Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session P25: Superconducting Tunneling: Josephson Effect and THz Emission |
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Sponsoring Units: DCMP Chair: Richard Klemm, University of Central Florida Room: 324 |
Wednesday, March 16, 2016 2:30PM - 2:42PM |
P25.00001: Effect of impurities on the Josephson current through helical metals: Exploiting a neutrino paradigm Pouyan Ghaemi, V. Parameswaran Nair In this talk we present our results on the effect of time-reversal symmetric impurities on the Josephson supercurrent through two dimensional helical metals such as on topological insulator surface state. We show that contrary to the usual superconducting-normal metal-superconducting junctions, the suppression of supercurrent in superconducting-helical metal-superconducting junction is mainly due to fluctuations of impurities in the junctions. Our results, which is a condensed matter realization of a part of the MSW effect for neutrinos, shows that the relationship between normal state conductance and critical current of Josephson junctions is significantly modified for Josephson junctions on the surface of topological insulators. We also study the temperature-dependence of supercurrent and present a two fluid model which can explain some of recent experimental results in Josephson junctions on the edge of topological insulators. [Preview Abstract] |
Wednesday, March 16, 2016 2:42PM - 2:54PM |
P25.00002: "Hybrid" multi-gap/single-gap Josephson junctions: Evidence of macroscopic quantum tunneling in superconducting-to-normal switching experiments on MgB2/I/Pb and MgB2/I/Sn junctions Steve Carabello, Joseph Lambert, Wenqing Dai, Qi Li, Ke Chen, Daniel Cunnane, X. X. Xi, Roberto Ramos We report results of superconducting-to-normal switching experiments on MgB$_2$/I/Pb and MgB$_2$/I/Sn junctions, with and without microwaves. These results suggest that the switching behavior is dominated by quantum tunneling through the washboard potential barrier, rather than thermal excitations or electronic noise. Evidence includes a leveling in the standard deviation of the switching current distribution below a crossover temperature, a Lorentzian shape of the escape rate enhancement peak upon excitation by microwaves, and a narrowing in the histogram of escape counts in the presence of resonant microwave excitation relative to that in the absence of microwaves. These are the first such results reported in ``hybrid" Josephson tunnel junctions, consisting of multi-gap and single-gap superconducting electrodes. [Preview Abstract] |
Wednesday, March 16, 2016 2:54PM - 3:06PM |
P25.00003: ABSTRACT WITHDRAWN |
Wednesday, March 16, 2016 3:06PM - 3:18PM |
P25.00004: Superconducting quantum interference devices made with normal metal and insulator barrier Josephson junctions in Y-Ba-Cu-O directly written with a focused helium beam Ethan Cho, Meng Ma, Chuong Huynh, Kevin Pratt, Doug Paulson, Victor Glyantsev, Robert Dynes, Shane Cybart We will present electrical transport data for Y-Ba-Cu-O superconducting quantum interference devices (SQUIDs) with focused helium ion damage Josephson junctions. The junctions were directly written with a 30~keV focused helium ion beam, which locally creates disorder in Y-Ba-Cu-O that induces a superconducting-insulator transition. SQUIDs with Josephson junctions written with a dose of 4$\times10^{16}$~He$^+$/cm$^2$ have metallic barriers and show a current-voltage characteristic (I-V) well-described by the resistively shunted junction model. The spectral density of the flux noise is 10~$\mu\Phi_0/\surd$Hz at 10~Hz and the white noise at higher frequencies is 2~$\mu\Phi_0/\surd$Hz. SQUIDs with junctions written with higher ion doses ($\sim9\times10^{16}$~He$^+$/cm$^2$) have insulating Josephson barriers with a critical current of 22~$\mu$A and a resistance of 12~$\Omega$ at 4~K. The I-V for all of these devices is not hysteretic due to the small capacitance and the resistance. At higher voltage the junction I-V curve shows tunnel-junction behavior and a superconducting energy gap edge at 20~mV. We will discuss how these results are a promising step forward for sensitive magnetic sensors made from high temperature superconductors at various temperatures. [Preview Abstract] |
Wednesday, March 16, 2016 3:18PM - 3:30PM |
P25.00005: Engineering the parity lifetime of NbTiN Cooper-pair transistors Attila Geresdi, David van Woerkom, Tamas Krivachy, Sebastian Rubbert, Anton R. Akhmerov, Leo P. Kouwenhoven Controlling the quasiparticle occupation of a superconducting island is of fundamental importance for superconducting circuits as single electron tunneling results in decoherence. Thus far, engineering superconducting tunnel junctions for quantum bits was done exclusively based on aluminum, which limits integration with systems requiring finite magnetic field, such as topological superconductors based on spin-orbit coupled nanowires or spin ensembles. Here we present parity modulation of the switching current of a niobium titanium nitride (NbTiN) Cooper-pair transistor coupled to aluminum (Al) leads for the first time. Owing to the gap profile $\Delta _{island}$\textgreater \textgreater $\Delta_{leads}$, we observe a parity lifetime exceeding 1 minute in combination with a Josephson energy of 50 $\mu $eV. We link this value to the finite subgap density of states of NbTiN, which is consistent with the subgap conductance measured by DC transport. We discuss our design of quasiparticle trapping and radiation shielding techniques, which resulted in a non-saturated parity lifetime down to a fridge temperature of 12 mK. Finally, we show that this circuit is compatible with magnetic fields in the range of 100 mT. [Preview Abstract] |
Wednesday, March 16, 2016 3:30PM - 3:42PM |
P25.00006: The cavity resonance mode of Bi$_{\mathrm{2}}$Sr$_{\mathrm{2}}$CaCu$_{\mathrm{2}}$O$_{\mathrm{8}}$ mesa terahertz sources as probed by scanning laser thermal microscopy Timothy Benseman, Alexei Koshelev, Vitalii Vlasko-Vlasov, Ulrich Welp, Wai-Kwong Kwok, Yang Hao, Boris Gross, Matthias Lange, Dieter Koelle, Reinhold Kleiner, Kazuo Kadowaki Stacked Intrinsic Josephson Junctions (IJJs) in the extremely anisotropic high-$T_{c}$ superconductor Bi$_{\mathrm{2}}$Sr$_{\mathrm{2}}$CaCu$_{\mathrm{2}}$O$_{\mathrm{8\thinspace }}$are a promising solid-state source of coherent terahertz radiation in the so-called ``THz gap'' range. In these devices, a geometric resonant mode of a stack of IJJs of typical dimensions 300 x 60 x 1 microns$^{\mathrm{3}}$ acts to synchronize the individual junctions, resulting in coherent far-field THz emission. This resonance can be probed by scanning thermal laser microscopy, in which a modulated optical laser beam is rastered across the top surface of a stack. The resulting thermal perturbation to the stack's cavity mode can thus be mapped via the resulting \textit{xy}-dependent modulation of the stack's electrical resistance. Here we discuss the experimentally measured scanning laser pattern of such a THz cavity mode, and the implications of its symmetry for the mechanism of IJJ synchronization in these devices. [Preview Abstract] |
Wednesday, March 16, 2016 3:42PM - 3:54PM |
P25.00007: Artificially induced hotspots in Bi$_{\mathrm{2}}$Sr$_{\mathrm{2}}$CaCu$_{\mathrm{2}}$O$_{\mathrm{8}}$ mesa terahertz sources Yang Hao, Ulrich Welp, Alexei Koshelev, Vitalii Vlasko-Vlasov, Wai-Kwong Kwok, Kazuo Kadowaki, Timothy Benseman Mesa-shaped devices comprising stacked Intrinsic Josephson Junctions (IJJs) in the high-temperature superconductor Bi$_{\mathrm{2}}$Sr$_{\mathrm{2}}$CaCu$_{\mathrm{2}}$O$_{\mathrm{8}}$ can be used as compact sources of coherent terahertz radiation. Achieving high emission levels of THz emission power from these devices depends on efficient synchronization of the approximately 600 IJJs in the stack. Theoretical simulations of stacked IJJs, as well as some empirical results, suggest that thermal inhomogeneity of the stack may enhance THz emission power. There are a number of possible mechanisms by which this might occur, including a hotspot acting as a local resistive shunt for the IJJs (thus altering the spread of bias voltages in the stack and the junction damping dynamics) or by local self-heating reducing the phase-stiffness of the superconducting condensate in critical locations. Here we report results of artificially inducing local heating in these devices with thin film micro-heaters patterned on their surfaces, in order to determine which mechanism(s) could be responsible for self-heating-induced THz emission enhancement. [Preview Abstract] |
Wednesday, March 16, 2016 3:54PM - 4:06PM |
P25.00008: Scattering to different vortex polarity in coupled long Josephson junctions Waltraut Wustmann, Kevin D. Osborn We theoretically study the motion of flux vortices (fluxons) in structures made from discrete long Josephson junctions (DLJJs) which may have applications in the fields of reversible and low-power computing. We investigate the scattering of fluxons at specially designed interfaces where multiple DLJJs meet. Once fluxons approach the interface, flux oscillations at the interface can be temporarily excited before the fluxons continue along to another DLJJ. Under some conditions the fluxons will change their polarity (to antifluxons) and in other cases the fluxon continues without a change in polarity. We explain the dynamics through the resonant interaction of the soliton with bound states at the interface. We also study a controlled polarity gate, where the polarity of the target fluxon depends on a control fluxon which enters and exits the interface through separate DLJJs. [Preview Abstract] |
Wednesday, March 16, 2016 4:06PM - 4:18PM |
P25.00009: Instability of Driven Josephson Vortices in Long Underdamped Junctions Ahmad Sheikhzada, Alex Gurevich We show that a Josephson vortex driven by a dc current can become unstable due to strong Cherenkov radiation resulting from intrinsic nonlocal electrodynamics of long underdamped Josephson junctions. This instability is not captured by the conventional sine-Gordon equation but is described by a more general integro-differential equation for the phase difference, $\theta(x,t)$. Our numerical simulations of this nonlinear dynamic equation for different junction geometries have shown that, as the vortex reaches a critical velocity, it triggers a cascade of expanding vortex-antivortex pairs. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. Our results suggest that a rapidly moving Josephson vortex can destroy the superconducting long-range order in a way that is similar to the crack propagation in solids. [Preview Abstract] |
Wednesday, March 16, 2016 4:18PM - 4:30PM |
P25.00010: Terahertz emission from a stack of intrinsic Josephson junctions in Bi$_{2}$Sr$_{2}$Ca$_{2}$Cu$_{3}$O$_{10+\delta }$ Manabu Tsujimoto, Itsuhiro Kakeya, Shintaro Adachi, Takao Watanabe, Takanari Kashiwagi, Hidetoshi Minami, Kazuo Kadowaki Terahertz radiation in the 0.3--10 THz frequency range is a technologically attractive form of electromagnetic radiation, because it has applications in numerous fields. Terahertz generation from stacks of intrinsic Josephson junctions fabricated from Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ (Bi-2212) has become a major focus of both experimental and theoretical research [U. Welp \textit{et al.}, Nat. Photonics \textbf{7}, 702 (2013)]. Here, we observe continuous terahertz emission from a stack of intrinsic Josephson junctions made of Bi$_{2}$Sr$_{2}$Ca$_{2}$Cu$_{3}$O$_{10+\delta }$ (Bi-2223). We investigate how triple CuO$_{2}$ planes affect the c-axis current--voltage and emission characteristics. The terahertz emission spectra are measured by Fourier-transform infrared spectroscopy. [Preview Abstract] |
Wednesday, March 16, 2016 4:30PM - 4:42PM |
P25.00011: Josephson radiation from InSb-nanowire junction David van Woerkom, Alexander Proutski, Tamas Krivachy, Daniel Bouman, Ruben van Gulik, Onder Gul, Maja Cassidy, Diana Car, Erik Bakkers, Leo Kouwenhoven, Attila Geresdi Semiconducting nanowire Josephson junctions has recently gained interest as building blocks for Majorana circuits and gate-tuneable superconducting qubits . Here we investigate the rich physics of the Andreev bound state spectrum of InSb nanowire junctions utilizing the AC Josephson relation 2eV\textunderscore bias$=$hf . We designed and characterized an on-chip microwave circuit coupling the nanowire junction to an Al/AlOx/Al tunnel junction. The DC response of the tunnel junction is affected by photon-assisted quasiparticle current, which gives us the possibility to measure the radiation spectrum of the nanowire junction up to several tens of GHz in frequency. Our circuit design allows for voltage or phase biasing of the Josephson junction enabling direct mapping of Andreev bound states. We discuss our fabrication methods and choice of materials to achieve radiation detection up to a magnetic field of few hundred milliTesla, compatible with Majorana states in spin-orbit coupled nanowires. [Preview Abstract] |
Wednesday, March 16, 2016 4:42PM - 4:54PM |
P25.00012: Interaction between fractional Josephson vortices in multi-gap superconductor tunnel junctions Ju H. Kim In a long Josephson junction (LJJ) with two-band superconductors, fractionalization of Josephson vortices (fluxons) can occur in the broken time reversal symmetry state when spatial phase textures (i-solitons) are excited. Excitation of i-solitons in each superconductor layer of the junction, arising due to the presence of two condensates and the interband Josephson effect, leads to spatial variation of the critical current density between the superconductor layers. Similar to the situation in a $YBa_{2}Cu_{3}O_{7-x}$ superconductor film grain boundary [1], this spatial dependence of the crtitical current density can self-generate magnetic flux in the insulator layer, resulting in fractional fluxons with large and small fraction of flux quantum. Similar to fluxons in one-band superconductor LJJ, these fractional fluxons are found to interact with each other. The interaction between large and small fractional fluxons determines the size of a fluxon which includes two (one large and one small) fractional fluxons. We discuss the nature of interaction between fractional fluxons and suggest that i-soliton excitations in multi-gap superconductor LJJs may be probed by using magnetic flux measurements. \\ \\ 1. R. Mint and I. Papiashvili, Phys. Rev. B 64, 134501 (2001). [Preview Abstract] |
Wednesday, March 16, 2016 4:54PM - 5:06PM |
P25.00013: The emission mechanism of THz electromagnetic waves from Bi2212 mesa device Chiharu Watanabe, Hidetoshi Minami, Takeo Kitamura, Takanari Kashiwagi, Richard Klemm, Kazuo Kadowaki From the detailed study of the severe temperature inhomogeneity of the Bi2212 IJJ mesa structure often forming ``hot-spot'' at relatively higher bias current region, while the electromagnetic waves are emitted, multi terminal potential measurement of the mesa device has revealed that the equipotential part of the mesa can only give universal ac-Josephson relationship between the potential difference and the frequency measured by the FT-IR spectrometer, and it is violated as the potential is measured in the region where the hot-spot is formed. This means that the deviation of the emission frequency from the ac-Josephson effect comes from a gradient of the electrical potential distribution. This strongly suggests that the electromagnetic waves at THz frequency may be generated in the superconducting part of the mesa, where the static electric potential is uniform, satisfying the ac-Josephson relation universally no matter how much temperature gradient is. [Preview Abstract] |
Wednesday, March 16, 2016 5:06PM - 5:18PM |
P25.00014: Tunable plasma edge in Josephson junction loaded wire array metamaterial Melissa Trepanier, Daimeng Zhang, V. P. Koshelets, Steven Anlage It is desirable to have a tunable negative permittivity medium that operates in the microwave domain. The effective plasma frequency of a JJ-loaded wire array can be tuned as a function of dc current and temperature in the low current limit. To demonstrate this effect we observe a change in transmission through a single layer of 8 superconducting Nb wires that spans a rectangular waveguide. A simple model that treats the wires as an artificial dielectric with a tunable effective permittivity shows good agreement with measured results for tuning of the plasma edge. In addition we have observed interesting behavior at higher current and rf input power. The dynamics are very rich, highly hysteretic, and nonlinear. [Preview Abstract] |
Wednesday, March 16, 2016 5:18PM - 5:30PM |
P25.00015: A high $T_{\mathrm{c}}$ superconducting terahertz emitter operated from 0.5 to 2.4 THz . T. Kashiwagi, K. Sakamoto, H. Kubo, Y. Shibano, T. Enomoto, T. Kitamura, K. Asanuma, T. Yasui, C. Watanabe, K. Nakade, Y. Saiwai, T. Katsuragawa, T. Tanaka, T. Yuasa, M. Tsujimoto, R. Yoshizaki, T. Yamamoto, H. Minami, R.A. Klemm, K. Kadowaki According to our previous studies, the efficiency of the THz radiation from a high $T_{\mathrm{c}}$ superconducting emitter can be improved greatly when the stand-alone mesa structure of Bi2212 single crystal is used for the emitter$^{\mathrm{1)}}$. The principal reason for that lies in the heat removal from the mesa. Recently, we developed a new device structure with high heat exhaust from the stand-alone mesa structures and studied the radiation characteristics from the different shape of mesa structures. The results obtained from a cylindrical stand alone mesa show very wide the radiation frequencies ranging from 0.5 to 2.4 THz. Strong emission power peaks were observed at about 1.0 THz and 1.6 THz$^{\mathrm{2)}}$. 1) T. Kitamura \textit{et al.}, Appl. Phys. Lett. \textbf{105}, 202603 (2014) 2) T. Kashiwagi \textit{et al.}, Appl. Phys. Lett. \textbf{107}, 082601 (2015) [Preview Abstract] |
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