Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session X34: Superconductivity: Magnetic Field Effects |
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Sponsoring Units: DCMP Chair: Milind Kunchur, University of South Carolina Room: 404 |
Thursday, March 19, 2009 2:30PM - 2:42PM |
X34.00001: Ballistic acceleration phase of a supercurrent Milind N. Kunchur, Gabriel Saracila One of the primitive but elusive current-voltage (I-V) responses of a superconductor is when its supercurrent grows steadily after a voltage is first applied, as per the first London equation. Because this phase lasts for a relatively short duration---until dissipative processes set in---it is difficult to conduct a correlated time-domain I-V measurement of it. The present work employed a measurement system that can simultaneously track and correlate I(t) and V(t) with sub-nanosecond timing accuracy, resulting in a clear time-domain measurement of this transient phase where the quantum system displays a Newtonian like response. The highly controlled technique used here measures the near equilibrium response and should be distinguished from an impulse response measurement, which may probe non-equilibrium processes. The present technique should be of value for the controlled investigation of other types of time-dependent and non-equilibrium phenomena. [Preview Abstract] |
Thursday, March 19, 2009 2:42PM - 2:54PM |
X34.00002: Spatial distribution of internal magnetic field in Hight - $T_c$ superconductors with pancake vortices W.P. Halperin, S. Mukhopadhyay, A.M. Mounce, S. Oh, A.P. Reyes, P. Kuhns, H. Takagi, S. Uchida We report here $^{17}$O $T_1$ measurements in single crystals of slightly overdoped ($T_C = 82$ K) Bi2212 at 5 K, in magnetic fields from 15 -- 30 T. In previous work the internal magnetic field distribution in YBCO aligned powders at high magnetic fields has been probed by NMR imaging experiments~[1]. Our results for single crystals of the highly anisotropic superconductor, BSCCO, are remarkably different, and is inconsistent with present theoretical predictions. At 5 K the system is in a 2-D vortex solid phase~[2]. We conclude that the magnetic field distribution for 2-D vortices in the presence of interlayer magnetic and Josephson coupling is radically different from a London vortex lattice.\\[0pt] [1]V.~F.~Mitrovi\ifmmode~\acute{c}\else \'{c}\fi{} \textit {et.al.}, Nature \textbf{413}, 501 (2001). \\[0pt] [2]Bo Chen \textit {et.al.}, Nature Physics \textbf{3}, 239 (2007). [Preview Abstract] |
Thursday, March 19, 2009 2:54PM - 3:06PM |
X34.00003: Intermittent propagation of magnetic flux in superconductors. Vitaliy Yurchenko, Atle Jorstad Qviller, Iouri Galperine, J{\O}rn Bindslev Hansen, Peter Mozhaev, Tom Henning Johansen Regular arrays of planar defects can be introduced in superconducting YBa2Cu3O7 thin films by depositing them on tilted substrates. This results in anisotropy of critical currents flowing in the plane of the film. At optimal tilt angles a substantial increase of the critical currents flowing in both directions, i.e. along and across the planar defects, has been observed. However, the artificially introduced defects also have a dramatic effect on dynamics of the flux propagation: it becomes intermittent. Previously we observed intermittent flux penetration in MgB2 thin films with thermo-magnetic instability, where such flux jumps trigger giant magnetic avalanches. In this report we present results of a real time magneto-optical visualization of the intermittent flux motion in YBCO and discuss possible consequences for its thermo-magnetic stability. [Preview Abstract] |
Thursday, March 19, 2009 3:06PM - 3:18PM |
X34.00004: Magnetic field-orientation independence of large basal-plane critical currents in RBCO films with correlated pinning nanostructure David Christen, Y.L. Zuev, S.H. Wee, A. Goyal, C. Cantoni, C. Tarantini, A. Gurevich, D. Larbalestier It has been widely confirmed that self-assembled columnar stacks of second-phase precipitates aligned near to the $c-$axis provide strong flux pinning in RBCO epitaxial films. Such growth-controlled nanostructures can be produced by at least two different deposition techniques and for several species of oxide precipitates. For many of these systems, the usual dependence of in-plane critical current densities, $J_{c}$, on field-orientation nearly vanishes at a specific temperature-dependent field, $B$*($T)$. The phenomenon can be described by a competition between intrinsic electronic anisotropy and orientation-dependent pinning. A simple model parameterizes the effect through the dependencies $H_{irr}(\theta )$ and the power-law decay exponent $\alpha (\theta )$, where $J_{c} \quad \propto $ $H^{-\alpha }$ in the intermediate field regime. Limits to and fundamental aspects of the model with respect to these parameters will be discussed. [Preview Abstract] |
Thursday, March 19, 2009 3:18PM - 3:30PM |
X34.00005: Angularly Dependent, Contact-free Current Density Measurements of YBCO Coated Conductor J.W. Sinclair, J.R. Thompson, D.K. Christen, Y. Zhang Studying the angular dependence of the current density $J$ gives insight into vortex pinning. We investigated a coated conductor of YBa$_{2}$Cu$_{3}$O$_{\sim 7}$ containing $c$-axis correlated defects (stacks of BaZrO$_{3}$ particles), striated into six strips to give a high aspect ratio. The current density was determined inductively from the magnetic moment $m\sim J$, using a SQUID magnetometer. The sample was mounted on a horizontal rotating platform to vary the angle $\theta $ of the sample with respect to the vertical applied magnetic field. The magnetometer allows us to measure both the longitudinal and transverse components of moment \textbf{m}($\theta )$, enabling calculation of the angular dependence of $J$. For a large range of applied magnetic fields at various temperatures, we found a pronounced peak in $J(\theta )$ at an angular value ($\theta _{peak})$ near the $c$-axis. We observed that, for a large range of applied magnetic fields, $\theta _{peak}$ linearly scales with 1/$h$, where $h$ = ($H$/$H_{c2})$ is the reduced field. Research sponsored by DOE, Division of Materials Sciences and Engineering, and Office of Electricity Delivery and Energy Reliability. [Preview Abstract] |
Thursday, March 19, 2009 3:30PM - 3:42PM |
X34.00006: Vortex States in Intrinsic Josephson Junctions of B$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ in High Parallel Magnetic Fields Jovan Mirkovic, Saito Takashi, Yuimaru Kubo, Itsuhiro Kakeya, Ahmed Oral, Takashi Yamamoto, Kazuo Kadowaki The $I_{c}$-axis resistivity measurements were performed in the vicinity of the \textit{ab}-plane in order to investigate the interaction between Josephson vortices (JVs) and pancake vortices (PVs) in B$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ mesoscopic single crystals. It was found that the vortex lock-in transition becomes considerably broad in high magnetic fields, while the angular dependence of resistance exhibits the sharp lock-in features in low magnetic field region. The magnetic field dependence of the resistance exhibits the non-monotonic behavior probing the different vortex phases in tilted magnetic fields. Sharp dips and steps in the $c$-axis resistance were observed accompanied by penetration of quantized pancake vortices by tilting external fields from the \textit{ab}-plane. [Preview Abstract] |
Thursday, March 19, 2009 3:42PM - 3:54PM |
X34.00007: Hole doping-induced evolution of self-organized bulk vortex structure in the high temperature YBa$_2$Cu$_3$O$_{7-\delta}$ superconductor Ahmad Mansour, Rongchao Ma, Mehmet Egilmez, Mohamed Saber, Isaac Fan, Kim Chow, Jan Jung We present systematic studies of the persistent current relaxation of 24 different oxygen contents of YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) as a function of oxygen defect concentration $\delta$. These studies allowed us to map out the ($\delta$,$\mu$) phase diagram of the vortex matter, where the exponent $\mu$ of the vortex structure was obtained using the scaling properties of the energy barrier against vortex motion. The reduction of the hole-doping level (an increase of $\delta$) of the material leads to a transformation of the vortex lattice into a glass and subsequently into a liquid phase. These vortex phases self-organize and produce relaxation plateaus in regions between step-like changes in the dependence of relaxation kinetics on hole doping, revealing the existence of a previously unknown correlation between the vortex structure and the hole-doping level in a cuprate superconductor, such as YBCO. [Preview Abstract] |
Thursday, March 19, 2009 3:54PM - 4:06PM |
X34.00008: Temperature Dependence of Flux Pinning Properties for Dilute Impurity Doped Y123 Single Crystals Yui Ishii Most of studies on pinning properties and relating vortex nature of the RE123 system were performed at high temperatures around 77 K, while extensive applications at low temperatures are also expected. However, both pinning properties and vortex states at low temperatures have not been well understood for RE123 crystals having intentionally introduced pinning sites. On the other hand, we have developed the chemical and versatile technique to introduce effective pinning site in the cuprates, that is dilute impurity doping for the target cation sites. In addition, compositional fluctuations of light rare earth (LRE) elements, which induce disorder transition of vortex system, are known to contribute enhanced pinning properties of LRE123. In this paper, we report that the changes of vortex state and $J_{c}$ characteristics of RE123 single crystals in $H$ // $c$ at low temperatures by precise control of cation compositions. Our result suggested that dilute impurity doping to Cu (in CuO-chain) or Ba is more effective to enhance pinning strength of Y123 than introduction of compositional fluctuation for Gd123 single crystals at low temperatures below 70 K. [Preview Abstract] |
Thursday, March 19, 2009 4:06PM - 4:18PM |
X34.00009: Hysteresis Effects in Ag-Doped Superconducting Y-Ba-Cu-O Atilgan Altinkok, Kivilcim Kilic, Atilla Kilic, Murat Olutas, Hakan Yetis Time and hysteresis effects have been studied by magneto-voltage ($V-H$ curves) measurements in Ag doped sample of YBa$_{2}$Cu$_{3}$O$_{7-x}$ (YBCO/Ag) as functions of transport current ($I)$, sweep rate of external magnetic field (d$H$/d$t)$ and temperature. Ag was added in the amount of 3{\%} of nominal composition of Cu in YBCO. It was observed that the dissipation in V-H curves does not change as dH/dt increases. This suggests that Ag doping destroys the weak-link structure along inter-grain boundaries and thus the vortices can find enough time to move in the sample irrespective of varying of external H. .The hysteresis effects in V-H curves ride on a background voltage at the temperatures near the $T_{c}$. In one hand, the background voltage of V-H curves decreases by taking low values as the temperature decreases, in the other hand, the hysteresis effects become more significant. It was observed that the evolution of V-H curves depends also on the magnitude of transport current. The increase in $I$ causes a considerable enhancement in background voltage in V-H curves. Similar measurements were repeated for YBCO sample without Ag for a comparison. Experimental observations between YBCO/Ag and YBCO establish that adding of Ag into the superconducting matrix causes the formation of easy metallic flow paths for vortices and thus easy distribution of vortices along grain boundaries. [Preview Abstract] |
Thursday, March 19, 2009 4:18PM - 4:30PM |
X34.00010: Effect of pseudo-gap state to the vortices in the high-Tc cuprate superconductors Masaru Kato, Satoshi Tomita The scanning tunneling spectroscopy (STS) experiments for high-Tc cuprate superconductors(SC) show the local density of states (LDOS) around a single vortex is different from that in a purely d-wave superconductor (dSC). Theoretically, in the dSC, there is a quasi-particle bound states peak around the vortex core, which is similar to that for an s-wave superconductor. This discrepancy means the superconductivity in high-Tc superconductors is simple dSC. In the high-Tc SC, dSC always coexists with unknown pseudo-gap state. Recent angle-resolved photoemission spectroscopy experiments show the energy gaps of pseudo-gap states and d-wave superconductivity is different. In this study, we show that the quasi-particle structure is reproducible theoretically, if we take into account the effect of the pseudo-gap state. We consider d-spin density wave ( dSDW) state as the pseudo-gap state. We derived the Bogoliubov-de Gennes equation for the coexistence state with dSC and dSDW. And solving it numerically, we obtained the LDOS, which reproduce the experimental LDOS, qualitatively. This result shows that the pseudo-gap state affect the dSC, especially the bound state in the vortex core, in high-Tc SC's. [Preview Abstract] |
Thursday, March 19, 2009 4:30PM - 4:42PM |
X34.00011: Magnetic field dependence of quasiparticle recombination times in superconducting NbTiN at low laser fluence Xiaoxiang Xi, Jungseek Hwang, David Reitze, Christopher Stanton, David Tanner, Lawrence Carr We use a pump-probe technique to study the temperature and field dependent quasiparticle recombination process in superconducting Nb$_{0.5}$Ti$_{0.5}$N in the low laser fluence regime. The sample was excited by a picosecond near-infrared Ti:Sapphire laser pulses and probed with subnanosecond infrared synchrotron pulses at the National Synchrotron Light Source, Brookhaven National Laboratory. Time-resolved photoinduced transmission data were obtained as a function of temperature (2.2-10 K) and magnetic field (0-10 T), from which we calculated the quasiparticle effective lifetime. Both temperature and field dependence were observed, with the effective lifetime increasing as the field became stronger. A model of this phenomenon will be discussed. [Preview Abstract] |
Thursday, March 19, 2009 4:42PM - 4:54PM |
X34.00012: Spin and charge dynamics of photogenerated quasiparticles in superconducting NbTiN Jungseek Hwang, Xiaoxiang Xi, David Reitze, Christopher Stanton, David Tanner, Larry Carr We use time-resolved broadband far-infrared spectroscopy to study the dynamics of photogenerated quasiparticles in superconducting Nb$_{0.5}$Ti$_{0.5}$N. The pump-probe measurements used picosecond pulses from a near-infrared Ti:sapphire laser as a pump and subnanosecond pulses of infrared synchrotron radiation as the probe. Measurements were done as a function of fluence and applied magnetic field. The measurements were performed at the National Synchrotron Light Source, Brookhaven National Laboratory.; We report the photoinduced far-infrared transmission at 2 K for two different field orientations: perpendicular and parallel to the Nb$_{0.5} $Ti$_{0.5}$N film. The decay does not follow a simple exponential. We observed a linear scaling behavior between the number of photoexcited quasiparcles and the relaxation rate. In addition, the relaxation rate decreases linearly with magnetic field, attributed to spin polarization of the quasiparticles in the field. [Preview Abstract] |
Thursday, March 19, 2009 4:54PM - 5:06PM |
X34.00013: Quantum Oscillations from Fermi Arcs Tamar Pereg-Barnea, Gil Refael, Marcel Franz, Heidi Weber, Babak Seradjeh Recent experiments[1] in a variety of High Tc superconductors revel 1/B oscillations in the vortex-liquid state. The period of oscillations in underdoped samples is short and can be translated, via the Onsager relation to an area in k-space which makes up a few percents of the Brillouin zone. Quantum oscillations are usually thought of as arising from closed orbits in momentum space along the Fermi surface and are used to measure the Fermi vector. Thus, the observation of quantum oscillations in the cuprates seems to be at odds with the observation of Fermi arcs in ARPES experiments[2] due to their fragmented Fermi surface topology. In this talk we show that quantum oscillations can arise from a partially gapped Fermi surface. We adopt a phenomenological model of arcs which terminate at a regime with a superconducting gap of d-wave symmetry to describe the pseudo gap phase. Without invoking any additional order, quantization of energy is found well below the gap maximum. Semiclassically the quantization condition arises from closed orbits in real-space. When translated to momentum space, the area enclosed by the orbits is much smaller than that of the full Fermi surface. [1]N. Doiron-Leyaraud et al. nature 447, 565 (2007) [2]Kanigel et al. Nature Physics 2 447 (2006) [Preview Abstract] |
Thursday, March 19, 2009 5:06PM - 5:18PM |
X34.00014: Giant Thermomagnetic Effects in High-T$_c$ Cuprates: Fermi Liquid vs Vortex Liquid Andrei Sergeev, Michael Reizer, Vladimir Mitin We developed a gauge-invariant formulation of the thermomagnetic effects [1] and prove that the thermomagnetic coefficients in the Fermi liquid with particle and hole excitations are always proportional to the square of the particle-hole asymmetry. Therefore, thermomagnetic effects in the Fermi liquid are always small. Vortices are topological excitations which are completely different from particle-hole excitations. Thermomagnetic transport in the vortex liquid is widely described in terms of the ``transport entropy,'' S$_d$. According to the current views, the main contribution to S$_d$ originates from the electromagnetic energy of superconducting currents circulating around vortex cores. However, this concept strongly contradicts to the London postulate [2]. We revise the theory and show that the transport entropy is, in fact, the entropy of normal electrons in vortex cores determined with respect to the superconducting (or partly superconducting, if cores overlap) background [2]. Only in this form the theory becomes simultaneously consistent with the London postulate and Onsager principle. The theory naturally explains the observed temperature dependence of S$_d$. 1. A. Sergeev et al., Phys. Rev. B 77 064501 (2008). 2. A. Sergeev et al., arXiv:0807.0450. [Preview Abstract] |
Thursday, March 19, 2009 5:18PM - 5:30PM |
X34.00015: Absence of superfluid density anomaly at 0.6 K in superconducting PrOs$_4$Sb$_{12}$ D. E. MacLaughlin, Lei Shu, A. D. Hillier, Y. Aoki, D. Kikuchi, H. Sato, Y. Tunashima, H. Sugawara, T. A. Sayles, M. B. Maple The lower critical field $H_{c1}(T)$ in PrOs$_{4}$Sb$_{12}$ exhibits an enhancement below $T\mbox{*} = 0.6$ K [1], suggesting a transition between two superconducting phases. Small anomalies are observed at $T\mbox{*}$ in some other properties but not in the specific heat. We have carried out muon spin rotation experiments in the vortex state for fields just above $H_{c1}$. The muon spin relaxation rate, which is proportional to the rms width~$\delta B_{\rm rms}$ of the vortex-state field distribution, also shows no anomaly at $T\mbox{*}$. In a simple picture both $H_{c1}$ and $\delta B_{\rm rms}$ are proportional to the superfluid density~$\rho_s$, i.e., $\delta B_{\rm rms} \propto H_{c1}$ contrary to observation. Our results suggest that the $H_{c1}$ anomaly is due to flux pinning effects rather than a thermodynamic phase transition.\\ \frenchspacing [1] T. Cichorek et al., Phys. Rev. Lett. {\bf94}, 107002 (2005). [Preview Abstract] |
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