Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K31: Josephson Junctions |
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Sponsoring Units: DCMP Chair: James Valles, Brown University Room: LACC 407 |
Wednesday, March 7, 2018 8:00AM - 8:12AM |
K31.00001: Nano Josephson junctions patterned with a focused helium ion beam Ethan Cho, Yuchao Zhou, Shane Cybart We will present Y-Ba-Cu-O nano Josephson junctions directly written with a focused helium ion beam. Junctions with widths as small as 25 nm were created with precise control over junction parameters like resistance and critical current. In some geometries the voltage state resistance of these nano junctions can be made larger than 1kΩ! For typical planar Y-Ba-Cu-O junctions the Stewart-McCumber Parameter βC=2e*2π/h*IC*RN*RN*C is very small, however, in these devices we demonstrate high βC, hysteretic current-voltage characteristics by tuning junction resistance and capacitance. |
Wednesday, March 7, 2018 8:12AM - 8:24AM |
K31.00002: THz emission at 80 Kelvin from stacked Bi2Sr2CaCu2O8 Intrinsic Josephson Junctions Timothy Benseman, Alexei Koshelev, Vitalii Vlasko-Vlasov, Ulrich Welp, Wai-Kwong Kwok, Kazuo Kadowaki The extremely anisotropic high-temperature superconductor Bi2Sr2CaCu2O8 contains stacked 'intrinsic' Josephson junctions with a large superconducting gap energy. Mesa-shaped devices constructed from this material are therefore a promising source of coherent, continuous-wave radiation in the 'terahertz gap' range. However, a key issue for technological applications of these devices is their cryocooling requirements, and it is therefore highly desirable to optimize their performance to allow them to operate at 77 Kelvin or above. Here we report generation of 40 microwatts of coherent emission power at 0.45 THz at a bath temperature of 80 Kelvin. This was achieved by exciting the (3, 0) cavity mode of a stack containing 580 junctions and with dimensions 300 × 180 × 0.9 μm3. The device was heatsunk using PbSn solder and a copper substrate. We discuss the choice of mesa dimensions, and the implications of the choice of the cavity mode for THz-frequency dissipative losses - and therefore THz generation - close to the device's superconducting critical temperature of 86.5 Kelvin. |
Wednesday, March 7, 2018 8:24AM - 8:36AM |
K31.00003: Study of Joule heating characteristics of Bi2Sr2CaCu2O8+δ high-Tc superconducting terahertz emitters Takanari Kashiwagi, Taiga Tanaka, Chiharu Watanabe, Hiroyuki Kubo, Yuki Komori, Takumi Yuasa, Yuki Tanabe, Ryusei Ota, Genki Kuwano, Kento Nakamura, Manabu Tsujimoto, Hidetoshi Minami, Takashi Yamamoto, Richard Klemm, Kazuo Kadowaki In order to understand the emission characteristics of Bi2Sr2CaCu2O8+δ (Bi2212) high-Tc superconducting THz emitters, it is very important to clarify the Joule heating characteristics of the devices. Recently, in order to reduce the self-heating from the Bi2212-THz emitters, we have proposed a stand-alone mesa structure of Bi2212 single crystals and its sandwich structures. The radiation characteristics obtained from these devices indicate clearly that the thermal management of the THz emitters is most important issue in order to obtain good radiation performance and reproducibility. |
Wednesday, March 7, 2018 8:36AM - 8:48AM |
K31.00004: Fractional Fluxon dynamics in Long Josephson Junctions Lawrence Rhoads, Van Mayes, Ju Kim, Ram Shoham Fluxons are promising candidates for qubits in superconducting quantum computers. Fluxons are quantized loops of magnetic flux found in long Josephson Junctions. These fluxons arise due to the time reversal symmetry breaking in a long Josephson junction (LJJ) with two-band superconductors. The spatial dependence of the critical current density can generate magnetic flux in the insulator layer, creating two fractional fluxons. The interaction between the them is repulsive at short distances, but attractive at long distances, causing the formation of a fractional fluxon bound pair. An investigation of the dynamics of this pair as a function of various parameters is presented. The separation distance between fluxons as a function of bias current, the observability of each fluxon, and Macroscopic Quantum Tunneling (MQT) behavior through a barrier are examined. |
Wednesday, March 7, 2018 8:48AM - 9:00AM |
K31.00005: Tunable TaxN Josephson Junctions for Scalable, High Performance, Low Power Computing Matthaeus Wolak, Rupert Lewis, Michael Henry, Steven Wolfley, Lyle Brunke, Nancy Missert Viable alternatives for high performance, low-power dissipation computing has driven increased interest in superconducting electronics research. Although remarkable progress has been made with Nb/Al-AlOx/Nb Josephson junctions, the necessity for low-temperature processing and the electronic defects associated with AlOX may ultimately limit the ability to scale this technology to the required density. Alternative barriers such as TaN offer a feasible approach to achieve Josephson junctions with suitable IcRn product and thermal stability for existing microfabrication processes. |
Wednesday, March 7, 2018 9:00AM - 9:12AM |
K31.00006: Linewidth Dependence of Coherent Terahertz Waves Emitted from a Stack of Intrinsic Josephson Junctions in BSCCO Genki Kuwano, Takanari Kashiwagi, Yota Kaneko, Hidetoshi Minami, Kazuo Kadowaki, Yilmaz Simsek, Wai-Kwong Kwok, Ulrich Welp, Richard Klemm, Manabu Tsujimoto The observation of coherent terahertz radiation from a stack of intrinsic Josephson junctions in BSCCO [L. Ozyuzer et al., Science (2007)] highlighted the possibility of using high-transition-temperature superconductors (HTS) as a novel terahertz source. The coherence of the emitted waves from HTS was investigated by linewidth measurements using a superconducting integrated receiver [M. Li, et al., PRB (2012)]. A peculiar line shape with relatively narrower linewidth down to 23 MHz was observed in the high-bias regimes, where temperature distribution in the emitting stack is extremely inhomogeneous. Here, we present a new measurement system based on the heterodyne technique using a sub-harmonic diode mixer. In order to unveil the intrinsic behavior of linewidths independently of the temperature inhomogeneity in the stack, we measured the line shapes associated with the terahertz waves emitted from stand-alone-type mesa samples that form rather uniform temperature distributions due to better cooling. In this talk, we will present experimental results related to the linewidth measurements. |
Wednesday, March 7, 2018 9:12AM - 9:24AM |
K31.00007: Fabrication and characterization of van der Waals Josephson junctions Harpreet Singh Arora, Jash Banker, Youngjoon Choi, Jeannette Kemmer, Stevan Nadj-Perge Stacking of two-dimensional materials has given us the ability to create innumerable hybrid electronic systems, one such system being Josephson junctions (JJs). A major bottleneck in inducing proximity based superconductivity in 2-d materials is poor interface quality leading to low transparency. I will discuss our recent efforts in creating van der Waals JJs with 2-d superconductors like NbSe2 having pristine interfaces. Low temperature characterization of these JJs in the presence of magnetic fields will also be discussed. These junctions are a starting point for exploring unconventional Josephson physics and topological superconductivity. |
Wednesday, March 7, 2018 9:24AM - 9:36AM |
K31.00008: Graphene Josephson Junctions with Narrowly Defined Trenches Andrew Seredinski, Anne Draelos, Ming-Tso Wei, Chung-Ting Ke, Tate Fleming, Yash Mehta, Ethan Mancil, Hengming Li, Takashi Taniguchi, Kenji Watanabe, Seigo Tarucha, Michihisa Yamamoto, Ivan Borzenets, Francois Amet, Gleb Finkelstein We present new results obtained from encapsulated graphene/boron-nitride heterostructure devices in which narrow trenches have been etched. These trenches are created both through e-beam lithography / reactive ion etching as well as through helium ion milling. We confirm cut widths on the order of tens of nanometers using scanning electron microscopy and atomic force microscopy. We report on several Josephson junction devices made by contacting these mesas with superconducting electrodes and demonstrate supercurrent in the quantum Hall regime. The dependence of this supercurrent on magnetic field is studied and compared to geometrical expectations. |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K31.00009: Cherenkov Instability of Driven Vortices in a Stack of Intrinsic Josephson Junctions Ahmad Sheikhzada, Alexander Gurevich We investigated stability of flux flow of parallel vortices in a layered superconductor modeled by a stack of coupled Josephson junctions with parameters characteristic of BSCCO crystals. Our numerical simulations of vortices propagating along coupled layers have shown that, once a vortex reaches a critical velocity, it triggers a cascade of vortex-antivortex pairs which form a dissipative domain expanding both along and across the layers and ultimately driving the entire stack into a resistive state. This effect caused by a critical wake of Cherenkov radiation behind moving vortices is most pronounced in underdamped junctions at low temperatures for which the instability occurs at a threshold current density Js well below the Josephson critical current density of the interlayer junctions. Here Js(H) decreases as the density of vortices increases. In the resistive state at J>Js standing electromagnetic modes are generated in a stack of layers with open edges, or propagating waves are generated in a stack of annular Josephson junctions. |
Wednesday, March 7, 2018 9:48AM - 10:00AM |
K31.00010: Abstract Withdrawn
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Wednesday, March 7, 2018 10:00AM - 10:12AM |
K31.00011: Effect of in-plane magnetic field on the Fraunhofer pattern in Bi2Se3 based Josephson junction. Alexandre Assouline, Cheryl FEUILLET-PALMA, Tianzhen Zhang, Alexandre Zimmers, Nicolas Bergeal, Paola Atkinson, Mahmoud Eddrief, Massimiliano Marangolo, Marko KUZMANOVIC, Marco Aprili, Herve Aubin We present a study of Josephson junctions based on MBE grown Bi2Se3 thin films contacted to superconducting aluminum electrodes. While past works have already been published on this system, we present new results that highlight the role of spin-orbit coupling on the Josephson current. On the one hand, we present a measurement of the current-phase relationship, which is found to be sinusoidal as expected for conventional Josephson junctions. On the other hand, we present, in this system, the first measurement of the Fraunhofer pattern with an in-plane magnetic field. While the Fraunhofer pattern is symmetric at zero in-plane magnetic field, it becomes asymmetric upon increasing the amplitude of the in-plane magnetic field. Theoretically, this behavior is understood as the consequence of strong spin-orbit coupling and disorder [1], a behavior that has also been observed recently with the semiconductor InAs [2]. |
Wednesday, March 7, 2018 10:12AM - 10:24AM |
K31.00012: Principles of a cryogenic memory cell design using small arrays of coupled Josephson junctions Yehuda Braiman, Niketh Nair, Neena Imam We present a cryogenic memory cell design paradigm that is based on the dynamics of small coupled array of Josephson junctions [1, 2]. All the basic memory operations (e.g., Write, Read, and Reset) are implemented on the same circuit and different junctions in the array can in principle be utilized for these operations. The presented memory operation paradigm is fundamentally different from conventional single quantum flux operation logics (SFQ). We have calculated memory cell access times and access energies that are in the ranges of tens of ps for access times and 10-18-10-19 J for access energies. As an example, we will discuss memory cell operation driven by a SFQ pulse employing an inductively coupled array of three Josephson junctions. |
Wednesday, March 7, 2018 10:24AM - 10:36AM |
K31.00013: NbSe2–graphene–NbSe2 Van Der Waals-contacted Planar Josephson Junctions Jongyun Lee, Minsoo Kim, Kenji Watanabe, Takashi Taniguchi, Hu-Jong Lee Recently, many exotic characteristics of graphene and other cleavable two-dimensional (2D) materials have been investigated extensively. Above all, heterosturctures of those 2D materials built by van der Waals (vdW) coupling reveal assorted novel physical properties and atomically flat clean interfaces [1]. Here, we present our preliminary results on the transport characteristics of graphene planar Josephson junctions (JJs), where NbSe2 was used as a superconducting (SC) electrode material. Graphene–hexagonal-boron-nitride (hBN) bilayer was transferred onto NbSe2 flakes which were closely pre-arranged to make clean interfaces. Entire graphene and NbSe2 flakes are encapsulated by a hBN layer to protect the JJ from chemical contamination during the fabrication processes. The JJ thus fabricated by the chemical-free scheme can lead to enhancing the JJ performance. We characterize the Josephson coupling nature of the junctions by examining the temperature and magnetic field dependence of the junction critical current (Ic) and the SC energy gap (Δ), the size of the IcRN product (RN; normal-state junction resistance) in comparison with the 0 K value of Δ/e. |
Wednesday, March 7, 2018 10:36AM - 10:48AM |
K31.00014: Shaping the superconducting properties of nanoscale junctions by electromigration Joseph Lombardo, Xavier Baumans, Zeljko Jelic, Jeremy Brisbois, Gorky Shaw, Vyacheslav Zharinov, Jeroen Scheerder, Victor Moshchalkov, Ge He, Heshan Yu, Jie Yuan, Beiyi Zhu, Kui Jin, Roman B. G. Kramer, Milorad Milosevic, Joris Van de Vondel, Alejandro Silhanek High current densities in small metallic junctions can produce electron-assisted atomic diffusion known since the 60’s as responsible for failures in metallic interconnections. Controlling and using this phenomenon permits one to tune the material superconducting properties at the nanoscale[1]. Here we demonstrate its reversible character for three types of superconductors: Al, Nb and LCCO[2]. For the latter material, we show that selective migration of oxygen atoms and the consequent doping modification induces a transition from a superconducting state to an insulating state in a reversible way. For the case of Nb, a high level of control of the electromigration allowed us to locally change the material properties (superconducting critical temperature and normal state resistance) and to form in situ tunable weak links. Numerical simulations within the Ginzburg-Landau formalism are also presented and show excellent agreement with the experimental data. These findings provide an easy method for the in situ fabrication of weak links and pave the way for a reversible control of nanowires properties. |
Wednesday, March 7, 2018 10:48AM - 11:00AM |
K31.00015: Josephson Junctions in Graphene Constrictions in the Quantum Hall Regime Ming-Tso Wei, Anne Draelos, Andrew Seredinski, Chung-Ting Ke, Yash Mehta, Ethan Mancil, Kenji Watanabe, Takashi Taniguchi, Michihisa Yamamoto, Seigo Tarucha, Ivan Borzenets, Francois Amet, Gleb Finkelstein Several groups have recently reported on samples made of encapsulated graphene with superconducting contacts in the quantum Hall (QH) regime. Here, we study ballistic graphene Josephson devices based on ~100nm constrictions between superconducting molybdenum-rhenium electrodes in the QH regime. A robust supercurrent has been observed up to 2.5 T, well above the onset of the Hall quantization. We demonstrate that the supercurrent is conducted by the states within the short and narrow channel confined on each side by the gapped graphene bulk. This situation is different from our previous observation of supercurrent. |
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