Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session A38: Superconductivity-Vortex Matter |
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Sponsoring Units: DCMP Chair: Wai Kwok, Argonne National Laboratory Room: Baltimore Convention Center 341 |
Monday, March 13, 2006 8:00AM - 8:12AM |
A38.00001: Josephson-vortex states in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+y}$ Kazuto Hirata, Shuuichi Ooi, Takashi Mochiku Josephson-vortex (JV) states have been studied by measuring the flow resistance in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+y}$ (Bi-2212) as a function of the parallel magnetic field with the current along the $c$-axis. From the periodic oscillations, we can assign the three-dimensionally long-range-ordered state (3DLOS) of JVs (PRL\textbf{89}, 247002(2002), Physica \textbf{C412-414}, 454(2004)). The lower and upper boundaries of 3DLOS were determined from the magnetic field of beginning and stopping in the oscillations, respectively. From the flow resistance and the $I-V$ characteristics measurements crossing the upper boundary, we suggest that the JVs are in ordered state in \textit{in-plane}, but have less ordering along the $c$-axis. This JV state may correspond to the 2D-quasi-long-range ordered state, proposed by Hu{\&}Tachiki (PRB\textbf{70}, 064506(2004)). [Preview Abstract] |
Monday, March 13, 2006 8:12AM - 8:24AM |
A38.00002: Vortex phase diagram of nearly stoichiometric Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ single crystal Noriko Chikumoto There have been a large number of reports on the vortex phase diagram of Bi2212. However, the Bi2212 crystals used for these studies mostly have Bi-rich composition, with typically Bi : Sr = 2.1 : 1.9. Recently, Eisaki {\it et al.} [1] reported that $T_c$ in Bi2212 single crystal is largely depressed by the cation disorder at the Sr-site, typically the substitution of Sr-site by Bi$^{3+}$. In the present study, we found that the Bi-Sr substitution also depress the vortex pinning. We have successfully grown Bi2212 single crystals with Bi : Sr ratio very close to 2 : 2. It showed very high critical current density, $2 ¥times 10^6$ A/cm$^2$, at 20K, and reduced reversible region ($J_c$ = 0 region) in the magnetic phase diagram. We also show the dependence of the irreversibility field on the cation nonstoichiometry. The author thanks K. Furusawa, H. Eisaki and Y. Nakayama for growing Bi2212 single crystals. [Preview Abstract] |
Monday, March 13, 2006 8:24AM - 8:36AM |
A38.00003: Melting of vortex solid phase in irradiated Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ single crystals in tilted magnetic fields Jovan Mirkovic, Sergey Savel`ev, Hirokazu Sato, Takashi Yamamoto, Itsuhiro Kakeya, Franco Nori, Kazuo Kadowaki The boundary between the vortex-solid and the vortex-liquid in $H_{c} - H_{ab}$ phase plane for irradiated Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$single crystals is studied by measuring the local ac-magnetic permeability by using the miniature coils in tilted magnetic fields. It was found that the $c$-axis magnetic field component at the phase transition decreases linearly when increasing the in-plane magnetic field at high temperatures even in a wider angular range than in pristine samples. At lower temperatures, this linear decrease transforms to a concave (hyperbolic-like) curve that differs even stronger from the usual elliptical phase boundary derived from Ginzburg-Landau theory. A theoretical approach to this challenging problem is discussed. [Preview Abstract] |
Monday, March 13, 2006 8:36AM - 8:48AM |
A38.00004: Field dependence of the lock-in transition of Josephson vortex in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ mesoscopic crystals Itsuhiro Kakeya, Yuimaru Kubo, Masashi Kohri, Takashi Yamamoto, Kazuo Kadowaki We have investigated vortex states in magnetic fields close to the $ab$-plane of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) by means of the $c$-axis resistivity $\rho_c$ in Bi2212 mesoscopic crystals fabricated by the FIB technique. When magnetic field $H \leq$ 1T was tilted from the $ab$-plane at $T=60$ K, a sharp drop in $\rho_c$ was observed at an angle $\theta_{th}$ ($\theta=0$ for ${\bf H} \parallel ab$-plane) depending on the field (typically $\theta_{th}$=0.5 deg. for $H=$1T). $\rho_c$ below $\theta_{th}$ does not depend on angle and is almost proportional to $H$, suggesting $\rho_c$ being Josephson vortex (JV) flow resistivity. Above $\theta_{th}$, it is considered that the JV flow is strongly impeded by pancake vortices (PVs), which attract with JVs and do not flow by the $c$-axis current, resulting in $\rho_c \approx 0$. Moreover, the penetration field of PVs $H\sin\theta_{th}$ decreases with increasing $H$. This is considered to be yielded by decrease of the line energy of pancake stacks due to the formation of the crossing lattice (CL). Therefore, the drop in $\rho_c$ corresponds to the transition from the lock-in (LI) state to the CL state. At high magnetic fields, the decrease in $\rho_c$ is broadened and has a shoulder structure. These results suggest that other vortex states between the LI and CL states emerge with increasing magnetic field and have intermediate JV viscosity. The expected vortex structures will be argued. [Preview Abstract] |
Monday, March 13, 2006 8:48AM - 9:00AM |
A38.00005: Vortex phase diagram from $^{17}$O NMR study in single crystal BSCCO Bo Chen, William Halperin One of the most fascinating aspects of high temperature superconductors is the extreme anisotropy and the effect this has on the properties of vortices. $_{ }$ At sufficiently high magnetic field it is expected that vortices are two dimensional and the melting transition temperature tends to a constant value, independent of field. For the most anisotropic materials such as Bi$_{2}$Sr$_{2}$Ca$_{1}$Cu$_{2}$O$_{8+\delta }$ such fields are attainable allowing almost complete decoupling of the two dimensional vortex pancakes from each other along the direction of the anisotropy axis. In our work the vortex melting phase diagram for single crystals of Bi$_{2}$Sr$_{2}$Ca$_{1}$Cu$_{2}$O$_{8+\delta }$ have been determined from $^{17}$O NMR up to 22 Tesla and can be related to results at low field for the more strongly coupled three dimensional case that has been extensively studied by transport and magnetization methods. Additionally, an abrupt change in vortex structure, seemingly an order-disorder transition, was found between 5 and 8 Tesla, below 10 K. [Preview Abstract] |
Monday, March 13, 2006 9:00AM - 9:12AM |
A38.00006: Anomalous angular dependence of the $c$-axis resistivity in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ mesas Takashi Tachiki, L. Ozyuzer, C. Kurter, U. Welp, A. Koshelev, D. Hinks, K. Gray, W. Kwok, K. Kadowaki We study flux-flow properties of Josephson vortices in highly anisotropic high-$T_{c}$ superconductors. The flux-flow resistance in pristine and HgBr$_{2}$-intercalated Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ (BSCCO) single crystals was measured as a function of the angle between the \textit{ab}-plane and an applied magnetic field. These samples have a mesa structure with the in-plane area of 200 $\mu $m x 20 $\mu $m and consist of 50 -- 70 intrinsic junctions. For both pristine and intercalated BSCCO, a sharp resistance peak was observed within a threshold angle of a few degrees. However, while the angle decreases with increasing field for the pristine BSCCO, the intercalated BSCCO shows the opposite field dependence. We interpret this peak and its field dependence as an interplay between two effects: initial penetration of pancake vortices and extra damping of Josephson-vortex lattice induced by pancake vortices. [Preview Abstract] |
Monday, March 13, 2006 9:12AM - 9:24AM |
A38.00007: Thermal depinning and transverse-field tilting transitions in a planar vortex array pinned by a columnar defect Leo Radzihovsky I will discuss results on a thermal and a transverse magnetic field response of a vortex line array confined to a plane with a dilute concentration of columnar pins. As a function of temperature, for a magnetic field aligned with defects this system exhibits a one-dimensional analog of a roughening transition, with a low-temperature ``smooth'' phase corresponding to a vortex array pinned by the defects, and a high-temperature ``rough'' phase in which at long scales thermal fluctuations effectively average away pinning by the defects. In the low-T pinned phase, the vortex lattice tilt response to a transverse magnetic field proceeds via a soliton proliferation ``transition'', governed by an integrable sine-Hilbert equation. Combining the aforementioned roughenning transitition with this commensurate-incommensurate transition, I map out the transverse-field---temperature phase diagram for this system. [Preview Abstract] |
Monday, March 13, 2006 9:24AM - 9:36AM |
A38.00008: RF-induced flux lattice annealing (RIFLA) in the electron-doped superconductor Pr$_{1.85}$Ce$_{0.15}$CuO$_{4-y}$. W.G. Clark, Guoqing Wu, S.E. Brown, R.L. Greene, H. Balci A strained flux lattice (FL) in a superconductor (SC) can be annealed to a lower free energy by the RF-field used to generate an NMR spin-echo signal [W.G. Clark et al., J. Phys. IV Proceedings \textbf{9}, Pr10-49-52 (1999)]. Here, this effect is reported for the SC phase of Pr$_{1.85}$Ce$_{0.15}$CuO$_{4-y}$. The distorted FL is prepared by rotating the sample through a small angle in a magnetic field well below the transition temperature, which leaves the FL pinned in a non-equilibrium configuration. Then, the first spin echo has almost no amplitude. Subsequent echoes have a progressively larger amplitude until a final, steady value is reached. The interpretation is that shaking of the distorted vortex lattice by the RF pulses progressively anneals it to a lower free energy configuration. The corresponding change in the local field between the de-phasing and re-phasing pulse for each echo then reduces the height of the echo. [Preview Abstract] |
Monday, March 13, 2006 9:36AM - 9:48AM |
A38.00009: Ground state of interlayer Josephson vortex systems: General description based on energy landscape Yoshihiko Nonomura, Xiao Hu Although Josephson vortex systems have been intensively studied, their phase diagrams have not been established yet even in the ground state. In the present study, we draw the full energy landscape with respect to magnetic field and the displacement from aligned vortex lattices by neglecting the spatial variation in the amplitude of superconductivity order parameter and in the gauge field in the Lawrence-Doniach model. We find that the ground state changes continuously from the aligned lattice to sheared lattices, and then to rotated lattices as the magnetic field decreases, and that rotated lattices are characterized by multi-valley structures of the energy landscape. Owing to effects of the underlying layer structures, the rotated vortex lattices realized at the valleys of the energy landscape are distorted from the rigid ones expected from the picture based on the London model, and this distortion becomes weak as the magnetic field decreases. We would like to thank Dr.~A.~E.~Koshelev for sending his article prior to publication. [Preview Abstract] |
Monday, March 13, 2006 9:48AM - 10:00AM |
A38.00010: Vortex dynamics investigated using low temperature scanning tunneling microscope: collective motion and collective pinning of vortices in NbSe$_{2}$ Jonghee Lee, Wang Hui, Dan Sullivan, Michael Dreyer, Barry I. Barker, Pavel Shuk, Mark Higgins, Eva Y. Andrei We report the observation of the collective motion and the collective pinning of vortices of NbSe$_{2}$ under various magnetic fields and from $\sim $6 K to $\sim $2 K using scanning tunneling microscopy (STM). Scanning Tunneling Spectroscopic maps were taken continuously, providing ``movies'' of the vortex motion. Based on the analysis of this data, the speed of the collective motion of vortices was $\sim $1 pm/s. The vortices showed clear signs of weak collective flux pinning. We will quantify the collective transport behavior of vortices based on our STM measurements and compare with the pertinent theories as well as related measurements done by other groups. [Preview Abstract] |
Monday, March 13, 2006 10:00AM - 10:12AM |
A38.00011: Observation of the Signatures of Glassy Vortex Dynamics in 2$H$-NbSe$_{2 }$ Xu Du, Guohong Li, Eva Y. Andrei, Mark J. Higgins, Pavel Shuk, Martha Greenblatt Using time resolved transport measurements, we observed clear evidence of glassy dynamics in the current driven vortex system in clean, weak pinning 2$H$-NbSe$_{2 }$single crystals prepared by field cooling through the superconducting transition. Simple aging was observed by means of scaling over the waiting times between two consecutive current pulses. A memory function was defined to describe how the previous pulse is ``memorized'' when the system is probed by a second pulse. The complex behavior of the driven vortex system in the glassy state is well characterized by a simple picture of the time evolution of the glassy states in configuration space. Preliminary results on direct imaging of the current driven vortices using Hall probe microscopy will be discussed. [Preview Abstract] |
Monday, March 13, 2006 10:12AM - 10:24AM |
A38.00012: Thermodynamic Measurements at the Bragg Glass Transition in Nb N. D. Daniilidis, I. K. Dimitrov, V. Mitrovic, C. Elbaum, X. S. Ling We report measurements of mixed-state entropy changes and specific-heat on a Nb single crystal, in which previous neutron scattering studies showed that an order-disorder transition of the vortex lattice occurs at the peak effect (PE). Preliminary measurements of (dS/dH) as a function of field applied in the [111] direction reveal a sharp peak at the PE. This corresponds to a discontinuity in the entropy of the vortex system of order $\Delta $s = 2.7 k$_{B}$ per vortex per (111) Nb plane at 5.16 K. The entropy discontinuity is found to decrease and finally disappear as the multicritical$^{1}$ point is approached on increasing temperature. The behavior of S(H,T) in the vicinity of the PE shows hysteresis on increasing and decreasing field due to nonequilibrium magnetization effects. In specific heat measurements there is no sign of latent heat at the PE, indicating that the latent heat is very small in this system. $^{1}$ S. R. Park \textit{et al.} PRL \textbf{91} 167003 (2003). [Preview Abstract] |
Monday, March 13, 2006 10:24AM - 10:36AM |
A38.00013: Vortex chains decoration in anisotropic spin-triplet superconductor Sr$_{2}$RuO$_{4}$ Klaus Hasselbach, Voicu Dolocan, Ying Liu, Pascal Lejay, Dominique Mailly We study flux structures in single crystals of the anisotropic spin triplet superconductor Sr$_{2}$RuO$_{4}$ by scanning microSQUID microscopy$^{1}$. The appearance of vortex chains is noted as the applied field is tilted towards the inplane direction of the 3D superconductor. The vortex chains are easily turned in the ab plane by rotation of the inplane component of the applied magnetic field. The decoration of vortex chains by crossing vortices is observed: two vortices orientations appear, one along the layers and the other closely perpendicular to the layers. The findings are discussed in view of the Lawrence-Doniach and Ginzburg Landau models of anisotropic superconductors. Ref. 1 V.O. Dolocan PRL Vol 95 (2005) 97004 [Preview Abstract] |
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