Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session X39: Superconductivity: JJ Effect, Graphene/oxide - based |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Mike Osofsky, Naval Research Laboratory Room: 386 |
Friday, March 17, 2017 8:00AM - 8:12AM |
X39.00001: Current-phase relations in low carrier density graphene Josephson junctions Philip Kratz, Francois Amet, Christopher Watson, Kathryn Moler, Chung Ke, Ivan Borzenets, Kenji Watanabe, Takashi Taniguchi, Russell Deacon, Michihisa Yamamoto, Yuriy Bomze, Seigo Tarucha, Gleb Finkelstein Ideal Dirac semimetals have the unique property of being gate tunable to arbitrarily low electron and hole carrier concentrations near the Dirac point, without suffering from conduction channel pinch-off or Fermi level pinning to band edges and deep-level charge traps, which are common in typical semiconductors. SNS junctions, where N is a Dirac semimetal, can provide a versatile platform for studying few-mode superconducting weak links, with potential device applications for superconducting logic and qubits. We will use an inductive readout technique, scanning superconducting quantum interference device (SQUID) magnetometry, to measure the current-phase relations of high-mobility graphene SNS junctions as a function of temperature and carrier density, complementing magnetic Fraunhofer diffraction analysis from transport measurements which previously have assumed sinusoidal current-phase relations for junction Andreev modes. Deviations from sinusoidal behavior convey information about resonant scattering processes, dissipation, and ballistic modes in few-mode superconducting weak links. [Preview Abstract] |
Friday, March 17, 2017 8:12AM - 8:24AM |
X39.00002: Superconducting coupling of $\backslash $nu $=$ 1 quantum Hall edges states in graphene Jing K. Shi, Gil-Ho Lee, Kenji Watanabe, Takashi Taniguchi, Philip Kim Over the past few years, there have been intense experimental and theoretical developments in engineering topological states with various material platforms. One candidate system of realizing zero energy Majorana mode is employing the coupling of superconductivity and spin non-degenerated quantum Hall edge states in a two-dimensional material. In this talk, we present quantum transport study on quasi-one dimensional superconducting electrodes fabricated on high-quality boron nitride encapsulated graphene. The crossed Andreev process and the Josephson effect are investigated at a graphene filling factor of $\backslash $nu $=$ 1 with different magnetic fields and temperatures, which would serve as direct probes of topological superconductivity. [Preview Abstract] |
Friday, March 17, 2017 8:24AM - 8:36AM |
X39.00003: Ballistic Graphene Josephson Junctions from the Short to the Long Junction Regimes: Part I- Governing Energy Scales of the Short and Long Junctions. Ivan Borzenets, Francois Amet, Chung Ting Ke, Anne Draelos, Ming-Tso Wei, Andrew Seredinski, Kenji Watanabe, Takashi Taniguchi, Yuriy Bomze, Michihisa Yamamoto, Seigo Tarucha, Gleb Finkelstein We examine the behavior of the critical current, in ballistic Josephson junctions made of encapsulated graphene/boron-nitride heterostructures. The temperature dependence of the critical current allows us to identify and observe the crossover from the short to the long junction regimes. (The operational regime of a junction is defined by the ratio of the superconducting coherence length $\xi $ to the junction length L). For each regime we extract the governing energy scales, which are found to be consistent with theory. In the short regime, the energy is consistent with the expected superconducting gap $\Delta $. While in the long regime, the governing energy $\delta $E is independent of the carrier density and proportional to the level spacing of the ballistic cavity, as determined from Fabry-Perot oscillations of the junction normal resistance. However, in the intermediate regime, we find that junctions behave as if in the long regime, but with $\delta $E (which is typically a function of L) rescaled as L$\to $L$+\xi $. [Preview Abstract] |
Friday, March 17, 2017 8:36AM - 8:48AM |
X39.00004: Ballistic Graphene Josephson Junctions from the Short to the Long Junction Regimes: Part II- Critical current scaling of the Short and Long Junctions. Chung-Ting Ke, Ivan Borzenets, Francois Amet, Anne Draelos, Ming-Tso Wei, Andrew Seredinski, Kenji Watanabe, Takashi Taniguchi, Yuriy Bomze, Michihisa Yamamoto, Seigo Tarucha, Gleb Finkelstein The Josephson effect describes the phenomenon of coupling a supercurrent between superconductors through a weak link. Using graphene as this weak link has seen much interest due to its tunable density and related Dirac fermion physics. Previously we have studied the critical current scaling in diffusive graphene samples with different junction lengths. For ballistic junctions, however, knowledge about transport properties remains scarce. With clean encapsulated graphene, studying the supercurrent transport mechanism in ballistic samples has now become feasible. We present measurements of ballistic graphene Josephson junctions from short to long junction limits. From their temperature dependence, we characterize the critical current in both the short and long junction cases by using the characteristic energies $\Delta $ and $\delta $E, where $\Delta $ is the superconducting gap and $\delta $E is the level spacing in the long junction case. At low temperatures, as K$_{\mathrm{B}}$T \textless $\Delta $ for short junctions and K$_{\mathrm{B}}$T \textless $\delta $E for long ones, we show that the critical current saturates at a level determined by the product of $\Delta $ (or $\delta $E) and the number of the junction's transversal modes. [Preview Abstract] |
Friday, March 17, 2017 8:48AM - 9:00AM |
X39.00005: Andreev reflection at graphene-superconductor interface in the quantum Hall regime. Da Wang, Evan Telford, Avishai Benyamini, Andrew Wieteska, James Hone, Cory Dean, Abhay Pasupathy At metal-superconductor interface Andreev processes occur where an electron tunneling into the superconductor carries with it a second electron, effectively reflecting a hole with opposite momentum back into the metal. This is due to the superconducting gap, which, at low energies, only allows the formation of cooper pairs inside the superconductor, representing an accessible way to measure many body tunneling phenomena. An important requirement for strong Andreev processes is a clean interface with a high transmission probability. As shown recently, graphene and bi-layer graphene are perfect candidates as they can have extremely clean interfaces to superconductors. Graphene also has a remarkably large mean free path, which allows accurate measurement of reflected and transmitted currents. In the quantum hall regime, chiral edge states open new possibilities to measure novel Andreev processes. So far, experimental evidence and a clear physical picture of Andreev processes at the interface of graphene systems in the quantum Hall regime is a work in progress. In this work, we present recent experimental results on graphene-superconductor interfaces created in a well-controlled inert atmosphere. [Preview Abstract] |
Friday, March 17, 2017 9:00AM - 9:12AM |
X39.00006: Robust 4$\pi$ periodicity in ballistic graphene Josephson junctions Anne Draelos, Chung-Ting Ke, Ivan Borzenets, Ming-Tso Wei, Andrew Seredenski, Kenji Watanabe, Takashi Taniguchi, Russell Deacon, Michihisa Yamamoto, Yuriy Bomze, Seigo Tarucha, Francois Amet, Gleb Finkelstein We present direct current magnetic interference measurements on ballistic graphene Josephson junctions. The observed Fabry-Perot cavity is studied by applying a small magnetic field up to 5 mT to modulate the phase of the Josephson junction. Unlike the monotonic behavior at highly doped regions, irregular interference patterns are observed near the Dirac point. For highly doped regions, the uniform distribution of supercurrent can be seen. In the Fabry-Perot cavity region, the supercurrent distribution shows an edge-bulk type alternating feature. This can be understood as cavity quantization off or on resonance. However, an unexpected periodicity doubling is also observed that results in a single electron SQUID interference pattern. Instead of regular h/2e periodicity, a single electron supercurrent state can result in h/e periodicity, which may be observed as 4$\pi$ periodicity in magnetic interference measurements. This 4$\pi$ periodicity is seen in several different samples at many back gate locations. Moreover, it is robust against temperature changes. [Preview Abstract] |
Friday, March 17, 2017 9:12AM - 9:24AM |
X39.00007: p-wave triggered superconductivity in single layer graphene on an electron-doped oxide superconductor Angelo Di Bernardo, Oded Millo, Matteo Barbone, Hen Alpern, Yoav Kalcheim, Ugo Sassi, Anna Ott, Domenico De Fazio, Duhee Yoon, Mario Amado, Andrea Ferrari, Jacob Linder, Jason Robinson Physical systems supporting unconventional superconducting states, where electrons pair up in a parallel spin (spin-triplet) state other than in a conventional antiparallel spin (spin-singlet) state, have been extensively investigated over the past few years due to their potential application in spintronics devices operating in the superconducting regime [1]. These systems include $p$-wave superconductors, where pairing correlations are intrinsically in a spin-triplet state, and magnetically inhomogeneous ferromagnet/$s$-wave superconductor heterostructures [2-3]. In this talk, I will discuss our low-temperature scanning tunneling spectroscopy results, which demonstrate evidence for the emergence of a $p$-wave superconducting state in single-layer graphene (SLG) proximity-coupled to the electron-doped high-temperature superconductor Pr$_{1.85}$Ce$_{0.15}$CuO$_{4\, }$[4]. [1] Linder, J. {\&} Robinson, J.W.A., Nat. Phys. 11, 307 (2015). [2] Di Bernardo, A. \textit{et al.}, Nat. Comm. 6, 8053 (2015). [3] Robinson, J.W.A: \textit{et al.}, Science 329, 59 (2010). [4] Di Bernardo, A. \textit{et al.}, accepted for publication. [Preview Abstract] |
Friday, March 17, 2017 9:24AM - 9:36AM |
X39.00008: Abstract Withdrawn
|
Friday, March 17, 2017 9:36AM - 9:48AM |
X39.00009: Electrolyte Gating of YBCO Josephson Junctions Sam Stanwyck, Ethan Cho, Shane Cybart, Robert Dynes, David Goldhaber-Gordon We report low-temperature transport measurements of electrolyte-gated Josephson junctions in thin films of YBa$_{2}$Cu$_{3}$O$_{7-d}$. The junctions are formed using ion damage from a 0.5 nm focused He-ion beam, allowing for junction barriers down to a few nm in length. The barrier can be tuned continuously from a reduced T$_{C}$ superconductor to a normal metal to an insulator by varying the ion dose. We use an ionic liquid electrolyte combined with a thin protective layer of hexagonal Boron Nitride to reversibly modify the junction properties. [Preview Abstract] |
Friday, March 17, 2017 9:48AM - 10:00AM |
X39.00010: Unusual Fraunhofer spectroscopy of superconductor-topological insulator-superconductor junctions Angela Chen, Moon Jip Park, Gregory MacDougall, Matthew Gilbert, Nadya Mason Three dimensional topological insulators are characterized by their conducting surface states, where electrons are spin momentum locked on the surfaces. Coupling the surface states of a topological insulator to an s-wave superconductor is expected to yield unconventional superconductivity. To better understand how supercurrents are carried on the surface states of a topological insulator, we perform Fraunhofer spectroscopy measurements on proximity-coupled Bi2Se3. In a junction with a conventional superconductor, the interference of uniformly distributed supercurrents would result in a standard single-slit Fraunhofer pattern. However, we find that by applying additional external magnetic fields, we can strongly modulate a standard Fraunhofer pattern into an interference pattern with unusual features. This may be an indication of spin momentum locked surface states in Bi2Se3. [Preview Abstract] |
Friday, March 17, 2017 10:00AM - 10:12AM |
X39.00011: Analysis of pairing symmetry for half-flux quantization measured in the YBCO-Pb corner junction and DC SQUIDs and in the tricrystal superconducting ring of YBCO Hyun-Tak Kim For cuprate high-Tc superconductors, the pairing symmetry of Cooper is still controversial and remains unsolved. This is a central issue for the mechanism of high-Tc superconductivity. For the measurements of flux quantization obtained in the YBCO-Pb corner junction [1], DC-SQUID SQUIDS [2,3,4] and in the tricrystal superconducting ring of YBCO [5,6], the results had suggested that the measured half fluxes are strong evidence of the dx2-y2 (or d) pairing symmetry. This has still an influence on the superconductor mechanism research. At this time, we feel reanalysis of the measured half-flux-quantum data, because of the unclear analysis on flux trap in the papers. The authors [1] analyzed that the Fraunhofer diffraction pattern is symmetry, and the authors [2-6] also suggested that the measured half-flux quantum comes from supercurrent induced by the superconducting ring. However, we found asymmetry of the Fraunhofer diffraction pattern, an anomalous large supercurrent, asymmetry in the half-flux quantum SQUID image. These are evidence of flux trap denying the d-wave symmetry. We suggest the s-wave pairing symmetry. [1] PRL 74(1995)797, [2] PRL 71(1993)2134, [3] PRL 74(1995)4523, [4] IEEE Trans. Appl. Super. 7(1997)2331, [5] PRL 73(1994)593, [6] Rev. Mod. Phys.. 72(2000)969. [Preview Abstract] |
Friday, March 17, 2017 10:12AM - 10:24AM |
X39.00012: Macroscopic quantum tunneling of bound fractional Josephson vortices in multi-gap superconductor tunnel junctions. Van Mayes, Ju Kim We investigate macroscopic quantum tunneling of bound fractional Josephson vortex (fluxon) pairs. These fractional fluxons can arise when spatial phase textures (i-solitons) are excited in the broken time reversal symmetry state of a long Josephson junction (LJJ) with two-band superconductors. Similar to the situation in a Y Ba$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7}}-$x superconductor film grain boundary [1], this spatial dependence of the critical current density can self-generate magnetic flux in the insulator layer, resulting in fractional fluxons with large and small fraction of flux quantum. Interaction between these fraction fluxons are repulsive at short distances, but it is attractive at longer distances, making them to form a fractional fluxon molecule. This factional fluxon molecule can tunnel through the barrier potential at low temperatures when it is placed in a metastable state formed by a microresistor in the insulator layer and bias current to LJJ. This is similar to quantum tunneling of a diatomic molecule through potential barriers. We estimate the temperature dependence of the tunneling rate of the fractional fluxon molecule. 1. R. Mint and I. Papiashvili, Phys. Rev. B 64, 134501 (2001). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700