct regimes are observed. Above $\sim$92 K, $|M|$ increases rapidly as $T\rightarrow T_c$ in step with the vortex Nernst signal. $M$ is strictly linear in $H$ in weak $H$, but shows strong curvature at large $H$ (5-14 T). The curvature provides a determination of the correlation length $\xi_{sc}$ which grows as a power law, viz. $\xi_{sc}\sim 1/t^\nu$. In the second regime, $86 < T < 92$ K, $M$ becomes nonlinear in $H$, viz. $M\sim H^{\alpha(T)}$, where the exponent $\alpha(T)$ decreases from 1 to 0. This interesting fractional-exponent behavior is highly unusual and fits poorly with conventional pictures of `fluctuating diamagnetism.' As previously known, $M$ is virtually $H$ independent below 2 Tesla at the ``crossing temperature'' $T_{cr} $ = 86 K. Below $T_{cr}$, $M$ is a function of $\log H$. We compare this behavior with predictions of the 3DXY and Kosterlitz-Thouless theory. Supported by funds from the U.S. National Science Foundation under grant DMR 0213706. [Preview Abstract] |
Wednesday, March 23, 2005 12:39PM - 12:51PM |
P13.00008: Normal-Superconducting Phase Transition Obscured by Current Noise M. C. Sullivan, S. Li, H. Xu, M. Lilly, C. J. Lobb There is a large volume of experimental research on the normal- superconducting phase transition, both in zero field and the so- called ``vortex-glass'' transition in a field. For these phase transitions, resistive behavior at low currents is expected for $T > T_c$, and non-linear current versus voltage isotherms are expected below $T_c$. We show theoretically and experimentally that the addition of current noise to nonlinear voltage versus current curves will create ohmic behavior. Thus, current noise will create ohmic behavior at low currents even for temperatures below $T_c$, and isotherms that are actually \textit{below} $T_c$ will appear to be \textit{above} $T_c$. This obscures the phase transition and leads to incorrect values for $T_c$ and the critical exponents $\nu$ and $z$. Most reports in the literature do not explicitly mention filtering, yet the transition temperature and the critical exponents extracted from the conventional analysis are inaccurate if current noise is not filtered out. Thus, current noise is a possible explanation for the wide range of critical exponents found in the literature. [Preview Abstract] |
Wednesday, March 23, 2005 12:51PM - 1:03PM |
P13.00009: Phase Transition from a Spin-Glass Metal to Superconductor in La2-xSrxCuO4 (x<0.05) Single Crystalline Films by Epitaxial Strain ATM Nazmul Islam, Satoshi Watauchi, Isao Tanaka Epitaxial growth of films is an effective way to induce high anisotropic pressure on films. In this work we have grown La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO) (0.03$<$x$<$0.05) films, having metallic behavior in bulk, by liquid phase epitaxy technique along the $<$100$>$ direction. For the desired kind of strain we have chosen overdoped LSCO ($\sim $x=0.19) as the substrate. We observed that the resistance versus temperature measurement, in a configuration where the film and substrate are in series, shows a two-step superconducting transition. We suggest that the other transition, which does not coincide with the T$_{c}$ of substrate, is due to superconductivity in film. The T$_{c}$ of the films with x=0.034, 0.040 and 0.045 are found to be 25K, 30K and 34K, respectively. Where as the x=0.0 film is not superconducting. In our work we have shown possible transition of a spin-glass metallic phase to a superconducting phase in LSCO (0.03$<$x$<$0.05) films induced by epitaxial strain. [Preview Abstract] |
Wednesday, March 23, 2005 1:03PM - 1:15PM |
P13.00010: Critical currents of $ex-situ$ YBCO thin films on ``RABiTS'' substrates: thickness, field and temperature dependencies A.O. Ijaduola, J.R. Thompson, R. Feenstra, D. K. Christen, A. A. Gapud The critical current density $J_c$ flowing in thin $YBa_2Cu_3O_ {7-\delta}$ (YBCO) films of various thicknesses $d$ has been studied magnetometrically, both as a function of applied field $H$ and temperature $T$. The films, grown by a BaF$_2$ $ex- situ$ process and deposited on buffered ``RABiTS'' substrates of Ni-5$\%$W, have thicknesses $d$ ranging from 28 nm to 1.5 $\mu$m. Isothermal magnetization loops $M(H;T)$ and remanent magnetization $M_{rem}(T)$ in $H=0$ were measured with $H$ $\|$ c-axis (i.e., normal to film plane). The $J_c(d)$ values, which were obtained from a modified critical state model, increase with thickness $d$, peak near $d \sim$ 150 nm, and thereafter decrease as the films get thicker. For a range of temperatures and intermediate fields, we find $J_c \propto H^{-\alpha}$ with $\alpha \sim (0.56 - 0.69)$ for all materials. This feature can be attributed to pinning by large random defects. At higher fields approaching the irreversibility line, $J_c(H)$ decreases faster. The $J_c$ at self field varies as $J_c(T,sf) \sim (1-T/T_c)^n$ with $n \sim$ 1.2 - 1.4. This points to ``$\delta T_c$ pinning'' (pinning that suppresses $T_c$ locally) in these YBCO materials. Work at UTK was supported by AFOSR Grant F49620-02-1-0182. ORNL is managed by UT-Battelle, LLC for the USDOE. [Preview Abstract] |
Wednesday, March 23, 2005 1:15PM - 1:27PM |
P13.00011: Current Percolation Characteristics of IBAD Coated Conductors G. You, K.R. Barraca, L.B. Wang, C. Kwon We have investigated IBAD coated conductors by variable temperature scanning laser microscopy (VTSLM) to map how current flows in superconducting transition and superconducting region. We examined various factors that make non-uniform current distribution and found that the current flow was affected by the grain boundary network, the physical bending of samples, and the surface contaminations. On the basis of data analysis, we deduced 65$\mu $m $\sim $ 150$\mu $m as percolation cluster feature sizes. Below the critical temperature, we have investigated J$_{c}$ to establish the relationship of the T$_{c}$ and $\delta $V and J$_{c}$, and we conclude that lower T$_{c}$ and higher $\delta $V area has lower J$_{c}$. We also found several circular shapes of about 100$\mu $m $\times $ 130$\mu $m diameter from a sample. Those dots had definitely higher T$_{c}$ than the surrounding area and created non-uniform current flow. In this presentation, we will report more about VTSLM images around the dots and the characteristics of current bottleneck features which are related with the lower J$_{c}$. [Preview Abstract] |
Wednesday, March 23, 2005 1:27PM - 1:39PM |
P13.00012: Reversible and irreversible magnetostriction of untwinned YBa$_2$Cu$_3$O$_{6.999}$ single crystals C. Meingast, P. Popovich, R. Lortz, S. Tajima, T. Masui We present anisotropic magnetostriction measurements of untwinned $YBa_2 Cu_3 O_{6.999} $ single crystals between 40 K and 150 K and in fields up to 10 T applied along the c-axis. The isothermal magnetostriction, which probes the pressure dependence of the magnetization, is nearly reversible above 55 K, which allows a thermodynamic analysis of the data. These data are used to derive the uniaxial pressure dependences of $T_c $, the thermodynamical critical field $H_c^o $and the electronic specific heat coefficient$\gamma _{electronic} $. The data also provide a unambiguous measure of the broadened$H_{c2} $, which shows excellent 3D-XY scaling. Below 55 K and above 6-8 T, the magnetostriction becomes irreversible due to increased flux pinning at the Bose-glass to vortex-glass transition of the vortex matter. In contrast to the magnetization, which shows the typical monotonic peak effect, the irreversible magnetostriction exhibits reproducible fine structure within the transition region. This may be due to nucleation of large vortex domains in the crystal and points to a first-order phase transition. [Preview Abstract] |
Wednesday, March 23, 2005 1:39PM - 1:51PM |
P13.00013: Superconductors in a Strong Low-Frequency ac Electric Field R. Tao The electric-field induced ball formation has been observed for high temperature superconducting particles, MgB$_2$ powder, and low temperature superconducting particles in a low frequency ac electric field. Different from the situation with a static electric field, the superconducting particles in an ac field first form chains along the field direction if the electric field is below a critical value $E_{c1} $. As soon as the field exceeds $E_{c1}$, the chains are broken and the particles aggregate into balls. The experiment has found that $E_{c1}$ is a function of frequency $\omega$. To understand the experimental results, we consider a bulk superconductor in an ac field. The electric field is along the x direction and the bulk superconductor has its surface at $x=0$, perpendicular to the field and is located at $x\ge 0$. The electric field penetrates into the superconductor: for $x>0$, ${\vec E}(x)={\vec e_x}E \exp(-x/l_s)\cos(\omega t)$, where $l_s$ is the electric-field's penetration depth and $E$ is the electric field at the surface of $x=0$. With this model, we have found that if the electric field is strong enough, Cooper pairs near the surface are depleted and a positive surface energy is produced. This induced surface energy is responsible for the formation of superconducting balls. The critical electric field to produce the positive surface energy $E_{c1}$ is found to be related to the binding energy of a Cooper pair$\Delta(T)=2\epsilon_f-\epsilon$ and the frequency $\omega$. As $\omega$ increases, $E_{c1}$ goes up, too. A comparison between the theory and experimental results will also be made. [Preview Abstract] |
Wednesday, March 23, 2005 1:51PM - 2:03PM |
P13.00014: Tuning the Insulator-Superconductor Transition in Ultrathin Films By Use of the Electric-Field Effect Kevin A. Parendo, K. H. Sarwa B. Tan, Allen M. Goldman A 10 {\AA} thick film of amorphous bismuth has been prepared in an electric-field effect device geometry. Its low temperature electrical properties have been continuously tuned from weakly insulating to fully superconducting by increasing the gate voltage. The systematics of this insulator-superconductor transition will be discussed in the context of a quantum phase transition. This work is supported in part by the National Science Foundation under grant NSF/DMR-0138209. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700