Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session N36: Superconductivity: Mesoscopic Techniques and Applications |
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Sponsoring Units: DCMP Chair: Timir Datta, University of South Carolina Room: 344 |
Wednesday, March 20, 2013 11:15AM - 11:27AM |
N36.00001: Cantilever micro-susceptometry of mesoscopic Bi2212 samples Hryhoriy Polshyn, Raffi Budakian, Genda Gu Fluxoid quantization provides a direct means to study phase coherence. In cuprate superconductors, there have been observations which suggest that phase coherent superconducting fluctuations may persist at temperatures significantly above Tc. The focus of this work is to study the vortex states in mesoscopic cuprate superconducting samples to directly probe phase coherence over a wide range of temperatures. We present cantilever torque susceptometry measurements of micron and sub-micron size Bi2212 rings and disks. The high sensitivity of this technique allowed observation of transitions between different fluxoid states of a single ring, and the discrete vortex states of micron size disks. The dependence of magnetic susceptibility on diameter and wall thickness of the ring was investigated. Measurements were made at different values of the in-plane magnetic field, and over a wide range of temperatures. [Preview Abstract] |
Wednesday, March 20, 2013 11:27AM - 11:39AM |
N36.00002: Measuring superconducting delta-doped strontium titanate bilayers using the scanning SQUID technique Hilary Noad, Katja C. Nowack, Hisashi Inoue, Christopher Bell, Yasuyuki Hikita, Harold Y. Hwang, Kathryn A. Moler Delta-doped strontium titanate is a highly tunable system well-suited for studying two-dimensional superconductivity. Bilayer structures, in particular, offer the possibility of modifying interlayer coupling between sheets of superconducting electrons. We can locally probe superconductivity and magnetism as a function of temperature using scanning SQUID susceptometry. We will discuss prospects for using the scanning SQUID technique to measure unusual effects, such as multi-component superconductivity, that may arise in delta-doped strontium titanate bilayers. [Preview Abstract] |
Wednesday, March 20, 2013 11:39AM - 11:51AM |
N36.00003: Fabrication of La$_{2-x}$Sr$_{x}$CuO$_{4}$ Superconductor Nanodevices Nicholas Litombe, Anthony Bollinger, Ivan Bozovic, Jenny Hoffman In order to investigate dimension-limited superconductivity in cuprates, we explore methods of nanopatterning La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO). We use high resolution e-beam and photo-lithographic fabrication techniques, coupled with appropriate chemical and physical pattern transfer techniques. In particular, we focus on quasi-1D LSCO nanowire devices where we study random telegraph noise (RTN) signals from possible nematic domain fluctuation dynamics. [Preview Abstract] |
Wednesday, March 20, 2013 11:51AM - 12:03PM |
N36.00004: Development of a Nb-AlxOy-Nb trilayer process at the University of Washington Andrew Wagner We present progress made at the Washington Micro-Fabrication Facility toward the production of SQUID amplifiers from a $\rm{Nb}-\rm{Al}_x\rm{O}_y-\rm{Nb}$ trilayer process. Details of a simplified trilayer process are presented and the capability to fabricate 3 micrometer Josephson Junctions from the process with controllable critical current densities is demonstrated. We discuss how these results can be applied to the production of SQUID, SLUG or Josephson Parametric amplifiers operating in the microwave band for the Axion Dark Matter eXperiment (ADMX) located at the University of Washington. [Preview Abstract] |
Wednesday, March 20, 2013 12:03PM - 12:15PM |
N36.00005: Superconducting spin switch with infinite magnetoresistance Bin Li, Niklas Roschewsky, Markus Munzenberg, Marius Eich, Marguerite Epstein-Martin, Jagadeesh S. Moodera Nearly five decades ago de Gennes theoretically predicted that below the superconducting transition temperature $T_{C}$ the resistance in a FI/S/FI (FI-ferromagnetic insulator; S-superconductor) trilayer structure depends on the magnetization direction of the two FI layers [de Gennes, \textit{Phys. Lett.} \textbf{23}, 10 (1966)]. This prediction is experimentally demonstrated here. We present magneto-transport properties in a EuS/Al/EuS structure, showing an infinite magnetoresistance by tuning the internal exchange field at the FI/S interface. The superconducting order parameter was suppressed when the magnetic moment of the two EuS layers aligned in parallel whereas it was least affected when the two EuS layers have their magnetizations in antiparallel alignment: one could tune between the superconducting and normal states by the FI magnetization configuration. Importantly either of these two states could be maintained in zero applied fields, thus creating a nonvolatile two-level memory state. It was also shown that this is entirely an interface proximity effect and could be destroyed by introducing just a monolayer of Al$_{2}$O$_{3}$ barrier in between the interfaces. Furthermore the observed resistance switching field correlated with the surface anisotropy of the EuS layers. [Preview Abstract] |
Wednesday, March 20, 2013 12:15PM - 12:27PM |
N36.00006: Thin semi-rigid coaxial cables for cryogenics applications Akihiro Kushino, Soichi Kasai We have developed cryogenic coaxial cables for low temperature signal readout from sensitive devices, such as transition edge sensors, superconducting tunnel junctions, and kinetic inductance detectors. In order to reduce heat penetration into cryogenic stages, low thermal conductivity metals were chosen for both center and outer electrical conductors. Various types of coaxial cables, employing stainless-steel, cupro-nickel, brass, beryllium-copper, phosphor-bronze, niobium, and niobium-titanium, were manufactured using drawing dies. Thermal and electrical properties were investigated between 1 and 8 K. Coaxial cables made of copper alloys showed thermal conductance roughly consistent with literature, meanwhile Nb coaxial cable must be affected by the drawing process and thermal conductance was lowered. Attenuation of superconducting Nb and NbTi coaxial cables were observed to be adequately small up to above 10 GHz compared to those of normal conducting coaxial cables, which are subject to the Wiedemann-Franz law. We also measured normal conducting coaxial cables with silver-plated center conductors to improve high frequency performance. [Preview Abstract] |
Wednesday, March 20, 2013 12:27PM - 12:39PM |
N36.00007: Novel structural transformation in the ultrathin films of cuprates and its influence on electronic and magnetic properties D. Samal, Tan Haiyan, H. Molegraaf, B. Kuiper, W. Siemons, Sara Bals, Jo Verbeeck, Gustaaf Van Tendeloo, Y. Takamura, Elke Arenholz, Catherine Jenkins, G. Rijnders, Gertjan Koster We report on the evidence found for structural transformation in ultrathin films of two cuprate systems viz. SrCuO$_{2}$(SCO) and CuO. In case of SCO ultrathin films, we show a transformation from the bulk planar to chain-like structure, below a critical thickness, due to associated electrostatic instability. Results based on X-ray diffraction, X-ray photoelectron diffraction and scanning transmission electron microscopy reveal an elongation of the unit cell by $\sim$0.5{\AA} along the $c$-axis and the presence of oxygen in the Sr plane for chain like structure. Polarized X-ray absorption spectroscopy reveals a preferential occupation of Cu 3$d_{{3z}^{2}-r^{2}}$ orbital in case of the chain like structure unlike to the planar one. For the case of ultrathin CuO films, we find strain induced structural transformation from monoclinic to tetragonal phase, akin to other 3d transition metal monoxides and reveals relatively higher Neel temperature. Our findings point to a unique structural stabilization process for ultrathin cuprate layers and provide new insight for the experimental realization of novel hybrids to look for enhanced superconducting properties. References: Zhong \textit{et.al,} PRB \textbf{85,} 12411(R) (2012); Siemons \textit{et.al,} Al.PRB \textbf{79},195122 (2009) [Preview Abstract] |
Wednesday, March 20, 2013 12:39PM - 12:51PM |
N36.00008: Dynamical I-V Characteristics of SNS Junctions Kevin Spahr, Jonathan Graveline, Christian Lupien, Marco Aprili, Bertrand Reulet We probe the dynamics of a Superconductor /Normal Metal/ Superconductor junction (SNS: Nb / Al above its critical temperature / Nb) by measuring~ its voltage / current characteristics while applying an ac current of frequency in the range 1-200 MHz. We observe a dynamical phase transition as a function of the frequency and amplitude of the ac current. At low frequency there is a continuous change in the dynamical behavior of the junction, replaced an abrupt change and hysteresis at high frequency. The crossover frequency between the two regimes has a strong temperature dependence similar to that of the electron-phonon interaction rate. [Preview Abstract] |
Wednesday, March 20, 2013 12:51PM - 1:03PM |
N36.00009: Spectroscopy of Andreev Bound States: revealing the hidden side of the Josephson effect \c{C}a\u{g}lar Girit, Landry Bretheau, Hugues Pothier, Daniel Esteve, Cristian Urbina The Josephson effect describes how phase coherence is established between two weakly coupled superconductors. Microscopically, the Josephson current is carried by Cooper pairs, occupying Andreev Bound States, localized at the weak link. Andreev Bound States, which come in particle-hole symmetric pairs, consitute a spin-like degree of freedom. In our experiment, we detect the transition to the \textit{excited} Andreev bound state in a superconducting atomic contact using a Josephson junction as a broadband (5-90 GHz) spectrometer. Not only do we clearly resolve the Andreev transition, but we also identify spectroscopic lines arising from anticrossings with a Josephson plasma mode of the environment. Our results demonstrate the accessibility of a pseudospin degree of freedom in the Josephson effect. [Preview Abstract] |
Wednesday, March 20, 2013 1:03PM - 1:15PM |
N36.00010: X-ray Structural Studies of Bi2Sr2CaCu2O8$+\delta $ Exfoliated Nanocrystals Andreea Lupascu, Renfei Feng, Luke J. Sandilands, Zixin Nie, Viktoriya Baydina, Genda Gu, Shimpei Ono, Yoichi Ando, Kenneth S. Burch, Young-June Kim Structural studies of nanocrystals produced via mechanical exfoliation are not only essential for examining structure quality or structural changes at reduced-dimensionality, but also for understanding the role of substrates in the exfoliation process. Highly focused, tunable synchrotron X-ray beams enable the use of non-destructive characterization tools to study exfoliated samples on a variety of substrates. We demonstrate that structural and spectroscopic information can be obtained on nanocrystals as thin as 6 nm, by using a combination of micro X-ray fluorescence ($\mu$ XRF), micro X-ray absorption near-edge spectroscopy ($\mu$ XANES), and X-ray microdiffraction ($\mu$ XRD) techniques. $\mu$ XRF is used to locate the sample of desired thickness; $\mu$ XANES and $\mu$ XRD are used to obtain electronic and structural information, respectively. We report a substantial substrate effect for Bi2Sr2CaCu2O8$+\delta $ nanocrystals exfoliated on Si/SiO2 and mica substrates. The ``4.7 b'' structural modulation, characteristic of bulk crystals, vanishes below a thickness of 60 nm on mica, and is drastically suppressed below 60 nm for the Si/SiO2 substrate. [Preview Abstract] |
Wednesday, March 20, 2013 1:15PM - 1:27PM |
N36.00011: Mechanical detection of single-quantum-level fluxoid relaxation in an Nb micro-ring Jae-Hyuk Choi, Heon-Hwa Choi, Yun-Won Kim, Soon-Gul Lee, Mahn-Soo Choi We developed a highly sensitive static force magnetometry, originally proposed for sub-pico-newton force standard, which enabled the observation of single fluxoids selectively and their dynamics in a superconducting micro-ring. For an Nb ring with inner diameter of 4.0 $\mu$m, the magnetic moment of a single fluxoid quantum was determined as 7.4 pico-emu, corresponding to the static force of 74 femto-newton, in good agreement with a theoretical estimate within 8\%. The magnetic relaxation of moderate number of fluxoids, ranging from 20 to 60, was also measured at temperatures of 4 $\sim$ 6 K and at zero magnetic field. The relaxation results with single-quantum-step feature were analyzed with a theoretical model for thermally activated transition. [Preview Abstract] |
Wednesday, March 20, 2013 1:27PM - 1:39PM |
N36.00012: Studying phonon and quasiparticle heating effects on SINIS Coolers Thomas Aref, Hung Nguyen, Juha Muhonen, Jukka Pekola A Normal-Insulating-Superconductor (NIS) tunnel junction can function as an electronic cooler. This is typically done in the SINIS configuration where the normal metal island is the object being cooled. By applying proper biasing, the bandgap in the superconductor can be used as an energy filter, allowing hot electrons to escape from the normal island and cold electrons to enter the island from the superconductor. This narrows the Fermi distribution of the electrons on the island, effectively lowering their temperature. By coupling this electronic refrigeration to phonons, the phononic temperature can be reduced as well. These SINIS coolers have potential for replacing other cryogen based refrigeration techniques at low temperatures. One primary aim is to produce an efficient, solid-state, cooling platform that cools small devices from 300 to 100 mK. Our most recent research has helped illuminate various effects that adversely affect the performance of these coolers. Examples of effects probed included geometrical factors, phonon heating, quasiparticle heating, substrate modification, ground planes and direct traps. [Preview Abstract] |
Wednesday, March 20, 2013 1:39PM - 1:51PM |
N36.00013: Coupling carbon nanotube mechanics to a superconducting circuit B.H. Schneider, S. Etaki, H.S.J. van der Zant, G.A. Steele The quantum behaviour of mechanical resonators is a new and emerging field driven by recent experiments reaching the quantum ground state. The high frequency, small mass, and large quality-factor of carbon nanotube resonators make them attractive for quantum nanomechanical applications. A common element in experiments achieving the resonator ground state is a second quantum system, such as coherent photons or a superconducting device, coupled to the resonators motion. For nanotubes, however, this is a challenge due to their small size. Here, we couple a carbon nanoelectromechanical (NEMS) device to a superconducting circuit. Suspended carbon nanotubes act as both superconducting junctions and moving elements in a Superconducting Quantum Interference Device (SQUID). We observe a strong modulation of the flux through the SQUID from displacements of the nanotube. Incorporating this SQUID into superconducting resonators and qubits should enable the detection and manipulation of nanotube mechanical quantum states at the single-phonon level. [Preview Abstract] |
Wednesday, March 20, 2013 1:51PM - 2:03PM |
N36.00014: Spin-precession-assisted tunneling in hybrid superconducting point contacts Cecilia Holmqvist, Wolfgang Belzig, Mikael Fogelstrom The charge and spin transport properties of a quantum point contact coupled to a nanomagnet depends strongly on the dynamics of the nanomagnet's spin. We analyze the current-voltage characteristics of a junction coupled to a spin whose dynamics is modeled as Larmor precession brought about by an external magnetic field. The interaction between the spin dynamics and the Josephson effect leads to a rich subgap structure due to spin-precession-assisted multiple Andreev reflections. Additionally, the spin current displays Shapiro-like resonances due to the interplay between the ac Josephson current and the Larmor precession. [Preview Abstract] |
Wednesday, March 20, 2013 2:03PM - 2:15PM |
N36.00015: Probing the Dynamics of Andreev States inĀ Coherent Normal/Superconducting ring: Evidence for a noisy supercurrent Bastien Dassonneville, Francesca Chiodi, Sophie Gueron, Meydi Ferrier, Helene Bouchiat Most properties of a non superconducting (N) metal connected to two superconductors (an SNS junction) can be seen as resulting from the phase dependent Andreev states (AS) in N. Density of states in N is then drastically changed with the emergence of a small energy gap, the minigap. Whereas AS equilibrium properties are well understood, AS dynamics is a more complex issue [1]. We perform experiments on a phase ($\phi$) biased NS ring coupled to a superconducting resonator. The modification of the resonances ($f$ from 200 MHz up to 14 GHz) yields the complex phase dependent susceptibility $\partial_\phi I_{ring}=\chi(f,\phi)=\chi'+i\chi''$. As expected, we find a non-dissipative $\chi'$ related to the supercurrent flowing through the ring. A more striking finding [2] is the existence of a dissipative $\chi''$ revealing a noisy supercurrent, predicted [3] but never observed before. Moreover, as $f$ increases we show that the main dissipation mechanism changes from population relaxation to microwave-induced transitions across the minigap.\\[4pt] [1] F. Chiodi et al, Sci. Rep, 1 (2011) \newline [2] B. Dassonneville et al, in preparation \newline [3] A. Martin-Rodero et al, PRB, 53 (1996) [Preview Abstract] |
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