Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session L52: Focus Session: Superconductivity, Vortex Matter I |
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Sponsoring Units: DMP Chair: Leonardo Civale, Los Alamos National Laboratory Room: Mile High Ballroom 1F |
Wednesday, March 5, 2014 8:00AM - 8:36AM |
L52.00001: Nonlinear dynamics of vortices in nano-structured superconductors Invited Speaker: Francois Peeters Nonlinear flux dynamics in superconductors is a prototype for many nonlinear phenomena occurring in different areas of physics. It is well-known that vortices in nano-structured superconductors with dimensions comparable to characteristic length scales behave very different from those in bulk materials, e.g. multi-quanta giant vortices and symmetry-induced vortex-antivortex pairs can nucleate which are impossible in bulk. I will give a few examples of the surprising behavior of vortex matter in different type of nano-structured superconducting films. Our analysis is based on the time-dependent Ginzburg-Landau theory. Where possible comparison with experiments.will be made. For example large resistance oscillations are found, different from the usual Little-Parks effect, that are due to current-excited moving vortices. Unusal field-induced increase in the critical current may be observed as a consequence of the nonlinear distribution of the current in a sample. In type-I superconductors even in the intermediate state the smallest building block turns out to be a flux quantum and the current driven nucleation of flux domains is discretized to a single fluxoid. Domains of opposite flux, when driven towards each other, annihilate through a discretized sequence of single vortex-antivortex pairs. [Preview Abstract] |
Wednesday, March 5, 2014 8:36AM - 8:48AM |
L52.00002: Superconducting Thin films with Periodic Ferromagnetic Nanostructures Wonbae Bang, K.D.D. Rathnayaka, I.F. Lyuksyutov, W. Teizer, D.G. Naugle Studies of the transport properties of superconducting Tin (Sn) thin films covered by periodic ferromagnetic nanostructures are reported. The Sn thin films and the periodic nanosized ferromagnetic configurations were patterned by electron-beam lithography and deposited by thermal quench condensation. A Germanium (Ge) layer was thermally evaporated at room temperature as an insulating barrier between the Sn thin films and the ferromagnetic structures. When a current was applied parallel to ferromagnetic stripes, the critical current and hysteresis exceeded the critical current perpendicular to the ferromagnetic stripes resulting in a strong anisotropy. We have observed that the critical currents show a matching field effect. [Preview Abstract] |
Wednesday, March 5, 2014 8:48AM - 9:00AM |
L52.00003: In-situ tunable vortex pinning with an array of ferromagnetic anti-dots Yong-Lei Wang, Zhili Xiao, Leo Ocola, Ralu Divan, George W. Crabtree, Wai-Kwong Kwok We investigated vortex pinning effects of a ferromagnetic antidot array in a superconducting film. A square antidot array of 30 nm thick permalloy (Py) was patterned onto a MoGe superconducting film with thickness of 100 nm. Although we found no evidence of vortex pinning enhancement by the pristine magnetic antidot array in perpendicular magnetic fields, we found that by applying an independently controlled in-plane magnetic field the magnetic antidot array can provide excellent vortex pinning, resulting in a tunable superconducting critical current enhancement. Through micromagnetic simulation and magnetic force microscopy imaging, we demonstrate that the tunable vortex pinning originates from spatially periodic stray field generated by the magnetic antidot array in the presence of an in-plane magnetic field. [Preview Abstract] |
Wednesday, March 5, 2014 9:00AM - 9:12AM |
L52.00004: Highly effective superconducting vortex pinning in conformal crystals S. Gu\'enon, Y.J. Rosen, Ali C. Basaran, Ivan K. Schuller In the last few years, the search for an artificial pinning center (APC) distribution that pins a vortex lattice in a superconducting thin film over a wide magnetic field range has attracted a lot of attention. Recently, a conformal crystal obtained by conformally mapping a hexagonal lattice was proposed [1]. We compared the magneto-transport measurements of a conformal crystal and a randomly diluted APC distribution with a triangular reference lattice. We discovered for both APC distributions that the magneto-resistance is significantly reduced in a magnetic field interval between the first matching fields of the triangular reference lattice. Moreover, in this interval, the magneto-resistance of the conformal crystal APC distribution is below the noise floor indicating highly effective vortex pinning over a wide magnetic field range.\\[4pt] [1] D. Ray et al., Phys. Rev. Lett. 110, 267001 (2013) [Preview Abstract] |
Wednesday, March 5, 2014 9:12AM - 9:24AM |
L52.00005: Ratchet effect in a conformal pinning array Boldizsar Janko, Dipanjan Ray, Cynthia Olson Reichhardt, Charles Reichhardt Pinning arrays where the pinning sites are located at the vertices of a conformally transformed hexagonal lattice, also known as conformal pinning arrays (CPA), have recently been shown to greatly enhance the critical current of type-II superconductors both in simulation and in experiment\footnote{D. Ray et al, Phys. Rev. Lett. 110, 267001 (2013); Y. L. Wang et al, Phys. Rev. B 87, 220501(R) (2013); S. Guenon et al, Appl. Phys. Lett. 102, 252602 (2013).}. Here we show using molecular dynamics simulations that the differing flux-flow resistance of the CPA in the forward and reverse directions causes it to function as a highly effective vortex ratchet. We drive the vortices using an applied external ac current, and we find that the resulting dc output voltage for the CPA ratchet is larger than that for a random pinning array with a pinning gradient\footnote{C. J. Olson et al, Phys. Rev. Lett. 87, 177002 (2001).} by up to an order of magnitude. The enhancement is robust over a wide range of vortex densities, temperatures, and ac drive amplitudes and frequencies. [Preview Abstract] |
Wednesday, March 5, 2014 9:24AM - 9:36AM |
L52.00006: Magnetic flux structures and superconducting structures in nano-sized polygon superconducting plates Masaru Kato, Osamu Sato Vortex structures in nano-sized superconductors under an external field have been studied for decades. It was shown that vortices in square superconducting plates are different form those in bulk superconductors. The vortices are affected by the shielding current at edges of superconductors. Therefore the vortex structure depends on the shape of the superconductor. We recently studied the vortex structures in a pentagon superconducting plate at low temperature and showed how vortex structures changes with increasing the magnetic field. These structures agree with the experiment by Ishida et al. [1]. In this study, we investigate the vortex structures around the transition temperature in various polygon superconducting plates under the external field. For this purpose we solve the Ginzburg-Landau (GL) equations, especially linearized GL equations, using the finite element method. We show the relation between shapes of superconductors and vortex structures and superconducting order parameter structures. [1] T. H. Huy, M. Kato, T. Ishida, Supercond. Sci. Technol. 26 (2013) 065001. [Preview Abstract] |
Wednesday, March 5, 2014 9:36AM - 10:12AM |
L52.00007: Tailored Large Critical Currents in Iron-based Superconductors Invited Speaker: Wai-Kwong Kwok Iron-based superconductors, with their relatively high superconducting transition temperatures, high critical currents and low anisotropy holds great potential for applications such as superconducting generators and motors where the magnetic field environment can greatly affect the critical current capacity. These materials may hold the key to developing an isotropic, high field, high critical current, high-temperature superconductor, one of the grand challenges of applied superconducting research. I will discuss our recent work on using various types of particle irradiation to elucidate the vortex pinning behavior of these materials and the remarkable enhancement of the critical current that can be achieved with no detrimental effect on the transition temperature. Furthermore, I will show that certain induced correlated disorder can lower the thermodynamic anisotropy of these superconductors. Finally, I will discuss the advantages of composite defects induced by compounded proton and heavy-ion irradiation in further enhancing the critical current at high magnetic fields. These results on iron-based superconductors will be compared with the performance of current state-of-the-art commercial YBCO coated conductors. [Preview Abstract] |
Wednesday, March 5, 2014 10:12AM - 10:24AM |
L52.00008: Huge Critical Current Density and Tailored Superconducting Anisotropy in SmFeAsO(0.8)F(0.15) by Low Density Columnar-Defect Incorporation U. Welp, L. Fang, Y. Jia, V. Mishra, C. Chaparro, V.K. Vlasko-Vlasov, A.E. Koshelev, G.W. Crabtree, S.F. Zhu, N.D. Zhigadlo, S. Katrych, J. Karpinski, W.K. Kwok SmFeAsO(0.8)F(0.15) is of great interest because it has the highest transition temperature of all the iron-based superconductors. We find that the introduction of a low density of correlated nano-scale defects enhances the critical current density up to 2 $\times$ 10$^{7}$A/cm$^{2}$ at 5 K without any suppression in the high superconducting transition temperature of 50 K and amounting to 20 {\%} of the theoretical depairing current density. We also observed a surprising reduction in the thermodynamic superconducting anisotropy from 8 to 4 upon irradiation. A model based on anisotropic electron scattering predicts that the superconducting anisotropy can be tailored via correlated defects in semi-metallic, fully gapped type II superconductors. - We acknowledge support by the Center for Emergent Superconductivity, an EFRC funded by the US DOE, Office of Basic Energy Sciences (LF, YJ, VM, AEK, WKK, GWC), by the DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 (CC, VKV, UW), by the EC Research Council project SuperIron (JK, SK), and by the Swiss National Science Foundation and the National Center of Competence in Research MaNEP (NDZ). [Preview Abstract] |
Wednesday, March 5, 2014 10:24AM - 10:36AM |
L52.00009: Doubling the Critical Current Density of 2G-Coated Conductors through Proton Irradiation Maxime Leroux, Y. Jia, D.J. Miller, J.G. Wen, W.K. Kwok, U. Welp, M. Rupich, S. Fleshler, A. Malozemoff, A. Kayani, O. Ayala-Valenzuela, L. Civale The in-field performance of production-line 2nd generation high temperature superconducting cable can be substantially improved by post-fabrication irradiation with 4 MeV protons. A dose of $8.10^{16} p/cm^2$ nearly doubles the critical current in fields of 6 T // c at 27 K and more generally the suppression of Jc in magnetic field is reduced. A mixed pinning landscape composed of preexisting precipitates and twin boundaries and small, finely dispersed irradiation induced defects may account for the improved vortex pinning in high magnetic fields. Our current data-set indicates that there is significant head-room for further enhancements.This work was supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (Y.J., M.L., W.K.K., U.W., O.A.V., L.C.) and by the Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02- 06CH11357 (D.J.M., J.G.W.). Irradiations were carried out at the Western Michigan University accelerator laboratory. Microstructure was characterized in the Electron Microscopy Center at Argonne, supported by the Office of Science-Basic Energy Science. [Preview Abstract] |
Wednesday, March 5, 2014 10:36AM - 10:48AM |
L52.00010: Time-dependent Ginzburg-Landau equations and vortex dynamics simulations on GPUs Ivan Sadovskyy, Andreas Glatz Most energy applications of superconductivity, such as electric power transmission over superconducting cables or powerful magnets, require low energy dissipation in high-temperature superconductors. Restricting the mobility of the vortices carrying magnetic field in the superconducting material by pinning them with admixed inclusions or confining their motion geometrically can minimize dissipation. We present modern simulation results of the time-dependent Ginzburg-Landau equation for large-scale mesoscopic superconductors, like narrow superconducting strips and nano-patterned superconductors. In particular, we discuss the case of nano-scale extended pinning inclusions, whose geometry has a non-trivial influence on the current-voltage characteristics. The required large-scale simulations were made possible with recent GPU computing techniques. [Preview Abstract] |
Wednesday, March 5, 2014 10:48AM - 11:00AM |
L52.00011: Thermal and quantum fluctuations effects on the vortex matter in Fe-based superconductors with naturally-grown and engineered pinning landscapes Leonardo Civale, Oscar Ayala Valenzuela, Boris Maiorov, Jeehoon Kim Vortex pinning and dynamics in Fe-based superconductors is at least as complex as in oxide superconductors. Clean single crystals may have very simple pinning landscapes dominated by a single type of defects and low critical current density ($J$$_c$). In contrast, thin films frequently show much higher $J$$_c$ arising from mixed pinning landscapes containing both uncorrelated and correlated disorder. On top of these features in as-grown samples, the pinning landscape can be effectively engineered by irradiation or by addition of non-superconducting second phases. A somewhat surprising characteristic of the vortex matter in Fe-based superconductors is that it tends to show large fluctuations effects similar or even larger than oxide HTS, such as fast flux creep and extended liquid phases. This is the case even in compounds where simple estimates based on the value of the Ginzburg number would suggest that fluctuation effects should be much smaller. I will present studies of vortex matter in Fe-based superconductors with naturally-grown and engineered pinning landscapes, and discuss the influence of thermal and quantum fluctuations and the characteristics of the vortex liquid phases. [Preview Abstract] |
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