Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session T34: Superconductivity: Vortex Statics and Dynamics |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Wai Kwok, Argonne National Laboratory Room: 404 |
Wednesday, March 18, 2009 2:30PM - 2:42PM |
T34.00001: Manipulation of interlayer ``kinks'' in individual vortices in underdoped YBa$_{2}$Cu$_{3}$O$_{6+x}$ Ophir Auslaender, Lan Luan, Douglas Bonn, Ruixing Liang, Walter Hardy, Kathryn Moler We use magnetic force microscopy (MFM) to both image and manipulate individual vortex lines threading single crystalline YBa$_{2}$Cu$_{3}$O$_{6+x}$, a layered superconductor. We find that when we pull the top of a pinned vortex, it may not tilt smoothly, as in more isotropic superconductors [1]. In some cases, we observe a vortex breaking into discrete segments that can be described as short stacks of two-dimensional pancake vortices. This is similar to the ``kinked'' structure proposed by Benkraouda and Clem [2]. Quantitative analysis gives an estimate of the pinning force and the coupling between the pancake stacks. Our measurements highlight the discrete nature of stacks of pancake vortices in layered superconductors. \begin{enumerate} \item O. M. Auslaender, Lan Luan, E. W. J. Straver, J. E. Hoffman, N. C. Koshnick, E. Zeldov, D. A. Bonn, Ruixing Liang, W. N. Hardy and K. A. Moler, Nat. Phys., in press (2008). \item M. Benkraouda and J.R. Clem, Phys. Rev. B, \textbf{53}, 438 (1996). \end{enumerate} [Preview Abstract] |
Wednesday, March 18, 2009 2:42PM - 2:54PM |
T34.00002: Moving flux quanta, driven by high density currents in low-impurity samples of V$_{3}$Si, LuNi$_{2}$B$_{2}$C, and NbSe$_{2}$ : Ordered flow and core-size effects S. Moraes, R.P. Khadka, A.A. Gapud, A.P. Reyes, L.L. Lumata, J.R. Thompson, D.K. Christen There is incomplete understanding about the dissipative motion of magnetic flux quanta in type II superconductors, especially under large Lorentz forces. This is mainly due to the technical challenges involving the application of large electric currents and the rarity of samples wherein flux quanta are relatively free to move -- i.e., samples with weak ``pinning'' -- which commonly make it impossible to observe dynamic phases. Progress towards overcoming these challenges is described, along with clear observations of flux-flow phases in high-quality samples of three ``low $T_{c}$'' superconductors, V$_{3}$Si, LuNi$_{2}$B$_{2}$C, and NbSe$_{2}$. Evidence of the rarely observed Bardeen-Stephen flux flow -- a highly ordered, collective motion of flux quanta in near-unison -- will be presented. These observations have also enabled an examination of a model by Kogan and Zelezhina [Kogan and Zhelezina, \textit{Phys Rev B} \textbf{71}, 134505 (2005)] predicting the effect of a field-dependent flux \textit{core size }on ordered flux flow, as will be discussed. \textit{Funded by the U. of South Alabama and by the Research Corporation. We thank P. Canfield and L. Delong for samples and helpful discussions. } [Preview Abstract] |
Wednesday, March 18, 2009 2:54PM - 3:06PM |
T34.00003: Lattice slips in slow moving magnetic vortex lattices in NbSe$_2$ Michael Dreyer, Jonghee Lee, Hui Wang, Barry Barker We studied vortex matter in NbSe$_2$, a type II superconductor, at magnetic fields of 0.25 - 0.75 T and temperatures of 4.2 K. At these fields the vortices form an Abrikosov lattice. Due to a small residual resistance in our superconducting magnet the applied magnetic field slowly decayed, driving the vortex lattice. The velocity was low enough to allow acquiring highly resolved time series using a low temperature scanning tunneling microscopy (STM). From the images we where able to extract local variations in the lattice constant as well as time series of the average vortex position (path) and velocity. A more subtle observation where closed loops on the order of nanometer in diameter in the averaged path of the vortices. Although this was observed in more than one data series it was at first dismissed as an artifact. Later, similar loops where observed in simulations. The loops occurred when a lattice dislocation traveled through the vortex lattice. This observation, unexpected in the simulation, gave new credence to the previously observed loops in the data. Since the vortex lattice in NbSe$_2$ was in the Bragg glass phase we would expect locally ordered domains of several micrometer in diameter. It is conceivable that lattice slips occur at the domain boundaries and lead to the observed loops. The observation and simulation will be compared in detail. We would like to thank Eva Andrej and Helmut Berger for providing NbSe$_2$ samples. [Preview Abstract] |
Wednesday, March 18, 2009 3:06PM - 3:18PM |
T34.00004: Vortex interactions in superconducting weak-pinning channel ratchets K. Yu, T.W. Heitmann, C. Song, M.P. DeFeo, B.L.T. Plourde, M.B.S. Hesselberth, P.H. Kes We report on measurements of vortex ratchets fabricated from weak-pinning superconducting a-NbGe channels bounded by strong-pinning NbN banks with asymmetric sawtooth edges. This configuration for the vortex confinement potential results in an asymmetric response for the vortex dynamics in the channels. Interactions between vortices, both within a channel and between neighboring channels, have a substantial influence on the ratchet behavior, including certain regimes where the net vortex motion through the ratchet reverses direction. We discuss our measurements in terms of a model for describing the vortex interactions in the ratchet channels. [Preview Abstract] |
Wednesday, March 18, 2009 3:18PM - 3:30PM |
T34.00005: Flux-flow noise in a superconducting Corbino vortex ratchet channel T.W. Heitmann, K. Yu, C. Song, M.P. DeFeo, B.L.T. Plourde, M.B.S. Hesselberth, P.H. Kes We report measurements of vortex dynamics in a single nanofabricated weak-pinning ratchet channel of a-NbGe with strong-pinning NbN channel edges. The channel is arranged in a circle on a Corbino disk geometry with a radial bias current, thus eliminating the influence of edge barriers to vortex entry on the dynamics and resulting in closed circular orbits for the vortices. An asymmetric sawtooth shape for the channel walls produces a ratchet effect, resulting in large differences in the critical current for the two flow directions. The SQUID picovoltmeter that we have developed for resolving the flux-flow voltage provides a low noise floor such that we can resolve structure in the flux-flow noise, with substantial asymmetries for vortex motion in the two directions through the ratchet channel. [Preview Abstract] |
Wednesday, March 18, 2009 3:30PM - 3:42PM |
T34.00006: Unconventional Vortex Dynamics in Mesoscopic Superconducting Corbino Disks Vyacheslav R. Misko, Nansheng Lin, Francois Peeters The dynamics of vortex {\it shells}, driven by an external current $I_0$, is studied in a Corbino setup, in mesoscopic disks with two to six shells. The transition from a rigid-body rotation to a separate rotation of shells is analyzed as a function of $I_0$ and temperature $T$. The critical current $I_c$ has a remarkable nonmonotonous dependence on the applied magnetic field due to a dynamically induced structural transition [1]. Thermally activated externally driven flux motion in a disk with pinning centers explains the dynamically induced two-step melting transition observed in experiment [2]. We analyze different scenarios of the current- driven angular melting of shell configurations determined by the interplay between the gradient Lorentz force and the (in) commensurability between the number of vortices in adjacent shells. The inter- and intra-shell defects lead to unconventional dynamics of vortex shells [3]. [1] V.R. Misko and F.M. Peeters, Phys. Rev. B {\bf 74}, 174507 (2006). [2] D. Lopez et al., Phys. Rev. Lett. {\bf 82}, 1277 (1999). [3] V.R. Misko, N. Lin, and F.M. Peeters, unpublished (2008). [Preview Abstract] |
Wednesday, March 18, 2009 3:42PM - 3:54PM |
T34.00007: Vortex dynamics simulation in high-T$_{c}$ superconductors with planar pinning arrays coexisting with point pinning sites Hidehiro Asai, Satoshi Watanabe The enhancement of critical currents $J_{c }$ by introducing artificial pinning sites is key issue in the application of high-T$_{c}$ superconductors. Planar defects such as twin boundary are well known as the possible candidates for tangible pinning sites. Recently, the improvement of $J_{c }$ has been reported in the samples having high-density planar defects. However, the pinning characteristics of planar defects, especially the change of the pinning efficiency in the presence of point pinning, are still unclear. We have studied the dynamics of vortices interacting with both planar pinning and point pinning sites using molecular dynamics simulation. We have fixed the pinning strength of planar pinning, and calculated the $J_{c}$ as a function of the point pinning strength $f_{p}$. With increasing $f_{p}$, $J_{c}$ changes from $J_{c}\mathbin{\lower.3ex\hbox{$\buildrel{\mathbin{\buildrel\scriptstyle.\hfill\over {\smash{\scriptstyle=}\vphantom{_{\scriptstyle x}}}}}\over {\hfill\smash{\scriptstyle\cdot}}$}} J_{pl}$ ($J_{pl}$: $J_{c}$ obtained in the system without point pinning) to $J_{c}\mathbin{\lower.3ex\hbox{$\buildrel{\mathbin{\buildrel\scriptstyle.\hfill\over {\smash{\scriptstyle=}\vphantom{_{\scriptstyle x}}}}}\over {\hfill\smash{\scriptstyle\cdot}}$}} J_{p}+\alpha $, ($J_{p}$: $J_{c}$ obtained in the system without planar pinning) and then to $J_{c}\mathbin{\lower.3ex\hbox{$\buildrel{\mathbin{\buildrel\scriptstyle.\hfill\over {\smash{\scriptstyle=}\vphantom{_{\scriptstyle x}}}}}\over {\hfill\smash{\scriptstyle\cdot}}$}} J_{p}$. This behavior corresponds to the appearance of the kink structure and the drastic change of $c$-axis correlation function of the vortices. We have also performed the similar calculation with different anisotropy parameters and observed that the stiffness of vortex line changes the $J_{c}$ behavior as a function of $f_{p}$. [Preview Abstract] |
Wednesday, March 18, 2009 3:54PM - 4:06PM |
T34.00008: The Peak Effect anomaly in low and high T$_{C}$ superconductors: stable and metaestables vortex lattice configurations Victoria Bekeris, Gabriela Pasquini, Diego Perez Daroca, Claudio Chiliotte, Gustavo Lozano Competing interactions in the vortex lattice (VL) of type II superconductors give rise to an order-disorder transition known as Peak Effect (PE) anomaly. The strong metastability related to the PE masks the stationary VL configurations (VLCs), both in low and in high T$_{C}$ superconductors. By means of linear \textit{ac} susceptibility experiments, that avoid VL reorganization, we explore quasi-static stable and metastable states, applying different shaking protocols before measurements. In low T$_{C }$ \textit{NbSe}$_{2}$ [1] crystals we identify T,H regions where stationary configurations are maximally ordered (Bragg Glass), fully disordered or where ordered and disordered stable phases coexist. In contrast, in high T$_{C}$ \textit{YBa}$_{2}$\textit{Cu}$_{3}O_{7-y}$ crystals, metaestability seems to dominate and different metaestable VLCs are accessed depending on the previous dynamic history, with no access to the lowest energy configuration. [1] G. Pasquini \textit{et al}. Phys. Rev. Lett. \textbf{100} 247003 (2008) [Preview Abstract] |
Wednesday, March 18, 2009 4:06PM - 4:18PM |
T34.00009: Dynamics of Josephson vortices mediated with pancake vortices Kazuto Hirata, Shuuichi Ooi, Takashi Mochiku Josephson vortices (JVs) flow very fast with a velocity up to tenth of the light velocity in Bi-2212. If the motion of JVs can be controlled, high-speed signal processing will be achieved. We have tried to apply symmetrical pinning centers in space and time-asymmetric input signals for controlling a dynamical behavior of JVs in Bi-2212. We have shown the periodic oscillations in JV flow-resistance against magnetic field in Bi-2212 (PRL89(2002)247002), which persist in wide range of temperature and magnetic field. Introducing pancake vortices (PVs) into JV system in Bi-2212, the JV flow-resistance abruptly decreases, because the JVs interact with the PVs strongly and the PVs are pinned in intrinsically existed pinning centers in Bi-2212. However, when the input current (signal) with two frequencies is applied, a finite dc voltage can be obtained even without the flow-resistance. This leads to a rectification effect in the JVs' motion by the PVs. The nonlinearity in I-V characteristics induces the rectification effect with time-asymmetric input signals of two harmonics. This may open a new application of HTSCs. [Preview Abstract] |
Wednesday, March 18, 2009 4:18PM - 4:30PM |
T34.00010: Exploring the Aging Effects in Pinned Vortex Lattices in Nb using Neutron Reflectometry Xi Wang, Helen Hanson, Xinsheng Ling, Brian Maranville We report the first experiment using neutron reflectometry to explore the aging effects in pinned vortex lattices in Nb. A striking prediction of the Bragg glass model is the existence of a pinned elastic Bragg glass solid matter in the vortex state of weakly disordered type-II superconductors. According to this model, the system is pinned in the random-manifold regime with local metastable states, yet at large length scale, the system remains elastic. This seemingly paradoxical property is predicted to lead to novel aging dynamics. This work was supported by a grant from DOE-BES. The experiments were carried out at NG-1- Advanced Neutron Diffractometer facility at NIST NCNR. [Preview Abstract] |
Wednesday, March 18, 2009 4:30PM - 4:42PM |
T34.00011: Measurement of Vortex Bragg Glass Structure Factor in Nb using Neutron Reflectometry Helen Hanson, Xi Wang, Xinsheng Ling, Brian Maranville One of the key predictions in the Bragg Glass model of weakly pinned vortex lattices is a power-law structure factor similar to that of a 2D solid. Previous attempts using SANS in Nb and HTSC have provided results that are consistent with the Bragg Glass model. Here we report the first experiment using neutron reflectometry to resolve S(Q) in a Nb single crystal. This work was supported by a grant from DOE-BES. The experiments were carried out at NG-1- Advanced Neutron Diffractometer facility at NIST NCNR. [Preview Abstract] |
Wednesday, March 18, 2009 4:42PM - 4:54PM |
T34.00012: Small-angle neutron scattering study of vortex matter in superconducting Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$ M. R. Eskildsen, T. Blasius, A. I. Goldman, J. M. Densmore, C. D. Dewhurst, N. Ni, A. Kreyssig, S. L. Bud'ko, P. C. Canfield We present small-angle neutron scattering studies of the superconducting vortices Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$. At all fields measured a ring of scattering was observed, indicating a highly disordered vortex configuration, and no discernable rocking curve could be measured. The field dependence of the magnitude of the scattering vector indicates vortex lattice domains of (distorted) hexagonal symmetry. An analysis of the scattered intensity due to the vortices shows a rapid decrease with increasing applied magnetic field, significantly exceeding what would be expected based on estimates of the upper critical field. These results are consistent with the existence of a vortex glass or Bragg glass phase in Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$. [Preview Abstract] |
Wednesday, March 18, 2009 4:54PM - 5:06PM |
T34.00013: Pauli Paramagnetic Effects in the Mixed State of CeCoIn$_5$ Revealed by Small Angle Neutron Scattering P. Das, M.R. Eskildsen, L. DeBeer-Schmitt, J.S. White, E.M. Forgan, A.D. Bianchi, M. Kenzelmann, J.L. Gavilano, M. Zolliker, S. Gerber, J. Mesot, C. Wang, E.D. Bauer, J.L. Sarrao, C. Petrovi\'{c} We report on extensive small-angle neutron scattering measurements on the vortex lattice (VL) in the mixed state of CeCoIn$_5$ with the magnetic field ($H$) both parallel and perpendicular to the $c$-axis. We obtain the $H$- and temperature ($T$)-dependence of the form factor ($|F|^2$) - a measure of the field contrast in the mixed state. At low $T$, competition between Pauli paramagnetism and the antiparallel spin alignment of $d$-wave pairing gives ``magnetized" VL cores, causing $|F|^2$ to increase with $H$ [L. DeBeer-Schmitt {\em et al.}, Phys. Rev. Lett. {\bf 99}, 167001 (2007); A.D. Bianchi {\em et al.}, Science {\bf 319}, 177 (2008)]. However, $|F|^2$ falls again near to $H_{c2}$; the fall-off extends outside the proposed FFLO region and is believed to arise from expansion of the magnetized cores. This core expansion may also explain the sequence of VL phase transitions observed in this material. At higher $T$, we observe a crossover towards more conventional behavior. [Preview Abstract] |
Wednesday, March 18, 2009 5:06PM - 5:18PM |
T34.00014: Vortex phase diagram in weakly pinned Rh17S15 S. Ramakrishnan, H.R. Naren, Arumugam Tamizhavel, Arun Grover A vortex phase diagram of the strongly correlated superconductor Rh$_{17}$S$_{15}$ has been constructed via exploration of the anomalous variations in critical current density extracted from ac and dc magnetization measurements. The iso-field in-phase ac susceptiblity data reveal the presence of multiple steps at different fields. The dc magnetisation hysteresis loops show the presence of a very broad fishtail commencing deep inside the mixed state and lasting upto H$_{c2}$ . We have also analysed the scan rate dependence of the hysteresis width in the vibrating sample magnetometer data with a view to distinguish between the different possible order-disorder transformations in the flux-line lattice. [Preview Abstract] |
Wednesday, March 18, 2009 5:18PM - 5:30PM |
T34.00015: ABSTRACT WITHDRAWN |
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