Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session D34: Superconductivity: Josephson Effects |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Ulrich Welp, Argonne National Laboratory Room: 404 |
Monday, March 16, 2009 2:30PM - 2:42PM |
D34.00001: Temperature and Field Dependence of the Emission of Terahertz Waves from Intrinsic Josephson Junctions Ulrich Welp, Alexei Koshelev, Lutfi Ozyuzer, Cihan Kurter, Masashi Tachiki, Kazuo Kadowaki, Taku Yamamoto, Ken Gray, Wai -K. Kwok We have recently succeeded in extracting coherent cw THz-radiation from intrinsic Josephson junctions in BSCCO [Science 318, 1291, (2007)]. An electromagnetic cavity resonance inside the sample generates a coherent state in which a large number of junctions are synchronized to oscillate in phase resulting in emission powers of up to 5 $\mu $W at frequencies up to 0.85 THz. The emission displays a non-monotonic temperature dependence with a sample dependent sharp maximum in the range of 25 to 45 K which we attribute to the interplay of self-heating effects and re-trapping of intrinsic junctions. Application of magnetic fields of less than 100 Oe parallel to the CuO$_{2}$ planes as well as perpendicular leads to the rapid suppression of the emission. [Preview Abstract] |
Monday, March 16, 2009 2:42PM - 2:54PM |
D34.00002: Spin-Josephson effect in antiferromagnetic tunnel junctions Dominique Chasse, A-M.S. Tremblay In the Josephson effect, coherent Cooper pair tunneling is driven by the phase difference between the superconducting order parameters on opposite sides of the junction. By analogy, differences in order parameters across a junction should lead to coherent tunneling of the condensed objects that exist in the broken symmetry state. To exhibit the generality of this phenomenon and make predictions from a realistic model, we study the case of a tunnel junction between two itinerant antiferromagnets. At the mean-field level, we find an equilibrium current of the staggered magnetization through the junction that is proportional the normal state conductance and to $\mathbf{S}_{L}\times \mathbf{S}_{R}$ where $\mathbf{S}_{L}$ and $\mathbf{S}_{R}$ are the staggered magnetizations on either sides. Microscopically, this effect comes from coherent tunneling of spin-one charge-zero particle-hole pairs that have a net wave vector equal to the antiferromagnetic one and zero spin projection along the direction of the order parameter. We explain similarities and differences with the standard DC and AC Josephson effects. [Preview Abstract] |
Monday, March 16, 2009 2:54PM - 3:06PM |
D34.00003: Angular dependence of the radiation power of a Josephson STAR-emitter Richard Klemm, Kazuo Kadowaki We calculate the angular dependence of the power of stimulated terahertz amplified radiation (STAR) emitted from a $dc$ voltage applied across a stack of intrinsic Josephson junctions. During coherent emission, we assume a spatially uniform $ac$ Josephson current density in the stack acts as a surface electric current density antenna source, and the cavity features of the stack are contained in a magnetic surface current density source. A superconducting substrate acts as a perfect magnetic conductor with $H_{||,ac}=0$ on its surface. The combined results agree very well with recent experimental observations. Existing Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ crystals atop perfect electric conductors could have Josephson STAR-emitter power in excess of 5 mW, acceptable for many device applications. [Preview Abstract] |
Monday, March 16, 2009 3:06PM - 3:18PM |
D34.00004: Surface effects in THz wave emission from intrinsic Josephson junctions Yoshihiko Nonomura Recently THz wave emission from intrinsic Josephson junctions without external fields [1] was observed experimentally. As possible states to characterize this emission, the McCumber-like state with little spatial dependence of electric fields (for the surface impedance $Z=1$) [2] and novel phase-kink state (for large and complex $Z$) [3] have been proposed. In the present study [4] it is numerically shown that both states are stationary and that the dynamical phase transition between these two states occurs as $Z$ is varied. The McCumber-like state is stable for low current and small $Z$. For higher current, the phase-kink state accompanied with symmetry breaking along the $c$ axis is stable even for $Z=1$, though strong emission in the vicinity of cavity resonance points only takes place for larger $Z$. Value of $Z$ is optimized for the strongest emission, and effect of surface roughness will also be discussed. [1] L.~Ozyuzer {\it et al.}, Science {\bf 318}, 1291 (2007); K. Kadowaki {\it et al.}, Physica C {\bf 468}, 634 (2008). [2] H.~Matsumoto {\it et al.}, Physica C {\bf 468}, 654, 1899 (2008). [3] S.~Lin and X.~Hu, Phys.\ Rev.\ Lett.\ {\bf 100}, 247006 (2008). [4] Y.~Nonomura, arXiv:0810.3756. [Preview Abstract] |
Monday, March 16, 2009 3:18PM - 3:30PM |
D34.00005: All-MgB$_{2}$ sandwich-type Josephson junctions with MgO barrier Ke Chen, Chenggang Zhuang, Qi Li, Ye Zhu, Paul Voyles, X. X. Xi Reproducible all-MgB$_{2}$ Josephson junctions have been made to meet the expectation for superconducting electronics that can work at above 20 K. The sandwich-type junctions were fabricated using MgB$_{2}$ electrodes grown by hybrid physical-chemical vapor deposition and MgO barrier deposited by RF magnetron sputtering. The $I-V$ characteristics show tunneling behavior with a small resistive shunt. The $I_{c}R_{n}$-product is 2.1 and 0.7 mV at 4.2 and 20 K, respectively, with temperature dependence following the theory qualitatively. The junctions exhibit good Fraunhofer pattern and Shapiro steps under applied magnetic field and microwave radiation, respectively. The $J_{c}$ of the junction varies exponentially with the barrier thickness, from 100 to 2$\times $10$^{5}$ A/cm$^{2}$. Transmission electron microscopy reveals both MgB$_{2}$ layers are epitaxially grown with $c$-axis parallel to the SiC (0001) substrate normal. With the same chip $J_{c}$ spead less than 10{\%}, this junction technology has the potential for MgB$_{2}$ circuits. [Preview Abstract] |
Monday, March 16, 2009 3:30PM - 3:42PM |
D34.00006: Direct observation of THz radiation from cylindrical structure of intrinsic Josephson junction system of Bi2212 M. Tsujimoto, T. Yamamoto, H. Minami, K. Kadowaki, M. Tachiki, U. Welp, W. Kwok Intense terahertz (THz) radiation was observed from a single crystalline high-$T_{c}$ superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ (Bi2212) system$^{1, 2)}$. We have performed various experiments on THz radiation with Bi2212 rectangular mesa structure fabricated by Argon-ion-milling and photolithography technique with changing the sample parameters. In this work, we report new experimental results obtained with samples which have a cylindrical structure fabricated by focused ion beam milling. The intense emission of electromagnetic radiation can be obtained in the return blanch only. The frequency is directly measured by FT-IR spectrometer to be $f$ = 0.474 THz in this particular sample of diameter with 90 $\mu $m. This frequency value is in good agreement with the fundamental cavity resonance mode frequency. 1) L. Ozyuzer et al., Science \textbf{318} (2007) 1291 2) K. Kadowaki et al., Physica C \textbf{468} (2008) 634-639 [Preview Abstract] |
Monday, March 16, 2009 3:42PM - 3:54PM |
D34.00007: Sin(2$\phi )$ component in the current-phase relation of SFS Josephson junctions near the 0-$\pi $ transition M.J.A. Stoutimore, A.Yu. Rusanov, V.A. Oboznov, V.V. Bolginov, A.N. Rossolenko, V.V. Ryazanov, D.J. Van Harlingen We directly determined the Josephson current-phase relation (CPR) of superconductor-ferromagnet-superconductor (SFS) junctions by rf-SQUID interferometry, and corroborated it with measurements of the critical current as a function of temperature and magnetic field and rf-induced Shapiro steps in the current-voltage characteristics. Our Nb-Cu$_{47}$Ni$_{53}$-Nb trilayer junctions, with 2x2$\mu $m$^{2}$ area and 7nm CuNi thickness, show a transition with temperature from the usual Josephson 0-junction state to a $\pi $-junction state, defined by a phase difference of $\pi $ in the ground state, at temperatures between 1.5K and 3.5K. Near the transition, we observe second harmonics in the CPR, deviations from the usual Fraunhofer diffraction pattern and half-integer Shapiro steps, all consistent with a sin(2$\phi )$ component in the CPR. [Preview Abstract] |
Monday, March 16, 2009 3:54PM - 4:06PM |
D34.00008: Josephson interferometry evidence for order parameter with anisotropic and possibly complex phase in UPt3 Joel Strand, Dale Van Harlingen, J. B. Kycia, J. P. Davis, William Halperin The unconventional superconductor UPt3 exhibits many interesting properties. Among the most exciting is that it has two superconducting transitions, believed to arise from two different degenerate order parameters, at least one of which breaks time-reversal symmetry. The nature of the order parameter in each of these phases and the crossover between them is still not fully understood. We have fabricated Josephson junctions on various faces of high quality single crystals of UPt3. Measuring the magnetic field dependence of the critical current through these junctions produces patterns that reveal the intrinsic phase differences and underlying symmetry of the order parameter. Our results point to an order parameter with anisotropic and possibly complex phase that extends throughout the entire crystal. This is in contrast with our work on Sr2RuO4, which also breaks time-reversal symmetry but exhibits a distribution of dynamic chiral order parameter domains. [Preview Abstract] |
Monday, March 16, 2009 4:06PM - 4:18PM |
D34.00009: Interactions between Josephson Junction Metamaterials and Evanescent Waves Laura Adams, Steven Anlage Amplification of evanescent waves is an exciting, yet controversial application of negative index of refraction metamaterials in pursuit of creating a ``perfect lens''. We will describe evanescent wave amplification experiments using lossless metamaterials, i.e. arrays of Josephson junctions (JJ). The effects of input power, temperature, and dc magnetic field on JJ arrays below the cutoff frequency of a waveguide have been investigated. At low temperatures a pronounced, tunable microwave resonance emerges in transmission. This resonance has been systematically studied in terms of its transmission and reflection coefficients. In the regime between -45 and -25 dBm, we observe a non-hysteretic emission of microwave photons that reverberate at the same frequency. Amplification of these photons (parametric amplification) will also be described. This work was supported by the Intelligence Community Postdoctoral Fellowship program. [Preview Abstract] |
Monday, March 16, 2009 4:18PM - 4:30PM |
D34.00010: Direct test of pairing fluctuations in the pseudogap phase of an underdoped cuprate Jerome Lesueur, Nicolas Bergeal, Marco Aprili, Brigitte Leridon, Giancarlo Faini, Jean-Pierre Contour In underdoped cuprates, many experiments have provided evidence for the presence of a gap-like structure in the electronic excitations spectrum, in a region above the critical temperature and below a characteristic temperature T*. The origin of this so-called pseudogap is still hardly debated and the answer to this question turns out to be essential for the understanding of high-Tc superconductivity. One doesn't know if the pseudogap is related to superconductivity or to an order in competition. In the former case, it has been suggested that superconducting pairing fluctuations may be responsible for the partial suppression of electronic excitations. This remains to be tested experimentally, but most of the probes used to investigate the pseudogap are not sensitive to pairs and therefore cannot provide such a test. Here, we report for the first time on a direct test of pairing fluctuations in the pseudogap regime using a Josephson-like experiment. Our results shows that fluctuations survive only in a restricted range of temperature close to Tc (T-Tc$<$15K), and therefore cannot be responsible for the opening of the pseudogap at high temperature. Nature Physics 4, 608 - 611 (2008) [Preview Abstract] |
Monday, March 16, 2009 4:30PM - 4:42PM |
D34.00011: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 4:42PM - 4:54PM |
D34.00012: Underdamped fluxon diffusion in a Josephson junction parallel array Kenneth Segall, Juan Mazo, Adam Dioguardi, Nikhil Fernandes We present experimental measurements and numerical simulations on the dynamics of fluxons in a parallel array of Josephson junctions. Fluxons trapped in a parallel array of Josephson junctions upon cooldown experience a periodic potential determined by the junction critical currents and the cell inductances. As shown in two recent papers [1,2], under certain conditions fluxons can move through the array in a series of noise-induced phase slips. This leads to a low-voltage diffusion branch in the current-voltage characteristics, similar to that in underdamped phase diffusion for a single junction. Unlike underdamped phase diffusion, however, this fluxon diffusion does not need frequency-dependent damping to occur. We demonstrate the existence of this state by direct measurements of the current-voltage characteristics and measurements of the switching current distribution of the array. 1. J.J. Mazo et al. Phys. Rev. B78, 174510 (2008) 2. K. Segall et al. http://arXiv.org/abs/0807.2978, to appear in J. Low Temp. Phys. [Preview Abstract] |
Monday, March 16, 2009 4:54PM - 5:06PM |
D34.00013: A tunable Josephson current in a Rashba Ring by Aharonov-Casher Phase Xin Liu, Mario F. Borunda , Xiong-Jun Liu, Jairo Sinova We study the interference effect induced by the Aharonov-Casher (A-C) phase on the transport between an asymmetrically confined two-dimensional electron ring system and the superconducting leads of a Josephson junction. The Josephson current and the Andreev levels are studied both analytically and numerically. Our results also predict oscillations in the Josephson current due to the A-C phase in the ring that can be tuned electrically via the spin-orbit (SO) interaction. Based on these oscillations, we propose a novel mechanism to observe the A-C phase in mesoscopic rings with gate tunable SO interaction attached to superconducting leads using the Josephson current oscillations. An applicable method to control the Josephson current by a tunable gate voltage can be realized due to these phenomena. [Preview Abstract] |
Monday, March 16, 2009 5:06PM - 5:18PM |
D34.00014: Enhanced thermal activation of a superconductor-normal metal quantum interference device Jian Wei, Paul Cadden-Zimansky, Venkat Chandrasekhar We measure the magnetoresistance and current-voltage characteristics (CVC) of a superconductor-normal metal quantum interference device in the form of a mesoscopic normal-metal loop in contact with two superconducting electrodes. Below the transition temperature of the superconducting leads, sharp switching from the zero-resistance state to a finite-resistance state is observed at half-integer flux quanta. The CVC in the finite-resistance state can be described by the Ambegaokar-Halperin (AH) theory of the effect of thermal fluctuations in Josephson junctions, but here this effect of thermal flucuations is greatly enhanced. The CVC in the zero-resistance state can be described by the Langer-Ambegaokar-McCumber-Halperin theory of thermally activated phase slips in one dimensional superconductors, but also with enhanced phase slipping rates, or equivalently, lowered energy barriers. [Preview Abstract] |
Monday, March 16, 2009 5:18PM - 5:30PM |
D34.00015: Static and dynamic effects in Superconducting/Normal metal/Superconducting long junctions Francesca Chiodi, Bertrand Reulet, H\'el\`ene Bouchiat We have studied four different Nb/Al long junctions at temperatures between 1.4 K and 4K (where the Al wire is still in the normal state). We have measured their low frequency current-voltage characteristics in the presence of an RF excitation (whose frequency varies from 100 kHz to 40 GHz). All the junctions show an important increase in critical current for frequencies above a threshold, which depends on the length of the normal wire. Is Thouless frequency playing a role? We have also studied the influence of geometry (narrow / square normal wire) on W/Au junctions. We have seen that the critical current/magnetic field curve changes from the well known Fraunhofer pattern (square wire) to a Gaussian dependence (narrow wire). We are now interested in dynamic properties of SN junctions: inductively coupling a multimode LC resonator to an AC SQUID we hope to define the behaviour of Andreev bound states when excitation time becomes lower than the typical diffusion time. [Preview Abstract] |
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