Confocal Annular Josephson Tunnel Junctions
Monaco, Roberto
2016-04-01
The physics of Josephson tunnel junctions drastically depends on their geometrical configurations and here we show that also tiny geometrical details play a determinant role. More specifically, we develop the theory of short and long annular Josephson tunnel junctions delimited by two confocal ellipses. The behavior of a circular annular Josephson tunnel junction is then seen to be simply a special case of the above result. For junctions having a normalized perimeter less than one, the threshold curves in the presence of an in-plane magnetic field of arbitrary orientations are derived and computed even in the case with trapped Josephson vortices. For longer junctions, a numerical analysis is carried out after the derivation of the appropriate motion equation for the Josephson phase. We found that the system is modeled by a modified and perturbed sine-Gordon equation with a space-dependent effective Josephson penetration length inversely proportional to the local junction width. Both the fluxon statics and dynamics are deeply affected by the non-uniform annulus width. Static zero-field multiple-fluxon solutions exist even in the presence of a large bias current. The tangential velocity of a traveling fluxon is not determined by the balance between the driving and drag forces due to the dissipative losses. Furthermore, the fluxon motion is characterized by a strong radial inward acceleration which causes electromagnetic radiation concentrated at the ellipse equatorial points.
Confocal Annular Josephson Tunnel Junctions
Monaco, Roberto
2016-09-01
The physics of Josephson tunnel junctions drastically depends on their geometrical configurations and here we show that also tiny geometrical details play a determinant role. More specifically, we develop the theory of short and long annular Josephson tunnel junctions delimited by two confocal ellipses. The behavior of a circular annular Josephson tunnel junction is then seen to be simply a special case of the above result. For junctions having a normalized perimeter less than one, the threshold curves in the presence of an in-plane magnetic field of arbitrary orientations are derived and computed even in the case with trapped Josephson vortices. For longer junctions, a numerical analysis is carried out after the derivation of the appropriate motion equation for the Josephson phase. We found that the system is modeled by a modified and perturbed sine-Gordon equation with a space-dependent effective Josephson penetration length inversely proportional to the local junction width. Both the fluxon statics and dynamics are deeply affected by the non-uniform annulus width. Static zero-field multiple-fluxon solutions exist even in the presence of a large bias current. The tangential velocity of a traveling fluxon is not determined by the balance between the driving and drag forces due to the dissipative losses. Furthermore, the fluxon motion is characterized by a strong radial inward acceleration which causes electromagnetic radiation concentrated at the ellipse equatorial points.
Fluxon dynamics in long annular Josephson tunnel junctions
Martucciello, N.; Mygind, Jesper; Koshelets, V.P.; Shchukin, A.V.; Filippenko, L.; Monaco, R
1998-01-01
Single-fluxon dynamics has been experimentally investigated in high-quality Nb/Al-AlOx/Nb annular Josephson tunnel junctions having a radius much larger than the Josephson penetration depth. Strong evidence of self-field effects is observed. An external magnetic field in the barrier plane acts on...
Fluxon dynamics in long annular Josephson tunnel junctions
Martucciello, N.; Mygind, Jesper; Koshelets, V. P.; Shchukin, A. V.; Filippenko, L.; Monaco, R.
1998-01-01
Single-fluxon dynamics has been experimentally investigated in high-quality Nb/Al-AlOx/Nb annular Josephson tunnel junctions having a radius much larger than the Josephson penetration depth. Strong evidence of self-field effects is observed. An external magnetic field in the barrier plane acts on the fluxon as a periodic potential and lowers its average speed. Further, the results of perturbative calculations do not fit the experimental current-voltage profile and, provided the temperature is...
New fluxon resonant mechanism in annular Josephson tunnel structures
A novel dynamical state has been observed in the dynamics of a perturbed sine-Gordon system. This resonant state has been experimentally observed as a singularity in the dc current-voltage characteristic of an annular Josephson tunnel junction, excited in the presence of a magnetic field. In this respect it can be assimilated to self-resonances known as Fiske steps. Differently from these, however, we demonstrate, on the basis of numerical simulations, that its detailed dynamics involves rotating fluxon pairs, a mechanism associated, so far, to self-resonances known as zero-field steps. This occurs because the size of nonlinear excitations is comparable with that of the system
Elliptic annular Josephson tunnel junctions in an external magnetic field: the statics
Monaco, Roberto; Granata, Carmine; Vettoliere, Antonio;
2015-01-01
We have investigated the static properties of one-dimensional planar Josephson tunnel junctions (JTJs) in the most general case of elliptic annuli. We have analyzed the dependence of the critical current in the presence of an external magnetic field applied either in the junction plane or in the...... perpendicular direction. We report a detailed study of both short and long elliptic annular junctions having different eccentricities. For junctions having a normalized perimeter less than one the threshold curves are derived and computed even in the case with one trapped Josephson vortex. For longer junctions...... a numerical analysis is carried out after the derivation of the appropriate perturbed sine-Gordon equation. For a given applied field we find that a number of different phase profiles exist which differ according to the number of fluxon-antifluxon pairs. We demonstrate that in samples made by...
Soliton bunching in annular Josephson junctions
Vernik, I.V; Lazarides, Nickos; Sørensen, Mads Peter;
1996-01-01
By studying soliton (fluxon) motion in long annular Josephson junctions it is possible to avoid the influence of the boundaries and soliton-soliton collisions present in linear junctions. A new experimental design consisting of a niobium coil placed on top of an annular junction has been used to...
Josephson tunnel junction microwave attenuator
Koshelets, V. P.; Shitov, S. V.; Shchukin, A. V.;
1993-01-01
A new element for superconducting electronic circuitry-a variable attenuator-has been proposed, designed, and successfully tested. The principle of operation is based on the change in the microwave impedance of a superconductor-insulator-superconductor (SIS) Josephson tunnel junction when dc biased...
Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope
Naaman, O.; Teizer, W.; Dynes, R. C.
2001-01-01
We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range 50-300 k$\\Omega$. We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltages. In the presence of microwave fields (f=15.0 GHz) the peak decreases in magnitude and shifts to higher voltages with increasing ...
DC intrinsic Josephson effect in 1{mu}m-lateral-size annular Bi-2212 stacks
Kim, S.J.; Yamashita, T. [Tohoku Univ., Sendai (Japan). Research Inst. of Electrical Comunication; Latyshev, Y.I.; Pavlenko, V.N. [Tohoku Univ., Sendai (Japan); Inst of Radio-Engineerig and Electronics Russian Academic of Sciences, Moscow (Russian Federation)
1999-11-10
Small annular junctions were the subjects of particular interest last decade because of possibility of flux trapping (see, e.g. [1]). Related magnetic field can contain radial component affecting Josephson critical current. Here we report on the first studies of intrinsic dc Josephson effect [2] in small annular type Bi-2212 mesas and its sensitivity to the trapped flux. (translated by NEDO)
delta-biased Josephson tunnel junctions
Monaco, R.; Mygind, Jesper; Koshelet, V.;
2010-01-01
Abstract: The behavior of a long Josephson tunnel junction drastically depends on the distribution of the dc bias current. We investigate the case in which the bias current is fed in the central point of a one-dimensional junction. Such junction configuration has been recently used to detect the...
Soliton excitations in Josephson tunnel junctions
Lomdahl, P. S.; Sørensen, O. H.; Christiansen, Peter Leth
1982-01-01
A detailed numerical study of a sine-Gordon model of the Josephson tunnel junction is compared with experimental measurements on junctions with different L / λJ ratios. The soliton picture is found to apply well on both relatively long (L / λJ=6) and intermediate (L / λJ=2) junctions. We find good...
Microscopic tunneling theory of long Josephson junctions
Grønbech-Jensen, N.; Hattel, Søren A.; Samuelsen, Mogens Rugholm
1992-01-01
We present a numerical scheme for solving a nonlinear partial integro-differential equation with nonlocal time dependence. The equation describes the dynamics in a long Josephson junction modeled by use of the microscopic theory for tunneling between superconductors. We demonstrate that the...
Recent achievements on annular Josephson structures and their application as radiation detectors
One of the stimulating area of superconductors investigations lies in the achieved and potential applications as radiation detectors. Results concerning annular Josephson junctions in this context are discussed. Fundamental aspects, mainly related to the fluxon dynamics in such structures, are discussed in detail. The results confirm the importance of the precious sharing of technological requests with fundamental physical implications. Peculiar results are reported dealing with new resonances occurring on these Josephson junctions of annular configuration
Josephson tunnel junctions in niobium films
A method of fabricating stable Josephson tunnel junctions with reproducible characteristics is described. The junctions have a sandwich structure consisting of a vacuum evaporated niobium film, a niobium oxide layer produced by the glow discharge method and a lead film deposited by vacuum evaporation. Difficulties in producing thin-film Josephson junctions are discussed. Experimental results suggest that the lower critical field of the niobium film is the most essential parameter when evaluating the quality of these junctions. The dependence of the lower critical field on the film thickness and on the Ginzburg-Landau parameter of the film is studied analytically. Comparison with the properties of the evaporated films and with the previous calculations for bulk specimens shows that the presented model is applicable for most of the prepared samples. (author)
δ-biased Josephson tunnel junctions
The behavior of a long Josephson tunnel junction drastically depends on the distribution of the dc bias current. We investigate the case in which the bias current is fed in the central point of a one-dimensional junction. Such junction configuration has been recently used to detect the persistent currents circulating in a superconducting loop. Analytical and numerical results indicate that the presence of fractional vortices leads to remarkable differences from the conventional case of uniformly distributed dc bias current. The theoretical findings are supported by detailed measurements on a number of δ-biased samples having different electrical and geometrical parameters.
Josephson tunnel junctions with ferromagnetic barrier layer
We have fabricated Nb/Al2O3/Ni0.6Cu0.4/Nb Josephson tunnel junctions. Depending on the thickness of the ferromagnetic Ni0.6Cu0.4 layer and on the ambient temperature, the junctions were in the 0 or π coupled ground state. The Al2O3 tunnel barrier allows to achieve rather low damping. The critical current density in the π state was up to 5 A/cm2 at T=2.1 K, resulting in a Josephson penetration depth λJ as low as 160 μm. Experimentally determined junction parameters are well described by theory taking into account spin-flip scattering in the Ni0.6Cu0.4 layer and different interface transparencies. Using a ferromagnetic layer with a step-like thickness we obtain a 0-π junction with equal lengths and critical currents of 0 and π parts. The Ic(H) pattern shows a clear minimum in the vicinity of zero field. The ground state of our 330 μm (1.3λJ) long junction corresponds to a spontaneous vortex of supercurrent pinned at the 0-π phase boundary, carrying ∝ 6.7% of the magnetic flux quantum Φ0. (orig.)
Theory of Josephson tunneling into proximity-effect sandwiches
We develop the microscopic theory of the superconducting proximity effect to allow the calculation of the Josephson current in tunnel junctions where one or both electrodes are proximity-effect bilayers. The Josephson current can then be calculated with the same theory that is used to interpret quasiparticle tunneling characteristics in quantitative detail. One significant result is that the Josephson current is much more rapidly attenuated by thin normal layers adjacent to the tunnel barrier than is the gap in the quasiparticle current. (orig.)
Josephson tunnel junctions with ferromagnetic interlayer
Superconductivity and ferromagnetism are well-known physical properties of solid states that have been widely studied and long thought about as antagonistic phenomena due to difference in spin ordering. It turns out that the combination of both superconductor and ferromagnet leads to a very rich and interesting physics. One particular example, the phase oscillations of the superconducting order parameter inside the ferromagnet, will play a major role for the devices discussed in this work. In this thesis, I present Josephson junctions with a thin Al2O3 tunnel barrier and a ferromagnetic interlayer, i.e. superconductor-insulator-ferromagnet-superconductor (SIFS) stacks. The fabrication of junctions was optimized regarding the insulation of electrodes and the homogeneity of the current transport. The junctions were either in the 0 or π coupled ground state, depending on the thickness of the ferromagnetic layer and on temperature. The influence of ferromagnetic layer thickness on the transport properties and the coupling (0, π) of SIFS tunnel junctions was studied. Furthermore, using a stepped ferromagnetic layer with well-chosen thicknesses, I obtained the so-called 0-π Josephson junction. At a certain temperature this 0-π junction can be made perfectly symmetric. In this case the ground state corresponds to a vortex of supercurrent creating a magnetic flux which is a fraction of the magnetic flux quantum Φ0. Such structures allow to study the physics of fractional vortices and to build various electronic circuits based on them. The SIFS junctions presented here have an exponentially vanishing damping at T → 0. The SIFS technology developed within the framework of this work may be used to construct classical and quantum devices such as oscillators, memory cells and qubits. (orig.)
Josephson tunnel junctions with ferromagnetic interlayer
Weides, M.P.
2006-07-01
Superconductivity and ferromagnetism are well-known physical properties of solid states that have been widely studied and long thought about as antagonistic phenomena due to difference in spin ordering. It turns out that the combination of both superconductor and ferromagnet leads to a very rich and interesting physics. One particular example, the phase oscillations of the superconducting order parameter inside the ferromagnet, will play a major role for the devices discussed in this work. In this thesis, I present Josephson junctions with a thin Al{sub 2}O{sub 3} tunnel barrier and a ferromagnetic interlayer, i.e. superconductor-insulator-ferromagnet-superconductor (SIFS) stacks. The fabrication of junctions was optimized regarding the insulation of electrodes and the homogeneity of the current transport. The junctions were either in the 0 or {pi} coupled ground state, depending on the thickness of the ferromagnetic layer and on temperature. The influence of ferromagnetic layer thickness on the transport properties and the coupling (0, {pi}) of SIFS tunnel junctions was studied. Furthermore, using a stepped ferromagnetic layer with well-chosen thicknesses, I obtained the so-called 0-{pi} Josephson junction. At a certain temperature this 0-{pi} junction can be made perfectly symmetric. In this case the ground state corresponds to a vortex of supercurrent creating a magnetic flux which is a fraction of the magnetic flux quantum {phi}{sub 0}. Such structures allow to study the physics of fractional vortices and to build various electronic circuits based on them. The SIFS junctions presented here have an exponentially vanishing damping at T {yields} 0. The SIFS technology developed within the framework of this work may be used to construct classical and quantum devices such as oscillators, memory cells and qubits. (orig.)
Existence, uniqueness and multiplicity of rotating fluxon waves in annular Josephson junctions
Katriel, Guy
2007-01-01
We prove that the equation modelling an annular Josephson junction has a rotating fluxon wave solution for all values of the parameters. We also obtain results on uniqueness of the rotating fluxon wave in some parameter regimes, and on multiplicity of rotating fluxon waves in other parameter regimes.
Parametric excitation of plasma oscillations in a Josephson tunnel junction
Bak, Christen Kjeldahl; Kofoed, Bent; Pedersen, Niels Falsig;
1975-01-01
Experimental evidence for subharmonic parametric excitation of plasma oscillations in Josephson tunnel junctions is presented. The experiments described are performed by measuring the microwave power necessary to switch a Josephson−tunnel junction biased in the zero−voltage state to a finite......−voltage state. Journal of Applied Physics is copyrighted by The American Institute of Physics....
A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy
Jäck, Berthold, E-mail: b.jaeck@fkf.mpg.de; Eltschka, Matthias; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R. [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Hardock, Andreas [Institut für Theoretische Elektrotechnik, Technische Universität Hamburg-Harburg, 21079 Hamburg (Germany); Kern, Klaus [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Institut de Physique de la Matière Condensée, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland)
2015-01-05
Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a λ/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25 GHz to 200 GHz and that large photon flux in excess of 10{sup 20 }cm{sup −2} s{sup −1} is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale.
A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy
Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a λ/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25 GHz to 200 GHz and that large photon flux in excess of 1020 cm−2 s−1 is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale
Soliton excitations in Josephson tunnel junctions
A detailed numerical study of a sine-Gordon model of the Josephson tunnel junction is compared with experimental measurements on junctions with different L/lambda/sub J/ ratios. The soliton picture is found to apply well on both relatively (L/lambda/sub J/ = 6) and intermediate (L/lambda/sub J/ = 2) junctions. We find good agreement for the current-voltage characteristics, power output, and for the shape and height of the zero-field steps (ZFS). Two distinct modes of solition oscillations are observed: (i) a bunched or congealed mode giving rise to the fundamental frequency ∫1 on all ZFS's and (ii) a ''symmetric'' mode which on the Nth ZFS yields the frequency N∫1. Coexistence of two adjacent frequencies is found on the third ZFS of the longer junction (L/lambda/sub J/ = 6) in a narrow range of bias current as also found in the experiments. Small asymmetries in the experimental environment, a weak magnetic field, e.g., is introduced via the boundary conditions of our numerical model. This gives a junction response to variations in the applied bias current close to that observed experimentally
Static properties of small Josephson tunnel junctions in an oblique magnetic field
Monaco, Roberto; Aarøe, Morten; Mygind, Jesper;
2009-01-01
We have carried out a detailed experimental investigation of the static properties of planar Josephson tunnel junctions in presence of a uniform external magnetic field applied in an arbitrary orientation with respect to the barrier plane. We considered annular junctions, as well as rectangular...... junctions (having both overlap and cross-type geometries) with different barrier aspect ratios. It is shown how most of the experimental findings in an oblique field can be reproduced invoking the superposition principle to combine the classical behavior of electrically small junctions in an in-plane field...
Planar Josephson tunnel junctions in a transverse magnetic field
Monacoa, R.; Aarøe, Morten; Mygind, Jesper;
2007-01-01
demagnetization effects imposed by the tunnel barrier and electrodes geometry are important. Measurements of the junction critical current versus magnetic field in planar Nb-based high-quality junctions with different geometry, size, and critical current density show that it is advantageous to use a transverse......Traditionally, since the discovery of the Josephson effect in 1962, the magnetic diffraction pattern of planar Josephson tunnel junctions has been recorded with the field applied in the plane of the junction. Here we discuss the static junction properties in a transverse magnetic field where...... magnetic field rather than an in-plane field. The conditions under which this occurs are discussed....
Monaco, R.; Mygind, Jesper; Aarøe, Morten;
2006-01-01
New scaling behavior has been both predicted and observed in the spontaneous production of fluxons in quenched Nb-Al/Al-ox/Nb annular Josephson tunnel junctions (JTJs) as a function of the quench time, tau(Q). The probability f(1) to trap a single defect during the normal-metal-superconductor pha...
Experiments investigating the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very small capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters; the tunneling rate in the moderately damped (Q ∼ 1) junction is seen to be reduced by a factor of 300 from that predicted for an undamped junction. The phase is seen to be a good quantum-mechanical variable. The experiments on small capacitance tunnel junctions extend the measurements on the larger-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wavefunction has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias. I present the first clear observation of the Coulomb blockade in single junctions. The electrical environment of the tunnel junction, however, strongly affects the behavior of the junction: higher resistance leads are observed to greatly sharpen the Coulomb blockade over that seen with lower resistance leads. I present theoretical descriptions of how the environment influences the junctions; comparisons with the experimental results are in reasonable agreement
Proximity effects in all refractory Josephson tunnel junctions
The theoretical approach to proximity effect based on the thermodynamic Green's functions is considered to investigate the behaviour of all refractory Josephson tunnel junctions. The experimental dependence of the maximum dc Josephson current on temperature is analysed. Two junction configurations are studied: Nb-Al/AlOx/Nb structures with a rather thick Al film and high quality Nb/Nb junctions with either a semimetallic or a metallic back-layer (Nb/AlOx/Nb-Bi, Nb/AlOx/Nb-Al). A satisfying agreement between theoretical calculations and experimental data is found. (orig.)
Properties of Josephson tunnel junction with trapped Abrikosov vortices
This paper investigates properties of the Nb/AlOx/Nb Josephson tunnel juncton (JTJ) with Abrikosov vortices (AV) trapped in electrodes. The trapping of AV was performed by a field-cooling process when the JTJ has been cooled through the critical temperature T either in applied perpendicular magnetic field (Bperpendicular) (mode 1) or by application of the perpendicular magnetic field Bperpendicular when the JTJ was at the temperature below Tc (mode 2). The effect of AV on dependences of Josephson critical supercurrent Ic in the parallel magnetic field B parallel has been studied
Submicron NbN Josephson tunnel junctions for digital applications
Submicron NbN/MgO/NbN Josephson tunnel junctions have been investigated to make Josephson integrated circuits. The junctions have been fabricated successfully by the cross-line-patterning (CLIP) method with an electron-beam (EB) direct-writing technique. All refractory fabrication process for logic circuits using the CLIP method is presented. This process is applied to fabrication of a logic gate of 4JL containing 0.8 μm-square junctions as an example of digital applications. The logic gate has been fabricated by this process. The authors also discuss the characteristics of the gate
Fabrication and tunneling properties of niobium/lead Josephson junctions
High quality Josephson tunneling junctions were fabricated by the process of electron beam evaporation of the Nb-base electrode. Thermal oxidation of Nb coated and uncoated surfaces was used in order to grow the oxide barrier at room temperature. Lead was used to complete the sandwich-type structure. The tunneling properties were profoundly sensitive to the surface properties of the Nb films. Markedly improved Josephson tunneling characteristics were found by depositing much higher residual resistance ratio (>100) films, which in this case seemed to be single crystal. One of the main deterrents for the practical use of high quality Nb/Nb:O/sub x//Pb Josephson junctions has been the high value of the specific capacitance of the native oxides which is drastically reduced by using single crystal Nb thin films. Some of the important parameters of the junctions can be modified by coating the Nb surface. It was demonstrated that Zr, Ti, and Al can be employed as oxidized barriers on single-crystal Nb films to produce high quality Josephson junctions that preserve the low values of the dielectric constant
Fabrication and Tunneling Properties of Niobium/lead Josephson Junctions
Celaschi, Sergio
High quality Josephson tunneling junctions have been fabricated by the process of electron beam evaporation of the Nb base electrode. Thermal oxidation of Nb coated and uncoated surfaces was used in order to grow the oxide barrier at room temperature. Lead was used to complete the sandwich-type structure. The tunneling properties were profoundly sensitive to the surface properties of the Nb films. We found markedly improved Josephson tunneling characteristics by depositing much higher residual resistance ratio (>100) films which in this case seemed to be single crystal. One of the main deterrents for the practical use of high quality Nb/Nb:O(,X)/Pb Josephson junctions has been the high value of the specific capacitance of the native oxides which is drastically reduced by using single crystal Nb thin films. Some of the important parameters of the junctions can be modified by coating the Nb surface. We have demonstrated that Zr, Ti, and Al can be employed as oxidized barriers on single-crystal Nb films to produce high quality Josephson junctions which preserve the low values of the dielectric constant.
Search for Second-Order Josephson tunneling in SFS Josephson junctions
Frolov, S. M.; Oboznov, V. A.
2005-03-01
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-π crossover at which the first-order Josephson component vanishes, it has been predicted that second-order Josephson tunneling, characterized by a sin(2φ) 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-π transition from a distribution of 0-junction and π-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 sin(2φ) component or from junction non-uniformity.
Multiple frequency generation by bunched solitons in Josephson tunnel junctions
Lomdahl, P. S.; Sørensen, O. H.; Christiansen, Peter Leth; Scott, A. C.; Eilbeck, J. C.
1981-01-01
A detailed numerical study of a long Josephson tunnel junction modeled by a perturbed sine-Gordon equation demonstrates the existence of a variety of bunched soliton configurations. Thus, on the third zero-field step of the V-I characteristic, two simultaneous adjacent frequencies are generated in...... a narrow bias current range. The analysis of the soliton modes provides an explanation of recent experimental observations....
Two-particle structures in high quality Nb/AlOx/Nb Josephson tunnel junctions
We have investigated both theoretically and experimentally the two-particle structures, which appear at low temperature in high quality Nb/AlOx/Nb Josephson tunnel junctions in the subgap region of the current-voltage characteristics. We performed measurements on low Josephson critical current density junctions and the results are discussed in the framework of the multiparticle tunnel theory. (orig.)
Josephson Effect in Pb/I/NbSe2 Scanning Tunneling Microscope Junctions
Naaman, O.; Dynes, R. C.; Bucher, E.
2003-01-01
We have developed a method for the reproducible fabrication of superconducting scanning tunneling microscope (STM) tips. We use these tips to form superconductor/insulator/superconductor tunnel junctions with the STM tip as one of the electrodes. We show that such junctions exhibit fluctuation dominated Josephson effects, and describe how the Josephson product IcRn can be inferred from the junctions' tunneling characteristics in this regime. This is first demonstrated for tunneling into Pb fi...
Q factor and resonance amplitude of Josephson tunnel junctions
The surface impedance of the superconducting films comprising the electrodes of Josephson tunnel junctions has been derived from the BCS theory in the extreme London limit. Expressions have been obtained for (i) the dependence of the penetration depth lambda on frequency and temperature, and (ii) the quality factor Q of the junction cavity, attributable to surface absorption in the electrodes. The effect of thin electrodes (t 9 or approx. = lambda) is also included in the calculations. Comparison of the calculated frequency dependence of lambda with resonance measurements on Pb-alloy and all-Nb tunnel junctions yields quite good agreement, indicating that the assumptions made in the theory are reasonable. Measurements of the (current) amplitude of the resonance peaks of the junctions have been compared with the values obtained from inclusion of the calculated Q in the theory by Kulik. In common with observations on microwave cavities by other workers, we find that a small residual conductivity must be added to the real part of the BCS value. With its inclusion, good agreement is found between calculation and experiment, within the range determined by the simplifying assumptions of Kulik's theory. From the results, we believe the calculation of Q to be reasonably accurate for the materials investigated. It is shown that the resonance amplitude of Josephson junctions can be calculated directly from the material constants and a knowledge of the residual conductivity
Resonant tunneling in small current-biased Josephson Junctions
Schmidt, J.M.
1994-05-01
Effects of resonant tunneling between bound quantum states of a current-biased Josephson tunnel junction is studied both theoretically and experimentally. Several effects are predicted to arise from resonant tunneling, including a series of voltage peaks along the supercurrent branch of the current-voltage characteristic, and enhanced rate of escape from zero voltage state to voltage state at particular values of bias current. A model is developed to estimate magnitude and duration of voltage peaks, and to estimate enhancement of the escape rate, which appears as peaks in the rate as a function of bias current. An experimental investigation was carried out in an attempt to observe these predicted peaks in the escape rate distribution in a current-biased DC SQUID, which is shown to be dynamically equivalent to a Josephson junction with adjustable critical current. Electrical contact to each SQUID (fabricated from aluminium) was made through high resistance thin film leads located on the substrate. These resistors provided a high impedance at the plasma frequency which is for the isolation of the SQUID from its electromagnetic environment. Measurements were carried out on a dilution refrigerator at temperatures as low as 19 mK. No evidence was found for resonant tunneling; this is attributed to effective temperatures of hundreds of millikelvin. The behavior is well explained by a heating model where the high effective temperatures are generated by ohmic heating of the electron gas of the isolation resistors, which decouples from the phonon system (hot electron effect). The prospects for further theoretical and experimental research are discussed.
Gaussian tunneling model of c-axis twist Josephson junctions
We calculate the critical current density JcJ((varphi)0) for Josephson tunneling between identical high-temperature superconductors twisted an angle (varphi)0 about the c axis. Regardless of the shape of the two-dimensional Fermi surface and for very general tunneling matrix elements, an order parameter (OP) with general d-wave symmetry leads to JcJ(π/4)=0. This general result is inconsistent with the data of Li et al. [Phys. Rev. Lett. 83, 4160 (1999)] on Bi2Sr2CaCu2O8+δ (Bi2212), which showed JcJ to be independent of (varphi)0. If the momentum parallel to the barrier is conserved in the tunneling process, JcJ should vary substantially with the twist angle (varphi)0 when the tight-binding Fermi surface appropriate for Bi2212 is taken into account, even if the OP is completely isotropic. We quantify the degree of momentum nonconservation necessary to render JcJ((varphi)0) constant within experimental error for a variety of pair states by interpolating between the coherent and incoherent limits using five specific models to describe the momentum dependence of the tunneling matrix element squared. From the data of Li et al., we conclude that the c-axis tunneling in Bi2212 must be very nearly incoherent, and that the OP must have a nonvanishing Fermi-surface average for Tc. We further show that the apparent conventional sum-rule violation observed by Basov et al. [Science 283, 49 (1999)] can be consistent with such strongly incoherent c-axis tunneling.
Long Josephson tunnel junctions with doubly connected electrodes
Monaco, R.; Mygind, J.; Koshelets, V. P.
2012-03-01
In order to mimic the phase changes in the primordial Big Bang, several cosmological solid-state experiments have been conceived, during the last decade, to investigate the spontaneous symmetry breaking in superconductors and superfluids cooled through their transition temperature. In one of such experiments, the number of magnetic flux quanta spontaneously trapped in a superconducting loop was measured by means of a long Josephson tunnel junction built on top of the loop itself. We have analyzed this system and found a number of interesting features not occurring in the conventional case with simply connected electrodes. In particular, the fluxoid quantization results in a frustration of the Josephson phase, which, in turn, reduces the junction critical current. Further, the possible stable states of the system are obtained by a self-consistent application of the principle of minimum energy. The theoretical findings are supported by measurements on a number of samples having different geometrical configuration. The experiments demonstrate that a very large signal-to-noise ratio can be achieved in the flux quanta detection.
Supersymmetric phase transition in Josephson-tunnel-junction arrays
Foda, O.
1988-08-31
The fully frustrated XY model in two dimensions exhibits a vortex-unbinding as well as an Ising transition. If the Ising transition overlaps with the critical line that ends on the vortex transition: T/sub I/less than or equal toT/sub V/, then the model is equivalent, at the overlap temperature, to a free massless field theory of 1 boson and 1 Majorana fermion, which is a superconformal field theory, of central charge c=3/2. The model is experimentally realized in terms of an array of Josephson-tunnel junctions in a transverse magnetic field. The experiment reveals a phase transition consistent with T/sub I/=T/sub V/. Thus, at the critical temperature, the array provides a physical realization of a supersymmetric quantum field theory.
A supersymmetric phase transition in Josephson-tunnel-junction arrays
The fully frustrated XY model in two dimensions exhibits a vortex-unbinding as well as an Ising transition. If the Ising transition overlaps with the critical line that ends on the vortex transition: TI≤TV, then the model is equivalent, at the overlap temperature, to a free massless field theory of 1 boson and 1 Majorana fermion, which is a superconformal field theory, of central charge c=3/2. The model is experimentally realized in terms of an array of Josephson-tunnel junctions in a transverse magnetic field. The experiment reveals a phase transition consistent with TI=TV. Thus, at the critical temperature, the array provides a physical realization of a supersymmetric quantum field theory. (orig.)
Long Josephson tunnel junctions with doubly connected electrodes
Monaco, R.; Mygind, J.; Koshelets, V. P.
2012-01-01
In order to mimic the phase changes in the primordial Big Bang, several cosmological solid-state experiments have been conceived, during the last decade, to investigate the spontaneous symmetry breaking in superconductors and superfluids cooled through their transition temperature. In one...... of such experiments, the number of magnetic flux quanta spontaneously trapped in a superconducting loop was measured by means of a long Josephson tunnel junction built on top of the loop itself. We have analyzed this system and found a number of interesting features not occurring in the conventional case with simply....... The theoretical findings are supported by measurements on a number of samples having different geometrical configuration. The experiments demonstrate that a very large signal-to-noise ratio can be achieved in the flux quanta detection....
Simultaneous quasiparticle and Josephson tunneling in BSCCO-2212 break junctions.
Ozyuzer, L.
1998-10-27
Tunneling measurements are reported for superconductor-insulator-superconductor (SIS) break junctions on underdoped, optimally-doped, and overdoped single crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212). The junction I-V characteristics exhibit well-defined quasiparticle current jumps at eV = 2A as well as hysteretic Josephson currents. The quasiparticle branch has been analyzed in the framework of d{sub x{sup 2}-y{sup 2}} (d-wave) superconductivity and indicates that there is preferential tunneling along the lobe directions of the d-wave gap. For overdoped Bi-2212 with T{sub c} = 62 K, the Josephson current is measured as a function of junction resistance, R{sub n}, which varied by two orders of magnitude (1 k{Omega} to 100 k{Omega}). I{sub c}R{sub n} product is proportional to the 0.47 power of I{sub c} and displays a maximum of 7.0 mV. When the hole doping is decreased from overdoped (T{sub c} = 62 K) to the underdoped regime (T{sub c} = 70 K), the average I{sub c}R{sub n} product increases as does the quasiparticle gap. The maximum I{sub c}R{sub n} is {approximately} 40% of the {Delta}/e at each doping level, with a value as high as 25 mV in underdoped Bi-2212.
Chaos and related nonlinear noise phenomena in Josephson tunnel junctions
The nonlinear dynamics of Josephson tunnel junctions shunted by a resistance with substantial self-inductance have been thoroughly investigated. The current-voltage characteristics of these devices exhibit stable regions of negative differential resistance. Very large increases in the low-frequency voltage noise with equivalent noise temperatures of 106 K or more, observed in the vicinity of these regions, arise from switching, or hopping, between subharmonic modes. Moderate increases in the noise, with temperatures of about 103 K, arise from chaotic behavior. Analog and digital simulations indicate that under somewhat rarer circumstances the same junction system can sustain a purely deterministic hopping between two unstable subharmonic modes, accompanied by excess low-frequency noise. Unlike the noise-induced case, this chaotic process occurs over a much narrower range in bias current and is destroyed by the addition of thermal noise. The differential equation describing the junction system can be reduced to a one-dimensional mapping in the vicinity of one of the unstable modes. A general analytical calculation of switching processes for a class of mappings yields the frequency dependence of the noise spectrum in terms of the parameters of the mapping. Finally, the concepts of noise-induced hopping near bifurcation thresholds are applied to the problem of the three-photon Josephson parametric amplifier. Analog simulations indicate that the noise rise observed in experimental devices arises from occasional hopping between a mode at the pump frequency ω/sub p/ and a mode at the half harmonic ω/sub p//2. The hopping is induced by thermal noise associated with the shunt resistance. 71 references
Asai, Hidehiro, E-mail: hd-asai@aist.go.jp [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ota, Yukihiro [CCSE, Japan Atomic Energy Agency, Kashiwa, Chiba 277-8587 (Japan); Kawabata, Shiro [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Nori, Franco [CEMS, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Physics Department, University of Michigan, Ann Arbor, MI 48109-1040 (United States)
2014-09-15
Highlights: • We study MQT in Josephson junctions composed of multi-gap superconductors. • We derive a formula of the MQT escape rate for multiple phase differences. • We investigate the effect of inter-band phase fluctuation on MQT. • The MQT escape rate is significantly enhanced by the inter-band phase fluctuation. - Abstract: We theoretically investigate macroscopic quantum tunneling (MQT) in a hetero Josephson junction formed by a conventional single-gap superconductor and a multi-gap superconductor. In such Josephson junctions, phase differences for each tunneling channel are defined, and the fluctuation of the relative phase differences appear which is referred to as Josephson–Leggett’s mode. We take into account the effect of the fluctuation in the tunneling process and calculate the MQT escape rate for various junction parameters. We show that the fluctuation of relative phase differences drastically enhances the escape rate.
Two-dimensional macroscopic quantum tunneling in multi-gap superconductor Josephson junctions
Low-temperature characters of superconducting devices yield definite probes for different superconducting phenomena. We study the macroscopic quantum tunneling (MQT) in a Josephson junction, composed of a single-gap superconductor and a two-gap superconductor. Since this junction has two kinds to the superconducting phase differences, calculating the MQT escape rate requires the analysis of quantum tunneling in a multi-dimensional configuration space. Our approach is the semi-classical approximation along a 1D curve in a 2D potential- energy landscape, connecting two adjacent potential (local) minimums through a saddle point. We find that this system has two plausible tunneling paths; an in-phase path and an out-of-phase path. The former is characterized by the Josephson-plasma frequency, whereas the latter is by the frequency of the characteristic collective mode in a two-band superconductor, Josephson- Leggett mode. Depending on external bias current and inter-band Josephson-coupling energy, one of them mainly contributes to the MQT. Our numerical calculations show that the difference between the in-phase path and the out-of-phase path is manifest, with respect to the bias- current-dependence of the MQT escape rate. This result suggests that our MQT setting be an indicator of the Josephson-Leggett mode
Doped Josephson tunneling junction for use in a sensitive IR detector
A superconductive tunneling device having a modified tunnel barrier capable of supporting Josephson tunneling current is provided. The tunnel barrier located between a pair of electrodes includes a molecular species which is capable of coupling incident radiation of a spectrum characteristic of the molecular species into the tunnel barrier. The coupled radiation modulates the known Josephson characteristics of the superconducting device. As a result of the present invention, a superconductive tunneling device can be tuned or made sensitive to a particular radiation associated with the dopant molecular species. The present invention is particularly useful in providing an improved infrared detector. The tunnel barrier region can be, for example, an oxide of an electrode or frozen gas. The molecular species can be intermixed with the barrier region such as the frozen gas or deposited as one or more layers of molecules on the barrier region. The deposited molecules of the molecular species are unbonded and capable of responding to a radiation characteristic of the molecules. Semi-conductor material can be utilized as the molecular species to provide an increased selective bandwidth response. Finally, appropriate detector equipment can be utilized to measure the modulation of any of the Josephson characteristics such as critical current, voltage steps, Lambe-Jaklevic peaks and plasma frequency. (auth)
Quantum tunneling of the magnetic moment in the S/F/S Josephson φ0 junction
Chudnovsky, Eugene M.
2016-04-01
We show that the S/F/S Josephson φ0 junction permits detection of macroscopic quantum tunneling and quantum oscillation of the magnetic moment by measuring the ac voltage across the junction. Exact expression for the tunnel splitting renormalized by the interaction with the superconducting order parameter is obtained. It is demonstrated that magnetic tunneling may become frozen at a sufficiently large φ0. The quality factor of quantum oscillations of the magnetic moment due to finite ohmic resistance of the junction is computed. It is shown that magnetic tunneling rate in the φ0 junction can be controlled by the bias current, with no need for the magnetic field.
One-third (period three) harmonic generation in microwave-driven Josephson tunnel junctions
Hansen, Jørn Bindslev; Clarke, J.; Mygind, Jesper; Ovsyannikov, G. A.; Svensmark, Henrik
1986-01-01
One-third harmonic signals have been generated in the zero voltage state of a Josephson tunnel junction driven with a microwave current in the frequency range 8–20 GHz. The signal was as much as 50 dB above the noise level of the detector with a linewidth of less than 100 Hz. The junction...
X-band singly degenerate parametric amplification in a Josephson tunnel junction
Mygind, Jesper; Pedersen, Niels Falsig; Sørensen, O. H.
1978-01-01
Preliminary measurements on a (quasi-) degenerate parametric amplifier using a single Josephson tunnel junction as the active element is reported. The pump frequency is at 18 GHz and the signal and idler frequencies are both at about 9 GHz. A power gain of 16 dB in a 4-MHz 3-dB bandwidth is...
Remanent effects and granular Josephson tunnelling in 1:2:3 micro-bridge junctions
A study has been made of supercurrent in a 1:2:3 micro-bridge or slot-junction. It is shown that the maximum supercurrent through a slot-junction is strongly dependent on temperature, applied magnetic field, and magnetic history. In addition, inter-granular Josephson tunnelling has been observed using field-modulation techniques
Control of Coulomb blockade in a mesoscopic Josephson junction using single electron tunneling
Hassel, J.; Seppä, Heikki; Delahaye, Julien; Hakonen, Pertti J.
2004-01-01
We study a circuit where a mesoscopic Josephson junction (JJ) is embedded in an environment consisting of a large bias resistor and a normal metal - superconductor tunnel junction (NIS). The effective Coulomb blockade of the JJ can be controlled by the tunneling current through the NIS junction leading to transistor-like characteristics. We show using phase correlation theory and numerical simulations that substantial current gain with low current noise ($i_{n}\\lesssim 1$ fA/$\\sqrt{\\text{Hz}}...
We investigated the phase dynamics of Bi-2212 intrinsic Josephson junctions with two types of junction geometry. We found that a crossover temperature to the macroscopic quantum tunneling regime was quite different between the two types of junction geometry. The observed behavior is discussed in terms of an edge effect in long Josephson junctions dependent on the junction geometry. We investigated the phase dynamics of long intrinsic Josephson junctions, which were fabricated on a narrow bridge structure of Bi2Sr2CaCu2Oy (Bi-2212) single crystals by using a focused ion-beam etching. We measured the probability distribution of the switching events from the zero-voltage state for two types of junction geometry. One is a junction where the bridge width (L1) is larger than the Josephson penetration depth, λJ, and the distance between two slits (L2) is comparable to λJ, while the other is a junction where L1 is comparable to λJ and L2 is larger than λJ. We found that a crossover temperature from the thermally activated regime to the macroscopic quantum tunneling regime was quite different between the two types of junction geometry. We discuss the observed behavior in terms of an edge effect in long Josephson junctions dependent on the junction geometry.
The authors have studied the phase-locking in a pair of individually biased, resistively and capacitively shunted Josephson junctions, coupled by a common resistive or capacitive shunt, on an analog computer. Under certain conditions locking is found to occur at all rational frequency ratios. A critical line is found in parameter space along which the steps form a complete devils staircase having a fractal dimension of 0.87. Beyond the critical line bifurcations occur on all steps following the Feigenbaum sequence to chaos. The Feigenbaum constants are recovered to a fair accuracy. Preliminary experiments with two Josephson tunnel junctions shunted on the chip by a gold-indium film are discussed
Mygind, Jesper; Pedersen, Niels Falsig; Sørensen, O. H.
1976-01-01
The first direct observation of the parametrically generated half-harmonic voltage in a Josephson tunnel junction is reported. A microwave signal at f=17.25 GHz is applied to the junction dc current biased at zero voltage such that the Josephson plasma resonance fp=f/2. Under these conditions a...... large-amplitude microwave signal is emitted at fp provided the input power exceeds a threshold value. The results are compared to existing theory. Applied Physics Letters is copyrighted by The American Institute of Physics....
Intrinsic Josephson effect and single Cooper pair tunneling
Yamashita, Tsutomu; Kim, Sang-Jae; Latyshev, Yuri; Nakajima, Kensuke
2000-06-01
We proposed a new, small and fast switching gate based on the intrinsic Josephson effect of single crystals of a cuprate superconductor. The switching time is of subpicosecond order, and the operating frequency is up to several terahertz. We used the focused-ion-beam (FIB) method for the fabrication of small Bi 2Sr 2CaCu 2O 8 (Bi-2212) stacked intrinsic Josephson junctions (IJJ) with in-plane size down to the submicron level without the degradation of their Tc. We observed clear Fraunhofer patterns in Ic- B curves and flux-flow velocity of up to 10 6 m/s for the stack junctions with the size of several micrometer scale. For the submicron junction, the low-temperature behavior is governed by the Coulomb-charging effects. This is the first observation of the Coulomb-charging effects in layered high- Tc materials.
Josephson tunnel junctions as fast nuclear particle position detectors
We present here some problems and solutions in using Josephson junctions as fast nuclear particle position detectors. The process of induced switching is modelled in terms of a reduction of the critical current due to a disturbed volume: the hot spot. The spurious thermal induced switching process is also taken into account. Calculations in order to choose the junction parameters are presented. The all refractory junction fabrication technology developed is capable of satisfying design prescriptions. (orig.)
Niobium nitride-niobium Josephson tunnel junctions with sputtered amorphous silicon barriers
Niobium nitride-niobium Josephson tunnel junctions with sputtered amorphous silicon barriers (NbN-αSi-Nb) have been prepared using processing that is fully compatible with integrated circuit fabrication. These junctions are of suitable quality and uniformity for digital circuit and S-I-S detector applications. The junction quality depends critically upon the properties of the NbN surface, and seems to correlate well with the UV/visible reflectivity of this surface
Josephson Effects in superconducting conventional/unconventional tunnel junctions and weak-links
The a.c. Josephson effect is perhaps the most striking manifestation of long-range phase coherence (broken gauge symmetry) in superconductors. Superconductivity in which gauge symmetry is broken in combination with one or more additional symmetries of the normal metallic state (unconventional superconductivity) may also occur. We discuss the Josephson effect for several models of an unconventional superconductor in contact with a conventional superconductor. An unconventional order parameter leads to qualitative changes in the current-phase relation which could be detected with a SQUID in which one arm of the interferometer is an unconventional superconductor. We also compare the current-phase relation for a tunnel junction with that of a weak-link connecting a conventional and unconventional superconductor. Selection rules for unconventional order parameters which enforce zero supercurrent in a tunnel junction are not relevant for weak-links connecting the same unconventional and conventional superconductor. We discuss the the a.c. Josephson effect for several popular models of unconventional superconductivity relevant to the CuO and heavy fermion superconductors. (orig.)
Noise performance of superconductive magnetometers based on long Josephson tunnel junctions
Granata, Carmine; Vettoliere, Antonio; Monaco, Roberto
2014-09-01
The low-current fluctuations at cryogenic temperatures together with the low dynamical resistance in the resonant states of Josephson tunnel junctions allow for the realization of superconducting oscillators up to the THz range with ultra-low spectral linewidth. By virtue of the Josephson frequency-voltage relationship, we show that the same properties can be exploited for the practical realization of magnetic flux-to-voltage transducers based on the flux-flow in long Josephson tunnel junctions whose intrinsic low-frequency voltage fluctuations at 4.2\\;K amount to few pV/H{{z}^{1/2}}, that is, too small to be measured by any present semiconductor electronics. Nevertheless, by using a double transformer SQUID amplifier we demonstrate that the (amplitude) voltage spectral density, S_{V}^{1/2}, of an all-niobium sensor does not exceed the level of 10\\;pV/H{{z}^{1/2}} and is not affected by 1/f excess noise at least down to few hertz. Such ultra-low white noise, corresponding to a magnetic field noise S_{B}^{1/2}\\leqslant 10\\;fT/H{{z}^{1/2}}, together with a highly linear and broadband voltage responsivity over a wide magnetic flux range, makes the flux-flow magnetometers potentially competitive with SQUID-based devices.
Noise performance of superconductive magnetometers based on long Josephson tunnel junctions
The low-current fluctuations at cryogenic temperatures together with the low dynamical resistance in the resonant states of Josephson tunnel junctions allow for the realization of superconducting oscillators up to the THz range with ultra-low spectral linewidth. By virtue of the Josephson frequency-voltage relationship, we show that the same properties can be exploited for the practical realization of magnetic flux-to-voltage transducers based on the flux–flow in long Josephson tunnel junctions whose intrinsic low-frequency voltage fluctuations at 4.2 K amount to few pV/Hz1/2, that is, too small to be measured by any present semiconductor electronics. Nevertheless, by using a double transformer SQUID amplifier we demonstrate that the (amplitude) voltage spectral density, SV1/2, of an all-niobium sensor does not exceed the level of 10 pV/Hz1/2 and is not affected by 1/f excess noise at least down to few hertz. Such ultra-low white noise, corresponding to a magnetic field noise SB1/2⩽10 fT/Hz1/2, together with a highly linear and broadband voltage responsivity over a wide magnetic flux range, makes the flux–flow magnetometers potentially competitive with SQUID-based devices. (paper)
New scaling behavior has been both predicted and observed in the spontaneous production of fluxons in quenched Nb-Al/Alox/Nb annular Josephson tunnel junctions (JTJs) as a function of the quench time, τQ. The probability f1 to trap a single defect during the normal-metal-superconductor phase transition clearly follows an allometric dependence on τQ with a scaling exponent σ=0.5, as predicted from the Zurek-Kibble mechanism for realistic JTJs formed by strongly coupled superconductors. This definitive experiment replaces one reported by us earlier, in which an idealized model was used that predicted σ=0.25, commensurate with the then much poorer data. Our experiment remains the only condensed matter experiment to date to have measured a scaling exponent with any reliability
The moderately damped regime in a Josephson junction (JJ) is quite common in devices characterized by low critical currents and therefore by low Josephson energies. Measurements of switching current distribution (SCD) are a direct way of discriminating the phase dynamics also in the nontrivial case of moderate damping, which is going to be more and more common with advances in nano-patterning superconductors and in materials science finalized to build hybrid systems. We report on measurements of SCDs, both in thermal and quantum regime, on moderately damped YBaCuO grain boundary biepitaxial JJs. A direct transition from phase diffusion regime to macroscopic quantum tunnelling occurs at about 130 mK. The crossover to the quantum regime is tuned by the magnetic field and phase dynamics is described by a fully consistent set of junction parameters derived through numerical simulations.
Theory for collective macroscopic tunneling in high- Tc intrinsic Josephson junctions
Machida, M.; Koyama, T.
2007-10-01
On the basis of the theory for the capacitive coupling in intrinsic Josephson junctions (IJJ's), we theoretically study the macroscopic quantum tunneling in the switching dynamics into the voltage states in IJJ. The effective action obtained by using the path integral formalism reveals that the capacitive coupling splits each of the lowest and higher quantum levels, which are given inside Josephson potential barrier of the single junction derived by dropping off the coupling, into levels composed of the number of junction (N). This level splitting can cause multiple low-frequency Rabi-oscillations and enhance the switching probability compared to the conventional Caldeira-Leggett theory. Furthermore, a possibility as a naturally built-in multi-qubit is discussed.
Macroscopic quantum tunnelling in a current biased Josephson junction
We discuss in this work an attempt to answer experimentally the question: do macroscopic variables obey quantum mechanics. More precisely, this experiment deals with the question of quantum-mechanical tunnelling of a macroscopic variable, a subject related to the famous Schrodinger's cat problem in the theory of measurement
Flicker (1/f) noise in Josephson tunnel junctions
The power spectrum was measured of the voltage fluctuations in shunted Josephson junctions biased at a constant current I greater than the critical current I/sub c/. Over the frequency range 5 x 10-2 to 50 Hz, the power spectra vary approximately as 1/f, where f is the frequency. At any single frequency, the noise decreases as I is increased. Experimental evidence is presented to show that the voltage noise arises from equilibrium fluctuations in the temperature T of the junction, which in turn modulate I/sub c/ and hence the voltage V across the junction. The magnitude of the power spectra is consistently predicted to within a factor of 5 by an extension of the semiempirical formula of Clarke and Voss: S/sub V/(f) = (dI/sub c//dT)2(partialV/partialI/sub c/)2/sub I/k/sub B/T2 / 3C/sub V/f. In this formula, it is postulated that C/sub V/ is the heat capacity of an ''effective'' junction volume given by the product of the junction area and the sum of the coherence lengths of the two superconductors. The dependence of S/sub V/(f) on (partialV/partialI/sub C/)2/sub I/ and (dI/sub c//dT)2 is experimentally established
Low-noise parametric amplification at 35 GHz in a single Josephson tunnel junction
Mygind, Jesper; Pedersen, Niels Falsig; Sørensen, O. H.; Dueholm, B.; Levinsen, M. T.
1979-01-01
Parametric amplification at 35 GHz has been obtained using a single Josephson tunnel junction as the active element. The amplifier was operated in the singly quasidegenerate mode with a pump frequency at 70 GHz. The noise temperature was measured and found correlated with the gain. At the highest...... gain achieved, 11.6 dB, the noise temperature was 400 K. The noise temperature was reduced considerably by decreasing the gain. At 8 and 4 dB we found 165±25 K and 50±30 K, respectively. Applied Physics Letters is copyrighted by The American Institute of Physics....
Vortex penetration and self-resonant effects in large Josephson tunnel junction
Discontinuity in the resonant voltage (traveling wave resonance) as a function of applied magnetic field has been observed in large Josephson tunnel junctions. It is believed that our results can be explained in terms of peculiar magnetic properties of large junctions of finite length L>>lambda/sub J/, i.e., the quantization of internal fields and magnetic hysteresis. The discontinuity corresponds to the change of number of vortices penetrating the junction barrier. The experimental voltage jumps are in fairly good agreement with these calculated from the theory
Metastable states and macroscopic quantum tunneling in a cold atom josephson ring
Solenov, Dmitry [Los Alamos National Laboratory; Mozyrsky, Dmitry [Los Alamos National Laboratory
2009-01-01
We study macroscopic properties of a system of weakly interacting neutral bosons confined in a ring-shaped potential with a Josephson junction. We derive an effective low energy action for this system and evaluate its properties. In particular we find that the system possesses a set of metastable current-carrying states and evaluate the rates of transitions between these states due to macroscopic quantum tunneling. Finally we discuss signatures of different metastable states in the time-of-flight images and argue that the effect is observable within currently available experimental technique.
Macroscopic quantum tunneling in a stack of capacitively-coupled intrinsic Josephson junctions
Koyama, Tomio; Machida, Masahiko
2008-04-01
A macroscopic quantum theory for the phase dynamics in capacitively-coupled intrinsic Josephson junctions (IJJ's) is constructed. We quantize the capacitively-coupled IJJ model in terms of the canonical quantization method. The multi-junction effect for the macroscopic quantum tunneling (MQT) to the first resistive branch is clarified. It is shown that the escape rate is greatly enhanced by the capacitive coupling between junctions. We also discuss the origin of the N2 -enhancement in the escape rate observed in the uniformly switching in Bi-2212 IJJ's.
Tunneling transport properties in (La,Sr)2CuO4 grain boundary Josephson junctions
We investigate tunneling transport properties in thin film grain boundary Josephson junctions (GBJ's) of epitaxially grown (La,Sr)2CuO4 (LSCO) on bicrystal substrates. These optimally doped LSCO films were made by molecular beam epitaxy producing a very smooth film at the grain boundary. Measurements of the critical current Ic at low magnetic fields B (mT range) are used to characterize the quality of the junctions. Deviations from the ideal Ic(B) pattern enable us to indicate the homogeneity of the GBJ. Measurements of the differential conductance in high magnetic fields (T range) are used to investigate quasiparticle tunneling across the grain boundary. Results are compared to theoretical predictions
Crystal engineering of oxide films in the fabrication of high-Tc Josephson tunnel junction
In relation to the authors' research for the fabrication of high-Tc Josephson tunnel junction composed of YBCO(S)/oxide insulator(I)/YBCO layers, two crystal engineering issues are presented and discussed on pulsed laser processing of oxide thin films. One is the epitaxial growth of highly crystalline and orientation-controlled YBCO films and the other is the molecular layer epitaxy of perovskite and rock salt oxides films. Quantitative results are presented on the crystal quality, surface atomic layers and morphology, and electronic properties of the films and junctions. Discussion will be made on such problems as the thermodynamics vs. kinetics in the film growth, identification and control of the topmost atomic layers of substrates and growing films, and electronic state of high-Tc films based on the scanning tunneling and photoelectron yield spectra
We address the excitation of quantum breathers in small nonlinear networks of two and three degrees of freedom, in order to study their properties. The invariance under permutation of two sites of these networks substitutes the translation invariance that is present in nonlinear lattices, where (classical) discrete breathers are time periodic space localized solutions of the underlying classical equations of motion. We do a systematic analysis of the spectrum and eigenstates of such small systems, characterizing quantum breather states by their tunneling rate (energy splitting), site correlations, fluctuations of the number of quanta, and entanglement. We observe how these properties are reflected in the time evolution of initially localized excitations. Quantum breathers manifest as pairs of nearly degenerate eigenstates that show strong site correlation of quanta, and are characterized by a strong excitation of quanta on one site of the network which perform slow coherent tunneling motion from one site to another. They enhance the fluctuations of quanta, and are the least entangled states among the group of eigenstates in the same range of the energy spectrum. We use our analysis methods to consider the excitation of quantum breathers in a cell of two coupled Josephson junctions, and study their properties as compared with those in the previous cases. We describe how quantum breathers could be experimentally observed by employing the already developed techniques for quantum information processing with Josephson junctions. (orig.)
Annular superconducting tunnel junction detectors: Experimental results under X-ray illumination
We present an experiment detecting X-rays by an annular Nb-based Superconducting Tunnel Junction (STJ). In one magnetic field configuration, we stably trapped a single magnetic fluxon in the STJ barrier during the transition to the superconducting state. This is an innovative configuration which avoids the use of an externally applied field during detector operation. This offers potential benefits for STJs used in imaging arrays. In this configuration, and also in the conventional one with an externally applied parallel magnetic field, we observed current pulses produced by single 6 keV X-rays. The pulses were identical for both configurations
R.F. self-field depression of microwave induced currents steps in Josephson tunnel junction
This paper reports that experimentally observed amplitudes of microwave induced steps in Josephson tunnel junctions are significantly reduced respect to the predictions of a simple model developed for a junction that is small respect to the Josephson penetration depth and radiation wavelength. In this approximation the amplitude of the n-th step in the critical current units (the reduced units will be used throughout the paper) is: ln = Jn(γb); γb = nvrf/Vn; Vn = (h/4πe)ωrn, where Jn (γ) is the Bessel function of the order n, ωrf radiation frequency and Vrf that amplitude of the r.f. signal. We will refer to this as the Bessel model. In resonant junctions the spatial variations of the microwave voltage in the barrier cannot be neglected. Pech and Sain-Michel considered the resonant junction irradiated at the frequency at which the half wavelength of the incident radiation matches the junction length (L = λ /2). Recently Costabile at al have solved the perturbed Sine-Gordon equation in the single mode approximation obtaining for the step height at the finite value of the standing wave ratio (SWR) and the intermediate junction length we will referred to this approximation as the SWR model
Effect of the subgap conductance on the metastable states in a Josephson tunnel junction
An investigation of the decay rate of metastable states in Josephson tunnel junctions in presence of thermal noise is presented. We have observed that, in the extremely underdamped regime, there is an exponential temperature dependence of the best fit value for the shunt conductance. Such a dependence shows a close relation with the temperature dependence of the subgap conductance, suggesting that the effective conductance for the escape from the metastable states obeys to a quasi-particle thermal activation mechanism. The introduction of this effective conductance into the lifetime expression for the zero-voltage states leads to significant changes in the width of the switching current distributions. A comparisons of the experimental data with the proposed model is reported. 7 refs., 2 figs
Wei, Peng; Katmis, Ferhat; Chang, Cui-Zu; Moodera, Jagadeesh S
2016-04-13
We report a unique experimental approach to create topological superconductors by inducing superconductivity into epitaxial metallic thin film with strong spin-orbit coupling. Utilizing molecular beam epitaxy technique under ultrahigh vacuum conditions, we are able to achieve (111) oriented single phase of gold (Au) thin film grown on a well-oriented vanadium (V) s-wave superconductor film with clean interface. We obtained atomically smooth Au thin films with thicknesses even down to below a nanometer showing near-ideal surface quality. The as-grown V/Au bilayer heterostructure exhibits superconducting transition at around 3.9 K. Clear Josephson tunneling and Andreev reflection are observed in S-I-S tunnel junctions fabricated from the epitaxial bilayers. The barrier thickness dependent tunneling and the associated subharmonic gap structures (SGS) confirmed the induced superconductivity in Au (111), paving the way for engineering thin film heterostructures based on p-wave superconductivity and nano devices exploiting Majorana Fermions for quantum computing. PMID:26943807
Xiong Bo; Liu Xun-Xu
2007-01-01
This paper studies the Josephson-like tunnelling in two-component Bose-Einstein condensates coupled with microwave field, which is in respond to various attractive and repulsive atomic interaction under the various aspect ratio of trapping potential. It is very interesting to find that the dynamic of Josephson-like tunnelling can be controlled from fast damped oscillations to nondamped oscillation, and relative number of atoms changes from asymmetric occupation to symmetric occupation correspondingly.
Josephson and Quasiparticle Tunneling Studies of LITHIUM-TITANIUM(2)-OXYGEN(4)
Ng, Kwok-Wai
Josephson and quasiparticle tunneling measurements have been performed on superconducting LiTi(,2)O(,4). High quality, dense samples were made by arc melting LiTi(,2)O(,4) pellets produced by sintering con- stituent powders of Li(,2)CO(,3), Ti(,2)O(,3) and TiO(,2). The conductive spinel phase was recovered by annealing the ingot for about two months. The sample was characterized by X-ray diffraction and a.c. suscepti- bility, and it was shown to be in the correct crystal structure with only a slight amount of impurity and have a proper superconducting criti- cal temperature of 11.3 K. The measured density was about 99.3% of the single crystal value, hence the sample was dense and suitable for the tunneling experiment. Josephson point contact tunneling between LiTi(,2)O(,4) and Nb reveals, under K-band microwave radiation of frequency (nu) = 25.2 GHz, Shapiro steps of spacing approximately h(nu)/2e. Assuming the validity of the analysis of Pals and van Haeringen, we were led to the conclusion that the pairing in superconducting LiTi(,2)O(,4) was of the s-wave type, as in Nb. The "squeezable junction" method of Moreland and Hansma has been applied to study the superconducting energy gap of an arc melted bulk LiTi(,2)O(,4) sample and also of co-sputtered MoRe films. The MoRe film was estimated to have an energy gap of 1.05 mV, corre- sponding to a Re concentration of 17%. The energy gap of LiTi(,2)O(,4) is determined to be 1.95 (+OR-) 0.03 mV corresponding to 2(DELTA)/k(,B)T(,c) = 4.00 (+OR-) 0.06, making this material a conventional, electron-phonon strong coupled superconductor. The new results for LiTi(,2)O(,4) rule out the recent suggestion of Alexandrov and Ranninger that this material. might exhibit a bipolaronic form superconductivity, for such a form would be gapless, contrary to our results. *DOE Report IS-T-1245. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.
Tunneling characteristics for nm-thick mesas consisting of a few intrinsic Josephson junctions
Suzuki, Minoru; Ohmaki, Masayuki; Takemura, Ryota; Hamada, Kenji; Watanabe, Takao; Ota, Kensuke; Kitano, Haruhisa; Maeda, Atsutaka
2008-10-01
Very thin mesa structures consisting of a few intrinsic Josephson junctions have been fabricated on single crystal surfaces of Bi2Sr2CaCu2O8+δ. In the fabrication procedure, annealing is conducted after the mesa structure is formed by Ar ion milling. Or, the annealing is skipped and, instead, the electrodes to the mesas have been deposited in vacuum immediately after crystals are cleaved. We have attained both uniform current-voltage (I-V) characteristics and small contact resistances, which are usually difficult to obtain at the same time in the case of nm-thick mesa structures. For the mesas thus fabricated, it is found that the Josephson critical current Jc of the top IJJ (the surface junction) is reduced significantly. The reduction of Jc is more significant when the doping level of the crystal used is lower. We argue that this is due to the proximity efiect of the surface junction, in which the top electrode is in close proximity with the Ag or Au film of a thickness of the order of 300 nm. For mesas obtained by this method, the switching probability distribution has been measured. It is found that when the mesa lateral size is larger than 2 μm the switching is unreproducible and lacking systematic temperature dependence. It is also found that escape temperature Tesc and the standard deviation σ for the switching probability distribution exhibits a large deviation from the Kramers' thermal activation theory. When the lateral size is no larger than 2 μm, the switching probability distribution results show coincidence with the theory in the temperature range from 1.3 K to 5 K. Below 0.5 K, the escape temperature tends to saturate and indicates a crossover near 0.5 K from the thermal activation to the macroscopic quantum tunneling.
Simulation of I-V curves of small Josephson tunnel junctions with finite capacitance
Results of digital and analog simulations of the I-V characteristics of small Josephson tunnel junctions are presented for a variety of cases, and are compared with the recent experimental results of Howard et al. [Appl. Phys. Lett. 35, 879 (1979)] on small-area, high-current-density junctions. The lumped-circuit-element model of Stewart and McCumber with an adjustable nonlinear quasiparticle conductance and various capacitance values is employed. The value of junction capacitance inferred from the digital simulation for a 10-9-cm2 junction is 9 x 10-15 F. This represents a normalized capacitance β/sub c/ = 0.3 for the junction considered, which had a critical current density roughly-equal105 A/cm2. The inferred capacitance is in agreement with the value extrapolated from previous experimental results. Both digital and analog simulations result in I-V curves which show a previously unreported crossing of the quasiparticle and total current curves. This crossing is due to an averaging in time of the voltage across the nonlinear quasiparticle-conductance channel. The crossing is not seen in the experimental results of Howard et al. Differences between the experimental and simulated I-V curves are discussed
Ultra-low-noise magnetic sensing with long Josephson tunnel junctions
We study how the magnetic field dependence of the Eck step voltage in long Josephson tunnel junctions (LJTJs) can allow for ultra-low-noise magnetic sensing. The field to be measured is applied perpendicular to a continuous superconducting pickup loop. Wherever the loop has a narrow constriction, the density of the flux-restoring circulating currents will become relatively high and will locally create a magnetic field large enough to bring a biased LJTJ into the flux-flow state, i.e., at a finite voltage proportional to the field strength. This method allows the realization of a novel family of robust and general-purpose superconducting devices which, despite their simplicity, function as ultra-low-noise, wide-band and high-dynamics magnetometers. The performance of low-Tc sensor prototypes, including a highly linear voltage responsivity and an intrinsic voltage spectral density SV1/2 in the pV Hz−1/2 range, promises to be competitive with that of the best superconducting quantum interference devices. (paper)
Grison, X
2000-11-15
This work, mainly experimental, is dedicated to the study of the Josephson effect and the tunnel spectroscopy of superconducting films. Thin films of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} oriented towards [0,0,1], [1,0,3], [1,1,0] or [1,0,0] axis have been made. The results concerning the [0,0,1] orientation are consistent with an order parameter having a d(x{sup 2}-y{sup 2}) symmetry but with a small component of s symmetry due to the orthorombicity of YBa{sub 2}Cu{sub 3}O{sub 7{delta}}. The results concerning the [1,1,0] orientation show the existence (near (1,1,0)-type surfaces) of an order parameter whose symmetry is d(x{sup 2}-y{sup 2}) {+-} i*s or more likely d(x{sup 2} - y{sup 2}) {+-} i*d(xy). The latter term implies the breaking of the time reversing symmetry. The i*d(xy) component is responsible for the Josephson coupling along the [1,1,0] axis, which means that the coupling is not or is little carried by the Andreev bound states contrarily to recent predictions. It is also shown that Josephson junctions can be fabricated by using ion irradiation. (A.C.)
Kubo, Yuimaru; Sboychakov, A. O.; Nori, Franco; Takahide, Y.; Ueda, S.; Tanaka, I.; Islam, A. T. M. N.; Takano, Y.
2012-10-01
We performed measurements of switching current distribution in a submicrometer La2-xSrxCuO4 (LSCO) intrinsic Josephson junction (IJJ) stack in a wide temperature range. The escape rate saturates below approximately 2 K, indicating that the escape event is dominated by a macroscopic quantum tunneling (MQT) process with a crossover temperature T*≈2K. We applied the theory of MQT for IJJ stacks, taking into account dissipation and the phase retrapping effect in the LSCO IJJ stack. The theory is in good agreement with the experiment both in the MQT and in the thermal activation regimes.
Koyama, Tomio; Ota, Yukihiro; Machida, Masahiko
2011-06-01
We investigate the resonance effect caused by the Josephson-Leggett (JL) mode in intrinsic Josephson junction stacks (IJJs) formed by a stack of multigap superconducting layers. Such an IJJ system is expected to be realized in a single crystal of highly anisotropic iron-based superconductors with thick blocking layers. It is shown that the JL mode is resonantly excited by the Josephson oscillations in the voltage state with inhomogeneous electric-field distribution along the c axis. The resonance creates a steplike structure with a negative resistance region in the I-V characteristics.
We report on a new experimental approach to the size estimation of the hot spot induced by ionizing particles in a Josephson tunnel junction. Here, in contrast to the case of a superconducting strip, it is possible to investigate the hot spot dynamics in absence of effects due to the heating induced by the bias current. The reported experiment is based on the motion of Abrikosov vortices, trapped in the thin films constituting the junction electrodes, under 5.6 MeV α-particle irradiation. The fast time evolution of a hot spot, combined with the presence of Abrikosov vortices, produces a change of the static magnetic field in the junction area and thus a change of the critical current value, Ic. Measurements of Ic during the α-particle irradiation and in presence of trapped Abrikosov vortices allow to determine the rate of appearance of those Ic changes. The behavior of the average appearance rate as function of the Abrikosov vortices density provides a direct determination of the maximum hot spot area. The experiment is performed on a high quality Nb/Al endash AlOx/Nb junction of circular geometry and with open-quotes smallclose quotes dimensions with respect to the Josephson penetration depth. A value of 4.7±1.2μm2 is found for the maximum hot spot area. copyright 1997 American Institute of Physics
Nomura, Yoshiki; Mizuno, Takaaki; Kambara, Hitoshi; Nakagawa, Yuya; Kakeya, Itsuhiro
2015-01-01
Macroscopic quantum tunneling (MQT) in an intrinsic Josephson junction (IJJ) stack of Bi1.9Pb0.1Sr1.39La0.63CuO6+δ (BiPb2201) has been investigated. For the first switch, from superconducting to the first resistive branch in current-voltage characteristics, the crossover between MQT and thermal activation (TA) takes place at 0.6 K. On the other hand, for the second switch, the MQT-TA crossover temperature is increased to 2.0 K. This result is interpreted as follows: the MQT rate of the second switch is enhanced by the charge coupling between adjacent IJJs as well as in Bi2Sr2CaCu2O8+δ. We consider that the enhancement of the MQT rate is a common feature among bismuth-cuprates with single and double CuO2 layers in their crystal structures.
We consider coherent atomic tunneling between two weakly coupled Bose-Einstein condensates (BEC) at T = 0 in (possibly asymmetric) double-well trap. The condensate dynamics of the macroscopic amplitudes in the two wells is modeled by two Gross-Pitaevskii equations (GPE) coupled by a tunneling matrix element. The evolution of the inter-well fractional population imbalance (related to the condensate phase difference) is obtained in terms of elliptic functions, generalizing well-known Josephson effects such as the 'ac' effect, the 'plasma oscillations', and the resonant Shapiro effect, to the nonsiusoidal regimes. We also present exact solutions for a novel 'macroscopic quantum self-trapping' effect arising from nonlinear atomic self-interaction in the GPE. The coherent BEC tunneling signatures are obtained in terms of the oscillations periods and the Fourier spectrum of the imbalance oscillations, as a function of the initial values of GPE parameters. Experimental procedures are suggested to make contact with theoretical predictions. (author). 44 refs, 8 figs
Quantum and thermal phase escape in extended Josephson systems
In this work I examine phase escape in long annular Josephson tunnel junctions. The sine-Gordon equation governs the dynamics of the phase variable along the junction. This equation supports topological soliton solutions, which correspond to quanta of magnetic flux trapped in the junction barrier. For such Josephson vortices an effective potential is formed by an external magnetic field, while a bias current acts as a driving force. Both together form a metastable potential well, which the vortex is trapped in. When the driving force exceeds the pinning force of the potential, the vortex escapes and the junction switches to the voltage state. At a finite temperature the driving force fluctuates. If the junction's energy scale is small, the phase variable can undergo a macroscopic quantum tunneling (MQT) process at temperatures below the crossover temperature. Without a vortex trapped, the metastable state is not a potential minimum in space, but a potential minimum at zero phase difference. (orig.)
Quantum and thermal phase escape in extended Josephson systems
Kemp, A.
2006-07-12
In this work I examine phase escape in long annular Josephson tunnel junctions. The sine-Gordon equation governs the dynamics of the phase variable along the junction. This equation supports topological soliton solutions, which correspond to quanta of magnetic flux trapped in the junction barrier. For such Josephson vortices an effective potential is formed by an external magnetic field, while a bias current acts as a driving force. Both together form a metastable potential well, which the vortex is trapped in. When the driving force exceeds the pinning force of the potential, the vortex escapes and the junction switches to the voltage state. At a finite temperature the driving force fluctuates. If the junction's energy scale is small, the phase variable can undergo a macroscopic quantum tunneling (MQT) process at temperatures below the crossover temperature. Without a vortex trapped, the metastable state is not a potential minimum in space, but a potential minimum at zero phase difference. (orig.)
Andersen, Christian Kraglund; Mølmer, Klaus
2013-01-01
variable: the phase change across a Josephson junction. The Josephson junction phase variable behaves as the position coordinate of a particle moving in a tilted washboard potential, and our general solution to the motion in such a potential with a time-dependent tilt reproduces a number of features...... associated with voltage switching in Josephson junctions. Apart from applications as artificial atoms in quantum information studies, the Josephson junction may serve as an electric field sensitive detector, and our studies provide a detailed understanding of how the voltage switching dynamics couples to the...
Analog simulation of the Josephson effects
Analog circuit techniques can be used to advantage to simulate the Josephson effects in a superconductor-insulator-superconductor tunnel junction. Details of an electronic Josephson simulator are presented, and the advantages of analog techniques over their digital counterparts for this application are discussed. The simulation of a Josephson microwave mixer is used as an example
Li, Shao-Xiong; Qiu, Wei; Han, Siyuan; Wei, Y. F.; Zhu, X. B.; Gu, C. Z.; Zhao, S. P.; Wang, H. B.
2007-07-01
We report on the first unambiguous observation of macroscopic quantum tunneling (MQT) in a single submicron Bi2Sr2CaCu2O8+δ surface intrinsic Josephson junction (IJJ) by measuring its temperature-dependent switching current distribution. All relevant junction parameters were determined in situ in the classical regime and were used to predict the behavior of the IJJ in the quantum regime via MQT theory. Experimental results agree quantitatively with the theoretical predictions, thus confirming the MQT picture. Furthermore, the data also indicate that the surface IJJ, where the current flows along the c axis of the crystal, has the conventional sinφ current-phase relationship.
Li, Shao-Xiong; Qiu, Wei; Han, Siyuan; Wei, Y F; Zhu, X B; Gu, C Z; Zhao, S P; Wang, H B
2007-07-20
We report on the first unambiguous observation of macroscopic quantum tunneling (MQT) in a single submicron Bi(2)Sr(2)CaCu(2)O(8+delta) surface intrinsic Josephson junction (IJJ) by measuring its temperature-dependent switching current distribution. All relevant junction parameters were determined in situ in the classical regime and were used to predict the behavior of the IJJ in the quantum regime via MQT theory. Experimental results agree quantitatively with the theoretical predictions, thus confirming the MQT picture. Furthermore, the data also indicate that the surface IJJ, where the current flows along the c axis of the crystal, has the conventional sinphi current-phase relationship. PMID:17678315
Pedersen, Niels Falsig; Sørensen, O. H.; Mygind, Jesper
1978-01-01
The microwave response at 9 GHz of Sn-O-Sn tunnel-junction current biased at zero dc voltage has been measured just below the critical temperature Tc of the Sn films. The temperature dependence of the cosφ conductance is determined from the resonant response at the junction plasma frequency fp as...... the temperature is decreased from Tc. We used three different schemes for observation of the plasma oscillations: (a) second-harmonic generation (excitation at ∼ 4.5 GHz, fp∼4.5 GHz); (b) mixing (excitations at ∼ 9 and ∼ 18 GHz, fp∼9 GHz); (c) parametric half-harmonic oscillation (excitation at ∼ 18...
The author presents an introduction to Josephson junctions. After an introduction to the physical principles of superconductivity and the Josephson effect some applications are described with special regards to the implementation in digital circuits. (HSI)
Fractional ac Josephson effect in unconventional superconductors
For certain orientations of Josephson junctions between two px-wave or two d-wave superconductors, the subgap Andreev bound states produce a 4π-periodic relation between the Josephson current I and the phase difference ψ: I propor to sin(ψ/2) . Consequently, the ac Josephson current has the fractional frequency eV/h where V is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (not square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by single electrons, rather than by Cooper pairs. The fractional ac Josephson effect can be observed experimentally by measuring frequency spectrum of microwave radiation from the junction
Phase locked 270-440 GHz local oscillator based on flux flow in long Josephson tunnel junctions
Koshelets, V. P.; Shitov, S. V.; Filippenko, L. V.; Vaks, V. L.; Mygind, Jesper; Baryshev, A.B.; Luinge, W.; Whyborn, N.
2000-01-01
The combination of narrow linewidth and wide band tunability makes the Josephson flux flow oscillator (FFO) a perfect on-chip local oscillator for integrated sub-mm wave receivers for, e.g., spectral radio astronomy. The feasibility of phase locking the FFO to an external reference oscillator is demonstrated experimentally. A FFO linewidth as low as 1 Hz (determined by the resolution bandwidth of the spectrum analyzer) has been measured in the frequency range 270–440 GHz relative to a referen...
Ota, K.; Hamada, K.; Takemura, R.; Ohmaki, M.; Machi, T.; Tanabe, K.; Suzuki, M.; Maeda, A.; Kitano, H.
2009-04-01
We investigated macroscopic quantum tunneling (MQT) of Bi2Sr2CaCu2Oy intrinsic Josephson junctions (IJJs) for two device structures. One is a small mesa, which is a few nanometers thick with only two or three IJJs, and the other is a stack of a few hundred IJJs in a narrow bridge structure. The experimental results regarding the switching-current distribution for the first switch from the zero-voltage state were in good agreement with the conventional theory for a single Josephson junction, indicating that the crossover temperature from thermal activation to the MQT regime for the former device structure was similar to that for the latter device structure. Together with the observation of multiphoton transitions between quantized energy levels in the MQT regime, these results strongly suggest that the observed MQT behavior is intrinsic to a single IJJ in high- Tc cuprates and is independent of the device structure. The switching-current distribution for the second switch from the first resistive state, which was carefully distinguished from the first switch, was also compared with respect to the two device structures. In spite of the differences between the heat transfer environments, the second switch exhibited a similar temperature-independent behavior for both devices up to a much higher temperature than the crossover temperature for the first switch. We argue that this cannot be explained in terms of self-heating caused by dissipative currents after the first switch. As possible candidates for this phenomenon, the MQT process for the second switch and the effective increase in the electronic temperature due to the quasiparticle injection are discussed.
Subharmonic gap structure and subharmonic Josephson steps
Subharmonic microwave-induced Josephson step is often observed in superconducting junctions that exhibit subharmonic gap structure. The two theories, multiparticle tunneling and self-coupling due to an electromagnetic field set up by the ac Josephson current, which have been suggested to explain the subharmonic gap structure are investigated with respect to the possible existence of subharmonic Josephson steps. Also treated is a Ginzburg-Landau calculation of the current--phase relation for Josephson junctions. All three theories give subharmonic Josephson steps with the same microwave-power dependence. The temperature dependence of the subharmonic step structure and the subharmonic gap structure is discussed. It seems the self-coupling is the main cause for both effects in tunnel junctions and for the subharmonic gap structure in Dayem bridges, while the subharmonic step structure in the Dayem bridge seems to be a geometrical effect related to ''multiparticle'' transfer processes. (3 figures)
Spin currents in TFT-Josephson junction
The spin of the Cooper pair in a triplet superconductor provides a new degree of freedom in Josephson junction physics. This can be accessed by using a magnetically-active tunneling barrier, leading to a rich variety of unconventional Josephson effects. Because of the triplet state of the pairing wavefunction, triplet superconductor junctions in general also display a Josephson spin current, which can flow even when the equilibrium charge current is vanishing. Using the quasiclassical Green's function theory, we have examined the more general situation of a magnetically-active barrier which does not conserve the spin of a tunneling Cooper-pair. We demonstrate that the Josephson spin currents on either side of the barrier need not be identical, with the magnitude, sign and orientation all allowed to differ. Not only do our calculations enhance the physical understanding of transport through triplet superconductor junctions, but they also open the possibility of novel spintronic Josephson devices.
... page: //medlineplus.gov/ency/article/001142.htm Annular pancreas To use the sharing features on this page, please enable JavaScript. An annular pancreas is a ring of pancreatic tissue that encircles ...
Cui, D. J.; Yu, H. F.; Peng, Z. H.; Cao, W. H.; Zhu, X. B.; Tian, Ye; Chen, G. H.; Lin, D. H.; Gu, C. Z.; Zheng, D. N.; Jing, X. N.; Lu, Li; Zhao, S. P.
2008-12-01
Macroscopic quantum tunneling (MQT) has been demonstrated recently in a Bi2Sr2CaCu2O8+δ surface intrinsic Josephson junction (SIJJ) with its critical current density Jc below 100 A cm-2 and its size below 1 µm. In this work, we present a study of the switching current distributions of SIJJs fabricated on the same crystal, with Jc>500 A cm-2 and size of 0.8 and 1.6 µm. MQT is clearly observed, and the crossover from MQT to thermal activation (TA) is seen. Our analysis shows that the data agree well with the theoretical predictions of MQT and TA for different-sized SIJJs when parameters that roughly scale with the SIJJ size are used. In the crossover regime, the data are found to be better fitted by considering quantum corrections to TA. We discuss the realistic design of phase- and flux-type qubits using the experimentally attainable SIJJ parameters, which shows that the SIJJs, with their controllable Jc and size (or junction capacitance), are feasible for qubit applications in the future.
Tunneling characteristics of YBa 2Cu 3O 7-δ-Pb window-type Josephson junctions
Frangi, F.; Dwir, B.; Pavuna, D.
1992-02-01
We present the results of tunneling measurements done on window-type, native-barrier YBa 2Cu 3O 7-δ-Pb junctions. We show features in the I-V curves which are related to the gap of YBa 2Cu 3O 7-δ, as well as to the Pb and YBa 2Cu 3O 7-δ phonon spectra. The nature of barrier in these structures is found to be semi-conducting. We can also see the asymmetry in the tunneling curves.
Phase locked 270-440 GHz local oscillator based on flux flow in long Josephson tunnel junctions
Koshelets, V.P.; Shitov, S.V.; Filippenko, L.V.; Vaks, V.L.; Mygind, Jesper; Baryshev, A.B.; Luinge, W.; Whyborn, N.
2000-01-01
-running tunnel junction. The results of residual FFO phase noise measurements are also presented. Finally, we propose a single-chip fully superconductive receiver with two superconductor–insulator–superconductor mixers and an integrated phase-locked loop. ©2000 American Institute of Physics....
Josephson super-current in graphene-superconductor junction
Sarvestani, E.; Jafari, S. A.
2011-01-01
Within the tunneling Hamiltonian formulation for the eight-component spinors,the Josephson critical super-current has been calculated in a planar superconductor-normal graphene-superconductor junction. Coupling between superconductor regions and graphene is taken into account by a tunneling Hamiltonian which contains two types of tunneling, intra-valley and inter-valley tunneling. Within the present tunneling approach, we find that the contributions of two kinds of tunneling to the critical s...
Solitons in Josephson junctions
Ustinov, A. V.
1998-11-01
Magnetic flux quanta in Josephson junctions, often called fluxons, in many cases behave as solitons. A review of recent experiments and modelling of fluxon dynamics in Josephson circuits is presented. Classic quasi-one-dimensional junctions, stacked junctions (Josephson superlattices), and discrete Josephson transmission lines (JTLs) are discussed. Applications of fluxon devices as high-frequency oscillators and digital circuits are also addressed.
Josephson supercurrent in a graphene-superconductor junction
Sarvestani, E.; Jafari, S. A.
2012-01-01
Within the tunneling Hamiltonian formulation for the eight-component spinors, the Josephson critical supercurrent has been calculated in a planar superconductor-normal graphene-superconductor junction. Coupling between superconductor regions and graphene is taken into account by a tunneling Hamiltonian which contains two types of tunneling, intravalley and intervalley tunneling. Within the present tunneling approach, we find that the contributions of two kinds of tunneling to the critical supercurrent are completely separable. Therefore, it is possible to consider the effect of the intervalley tunnelings in the critical supercurrent. The incorporation of these type of processes into the tunneling Hamiltonian exposes a special feature of the graphene Josephson junctions. The effect of intervalley tunneling appears in the length dependence plot of critical current in the form of oscillations. We also present the results for temperature dependence of critical supercurrent and compare with experimental results and other theoretical calculations.
Josephson supercurrent in a graphene-superconductor junction
Within the tunneling Hamiltonian formulation for the eight-component spinors, the Josephson critical supercurrent has been calculated in a planar superconductor-normal graphene-superconductor junction. Coupling between superconductor regions and graphene is taken into account by a tunneling Hamiltonian which contains two types of tunneling, intravalley and intervalley tunneling. Within the present tunneling approach, we find that the contributions of two kinds of tunneling to the critical supercurrent are completely separable. Therefore, it is possible to consider the effect of the intervalley tunnelings in the critical supercurrent. The incorporation of these type of processes into the tunneling Hamiltonian exposes a special feature of the graphene Josephson junctions. The effect of intervalley tunneling appears in the length dependence plot of critical current in the form of oscillations. We also present the results for temperature dependence of critical supercurrent and compare with experimental results and other theoretical calculations.
Josephson supercurrent in a graphene-superconductor junction
Sarvestani, Esmaeel [Institute for Advanced Simulation, Forschungszentrum Juelich, 52425 Juelich (Germany); Jafari, Seyed Akbar [Department of Physics, Sharif University of Technology, Tehran 11155-9161 (Iran, Islamic Republic of)
2013-07-01
Within the tunneling Hamiltonian formulation for the eight-component spinors, the Josephson critical supercurrent has been calculated in a planar superconductor-normal graphene-superconductor junction. Coupling between superconductor regions and graphene is taken into account by a tunneling Hamiltonian which contains two types of tunneling, intravalley and intervalley tunneling. Within the present tunneling approach, we find that the contributions of two kinds of tunneling to the critical supercurrent are completely separable. Therefore, it is possible to consider the effect of the intervalley tunnelings in the critical supercurrent. The incorporation of these type of processes into the tunneling Hamiltonian exposes a special feature of the graphene Josephson junctions. The effect of intervalley tunneling appears in the length dependence plot of critical current in the form of oscillations. We also present the results for temperature dependence of critical supercurrent and compare with experimental results and other theoretical calculations.
Scanning Josephson spectroscopy on the atomic scale
Randeria, Mallika T.; Feldman, Benjamin E.; Drozdov, Ilya K.; Yazdani, Ali
2016-04-01
The Josephson effect provides a direct method to probe the strength of the pairing interaction in superconductors. By measuring the phase fluctuating Josephson current between a superconducting tip of a scanning tunneling microscope and a BCS superconductor with isolated magnetic adatoms on its surface, we demonstrate that the spatial variation of the pairing order parameter can be characterized on the atomic scale. This system provides an example where the local pairing potential suppression is not directly reflected in the spectra measured via quasiparticle tunneling. Spectroscopy with such superconducting tips also shows signatures of previously unexplored Andreev processes through individual impurity-bound Shiba states. The atomic resolution achieved here establishes scanning Josephson spectroscopy as a promising technique for the study of novel superconducting phases.
Kitano, H.; Ota, K.; Hamada, K.; Takemura, R.; Ohmaki, M.; Maeda, A.; Suzuki, M.
2009-03-01
A nanometer-thick small mesa consiting of only two or three Bi2Sr2CaCu2Oy intrinsic Josephson junctions (IJJs) is studied through the switching current distribution measurements down to 0.4 K. Experimental results clearly show that the first switching events from the zero-voltage state for 1 K IJJs with several tens of junctions, in contrast to the recent result on a similar mesa-structured surface IJJ.
Multisoliton excitations in long Josephson junctions
Dueholm, B.; Levring, O. A.; Mygind, Jesper; Pedersen, Niels Falsig; Sørensen, O. H.; Cirillo, M.
1981-01-01
The microwave emission from long Josephson tunnel junctions dc-current biased on zero-field and Fiske steps has been measured. The frequency and power variation on all steps of the narrow-linewidth radiation near the fundamental cavity-mode frequency and the observed transitions between different...
Gupta, Diptesh; Hess, Brian; Bachegowda, Lohith
2010-01-01
We present a case of a 77-year-old, diabetic male with a 20-year history of a migratory erythematous, asymptomatic, generalized, nonscaly, and nonitchy rash that started over the dorsum of his left hand. On examination, there were multiple annular erythematous plaques, distributed symmetrically and diffusely over his torso and arms, with central clearing and no scales. A punch biopsy of the skin helped us to arrive at the diagnosis of a generalized granuloma annulare (GA). GA is a benign, self-limiting skin condition of unknown etiology that is often asymptomatic. The cause of this condition is unknown, but it has been associated with diabetes mellitus, infections such as HIV, and malignancies such as lymphoma. These lesions typically start as a ring of flesh-colored papules that slowly progress with central clearing. Lack of symptoms, scaling, or associated vesicles helps to differentiate GA from other skin conditions such as tinea corporis, pityriasis rosea, psoriasis, or erythema annulare centrifugum. Treatment is often not needed as the majority of these lesions are self-resolving within 2 years. Treatment may be pursued for cosmetic reasons. Available options include high-dose steroid creams, PUVA, cryotherapy, or drugs such as niacinamide, infliximab, Dapsone, and topical calcineurin inhibitors. PMID:20209383
Proposed Josephson voltage standard
Chang, C. C.; Holderman, L. B.; Toots, J.
1980-01-01
Relatively-simple microwave integrated circuit comprising two resonators linked by Josephson junction could be set up to generate standard Josephson volt in any industrial laboratory. Standard cells and electronic equipment could be readily compared and calibrated to this standard.
Fractional Solitons in Excitonic Josephson Junctions.
Hsu, Ya-Fen; Su, Jung-Jung
2015-01-01
The Josephson effect is especially appealing to physicists because it reveals macroscopically the quantum order and phase. In excitonic bilayers the effect is even subtler due to the counterflow of supercurrent as well as the tunneling between layers (interlayer tunneling). Here we study, in a quantum Hall bilayer, the excitonic Josephson junction: a conjunct of two exciton condensates with a relative phase ϕ0 applied. The system is mapped into a pseudospin ferromagnet then described numerically by the Landau-Lifshitz-Gilbert equation. In the presence of interlayer tunneling, we identify a family of fractional sine-Gordon solitons which resemble the static fractional Josephson vortices in the extended superconducting Josephson junctions. Each fractional soliton carries a topological charge Q that is not necessarily a half/full integer but can vary continuously. The calculated current-phase relation (CPR) shows that solitons with Q = ϕ0/2π is the lowest energy state starting from zero ϕ0 - until ϕ0 > π - then the alternative group of solitons with Q = ϕ0/2π - 1 takes place and switches the polarity of CPR. PMID:26511770
Fractional Solitons in Excitonic Josephson Junctions
Hsu, Ya-Fen; Su, Jung-Jung
2015-10-01
The Josephson effect is especially appealing to physicists because it reveals macroscopically the quantum order and phase. In excitonic bilayers the effect is even subtler due to the counterflow of supercurrent as well as the tunneling between layers (interlayer tunneling). Here we study, in a quantum Hall bilayer, the excitonic Josephson junction: a conjunct of two exciton condensates with a relative phase ϕ0 applied. The system is mapped into a pseudospin ferromagnet then described numerically by the Landau-Lifshitz-Gilbert equation. In the presence of interlayer tunneling, we identify a family of fractional sine-Gordon solitons which resemble the static fractional Josephson vortices in the extended superconducting Josephson junctions. Each fractional soliton carries a topological charge Q that is not necessarily a half/full integer but can vary continuously. The calculated current-phase relation (CPR) shows that solitons with Q = ϕ0/2π is the lowest energy state starting from zero ϕ0 - until ϕ0 > π - then the alternative group of solitons with Q = ϕ0/2π - 1 takes place and switches the polarity of CPR.
Josephson junctions with ferromagnetic interlayer
We report on the fabrication of superconductor/insulator/ferromagnetic metal/superconductor (Nb/AlOx/Pd0.82Ni0.18/Nb) Josephson junctions (SIFS JJs) with high critical current densities, large normal resistance times area products, and high quality factors. For these junctions, a transition from 0- to π-coupling is observed for a thickness dF=6 nm of the ferromagnetic Pd0.82Ni0.18 interlayer. The magnetic field dependence of the critical current of the junctions demonstrates good spatial homogeneity of the tunneling barrier and ferromagnetic interlayer. Magnetic characterization shows that the Pd0.82Ni0.18 has an out-of-plane anisotropy and large saturation magnetization indicating negligible dead layers at the interfaces. A careful analysis of Fiske modes up to about 400 GHz provides valuable information on the junction quality factor and the relevant damping mechanisms. Whereas losses due to quasiparticle tunneling dominate at low frequencies, at high frequencies the damping is explained by the finite surface resistance of the junction electrodes. High quality factors of up to 30 around 200 GHz have been achieved. They allow to study the junction dynamics, in particular the switching probability from the zero-voltage into the voltage state with and without microwave irradiation. The experiments with microwave irradiation are well explained within semi-classical models and numerical simulations. In contrast, at mK temperature the switching dynamics without applied microwaves clearly shows secondary quantum effects. Here, we could observe for the first time macroscopic quantum tunneling in Josephson junctions with a ferromagnetic interlayer. This observation excludes fluctuations of the critical current as a consequence of an unstable magnetic domain structure of the ferromagnetic interlayer and affirms the suitability of SIFS Josephson junctions for quantum information processing.
Josephson junctions with ferromagnetic interlayer
Wild, Georg Hermann
2012-03-04
We report on the fabrication of superconductor/insulator/ferromagnetic metal/superconductor (Nb/AlO{sub x}/Pd{sub 0.82}Ni{sub 0.18}/Nb) Josephson junctions (SIFS JJs) with high critical current densities, large normal resistance times area products, and high quality factors. For these junctions, a transition from 0- to {pi}-coupling is observed for a thickness d{sub F}=6 nm of the ferromagnetic Pd{sub 0.82}Ni{sub 0.18} interlayer. The magnetic field dependence of the critical current of the junctions demonstrates good spatial homogeneity of the tunneling barrier and ferromagnetic interlayer. Magnetic characterization shows that the Pd{sub 0.82}Ni{sub 0.18} has an out-of-plane anisotropy and large saturation magnetization indicating negligible dead layers at the interfaces. A careful analysis of Fiske modes up to about 400 GHz provides valuable information on the junction quality factor and the relevant damping mechanisms. Whereas losses due to quasiparticle tunneling dominate at low frequencies, at high frequencies the damping is explained by the finite surface resistance of the junction electrodes. High quality factors of up to 30 around 200 GHz have been achieved. They allow to study the junction dynamics, in particular the switching probability from the zero-voltage into the voltage state with and without microwave irradiation. The experiments with microwave irradiation are well explained within semi-classical models and numerical simulations. In contrast, at mK temperature the switching dynamics without applied microwaves clearly shows secondary quantum effects. Here, we could observe for the first time macroscopic quantum tunneling in Josephson junctions with a ferromagnetic interlayer. This observation excludes fluctuations of the critical current as a consequence of an unstable magnetic domain structure of the ferromagnetic interlayer and affirms the suitability of SIFS Josephson junctions for quantum information processing.
Design and Implementation of a Josephson Junction Spectrometer
Girit, Caglar; Goffman, Marcelo; Pothier, Hugues; Urbina, Cristián; Esteve, Daniel
2015-03-01
A Josephson tunnel junction can be used as an on-chip absorption spectrometer at frequencies up to several hundred gigahertz. As a result of the AC Josephson effect, a voltage biased junction acts as a microwave source. When emitted photons are absorbed in the junction's electromagnetic environment, a dc Cooper pair current flows (inelastic Cooper pair tunneling). By measuring this dc current as a function of applied voltage--the junction's current-voltage characteristic--one obtains a spectrum of the electromagnetic environment. We describe the design of a Josephson junction spectrometer which seeks to optimize bandwidth, sensitivity, coupling and linewidth. We present measurements of the spectra of miniature on-chip LC circuits with resonant frequencies in the 25-100 GHz range. Our Josephson junction spectrometer will be used to study level transitions in mesoscopic systems. Supported by Grant ANR-10-IDEX-0001-02 PSL.
Resonant modes in Josephson structures
It is well-know that a Josephson junction held at finite voltage V generates an alternating current at a frequency *o=(2e/h)V. When the junction is coupled to an external resonator self-induced dc current modes occur in the structure. The nonlinear interaction with the ac Josephson radiation gives rise to current singularities at voltages corresponding to the resonance frequencies of the resonator. These resonances appear in the dc current voltage characteristics as current singularities. They are due to a conversion of dc power to ac power that in turn is internally dissipated. In a tunneling junction the resonator is formed of the two superconducting electrodes separated by the oxide layer. In a two junctions interferometer the resonant structure is formed of the loop inductance and the junction capacitances. A good knowledge of the behaviour of these singularities is very important when switching properties are considered or ac power has to be extracted from the structure. In this paper we review the behaviour of resonant modes in Josephson junctions coupled to a resonant structure. A comparison between experimental data and the theoretical description at present available is reported
Phonon-mediated Josephson oscillations in excitonic and polaritonic condensates
Magnusson, E. B.; Flayac, H.; Malpuech, G.; Shelykh, I.A.
2010-01-01
We analyze theoretically the role of the exciton-phonon interactions in phenomena related to the Josephson effect between two spatially separated exciton and exciton-polariton condensates. We consider the role of the dephasing introduced by phonons in such phenomena as Josephson tunneling, self-trapping and spontaneous polarization separation. In the regime of cw pumping we find a remarkable bistability effect arising from exciton- exciton interactions as well as regimes of self- sustained re...
Scattering theory of the Josephson effect in iron based superconductors
We study the Josephson effect in S±IS± junctions made by a two band superconductor with s± wave symmetry. We derive the Andreev coefficients for the scattering problem at the junction interface and the temperature dependence of the critical current. We predict various features of the Josephson current for certain values of the second band strengths and tunnel barrier amplitude among which a high temperature π state coupling, and a π to 0 transition as the temperature lowers.
Resonator coupled Josephson junctions; parametric excitations and mutual locking
Jensen, H. Dalsgaard; Larsen, A.; Mygind, Jesper
Self-pumped parametric excitations and mutual locking in systems of Josephson tunnel junctions coupled to multimode resonators are reported. For the very large values of the coupling parameter, obtained with small Nb-Al2O3-Nb junctions integrated in superconducting microstrip resonators, the DC I......-V characteristic shows an equidistant series of current steps generated by subharmonic pumping of the fundamental resonator mode. This is confirmed by measurement of frequency and linewidth of the emitted Josephson radiation...
We review the development of low parasitic capacitance sub-micrometer cross-type Josephson tunnel junctions for their use in highly sensitive and field-stable SQUID magnetometers. The potential of such junctions is shown on I-V characteristics as well as on Fraunhofer diffraction patterns. The evaluation of Fiske steps lead to a specific junction capacitance of about 62 fF/μm2 for a critical current density of about 1.7 kA/cm2. The avoidance of any idle-region - the undesired overlap between superconducting electrodes around the junction - due to a self-aligned junction definition process lead to highly sensitive SQUIDs; multiloop SQUID magnetometers exhibiting exceptionally low magnetic field noise levels as low as 0.3 fT/Hz1/2, as well as large usable voltage swings of more than 150 μVpp. Furthermore, junction dimensions in the sub-micrometer range allowed for very high tolerable background fields during cool-down of up to 6.5 mT. In operation mode, the SQUID magnetometers recovered completely from magnetization pulses of up to 76 mT. With respect to their easy and reliable usage as well as their high sensitivity, the presented SQUID sensors are adequate for many applications, like in geophysics, biomagnetism or low-field magnetic resonance imaging.
Resistance of Josephson Junction Arrays at Low Temperatures
Ioffe, L. B.; Narozhny, B. N.
1997-01-01
We study motion of vortices in arrays of Josephson junctions at zero temperature where it is controlled by quantum tunneling from one plaquette to another. The tunneling process is characterized by a finite time and can be slow compared to the superconducting gap (so that $\\tau \\Delta >> 1$). The dissipation which accompanies this process arises from rare processes when a vortex excites a quasiparticle above the gap while tunneling through a single junction. We find that the dissipation is si...
Influence of noise and near-resonant perturbations on bifurcations in Josephson junctions
Svensmark, Henrik; Hansen, Jørn Bindslev; Pedersen, Niels Falsig
1987-01-01
The stabilization of a nonlinear system against period-doubling bifurcations by means of a periodic perturbation has been investigated. With the Josephson junction as a model system, both numerical simulations (including noise) and measurements on Josephson tunnel junctions have been performed. The...
Macroscopic quantum superposition of current states in a Josephson-junction loop
Wilhelm, F.K.; Wal, C.H. van der; Haar, A.C.J. ter; Schouten, R.N.; Harmans, C.J.P.M.; Mooij, J.E.; Orlando, T.P.; Lloyd, S.
2001-01-01
Superconducting circuits with Josephson tunnel junctions are interesting systems for research on quantum-mechanical behavior of macroscopic degrees of freedom. A particular realization is a small superconducting loop containing three Josephson junctions. Close to magnetic frustration 1/2, the physic
Josephson Junction electronics: materials issues and fabrication techniques
The discovery of superconducting tunneling and the Josephson effect in the early 1960s revolutionized the electronic applications of superconductivity, making possible large scale technical and economic uses of superconductors. Digital circuits with ultra-fast low-power Josephson Junctions make possible very high performance computers. Radio astronomy has benefited from development of electromagnetic radiation detectors using superconducting tunnel junctions. These new materials present fabrication problems due to material stresses, temperatures, electronic problems such as flux pinning, packaging, support matrixes, as well as other physical and metallurgical problems
Spectral linewidths of Josephson oscillators
Salerno, M; Samuelsen, Mogens Rugholm; Yulin, AV
2001-01-01
We show that the linewidth of a Josephson flux-flow oscillator has the same functional dependence on temperature, static, and dynamic resistances as the ones of Josephson single-fluxon oscillators and small Josephson junctions. This suggests a universal formula for the linewidth of Josephson osci...
Josephson gyroscope using superfluids
The Sagnac effect using matter (de Broglie) waves is considered for gyroscopic applications. Superfluid helium in a torus with a Josephson junction interrupting it would be an embodiment of this idea. An optical analog of the Josephson junction is discussed. An experimental search for the Sagnac effect in superfluid helium (isotope 4) is presented. 5 references
Josephson junctions as detectors for non-Gaussian noise
Non-Gaussian fluctuations of the electrical current can be detected with a Josephson junction placed on-chip with the noise source. We present preliminary measurements with an NIS junction as a noise source, and a Josephson junction in the thermal escape regime as a noise detector. It is shown that the Josephson junction detects not only the average noise, which manifests itself as an increased effective temperature, but also the noise asymmetry. A theoretical description of the thermal escape of a Josephson junction in presence of noise with a non-zero third cumulant is presented, together with numerical simulations when the noise source is a tunnel junction with Poisson noise. Comparison between experiment and theory is discussed. (Abstract Copyright [2007], Wiley Periodicals, Inc.)
Radiation comb generation with extended Josephson junctions
We propose the implementation of a Josephson radiation comb generator based on an extended Josephson junction subject to a time dependent magnetic field. The junction critical current shows known diffraction patterns and determines the position of the critical nodes when it vanishes. When the magnetic flux passes through one of such critical nodes, the superconducting phase must undergo a π-jump to minimize the Josephson energy. Correspondingly, a voltage pulse is generated at the extremes of the junction. Under periodic driving, this allows us to produce a comb-like voltage pulses sequence. In the frequency domain, it is possible to generate up to hundreds of harmonics of the fundamental driving frequency, thus mimicking the frequency comb used in optics and metrology. We discuss several implementations through a rectangular, cylindrical, and annular junction geometries, allowing us to generate different radiation spectra and to produce an output power up to 10 pW at 50 GHz for a driving frequency of 100 MHz
Intrinsic Josephson effects on superconducting films
Chana, O S
2002-01-01
Films of the high-T sub c superconductor Tl sub 2 Ba sub 2 CaCu sub 2 O sub 8 with the crystal c-axis misaligned from the substrate normal have been used to make intrinsic Josephson junctions. The copper-oxide layers in the cuprate superconductor are weakly coupled in the c-direction. This weak interplanar coupling is analogous to superconductor- insulator-superconductor stacks parallel to the c-direction in the film and this maps out to a series array of intrinsic Josephson junctions. A novel device geometry has been used to exploit this and series arrays of intrinsic Josephson junctions have been fabricated. The junctions are optimised in quality and have a high and critical-current- independent value for the product of the critical current and normal state resistance. The temperature dependence of the critical current fits the Ambegaokar-Baratoff theory for SIS tunnelling. X-band emission at around 12 GHz has been detected from the intrinsic Josephson bridge at 103 K. This confirms that the junctions are s...
Annular Flow Distribution test
This report documents the Babcock and Wilcox (B ampersand W) Annular Flow Distribution testing for the Savannah River Laboratory (SRL). The objective of the Annular Flow Distribution Test Program is to characterize the flow distribution between annular coolant channels for the Mark-22 fuel assembly with the bottom fitting insert (BFI) in place. Flow rate measurements for each annular channel were obtained by establishing ''hydraulic similarity'' between an instrumented fuel assembly with the BFI removed and a ''reference'' fuel assembly with the BFI installed. Empirical correlations of annular flow rates were generated for a range of boundary conditions
Quantum dissipative dynamics in nanostructure d-wave Josephson junctions
Kawabata, Shiro; Golubov, Alexander A.; Tanaka, Yukio; Kashiwaya, Satoshi
2007-01-01
The macroscopic quantum dynamics of nano-scale high-Tc superconductor Josephson junctions is investigated theoretically. We analytically obtained the macroscopic quantum tunneling (MQT) rate and showed that the presence of the zero energy bound states at the interface leads to a strong damping effec
Josephson current through a molecular transistor in a dissipative environment
Novotny, T; Rossini, Gianpaolo; Flensberg, Karsten
2005-01-01
We study the Josephson coupling between two superconductors through a single correlated molecular level, including Coulomb interaction on the level and coupling to a bosonic environment. All calculations are done to the lowest, i.e., the fourth, order in the tunneling coupling and we find a suppr...
Small-number arrays of intrinsic Josephson junctions
Yurgens, A.; Torstensson, M.; You, L. X.; Bauch, T.; Winkler, D.; Kakeya, I.; Kadowaki, K.
2008-04-01
Arrays of nanometre-thick Bi2212-intrinsic Josephson junctions (IJJ's) are studied in various geometries. The samples with only a few IJJ's allow for the intrinsic-tunnelling spectroscopy with minimum of Joule heating. The reproducible low-voltage peaks of the spectra probably stem from a superconducting gap which is half the usual size. We estimate the internal temperature in the IJJ stacks and analyze the importance of the self-heating for the macroscopic-quantum-tunnelling experiments involving IJJ's.
Holographic Josephson junction from massive gravity
Hu, Ya-Peng; Li, Huai-Fan; Zeng, Hua-Bi; Zhang, Hai-Qing
2016-05-01
We study the holographic superconductor-normal metal-superconductor (SNS) Josephson junction in de Rham-Gabadadze-Tolley massive gravity. If the boundary theory is independent of spatial directions, i.e., if the chemical potential is homogeneous in spatial directions, we find that the graviton mass parameter will make it more difficult for the normal metal-superconductor phase transition to take place. In the holographic model of the Josephson junction, it is found that the maximal tunneling current will decrease according to the graviton mass parameter. Besides, the coherence length of the junction decreases as well with respect to the graviton mass parameter. If one interprets the graviton mass parameter as the effect of momentum dissipation in the boundary field theory, this indicates that the stronger the momentum dissipation is, the smaller the coherence length is.
Disordered graphene Josephson junctions
Munoz, W. A.; Covaci, L.; Peeters, F. M.
2014-01-01
A tight-binding approach based on the Chebyshev-Bogoliubov-de Gennes method is used to describe disordered single-layer graphene Josephson junctions. Scattering by vacancies, ripples or charged impurities is included. We compute the Josephson current and investigate the nature of multiple Andreev reflections, which induce bound states appearing as peaks in the density of states for energies below the superconducting gap. In the presence of single atom vacancies, we observe a strong suppressio...
Nonlinearity in superconductivity and Josephson junctions
Within the framework of the Bardeen, Cooper and Schrieffers (BCS) theory, the influence of anisotropy on superconducting states are investigated. Crystal anisotropy exists in un-conventional low temperature superconductors as e.g. U1-xThxBe13 and in high temperature superconductors. Starting from a phenomenological pairing interaction of the electrons or holes, the BCS approach is used to derive a set of coupled nonlinear algebraic equations for the momentum dependent gap parameter. The emphasis is put on bifurcation phenomena between s-, d-wave and mixed s- and d-wave symmetry and the influence on measurable quantities as the electron specific heat, spin susceptibility and Josephson tunnelling. Pitch-fork and perturbed pitch-fork bifurcations have been found separating s- and d-wave superconducting states from mixed s- and d-wave states. The additional superconducting states give rise to jumps in the electron specific heat below the transition temperature. These jumps are rounded in the case of perturbed pitch-fork bifurcations. An experiment to measure the sign of the interlayer interaction using dc SQUIDS is suggested. The Ambegaokar-Baratoff formalism has been used for calculating the quasiparticle current and the two phase coherent tunnelling currents in a Josephson junction made of anisotropic superconductors. It is shown that anisotropy can lead to a reduction in the product of the normal resistance and the critical current. For low voltages across the junction the usual resistively shunted Josephson model can be used. Finally, bunching in long circular Josephson junctions and suppression of chaos in point junctions have been investigated. (au) 113 refs
Current distributions of thermal switching in extremely underdamped Josephson junctions
The first measurements of the switching current distribution of an extremely underdamped Josephson junction are presented at various temperatures. Careful fitting of the data provides an experimental verification of the thermal activation theory in the very low damping limit. Moreover, the fitting allows us to obtain the ''effective'' resistance of a Josephson tunnel junction, thus providing an important indication as to the proper junction resistance to be used in the resistively shunted junction model. These values of junction resistance show the temperature dependence of a subgap resistance, i.e., exp(Δ/k/sub B/T), due to activation of quasiparticles over the superconductor energy gap Δ
Experimental observation of subharmonic gap structures in long Josephson junctions
Nordahn, M.A.; Manscher, Martin; Mygind, Jesper;
1999-01-01
The subharmonic gap structure (SGS) in long-overlap Nb-AlOx-Nb Josephson tunnel junctions has been investigated. The experimental results show peaks in the differential conductance at both odd and even integer fractions of the gap voltage, VG Furthermore, the conductance peaks at V-G/2 has been...... observed to split into two peaks with different characteristics. At high magnetic fields, the I-V characteristics approach a single curve, while retaining the SGS conductance peaks. The gap structure and the SGS show the same temperature dependence. The SGS can be explained by a Josephson self...
Nondemolition measurements of a single quantum spin using Josephson oscillations
Bulaevskii, L.; Hruska, M.; Shnirman, A.; Smith, D.; Makhlin, Yu.
2005-01-01
We consider a Josephson junction containing a single localized spin 1/2 between conventional singlet superconducting electrodes. We study the spin dynamics and measurements when a dc-magnetic field ${\\bf B}\\parallel z$ acts on the spin and the junction is embedded into a dissipative circuit. We show that when tunneling or a voltage are turned on at time $t=0$ the Josephson current starts to oscillate with an amplitude depending on the initial ($t=0$) value of the spin $z$-component, $S_z= \\pm...
Characterization of superconducting devices spanning the charging to Josephson regimes
Charge states in mesoscopic Josephson devices are considered promising candidates for a solid-state implementation of quantum computing. We studied three superconducting single electron transistors (SSETs) fabricated with small Al/AlOx/Al tunnel junctions, which, with a different choice of the construction parameters, can realize both the quantum bit and the readout system for the qubit charge state. We varied the junction capacitance and barrier transparency, making the Josephson energy EJ of the device smaller, comparable and larger than the charging energy EC: the first case is suitable to build the qubit, while the latter can be suitable for the qubit readout. (author)
Low frequency noise in resonant Josephson soliton oscillators
Hansen, Jørn Bindslev; Holst, T.; Wellstood, Frederick C.;
1991-01-01
to the Nyquist voltage noise in a resistance equal to the dynamic resistance RD of the current-voltage characteristic of the bias point. In contrast, measurements of the linewidth of the microwave radiation from the same JTL showed that the spectral density of the underlying noise voltage scaled as R D2/RS where......The noise in the resonant soliton mode of long and narrow Josephson tunnel junctions (Josephson transmission lines or JTLs) have been measured in the frequency range from 0.1 Hz to 25 kHz by means of a DC SQUID. The measured white noise was found, to within a factor of two, to be equal...
Fabrication of high quality ferromagnetic Josephson junctions
Weides, M. [Institute for Solid State Research, Research Centre Juelich, D-52425 Juelich (Germany) and CNI-Center of Nanoelectronic Systems for Information Technology, Research Centre Juelich, D-52425 Juelich (Germany)]. E-mail: m.weides@fz-juelich.de; Tillmann, K. [Institute for Solid State Research, Research Centre Juelich, D-52425 Juelich (Germany); Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Research Centre Juelich, D-52425 Juelich (Germany); Kohlstedt, H. [Institute for Solid State Research, Research Centre Juelich, D-52425 Juelich (Germany); CNI-Center of Nanoelectronic Systems for Information Technology, Research Centre Juelich, D-52425 Juelich (Germany); Department of Material Science and Engineering and Department of Physics, University of Berkeley, CA 94720 (United States)
2006-05-15
We present ferromagnetic Nb/Al{sub 2}O{sub 3}/Ni{sub 60}Cu{sub 40}/Nb Josephson junctions (SIFS) with an ultrathin Al{sub 2}O{sub 3} tunnel barrier. The junction fabrication was optimized regarding junction insulation and homogeneity of current transport. Using ion-beam-etching and anodic oxidation we defined and insulated the junction mesas. The additional 2 nm thin Cu-layer below the ferromagnetic NiCu (SINFS) lowered interface roughness and ensured very homogeneous current transport. A high yield of junctional devices with j {sub c} spreads less than 2% was obtained.
Fabrication of high quality ferromagnetic Josephson junctions
We present ferromagnetic Nb/Al2O3/Ni60Cu40/Nb Josephson junctions (SIFS) with an ultrathin Al2O3 tunnel barrier. The junction fabrication was optimized regarding junction insulation and homogeneity of current transport. Using ion-beam-etching and anodic oxidation we defined and insulated the junction mesas. The additional 2 nm thin Cu-layer below the ferromagnetic NiCu (SINFS) lowered interface roughness and ensured very homogeneous current transport. A high yield of junctional devices with j c spreads less than 2% was obtained
Stochasticity in the Josephson map
The Josephson map describes nonlinear dynamics of systems characterized by standard map with the uniform external bias superposed. The intricate structures of the phase space portrait of the Josephson map are examined on the basis of the tangent map associated with the Josephson map. Numerical observation of the stochastic diffusion in the Josephson map is examined in comparison with the renormalized diffusion coefficient calculated by the method of characteristic function. The global stochasticity of the Josephson map occurs at the values of far smaller stochastic parameter than the case of the standard map. (author)
Josephson magnetic rotary valve
We propose a control element for a Josephson spin valve. It is a complex Josephson device containing ferromagnetic (F) layer in the weak-link area consisting of two regions, representing 0 and π Josephson junctions, respectively. The valve's state is defined by mutual orientations of the F-layer magnetization vector and boundary line between 0 and π sections of the device. We consider possible implementation of the control element by introduction of a thin normal metal layer in a part of the device area. By means of theoretical simulations, we study properties of the valve's structure as well as its operation, revealing such advantages as simplicity of control, high characteristic frequency, and good legibility of the basic states
Spin nutation effects in molecular nanomagnet$-$superconductor tunnel junctions
Abouie, J.; Abdollahipour, B.; A. A. Rostami
2013-01-01
We study the spin nutation effects of the molecular nanomagnet on the Josephson current through a superconductor$|$molecular nanomagnet$|$superconductor tunnel junction. We explicitly demonstrate that due to the spin nutation of the molecular nanomagnet two oscillatory terms emerge in the $ac$ Josephson current in addition to the conventional $ac$ Josephson current. Some resonances occur in the junction due to the interactions of the transported quasiparticles with the bias voltage and molecu...
Nondegenerate three-wave mixing with the Josephson ring modulator
Abdo, Baleegh; Kamal, Archana; Devoret, Michel
2013-01-01
The Josephson ring modulator (JRM) is a device, based on Josephson tunnel junctions, capable of performing nondegenerate mixing in the microwave regime without losses. The generic scattering matrix of the device is calculated by solving coupled quantum Langevin equations. Its form shows that the device can achieve quantum-limited noise performance both as an amplifier and a mixer. Fundamental limitations on simultaneous optimization of performance metrics like gain, bandwidth, and dynamic range (including the effect of pump depletion) are discussed. We also present three possible integrations of the JRM as the active medium in a different electromagnetic environment. The resulting circuits, named Josephson parametric converters (JPC), are discussed in detail, and experimental data on their dynamic range are found to be in good agreement with theoretical predictions. We also discuss future prospects and requisite optimization of JPC as a preamplifier for qubit readout applications.
Parametric excitation of plasma oscillations in Josephson Junctions
Pedersen, Niels Falsig; Samuelsen, Mogens Rugholm; Særmark, Knud
1973-01-01
A theory is presented for parametric excitation of plasma oscillations in a Josephson junction biased in the zero voltage mode. A threshold curve for the onset of the parametric excitation is deduced via the stability properties of a Mathieu differential equation obtained by a self-consistent lin......A theory is presented for parametric excitation of plasma oscillations in a Josephson junction biased in the zero voltage mode. A threshold curve for the onset of the parametric excitation is deduced via the stability properties of a Mathieu differential equation obtained by a self......-consistent linearization procedure. The important parameters turn out to be the plasma frequency and the circuit losses. The results of the calculation are compared with the experiments performed on a Josephson junction analog and good agreement is obtained. It is suggested that the effect should be observable in tunnel...
DC and AC Josephson Effect in a Superconductor-Luttinger Liquid-Superconductor System
Fazio, Rosario; Hekking, F. W. J.; Odintsov, A.A.; RevTex, 11 pages; figures, 9
1995-01-01
We calculate both the DC and the AC Josephson current through a one-dimensional system of interacting electrons, connected to two superconductors by tunnel junctions. We treat the (repulsive) Coulomb interaction in the framework of the one-channel, spin-$1/2$ Luttinger model. The Josephson current is obtained for two geometries of experimental relevance: a quantum wire and a ring. At zero temperature, the critical current is found to decay algebraically with increasing distance $d$ between th...
Field theoretic description of the abelian and non-abelian Josephson effect
Esposito, F. Paul; Guay, L. -P.; MacKenzie, R. B.; Paranjape, M. B.; Wijewardhana, L. C. R
2007-01-01
We formulate the Josephson effect in a field theoretic language which affords a straightforward generalization to the non-abelian case. Our formalism interprets Josephson tunneling as the excitation of pseudo-Goldstone bosons. We demonstrate the formalism through the consideration of a single junction separating two regions with a purely non-abelian order parameter and a sandwich of three regions where the central region is in a distinct phase. Applications to various non-abelian symmetry bre...
Madsen, Søren Find; Pedersen, Niels Falsig; Christiansen, Peter Leth
2010-01-01
Long Josephson junctions have for some time been considered as a source of THz radiation. Solitons moving coherently in the junctions is a possible source for this radiation. Analytical computations of the bunched state and bunching-inducing methods are reviewed. Experiments showing THz radiation...
Annular pancreas is an abnormal ring or collar of pancreatic tissue that encircles the duodenum (the part of the ... intestine that connects to stomach). This portion of pancreas can constrict the duodenum and block or impair ...
The c-axis dissipation in a magnetic field for oxygen-deficient YBa2Cu3O7-δ single crystals is shown to agree with that of a series stack of Josephson tunnel junctions. The intrinsic Josephson coupling energy, thus obtained, indicates the possibility of increased c-axis coherence below Tc
In this work the properties of josephson step contacts are investigated. After a short introduction into Josephson step contacts the structure, properties and the Josphson contacts of YBa2Cu3O7-x high-Tc superconductors is presented. The fabrication of HTSC step contacts and the microstructure is discussed. The electric properties of these contacts are measured together with the Josephson emission and the magnetic field dependence. The temperature dependence of the stationary transport properties is given. (WL)
Josephson φ_0-junction in nanowire quantum dots
Szombati, D. B.; Nadj-Perge, S.; Car, D.; Plissard, S.R.; Bakkers, E. P. A. M.; Kouwenhoven, L. P.
2015-01-01
The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference ϕ between the leads. Due to the chiral and time reversal symmetry of the Cooper pair tunneling process the current is strictly zero when ϕ vanishes. Only if these underlying symmetries are broken the supercurrent for ϕ = 0 may be finite. This corresponds to a ground state of the junction being offset by a ph...
Josephson $\\varphi_{0}$-junction in nanowire quantum dots
Szombati, D. B.; Nadj-Perge, S.; Car, D.; Plissard, S.R.; Bakkers, E. P. A. M.; Kouwenhoven, L. P.
2015-01-01
The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier [1]. This current is driven by a superconducting phase difference $\\phi$ between the leads. In the presence of chiral and time reversal symmetry of the Cooper pair tunneling process [2] the current is strictly zero when $\\phi$ vanishes. Only if these underlying symmetries are broken the supercurrent for $\\phi=0$ may be finite [3-5]. This corresponds to a ground state o...
Low-Tc, ramp-type Josephson junctions for SQUIDS
Podt, M.; Rolink, B.G.A.; Flokstra, J.; Rogalla, H.
2002-01-01
The Josephson tunnel junction is the basic element of a superconducting quantum interference device (SQUID). Amongst other parameters, the junction capacitance determines the characteristics of a (digital) SQUID. In a conventional dc SQUID, reducing the junction capacitance decreases the flux noise of the sensor, whereas in digital SQUIDs, the operating frequency can be increased when reducing the junction capacitance. For digital SQUIDs, this means that not only the flux noise decreases, but...
Running and testing of Josephson voltage standard series arrays
Gutmann, P.; Funck, T.; Grimm, L. [Physikalisch Technische Bundesanstalt, Braunschweig (Germany)
1994-12-31
It was found that the yield of the Josephson tunnel junction series arrays produced is limited by the test systems at present commonly in use to test and work them as voltage standards. We present a new voltage biasing system. It allows a junction-by-junction inspection of the array under test between zero and 10 volts with an excellent current resolution of 10{sup -7} A and an excellent voltage resolution of 10{sup -6}V.
Macroscopic quantum effects in intrinsic Josephson junction stacks
Koyama, T.; Machida, M.
2008-09-01
A macroscopic quantum theory for the capacitively-coupled intrinsic Josephson junctions (IJJ’s) is constructed. We clarify the multi-junction effect for the macroscopic quantum tunneling (MQT) to the first resistive branch. It is shown that the escape rate is greatly enhanced by the capacitive coupling between junctions. We also discuss the origin of the N2-enhancement in the escape rate observed in the uniformly switching in Bi-2212 IJJ’s.
Closed form solutions for the self-resonances in a short Josephson junction
We present a closed form solution for the self-resonances in a short Josephson tunnel junction. This solution is alternative to the well-known textbook result (Barone and Paterno (1982) and Kulik (1965)) based on a series expansion. Results are derived for the up-to-date case of a 0-π junction. - Highlights: We calculate the self-resonant modes of a 0-π Josephson tunnel junction. → We introduce a new method of calculation not based on a series solution. → Closed form expressions are derived for the phase dynamics and the supercurrent.
Disordered graphene Josephson junctions
Muñoz, W. A.; Covaci, L.; Peeters, F. M.
2015-02-01
A tight-binding approach based on the Chebyshev-Bogoliubov-de Gennes method is used to describe disordered single-layer graphene Josephson junctions. Scattering by vacancies, ripples, or charged impurities is included. We compute the Josephson current and investigate the nature of multiple Andreev reflections, which induce bound states appearing as peaks in the density of states for energies below the superconducting gap. In the presence of single-atom vacancies, we observe a strong suppression of the supercurrent, which is a consequence of strong intervalley scattering. Although lattice deformations should not induce intervalley scattering, we find that the supercurrent is still suppressed, which is due to the presence of pseudomagnetic barriers. For charged impurities, we consider two cases depending on whether the average doping is zero, i.e., existence of electron-hole puddles, or finite. In both cases, short-range impurities strongly affect the supercurrent, similar to the vacancies scenario.
Theoretical exploration of Josephson Plasma Emission in Intrinsic Josephson Junctions
In this paper, the authors theoretically predict the best efficient way for electromagnetic wave emission by Josephson plasma excitation in intrinsic Josephson junctions. First, they briefly derive basic equations describing dynamics of phase differences inside junction sites in intrinsic Josephson junctions, and review the nature of Josephson plasma excitation modes based on the equations. Especially, they make an attention to that Josephson plasma modes have much different dispersion relations depending on the propagating directions and their different modes can be recognized as N standing waves propagating along ah-plane in cases of finite stacked systems composed of N junctions. Second, they consider how to excite their modes and point out that excitations of in-phase mode with the highest propagation velocity among their N modes are the most efficient way for electromagnetic wave emissions. Finally, they clarify that in-phase excitations over all junctions are possible by using Josephson vortex flow states. They show simulation results of Josephson vortex flow states resonating with some Josephson plasma modes and predict that superradiance of electromagnetic field may occur in rectangular vortex flow state in which spatiotemporal oscillations of electromagnetic fields are perfectly in-phase
Microwave response and photon emission of a voltage baised Josephson junction
Jebari, Salha; Grimm, Alexander; Hazra, Dibyendu; Hofheinz, Max
The readout of superconducting qubits requires amplifiers combining noise close to the quantum limit, high gain, large bandwidth, and sufficient dynamic range. Josephson parametric amplifiers using Josephson junctions in the 0-voltage state, driven by a large microwave signals, begin to perform sufficiently well in all 4 of these aspects to be of practical use, but remain difficult to optimize and use. Recent experiments with superconducting circuits consisting of a DC voltage-biased Josephson junction in series with a resonator, showed that a tunneling Cooper pair can emit one or several photons with a total energy of 2e times the applied voltage. We present microwave reflection measurements on this device indicating that amplification is possible with a simple DC voltage-biased Josephson junction. We compare these measurements with the noise power emitted by the junction and show that, for low Josephson energy, transmission and noise emission can be explained within the framework of P(E) theory of inelastic Cooper pair tunneling. Combined with a theoretical model, our results indicate that voltage-biased Josephson junctions might be useful for amplification near the quantum limit, offering simpler design and a different trade-off between gain, bandwidth and dynamic range.
Josephson junction simulation of neurons
Crotty, Patrick; Schult, Daniel; Segall, Ken
2010-01-01
With the goal of understanding the intricate behavior and dynamics of collections of neurons, we present superconducting circuits containing Josephson junctions that model biologically realistic neurons. These "Josephson junction neurons" reproduce many characteristic behaviors of biological neurons such as action potentials, refractory periods, and firing thresholds. They can be coupled together in ways that mimic electrical and chemical synapses. Using existing fabrication technologies, lar...
Antonov, A. A.; Pankratov, A. L.; Yulin, A. V.; Mygind, Jesper
2000-01-01
The nonlinear dynamics of fluxons in Josephson systems with dispersion and thermal fluctuations is analyzed using the "quasiparticle" approach to investigate the influence of noise on the Cherenkov radiation effect. Analytical expressions for the stationary amplitude of the emitted radiation and its spectral distribution have been obtained in an annular geometry. It is demonstrated that noise reduces the amplitude of the radiated wave and broadens its spectrum. The effect of the radiated wave...
Visualization of the current density in Josephson junctions with 0- and π-facets
With Low-Temperature-Electron-Microscopy (LTSEM) it is possible to analyse the transport properties of solids at low temperatures. In particular it is possible to image the supercurrent density js in Josephson junctions. This was demonstrated by comparing TTREM-images with calculated values for js. In this thesis ramp-type Nd2-xCexCuO4-y/Nb-Josephson-junctions (NCCO/Nb) and Josephson junctions with a ferromagnetic interlayer Nb/Al-Al2O3/NiCu/Nb, so-called SIFS (superconductor-insulator-ferromagnet-superconductor) Josephson junctions were studied.It was demonstrated that LTSEM provides direct imaging of the sign change of the order parameter in superconductors with dx2-y2-symmetry. This was a controversial issue over the last decade. A step like variation in the thickness of the F-layer allows the fabrication of linear and annular Josephson junctions with different numbers of 0 and π facets. With the LTSEM 0-, π-, 0-π-, 0-π-0-, 0/2-π-0/2-, 20 x (0-π)- as well as square-shaped-, circular- and annular-Josephson-junctions were studied. It was demonstrated, that these junctions are of good quality and have critical current densities up to 42 A/cm2 at T=4.2 K, which is a record value for SIFS junctions with a NiCu F-layer so far. By comparing the measurements with simulations a first indication of a semifluxon at the 0-π-boundary was found. (orig.)
Generalized granuloma annulare
Khatri M
1995-01-01
Full Text Available A 35-years-old female patient had generalized pruritic papular lesions, distributed like dermatitis herpetiformis for last 4 years. Histopathologic changes were typical of granuloma annulare with negative results of direct immunofluorescence. The patient did not have association of diabetes mellitus or any other systemic disease. She failed to respond to dapsone therapy and 13-cis-retinoic acid.
Oscillating annular liquid membranes
The response of annular liquid membranes (e.g. used as protection systems in laser fusion reactors) to sinusoidal mass flow rate fluctuations at the nozzle exit is analyzed as a function of the amplitude and frequency of the axial velocity fluctuations at the nozzle exit and thermodynamic compression of the gas enclosed by the membrane. The pressure of the gases enclosed by the annular membrane and the axial distance at which the annular membrane merges on the symmetry axis are periodic functions of time which have the same period as that of the mass flow rate fluctuations at the nozzle exit. They are also nearly sinusoidal functions of time for small amplitudes of the mass flow rate fluctuations at the nozzle exit, and exhibit delay and lag times with respect to the sinusoidal axial velocity fluctuations at the nozzle exit. The delay and the lag times are functions of the amplitude and frequency of the mass flow rate fluctuations at the nozzle exit and the polytropic exponent. The amplitudes of both the pressure of the gases enclosed by the annular liquid membrane and the convergence length increase and decrease, resp., as the amplitude and frequency of the mass flow rate fluctuations at the nozzle exit, resp., are increased. They also increase as the polytropic exponent is increased. (orig.)
Annular Planar Monopole Antennas
Chen, Z. N.; Ammann, Max; Chia, W.Y. W.; See, T.S. P.
2002-01-01
A type of annular planar monopole antenna is presented. The impedance and radiation characteristics of the monopole with different holes and feed gaps are experimentally examined. The measured results demonstrate that the proposed antenna is capable of providing significantly broad impedance bandwidth with acceptable radiation performance.
Kolacek, Jan; Lipavsky, Pavel
2003-01-01
For type II superconductors, Josephson has shown that vortices moving with velocity v_L create an effective electric field E'=-v_L x B. By definition the effective electric field is gradient of the electrochemical potential, what is the quantity corresponding to voltage observed with the use of Ohmic contacts. It relates to the true electric field E via the local chemical potential mu as E'=E - grad(mu)/e. We argue that at low temperatures the true electric field in the bulk can be approximat...
Josephson arrays for dc and ac metrology
Large series arrays of underdamped SIS tunnel junctions are the basic element of the primary dc voltage standards used at present. The development of versatile quantum voltmeters for dc and ac metrology requires the preparation of large and perfect series arrays of overdamped Josephson junctions. Overdamped junctions can be realized by externally shunted SIS junctions or by internally shunted SNS or SINIS junctions. Arrays of up to 8000 SINIS junctions or 30000 SNS junctions were successfully operated at the 1 V dc level. In addition to being used in large arrays for voltage metrology and oscillators, the described junction types may become very useful for the preparation of highly integrated single-flux-quantum digital devices. (author)
Holographic Josephson Junction from Massive Gravity
Hu, Ya-Peng; Zeng, Hua-Bi; Zhang, Hai-Qing
2015-01-01
We study the holographic superconductor-normal metal-superconductor (SNS) Josephon junction in the massive gravity. In the homogeneous case of the chemical potential, we find that the graviton mass will make the normal metal-superconductor phase transition harder to take place. In the holographic model of Josephson junction, it is found that the maximal tunneling current will decrease according to the graviton mass. Besides, the coherence length of the junction decreases as well with respect to the graviton mass. If one interprets the graviton mass as the effect of momentum dissipation in the boundary field theory, it indicates that the stronger the momentum dissipation is, the smaller the coherence length is.
Josephson effect of a superconducting ferromagnet
A point contact tunneling technique has been used to investigate the existence of superconductivity in a long-range, magnetically ordered phase in the reentrant pseudoternary system (Er/sub 1-x/Ho/sub x/)Rh4B4 in the vicinity of the lower critical temperature T/sub c2/. In this experiment, Josephson-like current--voltage characteristics could be observed in a Nb--Nb oxide-- (Er/sub 0.58/HO/sub 0.42/) Rh4B4 junction even in a temperature region below T/sub c2/(approx.1.8--1.96 K), that is, in the magnetically ordered phase
Dissipation and traversal time in Josephson junctions
The various ways of evaluating dissipative effects in macroscopic quantum tunneling are re-examined. The results obtained by using functional integration, while confirming those of previously given treatments, enable a comparison with available experimental results relative to Josephson junctions. A criterion based on the shortening of the semiclassical traversal time τ of the barrier with regard to dissipation can be established, according to which Δτ/τ > or approx. N/Q, where Q is the quality factor of the junction and N is a numerical constant of order unity. The best agreement with the experiments is obtained for N=1.11, as it results from a semiempirical analysis based on an increase in the potential barrier caused by dissipative effects.
Josephson radiation from InSb-nanowire junction
van Woerkom, David; Proutski, Alexander; Krivachy, Tamas; Bouman, Daniel; van Gulik, Ruben; Gul, Onder; Cassidy, Maja; Car, Diana; Bakkers, Erik; Kouwenhoven, Leo; Geresdi, Attila
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_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. This work has been supported by the Netherlands Foundations FOM, Abstract NWO and Microsoft Corporation Station Q.
Quantum noise in Josephson-junction parametric amplifiers
Crossover between thermal and quantum noise in the externally-pumped Josephson-junction parametric amplifiers is theoretically followed. Two different approaches are used for the analysis: Josephson junction is replaced with its RSJ model with the equilibrium source of fluctuations; microscopic theory of the tunnel junctions is used, which takes into account not only thermal and quantum but also shot noise. Because of inconvenience of the noise temperature T /SUB N/ for the amplifier sensitivity characterization in the quantum limit, the authors express their results in terms of the figure theta /SUB N/ which is essentially the amplifier output noise energy, reduced to its input (in the classical limit, theta /SUB N/ =k /SUB B/ T /SUB N/). For the nondegenerate amplifier, the minimum value of theta /SUB N/ equals hω/2 and is due to quantum noise (zeropoint oscillations) in the idle-frequency resonator of the amplifier. For the degenerate amplifier, sensitive to only one quadrature component of the input signal, theta /SUB N/ can be made much less than the above ''quantum limit'' even at operation temperatures much higher than hω/k /SUB B/, if the Josephson junction characteristic frequency ω /SUB c/ is high enough, hω /SUB c/ k /SUB B/ T. An analysis of the experimental situation shows that the values theta /SUB N/ < can be achieved using two-dimensional arrays of a large number (N approx. = 100) single-tunnel-junction interferometers with low inductances, inductively coupled to a microwave cavity
Aspects of stochastic resonance in Josephson junction, bimodal maps and coupled map lattice
G Ambika; Kamala Menon; K P Harikrishnan
2005-04-01
We present the results of extensive numerical studies on stochastic resonance and its characteristic features in three model systems, namely, a model for Josephson tunnel junctions, the bistable cubic map and a coupled map lattice formed by coupling the cubic maps. Some interesting features regarding the mechanism including multisignal amplification and spatial stochastic resonance are shown.
Josephson junctions with ferromagnetic alloy interlayer
and IcRn by the s-layer thickness up to the value of nonmagnetic SIS junctions is notable. Additionally information on the emergence of superconductivity with the s-layer thickness was acquired. The introduction of this thesis (Chapter 1) is intended to motivate the experimental efforts and put them into the research context. An account on the evolving field of quantum information processing shall highlight the relevance of performance enhancements of superconducting devices. The chapter also introduces the theories of electron tunneling and effects at Josephson barriers, which are essential to analyse the experimental data. Moreover a description of magnetism along with mechanisms and experiments related to π Josephson junctions are presented. In the following (Chapter 2) an overview about machines and processes for the fabrication and characterisation of thin film devices is given. The preparation of samples was performed at facilities of the Technical Faculty of the University of Kiel. Also information about the experimental setup are given. A focus is put on the deposition of layers with thickness gradients across the wafer and combinatorial sputtering to achieve independent variations of two layer parameters. Finally (Chapter 3) experimental data for different types of Josephson junctions are shown. Related theories, relevant publications and a discussion are introduced along with the data.
Josephson junctions with ferromagnetic alloy interlayer
Himmel, Nico
2015-07-23
a variation of j{sub c} and I{sub c}R{sub n} by the s-layer thickness up to the value of nonmagnetic SIS junctions is notable. Additionally information on the emergence of superconductivity with the s-layer thickness was acquired. The introduction of this thesis (Chapter 1) is intended to motivate the experimental efforts and put them into the research context. An account on the evolving field of quantum information processing shall highlight the relevance of performance enhancements of superconducting devices. The chapter also introduces the theories of electron tunneling and effects at Josephson barriers, which are essential to analyse the experimental data. Moreover a description of magnetism along with mechanisms and experiments related to π Josephson junctions are presented. In the following (Chapter 2) an overview about machines and processes for the fabrication and characterisation of thin film devices is given. The preparation of samples was performed at facilities of the Technical Faculty of the University of Kiel. Also information about the experimental setup are given. A focus is put on the deposition of layers with thickness gradients across the wafer and combinatorial sputtering to achieve independent variations of two layer parameters. Finally (Chapter 3) experimental data for different types of Josephson junctions are shown. Related theories, relevant publications and a discussion are introduced along with the data.
Effect of quantum resonance-percolation trajectories on the parameters of a Josephson vortex
It is shown that, in the energy range of the tunneling resonances of a long superconductor-insulator-superconductor tunnel junction with a weak structural disorder (low impurity densities) in the insulator layer, the parameters of a Josephson vortex (flucson) are determined by the presence of quantum resonance-percolation trajectories that are randomly formed in the disordered insulator layer and connect the super-conducting banks of the junction
Spontaneous Currents in Josephson Devices
Radovic, Z.; Dobrosavljevic--Grujic, L.; Vujicic, B.
1999-01-01
The unconventional Josephson coupling in a ferromagnetic weak link between d-wave superconductors is studied theoretically. For strong ferromagnetic barrier influence, the unconventional coupling, with ground state phase difference across the link $0
Josephson spectroscopy on submillimeter waves
The Josephson high-temperature superconducting submillimeter spectrometer is developed, made and experimentally investigated. The integral receiving structure of the spectrometer comprises the YBCO Josephson junction on the bicrystal boundary, the two-gap (or logo-periodic) antenna and the low-inductive resistive shunt. The selective detector response and the response on the intermediate frequency 1.4 GHz are measured at the action of signals in the frequency range 350-1250 GHz. Th new spectroscopy method based on the mode of the mixer with self-pumping is proposed. The technique for the separation of the studied signal spectrum from the measured HF response is presented. This spectroscopy method with using the Josephson mixer with self-pumping at the high intermediate frequency allows one to improve the sensitivity, the spectral resolution and the dynamic range of the Josephson spectrometer
Josephson ϕ0-junction in nanowire quantum dots
Szombati, D. B.; Nadj-Perge, S.; Car, D.; Plissard, S. R.; Bakkers, E. P. A. M.; Kouwenhoven, L. P.
2016-06-01
The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference ϕ between the leads. In the presence of chiral and time-reversal symmetry of the Cooper pair tunnelling process, the current is strictly zero when ϕ vanishes. Only if these underlying symmetries are broken can the supercurrent for ϕ = 0 be finite. This corresponds to a ground state of the junction being offset by a phase ϕ0, different from 0 or π. Here, we report such a Josephson ϕ0-junction based on a nanowire quantum dot. We use a quantum interferometer device to investigate phase offsets and demonstrate that ϕ0 can be controlled by electrostatic gating. Our results may have far-reaching implications for superconducting flux- and phase-defined quantum bits as well as for exploring topological superconductivity in quantum dot systems.
MQT observation in Bi2212 intrinsic Josephson junctions
Kashiwaya, Satoshi; Matsumoto, Tetsuro; Kashiwaya, Hiromi; Shibata, Hajime; Eisaki, Hiroshi; Yoshida, Yoshiyuki; Kawabata, Shiro; Tanaka, Yukio
2007-09-01
The quantum dynamics of Bi 2Sr 2CaCu 2O 8+ δ intrinsic Josephson junctions (IJJ’s) is studied based on the escape rate measurements. The saturations observed in the escape temperature and the width of the switching current below 0.45 K (= T∗) indicate the transition of the switching mechanism from the thermal activation to the macroscopic quantum tunneling at T∗. It is shown that most of the switching properties are consistently explained in terms of the underdamped Josephson junction with quality factor of about 70 in spite of possible damping due to d-wave superconductivity. The present result gives the upper limit of the dissipation of IJJ’s.
The film tunneling junctions of the forms ErRh4B4-Lusub(x)Osub(y)-Sb and ErRh4B4-Lusub(x)Oy-In have been fabricated using a combination of sputtering and evaporating techniques. Single-particle tunneling measurements have been carried out on the junctions with Sb counterelectrodes. For junctions with In counterelectrodes pair tunneling or the Josephson effect has been studied as well. Manifestations of the onset of magnetic order have been observed in the temperature dependence of the zero-voltage Josephson current, in the Fraunhofer pattern of the magnetic field dependence of the Josephson current, and in the single-particle tunneling conductance. (orig.)
Diffractive analysis of annular resonators.
Morin, M; Bélanger, P A
1992-04-20
The modal properties of annular resonators are investigated by using an approximate version of the Kirchhoff-Fresnel integral. It is shown that the radial diffraction of a thin annular beam with a large inside radius is similar to that of a cylindrical field distribution. This permits the formal demonstration of the equivalence that exists between large Fresnel number annular resonators and infinite strip resonators. The model explains the properties of annular resonators that have been observed either experimentally or numerically by others, such as the lack of azimuthal discrimination. PMID:20720842
Josephson effect in fermionic superfluids across the BEC-BCS crossover.
Valtolina, Giacomo; Burchianti, Alessia; Amico, Andrea; Neri, Elettra; Xhani, Klejdja; Seman, Jorge Amin; Trombettoni, Andrea; Smerzi, Augusto; Zaccanti, Matteo; Inguscio, Massimo; Roati, Giacomo
2015-12-18
The Josephson effect is a macroscopic quantum phenomenon that reveals the broken symmetry associated with any superfluid state. Here we report on the observation of the Josephson effect between two fermionic superfluids coupled through a thin tunneling barrier. We show that the relative population and phase are canonically conjugate dynamical variables throughout the crossover from the molecular Bose-Einstein condensate (BEC) to the Bardeen-Cooper-Schrieffer (BCS) superfluid regime. For larger initial excitations from equilibrium, the dynamics of the superfluids become dissipative, which we ascribe to the propagation of vortices through the superfluid bulk. Our results highlight the robust nature of resonant superfluids. PMID:26680193
Field theoretic description of the abelian and non-abelian Josephson effect
Esposito, F Paul; MacKenzie, R B; Paranjape, M B; Wijewardhana, L C R
2007-01-01
We formulate the Josephson effect in a field theoretic language which affords a straightforward generalization to the non-abelian case. Our formalism interprets Josephson tunneling as the excitation of pseudo-Goldstone bosons. We demonstrate the formalism through the consideration of a single junction separating two regions with a purely non-abelian order parameter and a sandwich of three regions where the central region is in a distinct phase. Applications to various non-abelian symmetry breaking systems in particle and condensed matter physics are given.
Switching between dynamic states in intermediate-length Josephson junctions
S. Pagano; Sørensen, Mads Peter; Parmentier, R. D.; Christiansen, Peter Leth; Skovgaard, Ove; Mygind, Jesper; Pedersen, Niels Falsig; Samuelsen, Mogens Rugholm
1986-01-01
The appearance of zero-field steps (ZFS’s) in the current-voltage characteristics of intermediate-length overlap-geometry Josephson tunnel junctions described by a perturbed sine-Gordon equation (PSGE) is associated with the growth of parametrically excited instabilities of the McCumber background curve (MCB). A linear stability analysis of a McCumber solution of the PSGE in the asymptotic linear region of the MCB and in the absence of magnetic field yields a Hill’s equation which predicts ho...
Perturbed period-doubling bifurcation. II. Experiments on Josephson junctions
Eriksen, Gert Friis; Hansen, Jørn Bindslev
1990-01-01
We present experimental results on the effect of periodic perturbations on a driven, dynamic system that is close to a period-doubling bifurcation. In the preceding article a scaling law for the change of stability of such a system was derived for the case where the perturbation frequency ω......B as a function of the frequency and the amplitude of the perturbation signal ΔμB(ωS,AS) for a model system, the microwave-driven Josephson tunnel junction, and find reasonable agreement between the experimental results and the theory....
Fractional Josephson current through a Luttinger liquid with topological excitations
Recently, the Majorana fermion has received great attentions due to its promising application in the fault-tolerant quantum computation. This application requires more accessible methods to detect the motion and braiding of the Majorana fermions. We use a Luttinger liquid ring to achieve this goal, where the ring geometry is nontrivial in the sense that it leads to fermion-parity-dependent topological excitations. First, we briefly review the essential physics of the Luttinger liquid and the Majorana fermion, in order to give an introduction of the general framework used in the following main work. Then, we theoretically investigated the DC Josephson effect between two topological superconductors via a Luttinger liquid ring. A low-energy effective Hamiltonian is derived to show the existence of the fractional Josephson current. Also, we find that the amplitude of the Josephson current, which is determined by the correlation function of Luttinger liquid, exhibits different behaviors in terms of the parity of Luttinger liquid due to the topological excitations. Our results suggest a possible method to detect the Majorana fermions and their tunneling process
Thin-film Josephson junctions with alternating critical current density
Moshe, Maayan; Kogan, V. G.; Mints, R. G.
2009-01-01
We study the field dependence of the maximum current Im(H) in narrow edge-type thin-film Josephson junctions with alternating critical current density. Im(H) is evaluated within nonlocal Josephson electrodynamics taking into account the stray fields that affect the difference of the order-parameter phases across the junction and therefore the tunneling currents. We find that the phase difference along the junction is proportional to the applied field, depends on the junction geometry, but is independent of the Josephson critical current density gc , i.e., it is universal. An explicit form for this universal function is derived for small currents through junctions of the width W≪Λ , the Pearl length. The result is used to calculate Im(H) . It is shown that the maxima of Im(H)∝1/H and the zeros of Im(H) are equidistant but only in high fields. We find that the spacing between zeros is proportional to 1/W2 . The general approach is applied to calculate Im(H) for a superconducting quantum interference device with two narrow edge-type junctions. If gc changes sign periodically or randomly, as it does in grain boundaries of high- Tc materials and superconductor-ferromagnet-superconductor heterostructures, Im(H) not only acquires the major side peaks, but due to nonlocality the following peaks decay much slower than in bulk junctions.
Current-phase relation measurements of SFS π-Josephson junctions
Frolov, S. M.; van Harlingen, D. J.; Oboznov, V. A.; Ryazanov, V. V.
2004-03-01
We present measurements of the current-phase relation (CPR) of Superconductor-Ferromagnet-Superconductor (SFS) Josephson junctions as a function of temperature. The CPR is determined by incorporating the junction in an rf SQUID geometry coupled to a dc SQUID, allowing measurement of the junction phase difference. Junctions fabricated with a thin ( ˜25 nm) barrier of Cu_0.48Ni_0.52 sandwiched between Nb electrodes exhibit a re-entrant critical current with temperature, vanishing at T=T_π ˜2-4 K. We find a phase shift of π for T
Statistics of avalanches in the self-organized criticality state of a Josephson junction
Magnetic flux avalanches in Josephson junctions that include superconductor-insulator-superconductor (SIS) tunnel junctions and are magnetized at temperatures lower than approximately 5 K have been studied in detail. Avalanches are of stochastic character and appear when the magnetic field penetration depth λ into a junction becomes equal to the length a of the Josephson junction with a decrease in the temperature. The statistical properties of such avalanches are presented. The size distribution of the avalanches is a power law with a negative noninteger exponent about unity, indicating the self-organized criticality state. The self-organized criticality state is not observed in Josephson junctions with a superconductor-normal metal-superconductor (SNS) junction.
Suppression of the Josephson effect by quantum fluctuations in the fractional quantum Hall state
We use the Chern-Simons gauge theory for the fractional quantum Hall effect (FQHE) to calculate the Josephson current for two weakly coupled two-dimensional electron gas (2DEG) subsystems separated by a thin tunnel barrier, for the primary fractional quantum Hall states v=1/(2k+1) (k=0,1,2,...), at zero temperature. We find that the Josephson current amplitude is mainly suppressed by the long-range quantum fluctuations of the Chern-Simons gauge field, by a factor ∝exp{[-(2k+1)/4π](L/l0)} where L is the system size, and l0 is of the order of the magnetic length. Thus it is unlikely that the Josephson effect can be observed for weakly coupled 2DEG subsystems, despite the strong analogy between the FQHE in the Chern-Simons formulation and two-dimensional superconductivity
Observation of the AC JOSEPHSON effect inside copper oxide based superconductors
The experimental demonstration of the Josephson effect is a direct manifestation of the quantum phase of the superconductive order parameter and of the coupling of this phase to the electromagnetic field. The ac Josephson effect links the time evolution of the phase difference between two superconductors to the voltage between them. When this voltage is kept fixed externally, the phase difference increases linearly with time, giving rise to an oscillating supercurrent between the superconductors if they are coupled by a weak link such as a tunnel barrier. This effect depends only on the bose like character of the particles carrying the supercurrent. It was thus important to test if the Josephson effect could be observed with copper oxide based superconductors. This was achieved by our experiment performed at Saclay and by other experiments conducted independently. We will focus in this paper on our latest results and their discussion
Proximity Effect in BSCCO Intrinsic Josephson Junctions Contacted with a Normal Metal Layer
Suzuki, Minoru; Koizumi, Masayuki; Ohmaki, Masayuki; Kakeya, Itsuhiro; Shukrinov, Yu. M.
Superconductivity proximity effect is numerically evaluated based on McMillan's tunneling proximity model for a sandwich of a normal metal layer on top of the surface superconducting layer of intrinsic Josephson junctions in a Bi2Sr2CaCu2O8+δ (BSCCO) crystal. Due to the very thin thickness of 0.3 nm of the superconducting layer in IJJs, the surface layer is subject to influence of the proximity effect when the top layer is contacted with a normal metal layer. The effect manifests itself as a significant change in the characteristics of the IJJ surface Josephson junction. It is found that when the superconducting layer thickness is smaller than 0.6 nm, the pair potential reduces significantly, leading to an almost complete suppression of the critical Josephson current density for the surface junction. This result can partly explain the experimental results on the IJJ characteristics of a mesa type structure.
Axisymmetric annular curtain stability
A temporal stability analysis was carried out to investigate the stability of an axially moving viscous annular liquid jet subject to axisymmetric disturbances in surrounding co-flowing viscous gas media. We investigated in this study the effects of inertia, surface tension, the gas-to-liquid density ratio, the inner-to-outer radius ratio and the gas-to-liquid viscosity ratio on the stability of the jet. With an increase in inertia, the growth rate of the unstable disturbances is found to increase. The dominant (or most unstable) wavenumber decreases with increasing Reynolds number for larger values of the gas-to-liquid viscosity ratio. However, an opposite tendency for the most unstable wavenumber is predicted for small viscosity ratio in the same inertia range. The surrounding gas density, in the presence of viscosity, always reduces the growth rate, hence stabilizing the flow. There exists a critical value of the density ratio above which the flow becomes stable for very small viscosity ratio, whereas for large viscosity ratio, no stable flow appears in the same range of the density ratio. The curvature has a significant destabilizing effect on the thin annular jet, whereas for a relatively thick jet, the maximum growth rate decreases as the inner radius increases, irrespective of the surrounding gas viscosity. The degree of instability increases with Weber number for a relatively large viscosity ratio. In contrast, for small viscosity ratio, the growth rate exhibits a dramatic dependence on the surface tension. There is a small Weber number range, which depends on the viscosity ratio, where the flow is stable. The viscosity ratio always stabilizes the flow. However, the dominant wavenumber increases with increasing viscosity ratio. The range of unstable wavenumbers is affected only by the curvature effect. (paper)
Quantum Dynamics of a d-wave Josephson Junction
Bauch, Thilo
2007-03-01
Thilo Bauch ^1, Floriana Lombardi ^1, Tobias Lindstr"om ^2, Francesco Tafuri ^3, Giacomo Rotoli ^4, Per Delsing ^1, Tord Claeson ^1 1 Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, S-412 96 G"oteborg, Sweden. 2 National Physical Laboratory, Queens Road, Teddington, Middlesex TW11 0LW, UK. 3 Istituto Nazionale per la Fisica della Materia-Dipartimento Ingegneria dell'Informazione, Seconda Universita di Napoli, Aversa (CE), Italy. 4 Dipartimento di Ingegneria Meccanica, Energetica e Gestionale, Universita of L'Aquila, Localita Monteluco, L'Aquila, Italy. We present direct observation of macroscopic quantum properties in an all high critical temperature superconductor d-wave Josephson junction. Although dissipation caused by low energy excitations is expected to strongly suppress quantum effects we demonstrate macroscopic quantum tunneling [1] and energy level quantization [2] in our d-wave Josephson junction. The results clearly indicate that the role of dissipation mechanisms in high temperature superconductors has to be revised, and may also have consequences for a new class of solid state ``quiet'' quantum bit with superior coherence time. We show that the dynamics of the YBCO grain boundary Josephson junctions fabricated on a STO substrate are strongly affected by their environment. As a first approximation we model the environment by the stray capacitance and stray inductance of the junction electrodes. The total system consisting of the junction and stray elements has two degrees of freedom resulting in two characteristic resonance frequencies. Both frequencies have to be considered to describe the quantum mechanical behavior of the Josephson circuit. [1] T. Bauch et al, Phys. Rev. Lett. 94, 087003 (2005). [2] T. Bauch et al, Science 311, 57 (2006).
Measurements of quantum noise in resistively shunted Josephson junctions
Measurements have been made of the low-frequency spectral density of the voltage noise in current-biased resistively shunted Josephson tunnel junctions under conditions in which the noise mixed down from frequencies near the Josephson frequency (ν/sub J/) to the measurement frequency (k/sub B/T. In this limit, quantum corrections to the mixed-down noise are important. The spectral densities measured on junctions with current-voltage characteristics close to the Stewart-McCumber model were in excellent agreement with the predicted values, with no fitted parameters. The mixed-down noise for a wide range of bias voltages was used to infer the spectral density of the current noise in the shunt resistor at frequency ν. With no fitted parameters, this spectral density at frequencies up to 500 GHz was in excellent agreement with the prediction (2hν/R)coth(hν/2k/sub B/T). The presence of the zero-point term, 2hν/R, at frequencies hν>k/sub B/T was clearly demonstrated. The current-voltage characteristics of a junction with β/sub L/equivalent2πL/sub s/I0/Phi0approx.1 and β/sub C/equivalent2πI0R2C/Phi00 is the critical current, C is the junction capacitance, and L/sub s/ is the shunt inductance, showed structure at voltages where the Josephson frequency was near a subharmonic of the L/sub s/C resonant frequency. The additional nonlinearity of the I-V characteristic caused mixing down of noise near higher harmonics of the Josephson frequency, thereby greatly enhancing the voltage noise. The measured noise was in good agreement with that predicted by computer simulations
Supercurrent in Graphene Josephson Transistors
Bao, Wenzhong; Miao, Feng; Liu, Gang; Lau, Chunning
2008-03-01
We investigate electrical transport in single or bi-layer graphene devices coupled to superconducting electrodes. In these two-dimensional Josephson junctions, we observed gate tunable supercurrent, multiple Andreev reflections and hysteretic current-voltage characteristics. Latest experimental progress on dependence of supercurrent on temperature, number of layers and source-drain separation will be discussed.
High frequency detectors based on superconducting tunnel junctions
This review discusses high frequency detectors, in particular two examples: the quasiparticle mixer and the inductively shunted Josephson parametric amplifier. The quasiparticle mixer is now routinely operated at several radio astronomy observatories. At high frequency, in the quantum limit, photon assisted tunneling sets in and the mixer gives conversion gain. Its noise temperature is close to the ultimate quantum limit. The use of the mixer is steadily pushed upwards in frequency into the mm (and sub-mm) band. The authors discuss several high frequency obstacles: Josephson noise, Josephson interference, pair breaking, a finite number of photon assisted tunneling steps within the gap region, matching, and non-equilibrium superconductivity. A scale type experiment and modeling indicate that good conversion and low noise are possible at least up to the superconducting gap frequency. Arrays of tunnel junctions enable a higher signal saturation level of the mixer, easier-impedance match, tuning and fabrication, and a better electrical shock resistance
Josephson junction of non-Abelian superconductors and non-Abelian Josephson vortices
Nitta, Muneto
2015-01-01
A Josephson junction is made of two superconductors sandwiching an insulator, and a Josephson vortex is a magnetic vortex absorbed into the Josephson junction, whose dynamics can be described by the sine-Gordon equation. In a field theory framework, a flexible Josephson junction was proposed, in which the Josephson junction is represented by a domain wall separating two condensations and a Josephson vortex is a sine-Gordon soliton in the domain wall effective theory. In this paper, we propose a Josephson junction of non-Abelian color superconductors, that is described by a non-Abelian domain wall, and show that a non-Abelian vortex (color magnetic flux tube) absorbed into it is a non-Abelian Josephson vortex represented as a non-Abelian sine-Gordon soliton in the domain wall effective theory.
Josephson Coupling, Phase Correlations, and Josephson Plasma Resonance in Vortex Liquid Phase
Koshelev, A. E.; Bulaevskii, L. N.; Maley, M. P.
2000-01-01
Josephson plasma resonance has been introduced recently as a powerful tool to probe interlayer Josephson coupling in different regions of the vortex phase diagram in layered superconductors. In the liquid phase, the high temperature expansion with respect to the Josephson coupling connects the Josephson plasma frequency with the phase correlation function. This function, in turn, is directly related to the pair distribution function of the liquid. We develop a recipe to extract the phase and ...
Annular Hybrid Rocket Motor Project
National Aeronautics and Space Administration — Engineers at SpaceDev have conducted a preliminary design and analysis of a proprietary annular design concept for a hybrid motor. A U.S. Patent application has...
Antonov, A. A.; Pankratov, A. L.; Yulin, A. V.;
2000-01-01
The nonlinear dynamics of fluxons in Josephson systems with dispersion and thermal fluctuations is analyzed using the "quasiparticle" approach to investigate the influence of noise on the Cherenkov radiation effect. Analytical expressions for the stationary amplitude of the emitted radiation...... and its spectral distribution have been obtained in an annular geometry. It is demonstrated that noise reduces the amplitude of the radiated wave and broadens its spectrum. The effect of the radiated wave on the fluxon dynamics leads to a considerably smaller linewidth than observed in the usual flux flow...
Manufacture of annular cermet articles
Forsberg, Charles W.; Sikka, Vinod K.
2004-11-02
A method to produce annular-shaped, metal-clad cermet components directly produces the form and avoids multiple fabrication steps such as rolling and welding. The method includes the steps of: providing an annular hollow form with inner and outer side walls; filling the form with a particulate mixture of ceramic and metal; closing, evacuating, and hermetically sealing the form; heating the form to an appropriate temperature; and applying force to consolidate the particulate mixture into solid cermet.
Vertical Josephson Interferometer for Tunable Flux Qubit
We present a niobium-based Josephson device as prototype for quantum computation with flux qubits. The most interesting feature of this device is the use of a Josephson vertical interferometer to tune the flux qubit allowing the control of the off-diagonal Hamiltonian terms of the system. In the vertical interferometer, the Josephson current is precisely modulated from a maximum to zero with fine control by a small transversal magnetic field parallel to the rf superconducting loop plane
Behaviour of the energy gap in a model of Josephson coupled Bose-Einstein condensates
In this work we investigate the energy gap between the ground state and the first excited state in a model of two single-mode Bose-Einstein condensates coupled via Josephson tunnelling. The energy gap is never zero when the tunnelling interaction is non-zero. The gap exhibits no local minimum below a threshold coupling which separates a delocalized phase from a self-trapping phase that occurs in the absence of the external potential. Above this threshold point one minimum occurs close to the Josephson regime, and a set of minima and maxima appear in the Fock regime. Expressions for the position of these minima and maxima are obtained. The connection between these minima and maxima and the dynamics for the expectation value of the relative number of particles is analysed in detail. We find that the dynamics of the system changes as the coupling crosses these points
Jørgensen, E.; Koshelets, V. P.; Monaco, Roberto;
1982-01-01
The radiation emission from long and narrow Josephson tunnel junctions dc-current biased on zero-field steps has been ascribed to resonant motion of fluxons on the transmission line. Within this dynamic model a theoretical expression for the radiation linewidth is derived from a full statistical ...... treatment of thermal fluctuations in the fluxon velocity. The result appears to be very general and is corroborated by experimental determination of linewidth and frequency of radiation emitted from overlap Nb-I-Pb junctions.......The radiation emission from long and narrow Josephson tunnel junctions dc-current biased on zero-field steps has been ascribed to resonant motion of fluxons on the transmission line. Within this dynamic model a theoretical expression for the radiation linewidth is derived from a full statistical...
Interlayer Quasiparticle Transport in the Vortex State of Josephson Coupled Superconductors
Vekhter, I.; Bulaevskii, L. N.; Koshelev, A. E.; Maley, M. P.
1999-01-01
We calculate the dependence of the interlayer quasiparticle conductivity, $\\sigma_q$, in a Josephson coupled d-wave superconductor on the magnetic field B||c and the temperature T. We consider a clean superconductor with resonant impurity scattering and a dominant coherent interlayer tunneling. When pancake vortices in adjacent layers are weakly correlated at low T the conductivity increases sharply with B before reaching an extended region of slow linear growth, while at high T it initially ...
Thermal Escape from a Metastable State in Periodically Driven Josephson Junctions
Sun, Guozhu; Jian CHEN; Xu, Weiwei; Ji, Zhengming; Kang, Lin; Wu, Peiheng; Mao, Guangfeng; Dong, Ning; Yu, Yang; Xing, Dingyu
2006-01-01
Resonant activation and noise-enhanced stability were observed in an underdamped real physical system, i.e., Josephson tunnel junctions. With a weak sinusoidal driving force applied, the thermal activated escape from a potential well underwent resonance-like behavior as a function of the driving frequency. The resonance also crucially depended on the initial condition of the system. Numerical simulations showed good agreement with the experimental results.
Macroscopic quantum effects in capacitively- and inductively-coupled intrinsic Josephson junctions
Koyama, T.; Machida, M.
2009-03-01
A theory for macroscopic quantum tunneling (MQT) in intrinsic Josephson junction stacks is formulated. Both capacitive and inductive couplings between junctions are taken into account. We calculate the escape rate in the switching to the first resistive branch in the quantum regime. It is shown that the enhancement of the escape rate is caused mainly by the capacitive coupling between junctions in IJJ's with small in-plane area of ~ 1μm2.
Tolpygo, Sergey K.; Amparo, Denis; Hunt, Richard T.; Vivalda, John A.; Yohannes, Daniel T.
2010-01-01
New technology for superconductor integrated circuits has been developed and is presented. It employs diffusion stoplayers (DSLs) to protect Josephson junctions (JJs) from interlayer migration of impurities, improve JJ critical current (Ic) targeting and reproducibility, eliminate aging, and eliminate pattern-dependent effects in Ic and tunneling characteristics of Nb/Al/AlOx/Nb junctions in integrated circuits. The latter effects were recently found in Nb-based JJs integrated into multilayer...
Applications of Josephson effect
Week coupling superconducting systems are described, such as the tunnel system, the bridge-type system, the whisker connection of two superconductors, and the Clark SLUG (Superconducting Low-Inductance Undulatory Galvanometer). The equivalent diagram is presented. If the power supply resistance is greater than the barrier resistance, the hysteresis occurs of the volt-ampere characteristics as a function of the inherent capacitance and inductance of the system. In the opposite case, hysteresis decays and the negative differential resistance region may be effective. The d.c. and high-='requency SQUID (Superconducting Quantum Interference Device) systems are described. The whisker and bridge types are mainly used in the high-frequency region. These systems may be used as sources of electromagnetic radiation of up to 10 THz. The generated out.out is in the order of 10-10 W. (J.B.)
How coherent are Josephson junctions?
Paik, Hanhee; Bishop, Lev S; Kirchmair, G; Catelani, G; Sears, A P; Johnson, B R; Reagor, M J; Frunzio, L; Glazman, L; Schoelkopf, R J
2011-01-01
Attaining sufficient coherence is a requirement for realizing a large-scale quantum computer. We present a new implementation of a superconducting transmon qubit that is strongly coupled to a three-dimensional superconducting cavity. We observe a reproducible increase in the coherence times of qubit (both $T_1$ and $T_2$ > 10 microseconds) and cavity ($T_{cav}$ ~ 50 microseconds) by more than an order of magnitude compared to the current state-of-art superconducting qubits. This enables the study of the stability and quality of Josephson junctions at precisions exceeding one part per million. Surprisingly, we see no evidence for $1/f$ critical current noise. At elevated temperatures, we observe the dissipation due to a small density (< 1 - 10 ppm) of thermally-excited quasiparticles. The results suggest that the overall quality of Josephson junctions will allow error rates of a few $10^{-4}$, approaching the error correction threshold.
Josephson Persistent-Current Qubit
Mooij, J. E.; Orlando, T. P.; Levitov, L.; Tian , Lin; van der Wal, Caspar H.; Lloyd, Seth
1999-01-01
A qubit was designed that can be fabricated with conventional electron beam lithography and is suited for integration into a large quantum computer. The qubit consists of a micrometer-sized loop with three or four Josephson junctions; the two qubit states have persistent currents of opposite direction. Quantum superpositions of these states are obtained by pulsed microwave modulation of the enclosed magnetic flux by currents in control lines. A superconducting flux transporter allows for cont...
Spin nutation effects in molecular nanomagnet-superconductor tunnel junctions.
Abouie, J; Abdollahipour, B; Rostami, A A
2013-11-20
We study the spin nutation effects of a molecular nanomagnet on the Josephson current through a superconductor|molecular nanomagnet|superconductor tunnel junction. We explicitly demonstrate that, due to the spin nutation of the molecular nanomagnet, two oscillatory terms emerge in the ac Josephson current in addition to the conventional ac Josephson current. Some resonances occur in the junction due to the interactions of the transported quasiparticles with the bias voltage and molecular nanomagnet spin dynamics. Their appearance indicates that the energy exchanged during these interactions is in the range of the superconducting energy gap. We also show that the spin nutation is able to convert the ac Josephson current to a dc current, which is interesting for applications. PMID:24129308
Spin nutation effects in molecular nanomagnet–superconductor tunnel junctions
We study the spin nutation effects of a molecular nanomagnet on the Josephson current through a superconductor|molecular nanomagnet|superconductor tunnel junction. We explicitly demonstrate that, due to the spin nutation of the molecular nanomagnet, two oscillatory terms emerge in the ac Josephson current in addition to the conventional ac Josephson current. Some resonances occur in the junction due to the interactions of the transported quasiparticles with the bias voltage and molecular nanomagnet spin dynamics. Their appearance indicates that the energy exchanged during these interactions is in the range of the superconducting energy gap. We also show that the spin nutation is able to convert the ac Josephson current to a dc current, which is interesting for applications. (paper)
Adiabatic Steam-Water Annular Flow in an Annular Geometry
Andersen, P. S.; Würtz, J.
1981-01-01
Experimental results for fully developed steam-water annular flow in annular geometries are presented. Rod and tube film flow rates and axial pressure gradients were measured for mass fluxes between 500 and 2000 kg/m2s, steam qualities between 20 and 60 per cent and pressures ranging from 3 to 9...... MPa. It was found that the measured tube film flow rate per unit tube perimeter is always many times greater than the corresponding rod film flow rate. Possible explanations for this asymmetry are discussed....
dc and ac Josephson effect in a superconductor endash Luttinger-liquid endash superconductor system
We calculate both the dc and the ac Josephson current through a 1-D system of interacting electrons, connected to two superconductors by tunnel junctions. We treat the (repulsive) Coulomb interaction in the framework of the one-channel, spin-1/2 Luttinger model. The Josephson current is obtained for two geometries of experimental relevance: a quantum wire and a ring. At T=0, the critical current is found to decay algebraically with increasing distance d between the junctions. The decay is characterized by an exponent which depends on the strength of the interaction. At finite temperatures T, lower than the superconducting transition temperature Tc, there is a crossover from algebraic to exponential decay of the critical current as a function of d, at a distance of the order of ℎvF/kBT. Moreover, the dependence of critical current on temperature shows nonmonotonic behavior. If the Luttinger liquid is confined to a ring of circumference L, coupled capacitively to a gate voltage and threaded by a magnetic flux, the Josephson current shows remarkable parity effects under the variation of these parameters. For some values of the gate voltage and applied flux, the ring acts as a π junction. These features are robust against thermal fluctuations up to temperatures on the order of ℎvF/kBL. For the wire geometry, we have also studied the ac-Josephson effect. The amplitude and the phase of the time-dependent Josephson current are affected by electron-electron interactions. Specifically, the amplitude shows pronounced oscillations as a function of the bias voltage due to the difference between the velocities of spin and charge excitations in the Luttinger liquid. Therefore, the ac-Josephson effect can be used as a tool for the observation of spin-charge separation. copyright 1996 The American Physical Society
Shot noise in YBCO bicrystal Josephson junctions
Constantinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.; Mygind, Jesper; Pedersen, Niels Falsig
2003-01-01
We measured spectral noise density in YBCO symmetric bicrystal Josephson junctions on sapphire substrates at bias voltages up to 100 mV and T 4.2 K. Normal state resistance of the Josephson junctions, R-N = 20-90 Omega and ICRN up to 2.2 mV have been observed in the experimental samples. Noise me...
Guerlich, Christian
2010-05-11
With Low-Temperature-Electron-Microscopy (LTSEM) it is possible to analyse the transport properties of solids at low temperatures. In particular it is possible to image the supercurrent density j{sub s} in Josephson junctions. This was demonstrated by comparing TTREM-images with calculated values for j{sub s}. In this thesis ramp-type Nd{sub 2-x}Ce{sub x}CuO{sub 4-y}/Nb-Josephson-junctions (NCCO/Nb) and Josephson junctions with a ferromagnetic interlayer Nb/Al-Al{sub 2}O{sub 3}/NiCu/Nb, so-called SIFS (superconductor-insulator-ferromagnet-superconductor) Josephson junctions were studied.It was demonstrated that LTSEM provides direct imaging of the sign change of the order parameter in superconductors with d{sub x{sup 2}-y{sup 2}}-symmetry. This was a controversial issue over the last decade. A step like variation in the thickness of the F-layer allows the fabrication of linear and annular Josephson junctions with different numbers of 0 and {pi} facets. With the LTSEM 0-, {pi}-, 0-{pi}-, 0-{pi}-0-, 0/2-{pi}-0/2-, 20 x (0-{pi})- as well as square-shaped-, circular- and annular-Josephson-junctions were studied. It was demonstrated, that these junctions are of good quality and have critical current densities up to 42 A/cm{sup 2} at T=4.2 K, which is a record value for SIFS junctions with a NiCu F-layer so far. By comparing the measurements with simulations a first indication of a semifluxon at the 0-{pi}-boundary was found. (orig.)
Phase flow rate measurements of annular flows
Al-Yarubi, Qahtan
2010-01-01
In the international oil and gas industry multiphase annular flow in pipelines and wells is extremely important, but not well understood. This thesis reports the development of an efficient and cheap method for measuring the phase flow rates in two phase annular and annular mist flow, in which the liquid phase is electrically conducting, using ultrasonic and conductance techniques. The method measures changes in the conductance of the liquid film formed during annular flow and uses these to c...
Measure synchronization in a spin-orbit-coupled bosonic Josephson junction
Wang, Wen-Yuan; Liu, Jie; Fu, Li-Bin
2015-11-01
We present measure synchronization (MS) in a bosonic Josephson junction with spin-orbit coupling. The two atomic hyperfine states are coupled by a Raman dressing scheme, and they are regarded as two orientations of a pseudo-spin-1 /2 system. A feature specific to a spin-orbit-coupled (SOC) bosonic Josephson junction is that the transition from non-MS to MS dynamics can be modulated by Raman laser intensity, even in the absence of interspin atomic interaction. A phase diagram of non-MS and MS dynamics as functions of Raman laser intensity and Josephson tunneling amplitude is presented. Taking into account interspin atomic interactions, the system exhibits MS breaking dynamics resulting from the competition between intraspin and interspin atomic interactions. When interspin atomic interactions dominate in the competition, the system always exhibits MS dynamics. For interspin interaction weaker than intraspin interaction, a window for non-MS dynamics is present. Since SOC Bose-Einstein condensates provide a powerful platform for studies on physical problems in various fields, the study of MS dynamics is valuable in researching the collective coherent dynamical behavior in a spin-orbit-coupled bosonic Josephson junction.
Peculiarities of parameter effect of Josephson medium on vortex production and critical current
One studied theoretically the response of the intergranular Josephson junction to the Abrikosov vortex transfer in a superconducting polycrystal. The vortex line near the junction induces tunnel currents, generates one Josephson vortex and merges with it at the moment when it approaches the contact surface. Initiation of the Josephson vortex is shown to have to overcome the potential barrier that depends on the distance of the Abrikosov vortex to the junction, as well as, on the efficient thickness of the junction the value of which depends on the peculiar size of the granule, on the granular anisotropy and on the intensity of the intergranular bond. One determined the magnetic field dependence of the critical current of the intergranular Josephson junction at various granular and intergranular characteristics and in cases of triangular and square configurations of the Abrikosov vortex lattice. According to the results, it is very important to ensure high degree of granule size texturing, anisotropy and intensity of bond between granules to generate high critical currents in pure polycrystalline materials
High reliability Pb-alloy Josephson junctions for integrated circuits
The process developed and recently used at IBM for fabricating experimental Pb-alloy Josephson tunnel-junction devices, and the factors which influence the stability of such devices during repeated cycling between 300 K and 4.2 K are reviewed. A new, fine-grained Pb.84In.12Au.04 alloy base electrode material has been developed that has excellent thermal cycling stability. In an experiment carried out to evaluate the cyclability of devices prepared with this material, excellent results were obtained: the cyclability of large-area junctions was improved by approx. equal to 100x compared to that of similar junctions prepared with the recently used, larger-grained Pb.84In.12Au.04 base electrodes. In the best cases, populations of 2600 large junctions and 2350 interferometers were found to withstand 400 and 700 thermal cycles to 4.2 K, respectively, before the first failures were observed. These results indicate that with the use of fine-grained electrodes, Pb-alloy Josephson devices have good potential for meeting the cycling requirements of computer systems. (orig.)
Phase dynamics of low critical current density YBCO Josephson junctions
Highlights: • We study the phase dynamics of YBaCuO Josephson junctions using various tools. • We derive information on the dissipation in a wide range of transport parameters. • Dissipation in such devices can be described by a frequency dependent damping model. • The use of different substrates allows us to tune the shell circuit. - Abstract: High critical temperature superconductors (HTS) based devices can have impact in the study of the phase dynamics of Josephson junctions (JJs) thanks to the wide range of junction parameters they offer and to their unconventional properties. Measurements of current–voltage characteristics and of switching current distributions constitute a direct way to classify different regimes of the phase dynamics and of the transport, also in nontrivial case of the moderately damped regime (MDR). MDR is going to be more and more common in JJs with advances in nanopatterning superconductors and synthesizing novel hybrid systems. Distinctive signatures of macroscopic quantum tunneling and of thermal activation in presence of different tunable levels of dissipation have been detected in YBCO grain boundary JJs. Experimental data are supported by Monte Carlo simulations of the phase dynamics, in a wide range of temperatures and dissipation levels. This allows us to quantify dissipation in the MDR and partially reconstruct a phase diagram as guideline for a wide range of moderately damped systems
Atomic Tunnelling Dynamics of Two Squeezed Bose-Einstein Condensates
LI Jin-Hui; KUANG Le-Man
2003-01-01
In this paper, tunnelling dynamics of squeezed Bose-Einstein condensates (BEC's) in the presence of the nonlinear self-interaction of each species, the interspecies nonlinear interaction, and the Josephson-like tunnelling interaction is investigated by using the second quantization approach. The influence of BEC squeezing on macroscopic quantum self-trapping (MQST) and quantum coherent atomic tunnelling is analyzed in detail. It is shown that the MQST and coherent atomic tunnelling between two squeezed BEC's can be manipulated through changing squeezing amplitude and squeezing phase of BEC squeezed states.
Subcutaneous granuloma annulare: radiologic appearance
Objective. Granuloma annulare is an uncommon benign inflammatory dermatosis characterized by the formation of dermal papules with a tendency to form rings. There are several clinically distinct forms. The subcutaneous form is the most frequently encountered by radiologists, with the lesion presenting as a superficial mass. There are only a few scattered reports of the imaging appearance of this entity in the literature. We report the radiologic appearance of five cases of subcutaneous granuloma annulare. Design and patients. The radiologic images of five patients (three male, two female) with subcutaneous granuloma annulare were retrospectively studied. Mean patient age was 6.4 years (range, 2-13 years). The lesions occurred in the lower leg (two), foot, forearm, and hand. MR images were available for all lesions, gadolinium-enhanced imaging in three cases, radiographs in four, and bone scintigraphy in one. Results. Radiographs showed unmineralized nodular masses localized to the subcutaneous adipose tissue. The size range, in greatest dimension on imaging studies, was 1-4 cm. MR images show a mass with relatively decreased signal intensity on all pulse sequences, with variable but generally relatively well defined margins. There was extensive diffuse enhancement following gadolinium administration. Conclusion. The radiologic appearance of subcutaneous granuloma annulare is characteristic, typically demonstrating a nodular soft-tissue mass involving the subcutaneous adipose tissue. MR images show a mass with relatively decreased signal intensity on all pulse sequences and variable but generally well defined margins. There is extensive diffuse enhancement following gadolinium administration. Radiographs show a soft-tissue mass or soft-tissue swelling without evidence of bone involvement or mineralization. This radiologic appearance in a young individual is highly suggestive of subcutaneous granuloma annulare. (orig.)
Josephson 32-bit shift register
This paper reports on a 32-bit shift register designed by edge-triggered gates tested with ±25% bias margin and ±81% input margin for the full array. Simulations have shown ±55% bias margin at 3.3 GHz and working up to a maximum frequency of 30 GHz with a junction current density of 2000A/cm2 although the shift register has only been tested up to 500 MHz, limited by instrumentation. This edge-triggered gate consisting of a pair of conventional Josephson logic gates in series has the advantages of wide margins, short reset time, and insensitivity to global parameter-variations
Intrinsic Josephson effects in Bi-2212
Full text: The interesting physics that is seen in the behaviour of a Josephson junction (a weak connection between two superconductors) can be exploited in a wide range of devices. For example the inverse AC Josephson effect underpins today's voltage standard, SQUID technology is based on quantum interference between two Josephson junctions and the AC Josephson effect has the potential to be used to produce microwave sources. Recently it has been shown that a variety of layered superconductors form intrinsic Josephson junctions as a direct consequence of the highly anisotropic nature of their crystal structure. One such layered superconductor is Bi2Sr2CaCu2O8 in which the CuO2 planes act as the superconducting electrode and the non-superconducting Bi2O3 and SrO layers act as the barrier. We report here on a study of intrinsic Josephson effects in single crystals of Bi2Sr2CaCu2O8. The I-V characteristic shows behaviour consistent with the DC Josephson effect. Indeed, close examination reveals a branching pattern in which the difference between adjacent branches corresponds to a switching of one atomic scale junction to the resistive state. We also discuss the microwave response and the possibility of using single crystals of Bi2Sr2CaCu2O8 as sub-millimetre sources
Mesoscopic superconducting tunnel junction devices : experimental studies of performance limitations
Kivioja, Jani
2005-01-01
In this work four different mesoscopic superconducting devices have been experimentally studied: an ammeter based on a hysteretic Josephson junction switching from the superconducting state to the normal state, a conventional Cooper pair pump (CPP) based on two superconducting islands separated by tunnel junctions, a novel flux assisted Cooper pair pump and a thermometer based on a tunnel junction between a superconductor and a normal metal. These devices make use of phenomena related to supe...
Annular-Efficient Triangulations of 3-manifolds
Jaco, William
2011-01-01
A triangulation of a compact 3-manifold is annular-efficient if it is 0-efficient and the only normal, incompressible annuli are thin edge-linking. If a compact 3-manifold has an annular-efficient triangulation, then it is irreducible, boundary-irreducible, and an-annular. Conversely, it is shown that for a compact, irreducible, boundary-irreducible, and an-annular 3-manifold, any triangulation can be modified to an annular-efficient triangulation. It follows that for a manifold satisfying this hypothesis, there are only a finite number of boundary slopes for incompressible and boundary-incompressible surfaces of a bounded Euler characteristic.
Andreev levels in a Josephson superconductor graphene superconductor nanostructure
Manjarrés, Diego A., E-mail: damanjarrnsg@unal.edu.co; Gomez P, S., E-mail: sgomezp@unal.edu.co; Herrera, William J., E-mail: jherreraw@unal.edu.co
2014-12-15
We obtain the bound states in superconductor-graphene-superconductor nanostructure, which are responsible for the Josephson effect. The coupling between graphene and each superconducting region is modeled as two different hopping parameters in the respective SG and GS interfaces. With the purpose of determining the local density of states and the spectrum, the Green function of the junction is calculated resolving the Dyson equation. We obtain that the number of levels depends on the width and doping of graphene region and this occurs for the two types of edge (armchair or zigzag). We investigate the behavior of the bound states as a function of the transparency. In the limit of a transparent junction, the results obtained by the Green's function method reproduce those present in the literature. In the tunnel limit the spectrum is different for armchair and zigzag edges.
Andreev levels in a Josephson superconductor graphene superconductor nanostructure
We obtain the bound states in superconductor-graphene-superconductor nanostructure, which are responsible for the Josephson effect. The coupling between graphene and each superconducting region is modeled as two different hopping parameters in the respective SG and GS interfaces. With the purpose of determining the local density of states and the spectrum, the Green function of the junction is calculated resolving the Dyson equation. We obtain that the number of levels depends on the width and doping of graphene region and this occurs for the two types of edge (armchair or zigzag). We investigate the behavior of the bound states as a function of the transparency. In the limit of a transparent junction, the results obtained by the Green's function method reproduce those present in the literature. In the tunnel limit the spectrum is different for armchair and zigzag edges
Linewidth and phase locking of Josephson flux flow oscillators
Mygind, Jesper; Koshelets, V. P.; Shitov, S. V.;
2000-01-01
We report on measurements of the linewidth of the emitted radiation from Josephson Flux Row Oscillators (FFOs). Frequency and phase locking to an external 10 MHz reference oscillator an demonstrated experimentally in the frequency range 270-440 GHz. A linewidth as low as 1 Hz (as determined...... by the resolution bandwidth of the spectrum analyzer) has been measured. This linewidth is far below the fundamental level given by shot and thermal noise of the free-running tunnel junction. The damping mechanisms are discussed and related to the self-excitation Of quasiparticles. Narrow linewidth, wide......-band tunability and low noise are important for radio astronomy and air- and space-borne spectroscopy for atmospheric research and environmental monitoring. (C) 2000 Elsevier Science B.V. All rights reserved....
Tunable current-phase relation in double-dot Josephson junctions
Koch, Jens; Le Hur, Karyn
2008-03-01
The current-phase relation I() for a Josephson junction contains information about the microscopic nature of the Cooper pair transfer. In particular, junctions more complicated than the single tunnel junction exhibit characteristic non-sinusoidal forms. Here, we investigate the Josephson effect in a superconducting double dot device, similar to the devices studied experimentally by Y. A. Pashkin et al. [1] and E. Bibow et al. [2]. In the vicinity of a charge degeneracy line, the system reduces to a two-level system equivalent to a charge qubit. In this regime, we find that the interplay between sequential tunneling and cotunneling of Cooper pairs leads to a strongly non-sinusoidal current- phase relation, tunable via gate electrodes. We propose the measurement of I() in a SQUID configuration, analyze the implications of flux noise, and compare our results to different types of Josephson junctions such as single-dot systems and microbridges. [1] Y. A. Pashkin et al., Nature (London) 421 (2003), 823 [2] E. Bibow, P. Lafarge, L. L'evy, Phys. Rev. Lett. 88 (2002), 017003
Quantum tunnelling in condensed media
Kagan, Yu
1992-01-01
The essays in this book deal with of the problem of quantum tunnelling and related behavior of a microscopic or macroscopic system, which interacts strongly with an ""environment"" - this being some form of condensed matter. The ""system"" in question need not be physically distinct from its environment, but could, for example, be one particular degree of freedom on which attention is focussed, as in the case of the Josephson junction studied in several of the papers. This general problem has been studied in many hundreds, if not thousands, of articles in the literature, in contexts as diverse
Microwave integrated circuit for Josephson voltage standards
Holdeman, L. B.; Toots, J.; Chang, C. C. (Inventor)
1980-01-01
A microwave integrated circuit comprised of one or more Josephson junctions and short sections of microstrip or stripline transmission line is fabricated from thin layers of superconducting metal on a dielectric substrate. The short sections of transmission are combined to form the elements of the circuit and particularly, two microwave resonators. The Josephson junctions are located between the resonators and the impedance of the Josephson junctions forms part of the circuitry that couples the two resonators. The microwave integrated circuit has an application in Josephson voltage standards. In this application, the device is asymmetrically driven at a selected frequency (approximately equal to the resonance frequency of the resonators), and a d.c. bias is applied to the junction. By observing the current voltage characteristic of the junction, a precise voltage, proportional to the frequency of the microwave drive signal, is obtained.
Anomalous Interlayer Transport of Quantum Hall Bilayers in the Strongly Josephson-Coupled Regime
Zhang, Ding; Dietsche, Werner; von Klitzing, Klaus
2016-05-01
We investigate Josephson coupling in a closely spaced quantum Hall bilayer. Reduction of the interlayer barrier from the widely used values of 10-12 nm to the present one of 8 nm leads to qualitatively different interlayer transport properties. The breakdown of interlayer coherence can be spatially confined in regions that are smaller than the device size. Such a spatial inhomogeneity depends crucially on the Josephson-coupling strength and can be removed by adding an in-plane magnetic field of about 0.5 T. At higher in-plane fields, the interlayer tunneling I -V curve develops unexpected overshoot features. These results challenge current theoretical understanding and suggest that our bilayer system has entered a previously unexplored regime.
Design of a scanning Josephson junction microscope for submicron-resolution magnetic imaging
We describe a magnetic field scanning instrument designed to extend the spatial resolution of scanning superconducting quantum interference device microscopy into the submicron regime. This instrument, the scanning Josephson junction microscope, scans a single Josephson junction across the surface of a sample, detecting the local magnetic field by the modulation of the junction critical current. By using a submicron junction and a scanning tunneling microscope feedback system to maintain close proximity to the surface, magnetic field sensitivity of 10 μG with a spatial resolution of 0.3 μm should be attainable, opening up new opportunities for imaging vortex configurations and core structure in superconductors and magnetic domains in magnetic materials. copyright 1999 American Institute of Physics