Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session H41: Superconductivity: Proximity Effects |
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Sponsoring Units: DCMP Chair: Thomas Lemberger, Ohio State University Room: F152 |
Tuesday, March 16, 2010 8:00AM - 8:12AM |
H41.00001: Proximity Effect in Electron-Doped Cuprate Josephson junctions S. Charpentier, G. Roberge, S. Godin-Proulx, P. Fournier We study the proximity effect in Josephson junctions made from electron-doped high-T$_c$ cuprates Pr$_{2-x}$Ce$_x$CuO$_4$ (PCCO) as the electrodes and the barrier. For the electrodes, we use superconducting optimally doped PCCO (x = 0.15). PCCO x = 0.05, an antiferromagnetic metal, is used for the barrier. Our results demonstrate: 1) a conventional proximity effect; 2) but a coupling even if the barrier is antiferromagnetic. We determine the normal coherence length, $\xi _n$, which quantifies the extent of the pair wavefunction into the metal. Comparing this value with the theoretical expectations, we confirm that the coupling appears to be conventional through PCCO x = 0.05. Further results investigating the coupling through an insulating antiferromagnetic barrier and through a metal with no antiferromagnetic order will also be presented. [Preview Abstract] |
Tuesday, March 16, 2010 8:12AM - 8:24AM |
H41.00002: Possible triple superconductivity in Exchange-Spring/Superconductor hybrid system with a non-collinear magnetization Jiyeong Gu, Jefery Kusnadi, Chun-Yeol You We investigate the proximity effect in a superconductor/ferromagnet (S/F) hybrid system with a non-collinear magnetic configuration. A new structure of an S/exchange-spring (ES) magnet is fabricated, where an ES magnet is employed as an F layer since the magnetization configurations are varied from a collinear state to a non-collinear state by a rotating external magnetic field in a well controllable way. The superconducting property of the hybrid system was investigated as functions of the temperature, magnetic field, and the thicknesses of each layer. We found that the resistance decreases and the superconducting transition temperature increases, as non-collinearity is introduced starting from a collinear state. We explain our experimental observations mostly due to the contribution of the odd triplet superconducting condensates that survived in a non-collinear magnetization configuration in the ES magnet. [Preview Abstract] |
Tuesday, March 16, 2010 8:24AM - 8:36AM |
H41.00003: Correlation of Superfluid Density and $T_c $ Suppression in Superconducting/Ferromagnetic Bilayers Michael Hinton, Adam Hauser, Jeremy Lucy, Julia Meyer, Fengyuan Yang, Thomas Lemberger We report superfluid density measurements of thin film Nb and ferromagnet (Ni, Py, CoFe) bilayers. Data were taken by mutual inductance measurement using a two-coil technique on samples prepared with UHV sputtering. We present data showing, as the thickness of the ferromagnet increases, $T_c $ and superfluid density are suppressed to a limiting value. The limiting value in $T_c $ and superfluid density depends on the exchange field of the ferromagnet as well as the transparency of the interface. Values for $T_c $ and superfluid density at $T=0\mbox{ K}$ follow reasonably well the theory for bilayers with superconducting layer less than a coherence length thick despite our samples consisting of a superconducting layers more than twice a coherence length. [Preview Abstract] |
Tuesday, March 16, 2010 8:36AM - 8:48AM |
H41.00004: Angular Dependence of the Superconducting Transition Temperature in Ferromagnet-Superconductor-Ferromagnet Trilayers Jian Zhu, Ilya Krivorotov The superconducting transition temperature, T$_{\mathrm c}$, of a ferromagnet (F) -- superconductor (S) -- ferromagnet trilayer depends on the mutual orientation of the magnetic moments of the F layers. This effect has been previously observed in F/S/F systems as T$_{\mathrm c}$ difference between parallel and antiparallel configurations of the F layers [1]. Here we report measurements of the angular dependence of T$_{\mathrm c}$ in CuNi/Nb/CuNi trilayers. In our measurements, magnetization of one F layer is fixed by exchange bias while magnetization of the other F layer is rotated in the plane of the trilayer through 360 degrees, and T$_{\mathrm c}$ is measured as a function of the angle between the F layer magnetizations. The observed angular dependence of T$_{\mathrm c}$ depends on the thickness of the CuNi layers and it shows significant deviations from a simple cosine function for thin CuNi layers. The observed angular dependence is qualitatively similar to theoretical predictions taking into account odd triplet pairing in the non-collinear F/S/F geometry [2]. \\[4pt] [1] J. Y. Gu, C.-Y. You, J. S. Jiang, J. Pearson, Ya. B. Bazaliy, and S. D. Bader, \textit{Phys. Rev. Lett.} 89, 267001 (2002) \\[0pt] [2] Ya. V. Fominov, A. A. Golubov, and M. Yu. Kupriyanov, \textit{JETP Letters, Vol. 77, No. 9, 2003, pp. 510--515.} [Preview Abstract] |
Tuesday, March 16, 2010 8:48AM - 9:00AM |
H41.00005: Dissipation in Nanostructured Superconductors Serena Eley, James Eckstein, Nadya Mason Decoherence due to dissipative coupling to an environment is a topic of both fundamental and practical interest. To study the interplay between coherence and dissipation, we have fabricated planar arrays of proximity-coupled superconducting islands on metallic substrates. The superconducting islands are well-understood coherent systems with long-range electron interactions, while the intervening normal metal channels introduce known dissipation into the system. We will present results of low-temperature transport measurements of these systems, where we analyze the effects of dissipation by changing the island sizes and spacings. [Preview Abstract] |
Tuesday, March 16, 2010 9:00AM - 9:12AM |
H41.00006: Pair correlations in semiconductor-superconductor junctions James Eckstein, Michael Vissers, Stephanie Law, Allison Dove, Paul Goldbart We have studied the proximity effect in several different superconductor-semiconductor junction systems using a new three- terminal device which independently measures how both the junction conductance and semiconductor resistance change as a function of temperature. Both of these quantities are modified by proximity-induced pair correlations. We find that two factors are particularly important, namely the transmission coefficient of the junction between the semiconductor and the superconductor, and the thickness of the doped semiconductor layer. When the transmission coefficient is high, > 0.7, pair correlations are present below Tc, regardless of the thickness of the semiconductor film. If the transmission coefficient is < 0.04, pair correlations are evident only for very thin semiconductors; a thicker normal layer suppresses pair correlations, even at the interface. [Preview Abstract] |
Tuesday, March 16, 2010 9:12AM - 9:24AM |
H41.00007: Oscillation of the Critical Temperature in Proximity Systems Involving Graphite Julius C. De Rojas, Andreas Bill, Vladimir Z. Kresin We study properties of superconducting-graphite proximity systems as a function of graphite thickness. Size quantization effects become prominent for semi-metallic thin films and lead to oscillations of normal and superconducting properties. In particular, we discuss the oscillation of the density of states and of $T_c$ and compare to existing experimental data.\footnote{T.~Kubo {\it et al.} Physica C {\bf 420}, 78 (2005), {\it ibid.} {\bf 460-462}, 1013 (2007)} We also discuss the increase of the critical temperature in graphite/Nb thin films with respect to the observed value in a single Nb thin film. The result is analyzed in terms of additional pairing contributions and possible intrinsic superconductivity in graphite. We also address the situation when graphite is replaced by a graphene multilayer. [Preview Abstract] |
Tuesday, March 16, 2010 9:24AM - 9:36AM |
H41.00008: Long Range Longitudinal Proximity Effects in Superconducting/Normal-Metal Bilayers John Sadleir, John Clem, Stephen Smith, Caroline Kilbourne Measurements are presented of the temperature and magnetic field dependence of critical current measured over 7 orders of magnitude on square Mo/Au bilayers ranging in length from 8 to 290 microns. We find our measurements have a natural explanation in terms of a spatially varying order parameter that is enhanced in proximity of the higher transition temperature superconducting leads (the longitudinal proximity effect) and suppressed in proximity to the added normal metal structures (the lateral inverse proximity effect). We also discuss the implications of our results on transition-edge sensors for high-energy-resolution imaging-spectrometry currently under development at NASA for future space-based X-ray astrophysics observatories. [Preview Abstract] |
Tuesday, March 16, 2010 9:36AM - 9:48AM |
H41.00009: ABSTRACT WITHDRAWN |
Tuesday, March 16, 2010 9:48AM - 10:00AM |
H41.00010: Quantum Interference Proximity Transistor Francesco Giazotto, Joonas Peltonen, Matthias Meschke, Jukka Pekola We present the realization and characterization of a novel-concept interferometer, the superconducting quantum interference proximity transistor (SQUIPT). Its operation relies on the modulation with the magnetic field of the density of states (DOS) of a proximized metallic wire embedded in a superconducting ring. Flux noise down to $\sim $10$\mu \Phi _{0}$Hz$^{-1/2}$ ($\Phi _{0}$ is the flux quantum) can be achieved even for a non-optimized design, with an intrinsic power dissipation (of the order of $\sim $100 fW) which is several orders of magnitude smaller than in conventional superconducting interferometers. Our results are in good agreement with the theoretical prediction of the SQUIPT behavior, and suggest that optimization of the device parameters would lead to a large enhancement of sensitivity for the detection of tiny magnetic fields. The features of this setup and their potential relevance for applications are further discussed. [Preview Abstract] |
Tuesday, March 16, 2010 10:00AM - 10:12AM |
H41.00011: Anti-proximity Effect in Single Crystal Aluminum Nanowires Meenakshi Singh, Jian Wang, Mingliang Tian, Thomas Mallouk, Moses Chan A novel antiproximity effect in Zn nanowires was reported where it was found that superconductivity of an array of Zn nanowires, 40 nm in diameter, was suppressed by bulk superconducting electrodes. The Zn nanowire array recovered its superconductivity when the bulk electrodes were driven normal by an applied magnetic field. [Tian, M. et al. \textit{Phys. Rev. Lett.} \textbf{2005}, $95$, 076802. Tian, M et al. \textit{Phys. Rev. B} \textbf{2006}, $74$, 014515]. We have confirmed this counterintuitive effect in single-crystal superconducting Aluminum nanowires in array and single-wire measurements. The critical current of the Aluminum nanowires is found to increase when the bulk measuring electrodes are changed from superconducting to normal. [Preview Abstract] |
Tuesday, March 16, 2010 10:12AM - 10:24AM |
H41.00012: Inverse Spin Hall Effect in Josephson Contacts Severin Sadjina, Anatolii Mal'shukov, Arne Brataas We demonstrate that Rashba spin orbit coupling together with Zeeman fields create an effective electromagnetic vector-potential in the normal part of an SNS Josephson junction in thermal equilibrium. Consequently, a phase difference between order parameters of the two superconducting terminals is induced, in analogy to the Meissner effect. The resulting phase-coherent equilibrium supercurrent is a counterpart of the non-equilibrium inverse spin Hall effect in normal metals. The calculations have been carried out in the diffusive regime on the basis of Usadel equations and assuming low transparency tunneling contacts. Apart from this effect, we also consider an in-plane homogeneous Zeeman field in the transverse direction. [Preview Abstract] |
Tuesday, March 16, 2010 10:24AM - 10:36AM |
H41.00013: Crossover from clean to dirty limit in Josephson junctions with inhomogeneous ferromagnet Zoran Radovic, Luka Trifunovic, Zorica Popovic We study the Josephson effect and pairing correlations in SFFS junctions with two metallic monodomain ferromagnets with transparent and spin-inactive interfaces. We solve the Eilenberger equations self-consistently for arbitrary relative orientation of magnetizations of the two F layers in the clean limit and for moderate disorder in ferromagnets. Spatial variation of singlet and odd-frequency triplet pair amplitudes, as well as the Josephson current-phase relations, are calculated for different values of the ferromagnetic layer thickness and the angle between in-plane magnetizations. In the clean limit we find that both spin singlet and triplet pair amplitudes in F layers show a similar oscillatory decay with distance from the SF interfaces. For the singlet pair amplitude this decay gets faster as the impurity-scattering rate in ferromagnets is increased while the triplet amplitudes remain practically unaffected. In the dirty limit, the singlet amplitude penetrates into the ferromagnet over a short length scale determined by the exchange energy, while the triplet amplitudes are not suppressed and consequently they are long-ranged. [Preview Abstract] |
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