Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session B13: Josephson Junctions and SQUIDs I |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Malcolm Beasley, Stanford University Room: LACC 402B |
Monday, March 21, 2005 11:15AM - 11:27AM |
B13.00001: Properties of Nb-MoSi$_{2}$-Nb Josephson Junctions Yonuk Chong, Paul D. Dresselhaus, Samuel P. Benz We report a detailed study on the physical properties of Nb-MoSi$_{2}$-Nb Josephson junctions. MoSi$_{2}$-barrier junction turned out to be an excellent model system to study proximity-coupled Josephson junctions with rigid S/N boundary, in that it enables independent, good controls of the two relevant variables, the barrier thickness and the temperature. In addition, it can be tuned in a wide range of characteristic voltage with reasonable critical current density. These junctions have already been successfully applied to high-performance fast-programmable voltage standards with more than 100,000 junctions on a chip in the form of stacked junctions. The characteristic voltage is highly controllable, and shows exponential dependence on the barrier thickness at 4 K. The temperature dependence of the critical current density is well fit to the proximity-coupled junction theory, and we could extract relevant material parameters quantitatively. [Preview Abstract] |
Monday, March 21, 2005 11:27AM - 11:39AM |
B13.00002: Search for Second-Order Josephson tunneling in SFS Josephson junctions S.M. Frolov, D.J. Van Harlingen, V.A. Oboznov, V.V. Bolginov, A.K. Feofanov, V.V. Ryazanov SFS (Superconductor-Ferromagnet-Superconductor) Josephson junctions can exhibit transitions between ordinary Josephson (0-junction) tunneling and pi-junction behavior as a function of barrier thickness or temperature. Close to the 0-$\pi $ crossover at which the first-order Josephson component vanishes, it has been predicted that second-order Josephson tunneling, characterized by a \textit{sin(}2$\phi )$ component in the supercurrent, can dominate. If present, this component can be detected directly by measurements of the current-phase relation and can induce period doubling in the critical current diffraction patterns and generate half-integer Shapiro steps. However, such effects can also arise near the 0-$\pi $ transition from a distribution of 0-junction and $\pi $-junction regions due to a non-uniform ferromagnetic barrier. We compare the results of measurements on junctions with uniform and non-uniform ferromagnetic barriers to determine whether observed second harmonics arise from a microscopic \textit{sin(}2$\phi )$ component or from junction non-uniformity. [Preview Abstract] |
Monday, March 21, 2005 11:39AM - 11:51AM |
B13.00003: Non-equilibrium spin-transfer torque in voltage-biased SFS and SFNFS Josephson junctions Erhai Zhao, J. A. Sauls We report theoretical results for the non-equilibrium spin current and spin-transfer torque in voltage biased SFS and SFNFS Josephson structures. We discuss the role and interplay of spin filtering, spin rotation and Andreev scattering. These processes lead to identifiable structures in the d.c. and a.c. components of the spin current and the spin-transfer torque. Our calculations are based on a recent formulation of the boundary conditions for non-equilibrium quasiclassical Riccati equations.$^{\dag}$ \newline $^{\dag}$ E. Zhao, T. L\"ofwander, and J. A. Sauls, Phys. Rev. B 70, 134510 (2004). [Preview Abstract] |
Monday, March 21, 2005 11:51AM - 12:03PM |
B13.00004: Ratchet effect in Josephson junction arrays: simulations vs experiments Veronica I. Marconi, Daniel Dominguez The ratchet effect in Josephson Junction arrays (JJA) has been proposed and studied some years ago, but only very recently has been measured in a new design of JJA that generates a sawtooth potential (asymmetric and periodic pinning potential) for vortices and antivortices. With transport measurements they were able to show the rectified motion of excitations. Here we presents simulations on the dynamics of vortices in overdamped modulated JJA at finite temperature, where we create the ratchet potential modifying the critical currents of the sample as it was done in the experiments. A good agreement with the experiments in the voltage response when an ac current is applied, was obtained. We were able to characterized the vortex structures for different vortex densities and different ratchet potentials as a function of the amplitude of the ac-current applied. [Preview Abstract] |
Monday, March 21, 2005 12:03PM - 12:15PM |
B13.00005: Macroscopic quantum tunneling of phase-locked fluxons in coupled long Josephson junctions Ju Kim, Kyungsun Moon Macroscopic quantum tunneling (MQT) of phase-locked fluxon- fluxon (FF) and fluxon-antifluxon (FAF) pairs from a metastable state in two inductively coupled long Josephson junctions (LJJ) is investigated. We show that, in the absence of a magentic field, the fluxons in the FF pair and the fluxon and antifluxon in the FAF pair tunnel as independent particles when the magnetic induction effect is weaker than the pinning effect due to columnar defects. However, the FAF pair tunnel coherently as a single quantum particle when the magnetic induction effect becomes stronger. We show that the tunneling rate is modified by the magnetic induction effect. [Preview Abstract] |
Monday, March 21, 2005 12:15PM - 12:27PM |
B13.00006: Phase diagram of two capacitively coupled Josephson Guillermo Ramirez-Santiago, Jorge Jose V We study the phase diagram of two capacitively coupled Josephson junction arrays with charging energy $E_{c}$, and Josephson coupling energy $E_{J}$ in a perpendicular homogeneous magnetic field with frustration $F=$ 1/2 and 1/3. The results are obtained using a path integral Quantum Monte Carlo algorithm. The parameter $\alpha_i$ that quantifies the quantum fluctuations in the i-th array is defined by $\alpha_i={E_{c}}_i/{E_{J}}_i$. We find that thermal fluctuations are important when $\alpha \leq 1.5$ and the quantum fluctuations dominate when $\alpha > 2.0$. Vortices are the dominant excitations in the semiclassical limit, while the charge excitations are important in the quantum regime. There are also fractional charged vortices induced by the magnetic field in both arrays. We have extensively studied the interplay between the different types of vortex and charge excitations in both arrays. The phase diagrams for each array as a function of temperature, inter-layer capacitance and frustration are determined from results for the helicity modulus, $\Upsilon$ and the inverse dielectric constant, $\epsilon^{-1}$. When one of the arrays is in the quantum regime and the other one in the semi-classical limit, $\Upsilon$ decreases with temperature, while the $\epsilon^{-1}$ increases. At low temperatures there appears to be a {\it novel reentrant phase transitions} in the charge degrees of freedom for $F=1/2$. [Preview Abstract] |
Monday, March 21, 2005 12:27PM - 12:39PM |
B13.00007: Long Josepshon Junction in a Resonant Cavity Ivan Tornes, David Stroud We present a model for an underdamped long Josephson junction coupled to a single-mode electromagnetic cavity, and carry out numerical calculations using this model in various regimes. The coupling may occur through either the electric or the magnetic field of the cavity mode. When a current is injected into the junction, we find that the time-averaged voltage exhibits self-induced resonant steps due to coupling between the current in the junction and the electric field of the cavity mode. These steps are similar to those observed and calculated in small Josephson junctions. When a soliton is present in the junction (corresponding to a quantum of magnetic flux parallel to the junction plates), the SIRS's disappear if the electric field in the cavity is spatially uniform. If the cavity mode has a spatially varying electric field, there is a strong coupling between the soliton and the cavity mode. This coupling causes the soliton to become phase-locked to the cavity mode, and produces step-like anomalies on the soliton branch of the IV characteristics. If the coupling is strong enough, the frequency of the cavity mode is greatly red-shifted from its uncoupled value. We present simple geometrical arguments and a simple analytical model which account for this behavior. This work was supported by NSF grant DMR04-13395. [Preview Abstract] |
Monday, March 21, 2005 12:39PM - 12:51PM |
B13.00008: Effects of Coexistent Normal and Supercurrent in SNS Josephson Junctions M.S. Crosser, Norman O. Birge Injecting normal current into a superconductor/normal metal/superconductor (SNS) Josephson junction via another lead attached at the middle of the junction, creates a non- equilibrium situation in which a $\pi$-junction can be created [1]. In this three-terminal geometry, one side of the SNS junction has both normal and supercurrent flowing in the same direction while the other side has opposing current flows. This situation creates an effective energy gradient across the SNS junction, which appears in the distribution function of the normal wire [2]. We will present experimental measurements of the distribution function using tunneling spectroscopy with a superconducting probe. The distribution function exhibits oscillations near zero energy, which change sign under reversal of the supercurrent direction. [1] J. Huang et al., Phys. Rev B 66, 020507 (2002). [2] T.T. Heikkila et al., Phys. Rev. B 67, 100502 (2003). *Supported by NSF DMR-0104178 and 0405238. [Preview Abstract] |
Monday, March 21, 2005 12:51PM - 1:03PM |
B13.00009: Theory of a mesoscopic superconducting phase gradiometer David Pekker, Paul Goldbart, David Hopkins, Alexey Bezryadin We analyze an all-superconducting mesoscopic DC SQUID, comprising a pair of thin-film strips connected by a pair of parallel ultra-narrow wires. We focus on the magnetoresistance of the device in the size range in which the strips are narrower than the penetration depth (i.e.~the mesoscopic regime), and especially on the low-magnetic-field regime, in which no vortices are present in the strips. The resistance originates in dissipative order-parameter fluctuations in the wires, and its magnetic-field dependence comes from the phase-gradient of the order parameter in the strips, associated with screening currents. We present a theory of the magnetoresistance of this mesoscopic DC SQUID, based on the theory of intrinsic resistance (e.g.~of Josephson junctions or superconducting nanowires). We compare this theory with recent experimental data obtained from DNA-templated devices, and discuss why the device can be regarded as a superconducting phase gradiometer. [Preview Abstract] |
Monday, March 21, 2005 1:03PM - 1:15PM |
B13.00010: Spin and Spin-Wave Dynamics in Josephson Junctions Zohar Nussinov, Alexander Shnirman, Dan Arovas, Alexander Balatsky , Jian-Xin Zhu We explore the dynamics of a single spin and spin wave dynamics of ferromagnets when these are inserted between superconducting leads. Several new effects are reported. Chief amongst these are new nutations of single $s=\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}$ spins in Josephson junctions. These nutations are sparked by the superconducting pairing correlations. Similarly, we find that on rather universal grounds, magnets display unconventional spin wave dynamics when placed in Josephson junctions. These lead to modifications in the tunneling current. [Preview Abstract] |
Monday, March 21, 2005 1:15PM - 1:27PM |
B13.00011: Floating phase in a dissipative Josephson junction array Sumanta Tewari, John Toner, Sudip Chakravarty We consider dissipative quantum phase transitions (QPT) in Josephson junction arrays and show that the disordered phase in this system can be viewed as an unusual floating phase in which the states of local $(0+1)$-dimensional elements (single Josephson junctions) can slide past each other despite arbitrary range spatial couplings among them. While the order parameters on the grains are long-range-correlated in time, they are only short-range-correlated spatially. The dissipative QPT between this unusual floating phase, which is metallic, and a global superconductor is controlled by a locus of critical points determined entirely by the {\it local} topology of the lattice, and hence exists in arbitrary dimension. The unusual character of this phase transition can be tested by measurements of the current voltage characteristics. [Preview Abstract] |
Monday, March 21, 2005 1:27PM - 1:39PM |
B13.00012: Half - h/2e - Oscillations of SQUIDs Jochen Mannhart, Christof Schneider, German Hammerl, Gennadij Logvenov, Thilo Kopp, John Kirtley, Peter Hirschfeld, Hel\`ene Raffy The current-voltage-voltage characteristics of Superconducting Quantum Interference Devices (SQUIDs) are known to modulate as a function of applied magnetic filed with a period of one flux quantum $\Phi _{0}=h$/2e. Here we report on the fabrication and properties of SQUIDs modulating with a period of 1/2 x $\Phi _{0}$. The characteristics of these bicrystal SQUIDs are consistent with either a strong sin(2\textit{$\phi )$} component of the current-phase relation o f the Josephson current, or with an interaction between the Cooper-pairs, causing an admixture of quartets to the condensate. [Preview Abstract] |
Monday, March 21, 2005 1:39PM - 1:51PM |
B13.00013: Simulating one-dimensional Josephson junction arrays in the presence of dissipation Michael Zwolak, Guifre Vidal Recently, we have presented an algorithm to study mixed state dynamics in one-dimensional quantum many-body systems. This algorithm can be used to construct thermal states and to simulate real time evolution as given by a generic master equation. We use this algorithm to study the superconductor-insulator transition in Josephson junction arrays driven by dissipation. We present a formulation of the problem in terms of a master equation with local dissipation. We show results for correlation functions and resistance for different strengths of dissipation and Josephson coupling. [Preview Abstract] |
Monday, March 21, 2005 1:51PM - 2:03PM |
B13.00014: Helical vortex phase in the non-centrosymmetric CePt$_3$Si Raminder Kaur, Daniel Agterberg, Manfred Sigrist The recently discovered heavy fermion superconductor CePt$_3$Si [{\it E. Bauer et al., Phys. Rev. Lett. {\bf 92}, 027003 (2004)}] has triggered many experimental and theoretical studies. There are two features which have caused this attention: the absence of inversion symmetry; and the comparatively high upper critical magnetic field ($H_{c2}$). We have studied the role of magnetic fields on the broken inversion superconductor CePt$_3$Si and found that the upper critical field for a field along the c-axis exhibits a strong suppression of the paramagnetic effect, while a field applied perpendicular to the c-axis still exhibits a strong paramagnetic effect. This in-plane paramagnetic effect is reduced by the appearance of helical structure in the order parameter. We have proposed a Josephson junction experiment that can be used to detect this helical order. In particular, we have predicted that Josephson current will exhibit a magnetic interference pattern for a magnetic field applied {\it perpendicular} to the junction normal. [Preview Abstract] |
Monday, March 21, 2005 2:03PM - 2:15PM |
B13.00015: Josephson Effect in Presence of Spin Berry Phase Hiroshi Kohno, Gen Tatara, Naoto Nagaosa, Alexander Balatsky Spin Berry phase is known to contribute to the phase coherent electronic transport in normal mecoscopic rings. Here we show that spin Berry phase can produce a persistent Josephson current as a result of the coupling between tunneling electrons and spins in the junctions. The simplest geometry where this effect is realized is a ring with three Josephson junctions with spins in each of them. Spin chirality C$_{123}$ = (S$_1$ $\times$ S$_2$) $\cdot$ S$_3$ is shown to couple to superconducting current in a way, similar to the external magnetic field coupling. Effect is shown to be a result of the interference of the Cooper pair virtual tunneling across opposite arms of the ring and is decaying exponentially with the distance with the superconducting coherence length as a natural length scale. We discuss possible realization of this effect in a multilayered magnetic-superconducting structure. [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