Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session R36: Superconducting Proximity Effects: Mesoscopic and Related |
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Sponsoring Units: DCMP Chair: Zhiqiang Mao, Tulane University Room: 344 |
Wednesday, March 20, 2013 2:30PM - 2:42PM |
R36.00001: Nonlocal correlations in a proximity-coupled normal metal Taewan Noh, Sam Davis, Venkat Chandrasekhar We report evidence of large, nonlocal correlations between two spatially separated normal metals in superconductor/normal-metal (SN) heterostructures, which manifest themselves a nonlocal voltage generated in response to a driving current. Unlike prior experiments in SN heterostructures, the nonlocal correlations are mediated not by a superconductor, but by a proximity-coupled normal metal. The nonlocal correlations extend over relatively long length scales in comparison to the superconduncting case. At very low temperatures, we find a reduction in the nonlocal voltage for small applied currents that cannot be explained by the quasiclassical theory of superconductivity. We believe is a signature of new long-range quantum correlations in the system. [Preview Abstract] |
Wednesday, March 20, 2013 2:42PM - 2:54PM |
R36.00002: Superconducting proximity effect in MBE grown Nb-InAs junctions Carolyn Kan, Chi Xue, Stephanie Law, James Eckstein Several proposals for the realization of Majorana fermions rely on excellent quality proximity coupling between a superconductor and a high-mobility semiconductor. We examine the long-range proximity coupling between MBE-grown InAs and in situ grown superconducting overlayers by fabricating transport devices, and investigate the effect of substrate choice and growth conditions on the quality of the MBE InAs. GaAs is commonly available as a high quality insulating substrate. Overcoming its lattice mismatch with InAs using GaSb and AlSb layers results in locally smooth terraced surfaces, but global spiral dislocation structures also appear and have a negative impact on the InAs mobility. Growing InAs on homoepitaxial GaSb results in improved morphology and increases the mean free path. We compare the proximity effect in devices made both ways. [Preview Abstract] |
Wednesday, March 20, 2013 2:54PM - 3:06PM |
R36.00003: Electrostatic Tuning of the Proximity-Induced Exchange Field in EuS/Al Bilayers Tijiang Liu, Joseph Prestigiacomo, Philip Adams We demonstrate that the proximity-induced exchange field, $H_{ex}$ in ferromagnetic/paramagnetic bilayers can be modulated with an electric field. An electrostatic gate arrangement is used to tune the magnitude of $H_{ex}$ in the Al component of EuS/Al bilayers. We produced modulations of $\sim30$ Oe in $H_{ex}$ with the application of perpendicular electric fields of the order of $\pm 10^6$ V/cm. Several possible mechanisms accounting for the electric field's influence on the interfacial coupling between the Al layer and the ferromagnetic insulator EuS will be discussed. [Preview Abstract] |
Wednesday, March 20, 2013 3:06PM - 3:18PM |
R36.00004: Unbiased Analysis of Super/Ferro Bilayer Physics Thomas Lemberger, Michael Hinton, Jie Yong, Adam Hauser, Fengyuan Yang, Julia Meyer S/F bilayer physics has been studied for some time now. With a large number of unknown and seemingly-known parameters, some values are traditionally and understandably assumed to be fixed quantities. In particular, the exchange energy, $E_{ex}/k_B$, is believed to be comparable to the Curie temperature. We analyze the data assuming only that the Fermi velocity $v_F$ in F and the density of states, $2N_S(0)$, in S are known. Fitting $T_c$ vs. $d_F$ with the dirty-limit theory, we determine the interface resistance, $R_b$, the ratio $E_{ex}/\rho_F\ell_F$, and the ferromagnetic coherence length $\xi_F$. For physically plausible values of $\rho_F\ell_F$, the dephasing rate of cooper pairs in F is 10 times smaller than expected from the known Curie temperature of F. We propose that dephasing is mitigated by spin-orbit scattering. We also find that the transmission probability for electrons striking the F/S interface is much less than unity. [Preview Abstract] |
Wednesday, March 20, 2013 3:18PM - 3:30PM |
R36.00005: Exploring the mini-gap state and magnetoresistance in platinum nanowires Daniel Slotcavage, Meenakshi Singh, Thomas Mallouk, Moses Chan Periodic oscillations in differential magnetoresistance and a superconducting mini-gap state were found in single-crystal gold nanowires [Wang et al., PRL 102, 247003 (2009)]. The oscillations were attributed to motion of individual vortices in the nanowire. We have studied proximity-induced superconductivity in polycrystalline platinum nanowires grown using template-based electrodeposition. Systematic studies of the dependence of the mini-gap state on temperature, magnetic field, and sample morphology and geometry were conducted. We found the mini-gap state to persist in polycrystalline samples. The presence of the mini-gap state in polycrystalline samples demonstrates its robustness with respect to sample morphology. On the other hand, the differential magnetoresistance oscillations was not found in these wires. Future work will focus on determining the conditions required for the occurrence of these oscillations. [Preview Abstract] |
Wednesday, March 20, 2013 3:30PM - 3:42PM |
R36.00006: Unconventional quantum oscillations in mesoscopic rings of spin-triplet superconductor Sr$_2$RuO$_4$ Xinxin Cai, Yiqun Ying, Neal Staley, Yan Xin, David Fobes, Tijiang Liu, Zhiqiang Mao, Ying Liu Spin-triplet superconductor Sr$_2$RuO$_4$ has been found to feature exotic vortex physics including the formation of vortex lattices at low fields and most recently, evidence for half-flux quanta trapped in a doubly connected sample. We carried out the magnetoresistance measurements in mesoscopic ring samples of Sr$_2$RuO$_4$ fabricated on mechanically exfoliated single crystals of Sr$_2$RuO$_4$ by photolithography and focused ion beam. With the magnetic field applied perpendicular to the in-plane direction, thin-wall rings of Sr$_2$RuO$_4$ were found to exhibit a large number of full-flux quantum oscillations with pronounced amplitudes unexpected from the conventional Little-Parks effect. Furthermore, in thick-wall rings, two distinct periods were observed in both resistance and critical current oscillations, which we attribute to the effect of vortices, namely, the ``lock-in" effect of a vortex lattice in Sr$_2$RuO$_4$. No evidence for half-flux-quantum oscillations were identified in any sample measured so far without the presence of an in-plane field. The measurements with an in-plane field are being pursued. [Preview Abstract] |
Wednesday, March 20, 2013 3:42PM - 3:54PM |
R36.00007: Analytic Description of Superconducting-Ferromagnetic Proximity Systems Thomas E. Baker, Ovidiu E. Icreverzi, Adam K. Moke, Andreas Bill We present the exact analytic solution of the Usadel equations for a proximity system made of a superconductor and a ferromagnet in the wide dirty limit, including spin-flip scattering. The solution was found by mathematical analogy to the Jacobi elliptic function description of a classical mechanics system known as the bead on a hoop [1]. We highlight the parallels between the two systems and present an analysis of the solution with special attention to long rage triplet effects and the inverse Fulde-Ferrell-Larkin-Ovchinnikov state. We determine the Josephson critical current and the variation of the critical temperature with spin-flip scattering.\\[4pt] [1] T.E.~Baker and A.~Bill, {\it Am.~J.~Phys.} {\bf 80}, 506 (2012) [Preview Abstract] |
Wednesday, March 20, 2013 3:54PM - 4:06PM |
R36.00008: Microscopic Study of c-axis Proximity Effect in Cuprate-Manganite Heterostructures H. Zhang, I. Fridman, N. Gauquelin, G.A Botton, J. Y.T. Wei Recent studies have reported long-ranged proximity effect in epitaxial thin-film heterostructures of ferromagnetic manganites and superconducting cuprates, with possible origins in novel spin-triplet correlations [1]. A key evidence for this effect is the suppression of the superconducting $T_c$ observed in multilayer films of La$_{2/3}$Ca$_{1/3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-\delta}$ (LCMO/YBCO). However, scanning tunnelling spectroscopy on $c$-axis LCMO/YBCO bilayers have not seen direct evidence for proximity-induced pairing down to 5nm LCMO thickness [2]. We re-examine the $T_c$ suppression by performing atomically-resolved transmission electron microscopy and resistivity measurements on $c$-axis YBCO/LCMO films grown by pulsed laser deposition, and relating the microstructure in YBCO with the layer thickness and $T_c$. The microscopy revealed double CuO-chain intergrowths forming non-stoichiometric YBCO-247 regions that do not appear in x-ray diffraction, but can be related to the $T_c$ suppression. We attribute these intergrowths to heteroepitaxial strain, by comparing all the lattice parameters and symmetries involved. [1] Z. Sefrioui \emph{et al.}, PRB 67, 214511 (2003); C. Visani \emph{et al}, Nat. Phys. 8, 539 (2012). [2]I. Fridman \emph{et al}, PRB 84, 104522 (2011). [Preview Abstract] |
Wednesday, March 20, 2013 4:06PM - 4:18PM |
R36.00009: ABSTRACT WITHDRAWN |
Wednesday, March 20, 2013 4:18PM - 4:30PM |
R36.00010: New structural features in solution-derived YBCO nanocomposite films responsible for a successful novel pinning mechanism J. Gazquez, R. Guzman, J. Salafranca, R. Mishra, M. Varela, A. Palau, V. Rouco, M. Coll, A. Llordes, G. Deutscher, X. Obradors, T. Puig The optimization of high temperature superconductors calls for a detailed knowledge about the effects of materials' manipulations on the subnanometer scale, since the subtle interplay of a variety of nanoscale defect structures that pin the magnetic flux lattice will dictate the performance of these materials. The outstanding properties of solution deposited-YBa$_{2}$Cu$_{3}$O$_{7-d}$ nanocomposites arise from the strains associated to the network of YBa$_{2}$Cu$_{4}$O$_{8}$ intergrowths emerging from the spontaneously segregated oxide nanoparticles, and a novel pinning mechanism coupling this lattice strain with superconducting pairing [1]. However, YBa$_{2}$Cu$_{4}$O$_{8}$ intergrowths involve the addition of an extra CuO chain and their ubiquity may lead to an off-stoichiometry that could jeopardize the superconducting properties of the film. Conversely, we will show, by means of aberration corrected scanning transmission microscopy in combination with electron energy loss spectroscopy, how the system balance this deficiency of Cu through new structural features, previously unforeseen, that may constitute new and effective pinning centers and may be responsible for the novel pinning mechanism proposed.\\[4pt] [1] A. Llordes \textit{et al} Nature Mater2012. [Preview Abstract] |
Wednesday, March 20, 2013 4:30PM - 4:42PM |
R36.00011: Crossover from Peierls distortion to one-dimensional superconductivity in arrays of (5,0) carbon nanotubes Ting Zhang, Ming Yuan Sun, Zhe Wang, Wu Shi, Ping Sheng We consider the electronic instabilities in (3,3)@(8,8) and (5,0)@(15,0) metallic double wall carbon nanotubes. Using 2rd order renormalization group method, we find that in the single wall (3,3) and (5,0) CNTs, the Peierls transition dominates, while if dressed with metallic outer shell, namely the (8,8) CNT and (15,0) CNT to form double wall carbon nanotube system(DWNT), the screening effect greatly reduces the Coulomb interaction of inner tubes, and supercondutivity(SS) instability is identified to be the groud state, although the crossover temperature of which SS response functions take over could be very low. [Preview Abstract] |
Wednesday, March 20, 2013 4:42PM - 4:54PM |
R36.00012: 1D to 3D Crossover Transition in a System of Weakly Coupled Superconducting Nanowires Qihong Chen, Ming Yuan Sun, Zhi Lin Hou, Ting Zhang, Zhe Wang, Wu Shi, Rolf W. Lortz, Ping Sheng Recent Results have shown the existence of superconductivity in quasi-one-dimensional systems, e.g., the 4{\AA} superconducting carbon nanotubes embedded in the aligned, linear pores of the aluminophosphate-five (AFI) zeolite. In order to understand theoretically the experimental observations on the thermal specific heat and the electrical resistance variation as a function of temperature, we have carried out Monte Carlo simulations on a Ginzburg-Landau (GL) model of Josephson-coupled superconducting nanowires. The results show that the competition between 1D fluctuations and the weak transverse Josephson coupling between the nanowires can give rise to a 1D-3D crossover transition at a temperature $T_{C} $ below the mean field $T_{C}^{O} $ of the wires. The electrical resistance can experience a sharp drop at $T_{C} $, at which point the nanowires become phase coherent. The simulated specific heat exhibits a rounded peak between $T_{C} $and $T_{C}^{O} $, whereas the phase correlation length within the ab plane diverges at $T_{C} $ from above, in a manner that is consistent with the occurrence of a BKT-transition in the ab plane. These Monte Carlo simulated behaviors are in excellent agreement with the experimental data. [Preview Abstract] |
Wednesday, March 20, 2013 4:54PM - 5:06PM |
R36.00013: Phase slip in large array superconducting anti-dot thin films Wei-Li Lee, Hsiang-Hsi Kung, Ting-Hui Chen, Chia-Tso Hsieh, Chi-Chih Ho, Keng-Hui Lin, Wen-Tau Juan Phase slip is one of the most intriguing phenomena in superconducting nanostructure, which gives rise to a finite resistance below superconducting transition temperature. By using a special technique we developed previously for the preparation of a monolayer polymer/nanosphere hybrid, we fabricated a series of large array niobium antidot thin films with niobium line width ranging from about 36 nm to 90 nm. From the resistance and magnetization measurement, we found that the transition width decreases with increasing magnetic field applied along the normal direction of the antidot thin film, which becomes more significant in samples with smaller niobium line width. We argue that this phenomenon provides an evidence for the existence of thermal activated phase slip effect that was discovered for the first time in superconducting antidot thin film structure. Detailed results and analysis will be discussed. [Preview Abstract] |
Wednesday, March 20, 2013 5:06PM - 5:18PM |
R36.00014: p-wave Superconductor in a Mesoscopic Size Grain Sungkit Yip, Bor-Luen Huang Motivated by the claim that Sr2RuO4 is a p-wave superconductor with broken time-reversal symmetry in the bulk, and many recent experimental studies of superconductors in mesoscopic size grains, we study theoretically a two-component p-wave superconductor in confined geometries, considering circular disks and rectangular samples, using both Ginzburg-Landau (GL) and quasiclassical (QC) Green function theories. For GL theory with parameters near the weak-coupling limit, we find that a sufficiently small circular disk remains normal. For zero field and intermediate sizes, a disk with sufficiently smooth boundary is in a time-reversal symmetric state, where the order parameter can be represented by a real vector forming a vortex-like structure. Only for larger grains and at lower temperatures can a broken time-reversal state be recovered. For intermediate sizes but with finite external magnetic field, the system can have possibly re-entrant phase transitions. For rectangular samples with sufficiently large aspect ratios, the superconductor near its transition temperature at zero fields has its order parameter vector parallel to the long side of the sample. Within a critical aspect ratio however, the order parameter vector forms a vortex-like structure, much like for the disk. [Preview Abstract] |
Wednesday, March 20, 2013 5:18PM - 5:30PM |
R36.00015: Superconductivity and anomalous magnetic phase in LuGe$_2$ single crystals Nakheon Sung, B.K. Cho, Y.J. Jo, S.K. Choi, A.I. Coldea, H. Kim, R. Prozorov LuGe$_2$ single crystals (ZrSi$_2$-type orthorhombic structure, $C_{mcm}$) were synthesized by the high temperature metal flux method. LuGe$_2$ was found to be the type-II superconductivity below superconducting transition temperature, $T_c$ = 2.3 K. An anomalous magnetic and electric phase below $T^*$ = 4 K was found only along $b$-axis in electrical transport measurement, and confirmed additionally by magnetization and heat capacity measurement. From the heat capacity data, LuGe$_2$ was found to be the weak coupling BCS type superconductivity at $T_c$, whereas the anomalous phase above $T_c$ seems to have a close correlation with the superconducting state below $T_c$. Upper critical field, $H_{c2}$($T$), of the superconductivity exhibits significant anisotropy either along $b$-axis or along $a$ (and $c$)-axis. Recently, a possible second superconducting state in superconducting YbSb$_2$ single crystals, which has the same structure as LuGe$_2$, was reported. [1] Thus, we will discuss in detail on the anisotropic superconducting properties and the anomalous phase above $T_c$ in terms of the possible second superconductivity as in YbSb$_2$.\\[4pt] [1] Liang L. Zhao, Stefan Lausberg, H. Kim, M. A. Tanatar, Manuel Brando, R. Prozorov, and E. Morosan, Phys. Rev. B 85, 214526 (2012) [Preview Abstract] |
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