Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session V23: Superconductivity: Josephson Effects II |
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Sponsoring Units: DCMP Chair: Victor Vakaryuk, Argonne National Laboratory Room: D165 |
Thursday, March 24, 2011 8:00AM - 8:12AM |
V23.00001: Lorentzian crater in superconducting microwave resonators with inserted nanowires Alexey Bezryadin, Matthew W. Brenner, Sarang Gopalakrishnan, Jaseung Ku, Nayana Shah, Paul M. Goldbart We report on observations of nonequilibrium pulsing states in microwave (i.e., GHz) coplanar waveguide(CPW) resonators consisting of superconducting MoGe strips interrupted by a trench and connected by one or more suspended superconducting nanowires. The Lorentzian resonance peak shows a ``crater'' when driven past the critical current of the nanowire, leading to a ``pulsing'' state. In the pulsing state, the supercurrent grows until it reaches the critical current, at which point all stored energy quickly dissipates through Joule heating. We develop a phenomenological model of resonator-nanowire systems, which explains the experimental data quantitatively. For the case of resonators comprising two parallel nanowires and subject to an external magnetic field, we find field-driven oscillations of the onset power for crater formation, as well as the occurrence of a new state, in which the periodic pulsing effect is such that only the weaker wire participates in the dissipation process. [Preview Abstract] |
Thursday, March 24, 2011 8:12AM - 8:24AM |
V23.00002: Characterizing Chiral Domains in Sr2RuO4 via Nanoscale Josephson Junctions D. Bahr, J.D. Strand, D.J. Van Harlingen, Y. Maeno There is substantial evidence that the ruthenate superconductor Sr$_{2}$RuO$_{4}$ has a chiral order parameter of the form p$_{x}\pm $ip$_{y}$ and forms chiral domains. In order to verify this picture and determine the size of the domains, we have fabricated Josephson junctions on the order of and smaller than the domain width of $\sim $1$\mu $m implied by Josephson interferometer experiments. Using Focused Ion Beam milling, we have patterned Sr$_{2}$RuO$_{4}$-Cu-PbIn junctions ranging in size from 0.5$\mu $m x 0.5$\mu $m to 4$\mu $m x 4$\mu $m on the edge face of a Sr$_{2}$RuO$_{4}$ crystal. By measuring the magnetic field modulation of the Josephson critical current, we can probe the phase anisotropy across the junction and determine the size and dynamics of chiral domains. Our data is consistent with the predicted domain width but also exhibits signatures that suggest the formation of chiral domain structure along the c-axis. The theoretical model of domain wall movement proposed by Bouhon and Sigrist is supported by our data. [Preview Abstract] |
Thursday, March 24, 2011 8:24AM - 8:36AM |
V23.00003: Josephson effect and Andreev scattering in a three-terminal quantum dot in the Kondo regime Akira Oguri, Yoichi Tanaka We study low-temperature transport through a single quantum dot (QD) connected to three terminals, consisting of two superconducting (SC) leads and one additional normal lead. This system shows interesting behavior caused by an interplay between Josephson, Andreev and Kondo physics. The low-energy excitations of this system can be described by a local Fermi liquid theory for the renormalized Bogoliubov particles. We calculate the renormalized parameters using the Wilson numerical renormalization group approach. The Kondo temperature and the residual interaction between the renormalized Bogoliubov particles depend sensitively on the Josephson phase $\phi$ at the crossover region between the local Cooper paring and the Kondo singlet. This crossover reflects the quantum phase transition between non-magnetic singlet and magnetic doublet states, which takes place in the case where the addition normal lead is disconnected. We will also discuss the results for the Josephson current and the DC conductance due to the Andreev reflection. [Preview Abstract] |
Thursday, March 24, 2011 8:36AM - 8:48AM |
V23.00004: Dissipation of mobile vortices in self-dual Josephson junction arrays Said Sakhi Mutual U(1) $\times $ U(1) Chern-Simons Landau-Ginzburg theory appears as an effective field theory in self-dual Josephson junction arrays. In this theory two complex fields associated with disordering electric and magnetic charges are minimally coupled to two gauge fields related to the currents of Cooper pairs and vortices. The condensation of disorder fields is employed to explore the various phases (superconducting, insulating, and metallic) of the model. In this work we investigate the interplay between the dissipation of mobile vortices and the condensation of magnetic and charge excitations. We evaluate the electromagnetic response functions of the system, and we analyze the longitudinal and the Hall conductivities as a function of the strength of dissipation. [Preview Abstract] |
Thursday, March 24, 2011 8:48AM - 9:00AM |
V23.00005: Measurement of a weak-link Josephson junction in a p-wave superconducting ring Joonho Jang, Raffi Budakian, David Ferguson, Victor Vakaryuk, Paul Goldbart, Yoshiteru Maeno We report the fabrication of a weak-link Josephson junction in a micron-size Sr$_{2}$RuO$_{4}$ ring by focused ion beam milling, and the measurement of the current-phase relation (CPR) using cantilever torque magnetometry. In the presence of a magnetic field applied perpendicular to the crystal $c-$axis, a second harmonic term in the CPR appears which may be related to the underlying spin texture of the spin-triplet condensate. The observed CPR is similar to that previously reported for weak-link junctions in $^{3}$He-B. By including the contribution from both the charge and the spin current into the Gibbs-free energy, we can accurately model the observed CPR of the Sr$_{2}$RuO$_{4}$ weak-link junction. [Preview Abstract] |
Thursday, March 24, 2011 9:00AM - 9:12AM |
V23.00006: Periodic critical current pattern in the superconductor-graphene-superconductor junction induced by the current in one of the leads Ulas Coskun, Ivan Borzenets, Gleb Finkelstein We have formed superconducting metal contacts to graphene, resulting in supercurrent through graphene visible up to several degrees Kelvin. In our geometry, graphene bridges a gap between two closely spaced superconducting wires. We have found that passing a current along the length of one of the wires periodically modulates the magnitude of the supercurrent through graphene. We discuss the origins of the observed interference patterns [Preview Abstract] |
Thursday, March 24, 2011 9:12AM - 9:24AM |
V23.00007: Intrinsic Josephson Junctions with Intermediate Damping Paul A. Warburton, Sajid Saleem, Jon C. Fenton, Susie Speller, Chris R.M. Grovenor In cuprate superconductors, adjacent cuprate double-planes are intrinsically Josephson-coupled. For bias currents perpendicular to the planes, the current-voltage characteristics correspond to those of an array of underdamped Josephson junctions. We will discuss our experiments on sub-micron Tl-2212 intrinsic Josephson junctions (IJJs). The dynamics of the IJJs at the plasma frequency are moderately damped (Q $\approx$ 8). This results in a number of counter-intuitive observations, including both a suppression of the effect of thermal fluctuations and a shift of the skewness of the switching current distributions from negative to positive as the temperature is increased. Simulations confirm that these phenomena result from repeated phase slips as the IJJ switches from the zero-voltage to the running state. We further show that increased dissipation counter-intuitively increases the maximum supercurrent in the intermediate damping regime (PRL vol. 103, art. no. 217002). We discuss the role of environmental dissipation on the dynamics and describe experiments with on-chip lumped-element passive components in order control the environment seen by the IJJs. [Preview Abstract] |
Thursday, March 24, 2011 9:24AM - 9:36AM |
V23.00008: Intrinsic Josephson effect in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ after doping by current injection S. Probst, X.Y. Jin, Y. Simsek, C. Steiner, C. Bergmann, Y. Koval, P. M\"uller By current injection we can change the properties of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ single crystals electronically in a wide range. In this work the properties of the same sample were changed multiple times in very small steps in order to investigate the doping process by current injection in greater detail. By measuring the IV characteristic of the intrinsic Josephson junctions as well as doping current and doping voltage simultaneously, the change of superconducting properties is monitored. Macroscopic quantum tunneling experiments in intrinsic Josephson junctions were performed. An exponential increase of the critical current density with hole concentration was observed. Simultaneously, the capacitance of the intrinsic Josephson junctions increases with the doping level by a factor of 5. We will discuss possible reasons for these results. [Preview Abstract] |
Thursday, March 24, 2011 9:36AM - 9:48AM |
V23.00009: Statistics of voltage fluctuations in resistively shunted Josephson junctions Michael Marthaler, Dmitry Golubev, Yasuhiro Utsumi, Gerd Sch\"on The intrinsic nonlinearity of Josephson junctions converts Gaussian current noise in the input into non-Gaussian voltage noise in the output. For a resistively shunted Josephson junction with white input noise we determine numerically exactly the properties of the few lowest cumulants of the voltage fluctuations, and we derive analytical expressions for these cumulants in several important limits. The statistics of the voltage fluctuations is found to be Gaussian at bias currents well above the Josephson critical current, but Poissonian at currents below the critical value. In the transition region close to the critical current the higher-order cumulants oscillate and the voltage noise is strongly non-Gaussian. For coloured input noise we determine the third cumulant of the voltage. [Preview Abstract] |
Thursday, March 24, 2011 9:48AM - 10:00AM |
V23.00010: Josephson effect in S/F/S junctions: spin bandwidth asymmetry vs. Stoner exchange Henrik Enoksen, Gaetano Annunziata, Jacob Linder, Mario Cuoco, Canio Noce, Asle Sudbo We analyze the dc Josephson effect in a ballistic S/F/S junction in the quasiclassical Andreev approximation. We consider the possibility of ferromagnetism originating from a mass renormalization of carriers of opposite spin, i.e. a spin bandwidth asymmetry (SBAF). We provide a general formula for Andreev levels which is valid for arbitrary interface transparency, exchange interaction, and bandwidth asymmetry. We analyze the current-phase relation, the critical current, and the free energy in the short junction regime, showing that a larger number of $0-\pi$ transitions is expected when the ferromagnetism is driven by SBAF compared to Stoner magnetism. We compare the phase diagrams of two identical junctions differing only in the mechanism by which the mid layer becomes magnetic, pointing out that the phase difference across the junction in the ground state need not be the same, even for equal polarizations. [Preview Abstract] |
Thursday, March 24, 2011 10:00AM - 10:12AM |
V23.00011: Fluxon dynamics in two-band superconductor-based long Josephson junctions Bal-Ram Ghimire, Hao-yu Tsai, Ju Kim We investigate the phase dynamics of a long Josephson junction (LJJ) with two-band superconductors such as $MgB_2$ and iron pnictides. Due to two condensates in each superconductor layer, the phase dynamics of a two-band LJJ, described by the perturbed sine-Grodon equation, becomes more complex than that for the usual LJJ with one-band superconductors. This complexity arises from the presence of inter-band Josephson current that yields soliton-like excitation. This excitation represents a large stable variation of the phase difference of the two condensates. Accounting for the soliton- like excitation, we find that the fluxon dynamics in the LJJ with two-band superconductors is influenced by the modulation of Josephson current. The Josephson current modulation yields radiation emission by the moving fluxon. Also, we discuss the effects of this current modulation on the current- voltage characteristics of the LJJ. [Preview Abstract] |
Thursday, March 24, 2011 10:12AM - 10:24AM |
V23.00012: Enhancement of macroscopic quantum tunneling in Josephson junctions with multigap superconductors through zero-point fluctuations of Josephson-Leggett mode Yukihiro Ota, Masahiko Machida, Tomio Koyama We theoretically study macroscopic quantum tunneling (MQT) in a hetero Josephson junction formed by a conventional single-gap superconductor and a multigap one such as $\mbox{MgB}_{2}$ and iron-based superconductors. In such a Josephson junction, multiple phase differences are defined and MQT dynamics are extended on a space expanded by the multiple phases. We clarify the quantum dynamics of the multiple phase differences and construct a theory for the MQT in Josephson junctions with multiple gaps. The dynamics of the phase differences are strongly affected by Josephson-Leggett mode, i.e., the fluctuation mode between the multiple phase differences and the escape rate characterizing MQT dynamics is calculated based on the effective action renormalized by the Josephson-Leggett mode. We show that the escape rate is drastically enhanced when the frequency of the Josephson-Leggett mode is less than the Josephson-plasma frequency. [Preview Abstract] |
Thursday, March 24, 2011 10:24AM - 10:36AM |
V23.00013: Parametric Amplification in Discrete Josephson Transmission Line Hamid Reza Mohebbi, A. Majedi Majedi A Series-connected discrete Josephson transmission line (DJTL) which is periodically loaded by open stubs is studied to investigate various aspects of traveling-wave parametric amplification. The dispersion analysis is made to ensure the existence of three non-degenerate time-harmonic waves interacting with each other through the phase matching condition which is imposed by the cubic nonlinearity associated with each junction. Having weak nonlinearity and slow varying assumptions, we exploit the perturbation theory with the multiple scale technique to derive the three coupled nonlinear partial differential equations to describe their spatial and temporal amplitude variations in this parametric interaction. Cases of perfect phase-matching and slight mismatching are addressed in this work. The numerical analysis based on the spectral method in space and finite difference in time domain are used to monitor the unilateral gain, stability and bandwidth of the proposed structure. This structure can be used as a mesoscopic platform to study the creation of squeezed states of the microwave radiation. These properties make this structure desirable for applications ranging from superconducting optoelectronics to dispersive readout of superconducting qubits where high sensitivity, fast speed and low-noise operation is required. [Preview Abstract] |
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