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.
Soliton bunching in annular Josephson junctions
DEFF Research Database (Denmark)
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...
Fluxon dynamics in long annular Josephson tunnel junctions
DEFF Research Database (Denmark)
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...
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.
Elliptic annular Josephson tunnel junctions in an external magnetic field: the statics
DEFF Research Database (Denmark)
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...
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.
DEFF Research Database (Denmark)
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...
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...
DC intrinsic Josephson effect in 1{mu}m-lateral-size annular Bi-2212 stacks
Energy Technology Data Exchange (ETDEWEB)
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)
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.
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...
Recent achievements on annular Josephson structures and their application as radiation detectors
International Nuclear Information System (INIS)
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
Radiation comb generation with extended Josephson junctions
International Nuclear Information System (INIS)
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
New fluxon resonant mechanism in annular Josephson tunnel structures
International Nuclear Information System (INIS)
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
Josephson tunnel junction microwave attenuator
DEFF Research Database (Denmark)
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...
Josephson junctions with ferromagnetic interlayer
International Nuclear Information System (INIS)
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
Energy Technology Data Exchange (ETDEWEB)
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.
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.
Theoretical exploration of Josephson Plasma Emission in Intrinsic Josephson Junctions
International Nuclear Information System (INIS)
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
Shot noise in YBCO bicrystal Josephson junctions
DEFF Research Database (Denmark)
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...
The Fluxion in a Curved Josephson Junction
Dobrowolski, Tomasz
2014-01-01
The curved Josephson junction is described. In the framework of the Maxwell equations the equation that describes the influence of the curvature on the fluxion motion was obtained. The method of geometrical reduction of the sine-Gordon model from three to lower dimensional manifold was applied to the long Josephson junction. It was argued that the geometrical reduction describes the junctions with slowly varying curvatures.
Spin currents in TFT-Josephson junction
International Nuclear Information System (INIS)
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.
delta-biased Josephson tunnel junctions
DEFF Research Database (Denmark)
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
DEFF Research Database (Denmark)
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...
Microwave photonics with Josephson junction arrays
Zueco, David; Solano, Enrique; García-Ripoll, Juan José
2011-01-01
We introduce an architecture for a photonic crystal in the microwave regime based on superconducting transmission lines interrupted by Josephson junctions. A study of the scattering properties of a single junction in the line shows that the junction behaves as a perfect mirror when the photon frequency matches the Josephson plasma frequency. We generalize our calculations to periodic arrangements of junctions, demonstrating that they can be used for tunable band engineering, forming what we call a quantum circuit crystal. As a relevant application, we discuss the creation of stationary entanglement between two superconducting qubits interacting through a disordered media.
Josephson junctions based on pnictide superconductors
International Nuclear Information System (INIS)
Josephson junctions are a powerful tool for understanding more about the physical behaviour of pnictide superconductors. We built different kinds of Josephson junctions based on pnictide thin films. Planar junctions, edge type junctions, and junctions on bicrystalline substrates were prepared. We present manufacturing techniques and also the electronical properties of the different junctions and compare them. The measurement of I-V-characteristics show a strong excess current. We have to mind this when calculating the IcRN product. The effective IcRN values are 6.5 μV for the grain boundary junction, 7.9 μV for the planar structure, and 7.5 μV for the edge junction.
Supercurrent decay in extremely underdamped Josephson junctions
International Nuclear Information System (INIS)
We present an experimental study of the effective dissipation relevant in the thermally activated supercurrent decay of extremely underdamped Josephson junctions. Data referring to the supercurrent decay of Nb/AlOx/Nb Josephson junctions are compared with the Kramers theory. Our measurements allow us to obtain the open-quotes effectiveclose quotes resistance to be used in the resistively shunted junction model that results to be the subgap resistance due to the presence of thermally activated quasiparticles. The extremely low dissipation level obtained at low temperatures renders our result quite interesting in view of experiments in the quantum limit. copyright 1998 The American Physical Society
Hysteresis development in superconducting Josephson junctions
International Nuclear Information System (INIS)
The resistively and capacitive shunted junction model is used to investigate hysteresis development in superconducting Josephson junctions. Two empirical formulas that relate the hysteresis width and the quasi-particle diffusion length in terms of the junctions electrical parameters, temperature and frequency are obtained. The obtained formulas provide a simple tool to investigate the full potentials of the hysteresis phenomena. (author). 9 refs, 3 figs
Numerical Investigation of Josephson Junction Structures
International Nuclear Information System (INIS)
Multilayered long Josephson Junction Structures form an interesting physical system where both nonlinearity and interaction between subsystems play an important role. Such systems allow to study physical effects that do not occur in single Josephson junction.The Sakai-Bodin-Pedersen model--a system of perturbed sine-Gordon equations--is used to study the dynamic states of stacks of inductively coupled long Josephson Junctions (LJJs). The corresponding static problem is numerically investigated as well. In order to study the stability of possible static solutions a Sturm-Liouville problem is generated and solved.The transitions from static to dynamic state and the scenario of these transitions are analyzed depending on the model parameters. Different physical characteristics--current-voltage characteristics, individual instant voltages and internal magnetic fields, are calculated and interpreted.
Fabrication of high quality ferromagnetic Josephson junctions
Energy Technology Data Exchange (ETDEWEB)
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
International Nuclear Information System (INIS)
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
Cylindrical Josephson junctions in magnetic fields
International Nuclear Information System (INIS)
The radial Josephson current I/sub J/ between co-axial cylinders was measured as a function of axial and azimuthal magnetic fields. The junctions were of two types: 0.25 mm diameter Nb-oxide-Sn single junctions and 0.25 mm film diameter Nb-oxide-Sn film double junctions. The Sn film of the single junctions was 160 nm or 200 nm. The Sn films of the double junctions were both either 155 nm or 230 nm. For a pair of cylinders I/sub J/ is zero except when both members are in the same fluxoid quantum state. When I/sub J/not equal to O, the relative phase is independent of aximuthal angle theta. In all measurements the cylinders were in fluxoid state zero. There was a critical value of axial field B/sub s/ which destroyed the Josephson coupling for each junction. This critical field is smallest for the outer tin junction of the double junction. It depends upon geometry and film thickness but is independent of the value of I/sub J/. The calculated value of the Gibbs function per unit volume of the tin films is, however, nearly the same for all junctions at their respective critical fields. Th Josephson current for the 160 nm Sn film single cylindrical junction was measured as a function of axial field B/sub z/ and azimuthal field B/sub theta/. When the axial field was zero the Josephson current as a function of azimuthal field showed the Fraunhofer like pattern of a flat junction in a magnetic field. As the axial field was increased, the central lobe of the Fraunhofer pattern decreased and disappeared at the critical field leaving the side lobes broadened. It is well known that a Josephson junction may switch to the voltage state at any current less than the maximum Josephson current. For some cylindrical junctions the switching currents are not continuously distributed but discrete with certain values occurring repeatedly. This observation is not understood
Spin accumulation in triplet Josephson junction
International Nuclear Information System (INIS)
We employ a Hamiltonian method to study the equal-spin pairing triplet Josephson junction with different orbital symmetries of pair potentials. Both the spin/charge supercurrent and possible spin accumulation at the interface of the junction are analyzed by means of the Keldysh Green's function. It is found that a spontaneous angle-resolved spin accumulation can form at the junction's interface when the orbital symmetries of Cooper pairs in two triplet superconductors are different, the physical origin is the combined effect of the different orbital symmetries and different spin states of Cooper pairs due to the misalignment of two d vectors in triplet leads. An abrupt current reversal effect induced by misalignment of d vectors is observed and can survive in a strong interface barrier scattering because the zero-energy state appears at the interface of the junction. These properties of the p-wave Josephson junction may be helpful for identifying the order parameter symmetry.
Supercurrent in long ballistic graphene Josephson junctions
Borzenets, I. V.; Amet, F.; Ke, C. T.; Watanabe, K.; Taniguchi, T; Yamamoto, M.; Tarucha, S.; Finkelstein, G
2016-01-01
We investigate the critical current $I_C$ in Josephson junctions made of encapsulated graphene/boron-nitride heterostructures. $I_C$ is found to scale with temperature $T$ as $\\propto exp(-k_bT/\\delta E)$, which is consistent with the conventional model for ballistic Josephson junctions that are long compared to the thermal length. The extracted energy $\\delta E$ is independent of the carrier density and consistent with the level spacing of the ballistic cavity, as determined from Fabry-Perot...
Josephson tunnel junctions in niobium films
International Nuclear Information System (INIS)
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)
Thermodynamics of two-dimensional Josephson junctions
International Nuclear Information System (INIS)
We derive the effective free energy of a two-dimensional Josephson junction in the presence of an external current and predict that the junction has a phase transition at a temperature TJ below the bulk transition temperature Tc. In the range TJ c is reduced by thermal fluctuations; for a junction of size L, Ic ∝ Lb(T) where b(T) J c vanishes at L → ∞) while 0 J. Our results may account for the absence of an observable supercurrent at temperatures below Tc in YBa2Cu3Ox-and Bi2Sr2CaCu2O8-based junctions. (orig.)
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.
Microscopic tunneling theory of long Josephson junctions
DEFF Research Database (Denmark)
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...
Fluxon density waves in long Josephson junctions
DEFF Research Database (Denmark)
Olsen, O. H.; Ustinov, A. V.; Pedersen, Niels Falsig
1993-01-01
Numerical simulations of the multiple fluxon dynamics stimulated by an external oscillating force applied at a boundary of a long Josephson junction are presented. The calculated IV characteristics agree well with a recent experimental observation of rf-induced satellite flux-flow steps. The volt...... density waves....
Multisoliton excitations in long Josephson junctions
DEFF Research Database (Denmark)
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...
TOPICAL REVIEW: Intrinsic Josephson junctions: recent developments
Yurgens, A. A.
2000-08-01
Some recent developments in the fabrication of intrinsic Josephson junctions (IJJ) and their application for studying high-temperature superconductors are discussed. The major advantages of IJJ and unsolved problems are outlined. The feasibility of three-terminal devices based on the stacked IJJ is briefly evaluated.
Electric Field Effect in Intrinsic Josephson Junctions
Koyama, T.
The electric field effect in intrinsic Josephson junction stacks (IJJ's) is investigated on the basis of the capacitively-coupled IJJ model. We clarify the current-voltage characteristics of the IJJ's in the presence of an external electric field. It is predicted that the IJJ's show a dynamical transition to the voltage state as the external electric field is increased.
Defect formation in long Josephson junctions
DEFF Research Database (Denmark)
Gordeeva, Anna; Pankratov, Andrey
2010-01-01
We study numerically a mechanism of vortex formation in a long Josephson junction within the framework of the one-dimensional sine-Gordon model. This mechanism is switched on below the critical temperature. It is shown that the number of fluxons versus velocity of cooling roughly scales according...
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.
Josephson junction microcalorimeter with a superconductor loop
Yoshihara, F; Shinada, K
2003-01-01
We propose a new microcalorimeter in which the critical current of a Josephson junction can be varied by an electron temperature in the normal metal barrier of the superconductor-normal metal-superconductor (SNS) or superconductor-normal metal-insulator-superconductor (SNIS) junctions. In this detector, a Josephson junction with a radiation absorber is included in a superconductor loop and the change of its critical current is converted into a change of magnetic flux in the loop. We estimated the energy resolution of this detector by calculating a noise equivalent power (NEP) of the detector. The estimated energy resolution and dynamic range are 4.2 eV/5.8 eV and 3.1 keV/6.2 keV, respectively with an Ag absorber of 500 x 500 x 2 mu m sup 3 at 100 mK.
Strain-tunable Josephson current in graphene-superconductor junction
Wang, Y.; Liu, Y.; Wang, B.
2013-10-01
Strain effects on Josephson current in a graphene-superconductor junction are explored theoretically. It is demonstrated that the supercurrent is an oscillatory function of zigzag direction strain with a strain-dependent oscillating frequency. Interestingly, it is found that the Josephson current under armchair direction strain can be turned on/off with a cutoff strain. In view of the on/off properties of the Josephson current, we propose the strained graphene Josephson junction to be utilized as a supercurrent switch.
δ-biased Josephson tunnel junctions
International Nuclear Information System (INIS)
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.
Visualization of the current density in Josephson junctions with 0- and π-facets
International Nuclear Information System (INIS)
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.)
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 alloy interlayer
International Nuclear Information System (INIS)
Josephson junctions are used as active devices in superconducting electronics and quantum information technology. Outstanding properties are their distinct non-linear electrical characteristics and a usually sinusoidal relation between the current and the superconducting phase difference across the junction. In general the insertion of ferromagnetic material in the barrier of a Josephson junction is associated with a suppression of superconducting correlations. But also new phenomena can arise which may allow new circuit layouts and enhance the performance of applications. This thesis presents a systematic investigation for two concepts to fabricate Josephson junctions with a rather uncommon negative critical current. Such devices exhibit an intrinsic phase slip of π between the electrodes, so they are also known as π junctions. Both studies go well beyond existing experiments and in one system a π junction is shown for the first time. All the thin film junctions are based on superconducting Nb electrodes. In a first approach, barriers made from Si and Fe were investigated with respect to the realisation of π junctions by spin-flip processes. The distribution of Fe in the Si matrix was varied from pure layers to disperse compounds. The systematic fabrication of alloy barriers was facilitated by the development of a novel timing-based combinatorial sputtering technique for planetary deposition systems. An orthogonal gradient approach allowed to create binary layer libraries with independent variations of thickness and composition. Second, Nb vertical stroke AlOx vertical stroke Nb vertical stroke Ni60Cu40 vertical stroke Nb (SIsFS) double barrier junctions were experimentally studied for the occurrence of proximity effect induced order parameter oscillations. Detailed dependencies of the critical current density on the thickness of s-layer and F-layer were acquired and show a remarkable agreement to existing theoretical predictions. Especially a variation of jc
Josephson junctions with ferromagnetic alloy interlayer
Energy Technology Data Exchange (ETDEWEB)
Himmel, Nico
2015-07-23
Josephson junctions are used as active devices in superconducting electronics and quantum information technology. Outstanding properties are their distinct non-linear electrical characteristics and a usually sinusoidal relation between the current and the superconducting phase difference across the junction. In general the insertion of ferromagnetic material in the barrier of a Josephson junction is associated with a suppression of superconducting correlations. But also new phenomena can arise which may allow new circuit layouts and enhance the performance of applications. This thesis presents a systematic investigation for two concepts to fabricate Josephson junctions with a rather uncommon negative critical current. Such devices exhibit an intrinsic phase slip of π between the electrodes, so they are also known as π junctions. Both studies go well beyond existing experiments and in one system a π junction is shown for the first time. All the thin film junctions are based on superconducting Nb electrodes. In a first approach, barriers made from Si and Fe were investigated with respect to the realisation of π junctions by spin-flip processes. The distribution of Fe in the Si matrix was varied from pure layers to disperse compounds. The systematic fabrication of alloy barriers was facilitated by the development of a novel timing-based combinatorial sputtering technique for planetary deposition systems. An orthogonal gradient approach allowed to create binary layer libraries with independent variations of thickness and composition. Second, Nb vertical stroke AlO{sub x} vertical stroke Nb vertical stroke Ni{sub 60}Cu{sub 40} vertical stroke Nb (SIsFS) double barrier junctions were experimentally studied for the occurrence of proximity effect induced order parameter oscillations. Detailed dependencies of the critical current density on the thickness of s-layer and F-layer were acquired and show a remarkable agreement to existing theoretical predictions. Especially
Quiet SDS Josephson Junctions for Quantum Computing
Ioffe, L. B.; Geshkenbein, V. B.; Feigelman, M. V.; Fauchere, A. L.; Blatter, G.
1998-01-01
Unconventional superconductors exhibit an order parameter symmetry lower than the symmetry of the underlying crystal lattice. Recent phase sensitive experiments on YBCO single crystals have established the d-wave nature of the cuprate materials, thus identifying unambiguously the first unconventional superconductor. The sign change in the order parameter can be exploited to construct a new type of s-wave - d-wave - s-wave Josephson junction exhibiting a degenerate ground state and a double-pe...
Nonlinearity in superconductivity and Josephson junctions
International Nuclear Information System (INIS)
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
Josephson junction in a thin film
International Nuclear Information System (INIS)
The phase difference φ(y) for a vortex at a line Josephson junction in a thin film attenuates at large distances as a power law, unlike the case of a bulk junction where it approaches exponentially the constant values at infinities. The field of a Josephson vortex is a superposition of fields of standard Pearl vortices distributed along the junction with the line density φ'(y)/2π. We study the integral equation for φ(y) and show that the phase is sensitive to the ratio l/Λ, where l=λJ2/λL, Λ=2λL2/d, λL, and λJ are the London and Josephson penetration depths, and d is the film thickness. For l2=λJ2λL/d/y2; i.e., it diverges as T→Tc. For l>>Λ, both the core and the tail have nearly the same characteristic length lΛ
Bursting behaviour in coupled Josephson junctions.
Hongray, Thotreithem; Balakrishnan, J; Dana, Syamal K
2015-12-01
We report an interesting bow-tie shaped bursting behaviour in a certain parameter regime of two resistive-capacitative shunted Josephson junctions, one in the oscillatory and the other in the excitable mode and coupled together resistively. The burst emerges in both the junctions and they show near-complete synchronization for strong enough couplings. We discuss a possible bifurcation scenario to explain the origin of the burst. An exhaustive study on the parameter space of the system is performed, demarcating the regions of bursting from other solutions. PMID:26723143
Josephson tunnel junctions with ferromagnetic barrier layer
International Nuclear Information System (INIS)
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.)
Inhomogeneous parallel arrays of Josephson junctions
International Nuclear Information System (INIS)
Highlights: → New long wave model of an inhomogeneous parallel array of Josephson junctions. → Adapted spectral problem giving resonances in the current-voltage characteristic. → At resonances solution is described by two ordinary differential equations. → Good agreement with the characteristic curve of a real five junction array. - Abstract: We model new inhomogeneous parallel arrays of small Josephson junctions by taking into account the time and space variations of the field in the cavity and the capacity miss-match at the junctions. The model consists in a wave equation with Dirac delta function sine nonlinearities. We introduce an adapted spectral problem whose spectrum gives the resonances in the current-voltage characteristic curve of any array. It is shown that at the resonances the solution is described by two simple ordinary differential equations. The resonances obtained by this approach are in good agreement with the characteristic curve of a real five junction array. This flexible approach is a first step towards building a device tailored for given purposes.
Static properties of small Josephson tunnel junctions in an oblique magnetic field
DEFF Research Database (Denmark)
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...
Intrinsic Josephson Junctions with Intermediate Damping
Warburton, Paul A.; Saleem, Sajid; Fenton, Jon C.; Speller, Susie; Grovenor, Chris R. M.
2011-03-01
In cuprate superconductors, adjacent cuprate double-planes are intrinsically Josephson-coupled. For bias currents perpendicular to the planes, the current-voltage characteristics correspond to those of an array of underdamped Josephson junctions. We will discuss our experiments on sub-micron Tl-2212 intrinsic Josephson junctions (IJJs). The dynamics of the IJJs at the plasma frequency are moderately damped (Q ~ 8). This results in a number of counter-intuitive observations, including both a suppression of the effect of thermal fluctuations and a shift of the skewness of the switching current distributions from negative to positive as the temperature is increased. Simulations confirm that these phenomena result from repeated phase slips as the IJJ switches from the zero-voltage to the running state. We further show that increased dissipation counter-intuitively increases the maximum supercurrent in the intermediate damping regime (PRL vol. 103, art. no. 217002). We discuss the role of environmental dissipation on the dynamics and describe experiments with on-chip lumped-element passive components in order control the environment seen by the IJJs. Work supported by EPSRC.
Josephson tunnel junctions with ferromagnetic interlayer
International Nuclear Information System (INIS)
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
Energy Technology Data Exchange (ETDEWEB)
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.)
Current–voltage characteristics of triple-barrier Josephson junctions
Energy Technology Data Exchange (ETDEWEB)
De Luca, R., E-mail: rdeluca@unisa.it; Giordano, A.
2015-06-15
Highlights: • I–V characteristics of triple-barrier Josephson junctions (TBJJs) are studied. • The I–V characteristics are identical to those of an ordinary single-barrier Josephson junction. • In the presence of r. f. radiation integer and fractional Shapiro steps appear. - Abstract: Current–voltage characteristics of triple-barrier Josephson junctions are analytically and numerically studied. In the presence of a constant current bias and for homogeneous Josephson coupling of all layers, these systems behave exactly as ordinary Josephson junctions, despite their non-canonical current-phase relation. Deviation from this behaviour is found for inhomogeneous Josephson coupling between different layers in the device. Appearance of integer and fractional Shapiro steps are predicted in the presence of r. f. frequency radiation. In particular, the amplitudes of these steps are calculated in the homogeneous case as clear footprints of the non-canonical current-phase relation in these systems.
Work fluctuations in bosonic Josephson junctions
Lena, R. G.; Palma, G. M.; De Chiara, G.
2016-05-01
We calculate the first two moments and full probability distribution of the work performed on a system of bosonic particles in a two-mode Bose-Hubbard Hamiltonian when the self-interaction term is varied instantaneously or with a finite-time ramp. In the instantaneous case, we show how the irreversible work scales differently depending on whether the system is driven to the Josephson or Fock regime of the bosonic Josephson junction. In the finite-time case, we use optimal control techniques to substantially decrease the irreversible work to negligible values. Our analysis can be implemented in present-day experiments with ultracold atoms and we show how to relate the work statistics to that of the population imbalance of the two modes.
Phase diffusion and charging effects in Josephson junctions
Grabert, Hermann; Ingold, Gert-Ludwig; Paul, Benjamin
1998-01-01
The supercurrent of a Josephson junction is reduced by phase diffusion. For ultrasmall capacitance junctions the current may be further decreased by Coulomb blockade effects. We calculate the Cooper pair current by means of time-dependent perturbation theory to all orders in the Josephson coupling energy and obtain the current-voltage characteristic in closed form in a range of parameters of experimental interest. The results comprehend phase diffusion of the coherent Josephson current in the...
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.
Shapiro and parametric resonances in coupled Josephson junctions
Gaafar, Ma. A.; Shukrinov, Yu. M.; Foda, A.
2012-01-01
The effect of microwave irradiation on the phase dynamics of intrinsic Josephson junctions in high temperature superconductors is investigated. We compare the current-voltage characteristics for a stack of coupled Josephson junctions under external irradiation calculated in the framework of CCJJ and CCJJ+DC models.
Shapiro and parametric resonances in coupled Josephson junctions
International Nuclear Information System (INIS)
The effect of microwave irradiation on the phase dynamics of intrinsic Josephson junctions in high temperature superconductors is investigated. We compare the current-voltage characteristics for a stack of coupled Josephson junctions under external irradiation calculated in the framework of CCJJ and CCJJ+DC models.
Current noise in disordered Josephson junctions
Energy Technology Data Exchange (ETDEWEB)
Dallaire-Demers, Pierre-Luc; Wilhelm-Mauch, Frank [Universitaet des Saarlandes, Saarbruecken (Germany); Ansari, Mohammad [Institute for Quantum Computing, Waterloo (Canada)
2013-07-01
Josephson junctions are one of the fundamental building blocks of mesoscopic superconducting circuits. Despite being dissipationless, spurious low-energy Andreev bound states inside those junctions could provide an intrinsic microscopic mechanism for fluctuations of the current, therefore limiting the coherent operation time of superconducting quantum circuits. Models of bound states arising from pinholes in different models of disorder were investigated and their current noise signatures were characterized with respect to temperature, phase difference and sample-to-sample fluctuations of the conductance. In this theoretical work, it is shown that the low-frequency noise signature of Josephson junctions is a property specific to each individual sample independent of the fabrication process. Furthermore, the comparison of sample-specific noise spectra and characteristic current-voltage relations reveals under which conditions the presence of those disorder-induced bound states may elude detection in a 4-probe measurement but still reveal themselves as dephasing of coherent observables in circuits dominated by inductive energy.
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.
Josephson junctions as detectors for non-Gaussian noise
International Nuclear Information System (INIS)
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.)
Dissipation and traversal time in Josephson junctions
International Nuclear Information System (INIS)
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.
Soliton excitations in Josephson tunnel junctions
International Nuclear Information System (INIS)
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
An ultra-small capacitance Josephson junction
International Nuclear Information System (INIS)
We consider a voltage biased ultra-small capacitance Josephson junction, with the coupling to the external source containing both resistive and inductive elements. In addition we include a phenomenological coupling to an external heat bath. Our goal is to extend and generalize previous studies of current biased ultra-small junctions. Charging effects, due to the presence of discrete charge carriers in the junction, play a crucial role. In particular we find an infinite resistance branch in the I-V characteristic for a d.c. bias, and resistive steps in the I-V curve when the external bias contains an additional a.c. component. These effects are reminiscent of the 'Coulomb blockade' and the inverse Shapiro steps, respectively, predicted earlier in the context of current biased circuits. As a response to an a.c. voltage bias we also predict spikes of the voltage across the junction and a noisy background, when this voltage is plotted as a function of either the external d.c. biasing voltage or the external frequency. Our analysis shows that various circuitry components may qualitatively affect the response of the junction to an external bias. (authors)
Josephson current in parallel SFS junctions
Ioselevich, Pavel; Ostrovsky, Pavel; Fominov, Yakov; Feigelman, Mikhail
We study a Josephson junction between superconductors connected by two parallel ferromagnetic arms. If the ferromagnets are fully polarised, supercurrent can only flow via Cooper pair splitting between the differently polarised arms. The disorder-average current is suppressed, but mesoscopic fluctuations lead to a significant typical current. We extract the typical current from a current-current correlator. The current is proportional to sin2 α / 2 , where α is the angle between the polarisations of the two arms, revealing the spin dependence of crossed Andreev reflection. Compared to an SNS device of the same geometry, the typical SFS current is small by a factor determined by the properties of the superconducting leads alone. The current is insensitive to the flux threading the area between the ferromagnetic arms of the junction. However, if the ferromagnetic arms are replaced by metal with magnetic impurities, or partially polarised ferromagnets, the Josephson current starts depending on the flux with a period of h / e , i.e. twice the superconducting flux quantum.
Fabrication of Niobium Nanobridge Josephson Junctions
Tachiki, T.; Horiguchi, K.; Uchida, T.
2014-05-01
To realize antenna-coupled Josephson detectors for microwave and millimeter-wave radiation, planar-type Nb nanobridge Josephson junctions were fabricated. Nb thin films whose thickness, the root mean square roughness and the critical temperature were 20.0 nm, 0.109 nm and 8.4 K, respectively were deposited using a DC magnetron sputtering at a substrate temperature of 700°C. Nanobridges were obtained from the film using 80-kV electron beam lithography and reactive ion-beam etching in CF4 (90%) + O2 (10%) gases. The minimum bridge area was 65 nm wide and 60 nm long. For the nanobridge whose width and length were less than 110 nm, an I-V characteristic showed resistively-shunted-junction behaviour near the critical temperature. Moreover, Shapiro steps were observed in the nanobridge with microwave irradiation at a frequency of 6 - 30 GHz. The Nb nanobridges can be used as detectors in the antenna-coupled devices.
Time domain analysis of dynamical switching in a Josephson junction
Sjostrand, Joachim; Walter, Jochen; Haviland, David; Hansson, Hans; Karlhede, Anders
2004-01-01
We have studied the switching behaviour of a small capacitance Josephson junction both in experiment, and by numerical simulation of a model circuit. The switching is a comples process involving the transition between two dynamical states of the non-linear circuit, arising from a frequency dependent damping of the Josephson junction. We show how a specific type of bias pulse-and-hold, can result in a fast detection of switching, even when the measurement bandwidth of the junction voltage is s...
Current distributions of thermal switching in extremely underdamped Josephson junctions
International Nuclear Information System (INIS)
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
Planar Josephson tunnel junctions in a transverse magnetic field
DEFF Research Database (Denmark)
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....
Numerical simulations of flux flow in stacked Josephson junctions
DEFF Research Database (Denmark)
Madsen, Søren Peder; Pedersen, Niels Falsig
2005-01-01
We numerically investigate Josephson vortex flux flow states in stacked Josephson junctions, motivated by recent experiments trying to observe the vortices in a square vortex lattice when a magnetic field is applied to layered high-Tc superconductors of the Bi2Sr2CaCu2Ox type. By extensive...
Josephson junction array protected from local noises.
Gladchenko, Sergey; Olaya, David; Dupont-Ferrier, Eva; Doucot, Benoit; Ioffe, Lev; Gershenson, Michael
2009-03-01
We have developed small arrays of Josephson junctions (JJs) that can be viewed as prototypes of superconducting qubits protected from local noises [1]. The array consists of twelve superconducting loops interrupted by four sub-micron JJs. The protected state is realized when each loop is threaded by half of the magnetic flux quantum. It has been observed that the array with the optimized amplitude of quantum fluctuations is protected against magnetic flux variations well beyond linear order, in agreement with theoretical predictions [2]. 1. S. Gladchenko et al., ``Superconducting Nanocircuits for Topologically Protected Qubits'', arXiv:cond-mat/0802.2295, to be published in Nature Physics. 2. L.B. Ioffe and M.V. Feigelman, Phys. Rev. B 66, 224503 (2002); B. Doucot et al., Phys. Rev. B 71, 024505 (2005); B. Doucot and L.B. Ioffe, Phys. Rev. B 76, 214507 (2007).
Curvature Effects in 1-D and 2-D Josephson Junctions
Dobrowolski, Tomasz
2016-01-01
The gauge invariant phase difference between superconducting electrodes is a dominating dynamical degree of freedom in the Josephson junction. This rapport concerns the influence of the curvature of the junction on the dynamic of this field variable. The effects of curvature are discussed in the long and large area junctions. In particular the dynamics of the fluxion and the kink front are studied.
Synchronisation of Josephson vortices in multi-junction systems
DEFF Research Database (Denmark)
Filatrella, G.; Pedersen, Niels Falsig; Wiesenfeld, K.
2006-01-01
A largely adopted model for the description of high-temperature superconductors such as BSCCO results in several long Josephson junctions one on the top of the other ("stacked"). The dynamics of the basic nonlinear excitation of the isolated long Josephson junction, the Josephson vortex, is......, that is mainly to retrieve the above described synchronous motion. We discuss the physics behind synchronization of nonlinear elements and we review applications to Josephson arrays. We discuss in the framework of a general model for synchronization, the Kuramoto model, a mechanism that can possibly...... modified by the coupling among the junctions, so the motion of the flux quanta in the various layers is affected by the flux dynamics in all other layers. Two basic states are possible: a synchronous motion, where all junctions are reflected at the edge at the same instant, and an out-of-phase motion...
High Tc Josephson Junctions, SQUIDs and magnetometers
International Nuclear Information System (INIS)
There has recently been considerable progress in the state-of-the-art of high-Tc magnetometers based on dc SQUIDs (Superconducting Quantum Interference Devices). This progress is due partly to the development of more manufacturable Josephson junctions, making SQUIDs easier to fabricate, and partly to the development of multiturn flux transformers that convert the high sensitivity of SQUIDs to magnetic flux to a correspondingly high sensitivity to magnetic field. Needless to say, today's high-Tc SQUIDs are still considerably less sensitive than their low-Tc counterparts, particularly at low frequencies (f) where their level of 1/f noise remains high. Nonetheless, the performance of the high-Tc devices has now reached the point where they are adequate for a number of the less demanding applications; furthermore, as we shall see, at least modest improvements in performance are expected in the near future. In this article, the author outlines these various developments. This is far from a comprehensive review of the field, however, and, apart from Sec. 2, he describes largely his own work. He begins in Sec. 2 with an overview of the various types of Josephson junctions that have been investigated, and in Sec. 3, he describes some of the SQUIDs that have been tested, and assess their performance. Section 4 discuss the development of the multilayer structures essential for an interconnect technology, and, in particular, for crossovers and vias. Section 5 shows how this technology enables one to fabricate multiturn flux transformers which, in turn, can be coupled to SQUIDs to make magnetometers. The performance and possible future improvements in these magnetometers are assessed, and some applications mentioned
Low Noise Current Amplifier Based on Mesoscopic Josephson Junction
Delahaye, Julien; Hassel, J.; Lindell, Rene; Sillanpää, Mika; Paalanen, Mikko; Seppä, Heikki; Hakonen, Pertti J.
2003-01-01
We utilize the band structure of a mesoscopic Josephson junction to construct low noise amplifiers. By taking advantage of the quantum dynamics of a Josephson junction, i.e. the interplay of interlevel transitions and the Coulomb blockade of Cooper pairs, we create transistor-like devices, Bloch oscillating transistors, with considerable current gain and high input impedance. In these transistors, correlated supercurrent of Cooper pairs is controlled by a small base current made of single ele...
Interference effects in isolated Josephson junction arrays with geometric symmetries
Ivanov, D. A.; Ioffe, L. B.; Geshkenbein, V. B.; Blatter, G.
2001-01-01
As the size of a Josephson junction is reduced, charging effects become important and the superconducting phase across the link turns into a periodic quantum variable. Isolated Josephson junction arrays are described in terms of such periodic quantum variables and thus exhibit pronounced quantum interference effects arising from paths with different winding numbers (Aharonov-Casher effects). These interference effects have strong implications for the excitation spectrum of the array which are...
Supercurrent reversal in Josephson junctions based on bilayer graphene flakes
Rameshti, Babak Zare; Zareyan, Malek; Moghaddam, Ali G.
2015-01-01
We investigate the Josephson effect in a bilayer graphene flake contacted by two monolayer sheet deposited by superconducting electrodes. It is found that when the electrodes are attached to the different layers of the bilayer, the Josephson current is in a $\\pi$ state when the bilayer region is undoped and in the absence of vertical bias. Applying doping or bias to the junction reveals $\\pi-0$ transitions which can be controlled by varying the temperature and the junction length. The supercu...
Tight-binding study of bilayer graphene Josephson junctions
Muñoz, W. A.; Covaci, L.; Peeters, F. M.
2012-01-01
Using highly efficient simulations of the tight-binding Bogoliubov-de Gennes model we solved self-consistently for the pair correlation and the Josephson current in a Superconducting-Bilayer graphene-Superconducting Josephson junction. Different doping levels for the non-superconducting link are considered in the short and long junction regime. Self-consistent results for the pair correlation and superconducting current resemble those reported previously for single layer graphene except in th...
Current-phase relation of graphene Josephson junctions
Chialvo, C.; Moraru, I. C.; Van Harlingen, D. J.; Mason, N.
2010-01-01
The current-phase relation (CPR) of a Josephson junction reveals valuable information about the microscopic processes and symmetries that influence the supercurrent. In this Letter, we present direct measurements of the CPR for Josephson junctions with a graphene barrier, obtained by a phase-sensitive SQUID interferometry technique. We find that the CPR is skewed with respect to the commonly observed sinusoidal behavior. The amount of skewness varies linearly with critical current (Ic) regard...
Resonator coupled Josephson junctions; parametric excitations and mutual locking
DEFF Research Database (Denmark)
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...
Josephson effect in supercondutor/ferromagnetic semiconductor/superconductor junctions
International Nuclear Information System (INIS)
Using a general expression for dc Josephson current, we study the Josephson effect in ballistic superconductor (SC)/ferromagnetic semiconductor (FS)/SC junctions, in which the mismatches of the effective mass and Fermi velocity between the FS and SC, spin polarization P in the FS, as well as strengths of potential scattering Z at the interfaces are included. It is shown that in the coherent regime, the oscillatory dependences of the maximum Josephson current on the FS layer thickness L and Josephson current on the macroscopic phase difference φ for the heavy and light holes, resulting from the spin splitting energy gained or lost by a quasiparticle Andreev-reflected at the FS/SC interface, are much different due to the different mismatches in the effective mass and Fermi velocity between the FS and the SC, which is related to the crossovers between positive (0) and negative (π) couplings or equivalently 0 and π junctions. Also, we find that, for the same reason, Z and P are required not to surpass different critical values for the Josephson currents of the heavy and light holes. Furthermore, it is found that, for the dependence of the Josephson current on φ, regardless of how L,Z, and P change, the Josephson junctions do not transit between 0 and π junctions for the light hole
Gate-tunable Supercurrent in Graphene-based Josephson Junction
Energy Technology Data Exchange (ETDEWEB)
Jeong, D.; Lee, G. H.; Lee, H. J. [Pohang University of Science and Technology, Pohang (Korea, Republic of); Doh, Y. J. [Korea University Sejong, Campus, Jochiwon (Korea, Republic of)
2011-08-15
Mono-atomic-layer graphene is an interesting system for studying the relativistic carrier transport arising from a linear energy-momentum dispersion relation. An easy control of the carrier density in graphene by applying an external gate field makes the system even more useful. In this study, we measured the Josephson current in a device consisting of mono-layer graphene sheet sandwiched between two closely spaced (-300 nm) aluminum superconducting electrodes. Gate dependence of the supercurrent in graphene Josephson junction follows the gate dependence of the normal-state conductance. The gate-tunable and relatively large supercurrent in a graphene Josephson junction would facilitate our understanding on the weak-link behavior in a superconducting-normal metal-superconducting (SNS) type Josephson junction.
Gate-tunable Supercurrent in Graphene-based Josephson Junction
International Nuclear Information System (INIS)
Mono-atomic-layer graphene is an interesting system for studying the relativistic carrier transport arising from a linear energy-momentum dispersion relation. An easy control of the carrier density in graphene by applying an external gate field makes the system even more useful. In this study, we measured the Josephson current in a device consisting of mono-layer graphene sheet sandwiched between two closely spaced (-300 nm) aluminum superconducting electrodes. Gate dependence of the supercurrent in graphene Josephson junction follows the gate dependence of the normal-state conductance. The gate-tunable and relatively large supercurrent in a graphene Josephson junction would facilitate our understanding on the weak-link behavior in a superconducting-normal metal-superconducting (SNS) type Josephson junction.
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...
Studying two-level systems in Josephson junctions with a Josephson junction defect spectrometer
Stoutimore, M. J. A.; Khalil, M. S.; Gladchenko, Sergiy; Simmonds, R. W.; Lobb, C. J.; Osborn, K. D.
2012-02-01
We have fabricated and measured Josephson junction defect spectrometers (JJDSs), which are frequency-tunable, nearly-harmonic oscillators that probe two-level systems (TLSs) in the barrier of a Josephson junction (JJ). A JJDS consists of the JJ under study fabricated with a parallel capacitor and inductor such that it can accommodate a wide range of junction inductances, LJ0, while maintaining an operating frequency, f01, in the range of 4-8 GHz. In this device, the parallel inductance helps the JJ maintain linearity over a wide range of frequencies. This architecture allows for the testing of JJs with a wide range of areas and barrier materials, and in the first devices we have tested Al/AlOx/Al JJs. By applying a magnetic flux bias to tune f01, we detect TLSs in the JJ barrier as splittings in the device spectrum. We will present our results toward identifying and quantifying these TLSs, which are known to cause decoherence in quantum devices that rely on JJs.
Josephson junctions in thin and narrow rectangular superconducting strips
Clem, John R.
2010-01-01
I consider a Josephson junction crossing the middle of a thin rectangular superconducting strip of length L and width W subjected to a perpendicular magnetic induction B. I calculate the spatial dependence of the gauge-invariant phase difference across the junction and the resulting B dependence of the critical current Ic(B).
Externally pumped millimeter-wave Josephson-junction parametric amplifier
DEFF Research Database (Denmark)
Levinsen, M.T; Pedersen, Niels Falsig; Sørensen, Ole;
1980-01-01
A unified theory of the singly and doubly degenerate Josephson-junction parametric amplifier is presented. Experiments with single junctions on both amplifier modes at frequencies 10, 35, and 70 GHz are discussed. Low-noise temperature (∼100 K, single sideband (SSB)) and reasonable gain (∼8 dB) w...
Parametric excitation of plasma oscillations in a Josephson tunnel junction
DEFF Research Database (Denmark)
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....
Fiske steps in Josephson junctions with alternating critical current density
International Nuclear Information System (INIS)
We have developed a simple model, in the framework of the Kulik theory of Fiske steps in Josephson junctions, for the electromagnetic resonances observed in the current voltage characteristics of certain high temperature superconductor grain boundary junctions. Some preliminary results are illustrated
Josephson junctions in thin and narrow rectangular superconducting strips
International Nuclear Information System (INIS)
I consider a Josephson junction crossing the middle of a thin rectangular superconducting strip of length L and width W subjected to a perpendicular magnetic induction B. I calculate the spatial dependence of the gauge-invariant phase difference across the junction and the resulting B dependence of the critical current Ic(B).
Conditions for synchronization in Josephson-junction arrays
Energy Technology Data Exchange (ETDEWEB)
Chernikov, A.A.; Schmidt, G. [Stevens Institute of Technology, Hoboken, NJ (United States)
1995-12-31
An effective perturbation theoretical method has been developed to study the dynamics of Josephson Junction series arrays. It is shown that the inclusion of Junction capacitances, often ignored, has a significant impact on synchronization. Comparison of analytic with computational results over a wide range of parameters shows excellent agreement.
Proximity effects in all refractory Josephson tunnel junctions
International Nuclear Information System (INIS)
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.)
Bloch Inductance in Small-Capacitance Josephson Junctions
International Nuclear Information System (INIS)
We show that the electrical impedance of a small-capacitance Josephson junction also includes, in addition to the capacitive term -i/ωCB, an inductive term iωLB. Similar to the known Bloch capacitance CB(q), the Bloch inductance LB(q) also depends periodically on the quasicharge, q, and its maximum value achieved at q=e(mod 2e) always exceeds the value of the Josephson inductance of this junction LJ(φ) at fixed φ=0. The effect of the Bloch inductance on the dynamics of a single junction and a one-dimensional array is described
Submicron NbN Josephson tunnel junctions for digital applications
International Nuclear Information System (INIS)
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
International Nuclear Information System (INIS)
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.
K. S. Ojo; Njah, A. N.; O. I. Olusola; Omeike, M. O.
2014-01-01
This paper investigates the reduced order projective and hybrid projective combination-combination synchronization of four chaotic Josephson junctions consisting of two third order Josephson junctions as the drives and two second order chaotic Josephson junctions as the response systems via active backstepping technique. The investigation confirms the achievement of reduced order projective and hybrid projective combination-combination synchronization among four chaotic Josephson junctions vi...
Revealing Topological Superconductivity in Extended Quantum Spin Hall Josephson Junctions
Lee, Shu-Ping; Michaeli, Karen; Alicea, Jason; Yacoby, Amir
2014-01-01
Quantum spin Hall-superconductor hybrids are promising sources of topological superconductivity and Majorana modes, particularly given recent progress on HgTe and InAs/GaSb. We propose a new method of revealing topological superconductivity in extended quantum spin Hall Josephson junctions supporting `fractional Josephson currents'. Specifically, we show that as one threads magnetic flux between the superconductors, the critical current traces an interference pattern featuring sharp fingerpri...
Josephson Current and Multiple Andreev Reflections in Graphene SNS Junctions
Du, Xu; Skachko, Ivan; Andrei, Eva Y.
2007-01-01
The Josephson Effect and Superconducting Proximity Effect were observed in Superconductor -Graphene-Superconductor (SGS) Josephson junctions with coherence lengths comparable to the distance between the superconducting leads. By comparing the measured temperature and doping dependence of the supercurrent and the proximity induced sub-gap features (multiple Andreev reflections) to theoretical predictions we find that, contrary to expectations, the ballistic transport model fails to describe th...
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.
4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions
Wiedenmann, J.; Bocquillon, E.; Deacon, R. S.; Hartinger, S.; HERMANN, O; Klapwijk, T. M.; L. Maier(Physik Department E12, Technische Universität München, Germany); Ames, C.; Brüne, C.; Gould, C.; Oiwa, A.; ISHIBASHI, K; Tarucha, S.; Buhmann, H.; Molenkamp, L. W.
2016-01-01
The Josephson effect describes the generic appearance of a supercurrent in a weak link between two superconductors. Its exact physical nature however deeply influences the properties of the supercurrent. Detailed studies of Josephson junctions can reveal microscopic properties of the superconducting pairing (spin-triplet correlations, $d$-wave symmetry) or of the electronic transport (quantum dot, ballistic channels). In recent years, considerable efforts have focused on the coupling of super...
Energy Technology Data Exchange (ETDEWEB)
Black-Schaffer, Annica M.
2010-04-06
We use a tight-binding Bogoliubov-de Gennes (BdG) formalism to self-consistently calculate the proximity effect, Josephson current, and local density of states in ballistic graphene SNS Josephson junctions. Both short and long junctions, with respect to the superconducting coherence length, are considered, as well as different doping levels of the graphene. We show that self-consistency does not notably change the current-phase relationship derived earlier for short junctions using the non-selfconsistent Dirac-BdG formalism but predict a significantly increased critical current with a stronger junction length dependence. In addition, we show that in junctions with no Fermi level mismatch between the N and S regions superconductivity persists even in the longest junctions we can investigate, indicating a diverging Ginzburg-Landau superconducting coherence length in the normal region.
Shunted-Josephson-junction model. I. The autonomous case
DEFF Research Database (Denmark)
Belykh, V. N.; Pedersen, Niels Falsig; Sørensen, O. H.
1977-01-01
The shunted-Josephson-junction model: the parallel combination of a capacitance, a phase-dependent conductance, and an ideal junction element biased by a constant current, is discussed for arbitrary values of the junction parameters. The main objective is to provide a qualitative understanding of...... current-voltage curves are presented. The case with a time-dependent monochromatic bias current is treated in a similar fashion in the companion paper....
Josephson tunnel junctions as fast nuclear particle position detectors
International Nuclear Information System (INIS)
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.)
The SNS Josephson junction with a third terminal
Prans, G. P.; Meissner, H.
1974-01-01
Discussion of the operating characteristics of a three-terminal thin-film SNS Josephson junction whose diameter is much greater than the electron pair coherence length in the N metal. It is shown that a junction of this type is essentially a two-terminal device even though the third terminal of the junction supplies the control current. The mechanism underlying this finding is discussed.
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.
Holographic Josephson Junctions and Berry holonomy from D-branes
Domokos, Sophia K; Sonnenschein, Jacob
2012-01-01
We construct a holographic model for Josephson junctions with a defect system of a Dp brane intersecting a D(p+2) brane. In addition to providing a geometrical picture for the holographic dual, this leads us very naturally to suggest the possibility of non-Abelian Josephson junctions characterized in terms of the topological properties of the branes. The difference between the locations of the endpoints of the Dp brane on either side of the defect translates into the phase difference of the condensate in the Josephson junction. We also add a magnetic flux on the D(p+2) brane and allow it evolve adiabatically along a closed curve in the space of the magnetic flux, while generating a non-trivial Berry holonomy.
Parametric excitation of plasma oscillations in Josephson Junctions
DEFF Research Database (Denmark)
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...
Collective Dynamics of Intrinsic Josephson Junctions in HTSC
Shukrinov, Yu M.; Mahfouzi, F.
2006-06-01
The dynamics of a stack of intrinsic Josephson junctions (IJJ) in the high-Tc superconductors is theoretically investigated with both the quasineutrality breakdown effect and quasiparticle charge imbalance effect taken into account. The current-voltage characteristics (IVC) of IJJ are numerically calculated in the framework of capacitively coupled Josephson junctions model and charge imbalance model including set of differential equations for phase differences, kinetic equations and generalized Josephson relations. We obtain the branch structure in IVC and investigate it as a function of model parameters such as coupling constant, McCumber parameter and number of junctions in the stack. The dependence of branch slopes and branch endpoints on the coupling and disequilibrium parameters are found. We study the nonequilibrium effects created by current injection and show that the increase in the disequilibrium parameter changes essentially the character of IVC. The new features of the hysteresis behavior of IVC of IJJ are obtained.
Suspended InAs nanowire Josephson junctions assembled via dielectrophoresis
Montemurro, D.; Stornaiuolo, D.; Massarotti, D.; Ercolani, D.; Sorba, L.; Beltram, F.; Tafuri, F.; Roddaro, S.
2015-09-01
We present a novel technique for the realization of suspended Josephson junctions based on InAs semiconductor nanowires. The devices are assembled using a technique of drop-casting guided by dielectrophoresis, which allows one to finely align the nanostructures on top of the electrodes. The proposed architecture removes the interaction between the nanowire and the substrate which is known to influence disorder and the orientation of the Rashba vector. The relevance of this approach in view of the implementation of hybrid Josephson junctions based on semiconducting nanowires coupled with high-temperature superconductors is discussed.
Bloch inductance in small-capacitance Josephson junctions
Zorin, A. B.
2005-01-01
We show that the electrical impedance of a small-capacitance Josephson junction includes besides the capacitive term $-i/\\omega C_B$ also an inductive term $i\\omega L_B$. Similar to the known Bloch capacitance $C_B(q)$, the Bloch inductance $L_B(q)$ also depends periodically on the quasicharge $q$, and its maximum value achieved at $q=e (\\textrm{mod} 2e)$ always exceeds the value of the Josephson inductance of this junction $L_J(\\phi)$ at fixed $\\phi=0$. The effect of the Bloch inductance on ...
Quantum phases in intrinsic Josephson junctions: Quantum magnetism analogy
Machida, Masahiko; Kobayashi, Keita; Koyama, Tomio
2013-08-01
We explore quantum phases in intrinsic Josephson junction (IJJ) stacks, whose in-plane area is so small that the capacitive coupling has a dominant role in the superconducting phase dynamics. In such cases, the effective Hamiltonian for the superconducting phase can be mapped onto that of one-dimensional ferromagnetically-interacting spin model, whose spin length S depends on the magnitude of the on-site Coulomb repulsion. The ferromagnetic model for IJJ’s prefers synchronized quantum features in contrast to the antiferromagnetically-interacting model in the conventional Josephson junction arrays.
Josephson Junction electronics: materials issues and fabrication techniques
International Nuclear Information System (INIS)
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
Field theoretical model of multi-layered Josephson junction and dynamics of Josephson vortices
Fujimori, Toshiaki; Nitta, Muneto
2016-01-01
Multi-layered Josephson junctions are modeled in the context of a field theory, and dynamics of Josephson vortices trapped inside insulators are studied. Starting from a theory consisting of complex and real scalar fields coupled to a U(1) gauge field which admit parallel $N-1$ domain-wall solutions, Josephson couplings are introduced weakly between the complex scalar fields. The $N-1$ domain walls behave as insulators separating $N$ superconductors. We construct the effective Lagrangian on the domain walls, which reduces to a coupled sine-Gordon model for well-separated walls and contains more interactions for walls at short distance. We then construct sine-Gordon solitons emerging in the effective theory that we identify Josephson vortices carrying singly quantized magnetic fluxes. When two neighboring superconductors tend to have the same phase, the ground state does not change with the positions of domain walls. On the other hand, when two neighboring superconductors tend to have the $\\pi$ phase differenc...
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.
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.
DEFF Research Database (Denmark)
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...
Tight-binding study of bilayer graphene Josephson junctions
Muñoz, W. A.; Covaci, L.; Peeters, F. M.
2012-11-01
Using highly efficient simulations of the tight-binding Bogoliubov-de-Gennes model, we solved self-consistently for the pair correlation and the Josephson current in a superconducting-bilayer graphene-superconducting Josephson junction. Different doping levels for the non-superconducting link are considered in the short- and long-junction regimes. Self-consistent results for the pair correlation and superconducting current resemble those reported previously for single-layer graphene except at the Dirac point, where remarkable differences in the proximity effect are found, as well as a suppression of the superconducting current in the long-junction regime. Inversion symmetry is broken by considering a potential difference between the layers and we found that the supercurrent can be switched if the junction length is larger than the Fermi length.
Evidence for Nonlocal Electrodynamics in Planar Josephson Junctions
Boris, A. A.; Rydh, A.; Golod, T.; Motzkau, H.; Klushin, A. M.; Krasnov, V. M.
2013-09-01
We study the temperature dependence of the critical current modulation Ic(H) for two types of planar Josephson junctions: a low-Tc Nb/CuNi/Nb and a high-Tc YBa2Cu3O7-δ bicrystal grain-boundary junction. At low T both junctions exhibit a conventional behavior, described by the local sine-Gordon equation. However, at elevated T the behavior becomes qualitatively different: the Ic(H) modulation field ΔH becomes almost T independent and neither ΔH nor the critical field for the penetration of Josephson vortices vanish at Tc. Such an unusual behavior is in good agreement with theoretical predictions for junctions with nonlocal electrodynamics. We extract absolute values of the London penetration depth λ from our data and show that a crossover from local to nonlocal electrodynamics occurs with increasing T when λ(T) becomes larger than the electrode thickness.
Critical currents and Josephson penetration depth in planar thin-film high-Tc Josephson junctions
International Nuclear Information System (INIS)
The temperature dependence of the critical current in planar high-Tc Josephson junctions fabricated in YBa2Cu3O7 thin films by focused electron irradiation has been studied. It is shown that in the range of critical current densities spanning more than five orders of magnitude and temperature range 0.1≤T/Tc≤1, the critical current density jc varies as (1-T/Tc)2. The T dependence of the critical current, however, is affected by the transition from the narrow junction to the wide junction limit as jc increases. An expression for the Josephson penetration depth in thin-film coplanar structures is derived, and magnetic field penetration depth in junction banks is extracted from the Ic(T) dependences. copyright 1996 American Institute of Physics
Nonsinusoidal Current-Phase Relation in SFS Josephson Junctions
Golubov, A. A.; Kupriyanov, M. Yu.; Fominov, Ya. V.
2002-06-01
Various types of the current-phase relation I(phi) in superconductor-ferromagnet-superconductor (SFS) point contacts and planar double-barrier junctions are studied within the quasiclassical theory in the limit of thin diffusive ferromagnetic interlayers. The physical mechanisms leading to highly nontrivial I(phi) dependence are identified by studying the spectral supercurrent density. These mechanisms are also responsible for the 0-pi transition in SFS Josephson junctions.
Nonsinusoidal current-phase relation in SFS Josephson junctions
International Nuclear Information System (INIS)
Various types of the current-phase relation I(ψ) in superconductor-ferromagnet-superconductor (SFS) point contacts and planar double-barrier junctions are studied within the quasiclassical theory in the limit of thin diffusive ferromagnetic interlayers. The physical mechanisms, leading to highly nontrivial I(ψ) dependence, are identified by studying the spectral supercurrent density. These mechanisms are also responsible for the 0-π transition in SFS Josephson junctions
Using ion irradiation to make high-Tc Josephson junctions
International Nuclear Information System (INIS)
In this article we describe the effect of ion irradiation on high-Tc superconductor thin film and its interest for the fabrication of Josephson junctions. In particular, we show that these alternative techniques allow to go beyond most of the limitations encountered in standard junction fabrication methods, both in the case of fundamental and technological purposes. Two different geometries are presented: a planar one using a single high-Tc film and a mesa one defined in a trilayer structure
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...
Negative conductances of Josephson junctions: Voltage fluctuations and energetics
Machura, L.; Kostur, M.; Talkner, P.; Hanggi, P.; Luczka, J.
2009-01-01
We study a resistively and capacitively shunted Josephson junction, which is driven by a combination of time-periodic and constant currents. Our investigations concern three main problems: (A) The voltage fluctuations across the junction; (B) The quality of transport expressed in terms of the P\\'eclet number; (C) The efficiency of energy transduction from external currents. These issues are discussed in different parameter regimes that lead to: (i) absolute negative conductance; (ii) negative...
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...
Breathers in Josephson junction ladders: Resonances and electromagnetic wave spectroscopy
DEFF Research Database (Denmark)
Miroshnichenko, A. E.; Flach, S.; Fistul, M.;
2001-01-01
We present a theoretical study of the resonant interaction between dynamical localized states (discrete breathers) and linear electromagnetic excitations (EE's) in Josephson junction ladders. By making use of direct numerical simulations we find that such an interaction manifests itself by resonant...
The lateral S-(S/F)-S Josephson junctions
International Nuclear Information System (INIS)
Up to now the proximity effect at the superconductor-ferromagnet (S-F) interface was mainly demonstrated by the transport properties across the S-F interface. We present the results on lateral transport along the S-F interface and its utilization as a Josephson junction. We have prepared Nb based Josephson junctions which consist of Nb micro bridges with a Pd0.95Fe0.05 or Fe strip deposited perpendicular to the bridge. The width of the ferromagnetic strip was varied between 50 and 800 nm. The critical current (IC) of the Nb-Pd0.95Fe0.05 and Nb-Fe bi-layer, respectively, is found to be significantly reduced by the proximity effect with the ferromagnet. We have studied the temperature and magnetic field (B) dependencies of the critical current. In magnetic field an interference pattern IC(B) is observed. In perpendicular magnetic field the junction exhibits IC(B) dependence similar to a Fraunhofer pattern which proves the dc Josephson effect. We also investigate the dependence of IC(B) oscillations on the orientation of the magnetic field. The control of the Josephson junction parameters is provided by third electrode connected to the F strip.
Control of chaotic patterns in a Josephson junction model
DEFF Research Database (Denmark)
Olsen, Ole Hvilsted; Samuelsen, Mogens Rugholm
The effect of an applied rf signal on the dynamics of a large-area Josephson junction is examined. The problem of controlling spatiotemporal chaotic patterns induced by the external magnetic field is addressed. Chaos control is conducted by a weak spatially distributed force. (C) 2000 Elsevier...
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
Self-field effects in Josephson junction arrays
DEFF Research Database (Denmark)
Petraglia, Antonio; Filatrella, G.; Rotoli, G.
1996-01-01
The purpose of this work is to compare the dynamics of arrays of Josephson junctions in the presence of a magnetic field in two different frameworks: the so-called XY frustrated model with no self-inductance and an approach that takes into account the self-field generated by the screening current...
Macroscopic Quantum Superposition in a Three-Josephson-Junction Loop
Wal, Caspar H. van der; Haar, A.C.J. ter; Wilhelm, F.K.; Schouten, R.N.; Harmans, C.J.P.M.; Orlando, T.P.; Lloyd, Seth; Mooij, J.E.
2001-01-01
We present microwave-spectroscopy experiments on two quantum levels of a superconducting loop with three Josephson junctions. The level separation between the ground state and first excited state shows an anti-crossing where two classical persistent-current states with opposite polarity are degenera
Fabrication and tunneling properties of niobium/lead Josephson junctions
International Nuclear Information System (INIS)
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.
Vortex dynamics in Josephson junctions arrays
International Nuclear Information System (INIS)
In this work we study the dynamics of vortices in two-dimensional overdamped Josephson Junctions Arrays (JJA) driven by dc current in a wide range of conditions varying magnetic field and temperature using experiments, numerical simulations and analytic studies.We develop the Fixed Phase method, a variation of numeric relaxation techniques in which we fix and control the phase of some islands, adjacent to the vortex center, while allowing all other phases in the system to relax.In this way we are able to pull and push the vortex uphill, as we are forcing the center of rotation of the vortex currents to be in a defined location, allowing us to calculate the potential energy of a vortex located in any arbitrary position.We use this method to study the potential energy of a vortex in a variety of situations in homogeneous and non-homogeneous JJA, such as arrays with defects, channel arrays and ratchets.We study the finite size effects in JJA by means of analytic and numerical tools.We implement the rings model, in which we replace the two-dimensional square array by a series of square, concentric, uncoupled rings. This is equivalent to disregarding the radial junctions that couple consecutive rings.In spite of its extreme simplicity, this model holds the main ingredients of the magnetic dependence of the energy.We combine this model with other terms that take into account the dependence in the position of the vortex to obtain a general expression for the potential energy of a vortex in a finite JJA with applied magnetic field.We also present an expression for the first critical field, corresponding to the value of the magnetic field in which the entrance of the first vortex becomes energetically favorable.We build and study JJA modulated to form periodic and asymmetrical potentials for the vortices, named ratchet potentials.The experimental results clearly show the existence of a rectification in the motion of vortices in these potentials.Under certain conditions we
Dynamics of three coupled long Josephson junctions
DEFF Research Database (Denmark)
Hattel, Søren A.; Grunnet-Jepsen, Anders; Samuelsen, Mogens Rugholm
1996-01-01
The dynamics of a system of three long Josephson transmission lines coupled at a common end point is investigated. We report several periodic fluxon states and trace out the corresponding zero field steps. The boundary conditions at the common point lead to a very different stability of steps for...
Kink motion in a curved Josephson junction
DEFF Research Database (Denmark)
Sørensen, Mads Peter
The sine-Gordon equation is one of the three classical nonlinear partial differential equations possessing soliton solutions in the case of one spatial dimension. Extending the sine-Gordon equation to two spatial dimensions is relevant for applications to the dynamics of large area Josephson...
Quantum noise in Josephson-junction parametric amplifiers
International Nuclear Information System (INIS)
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
Thin film hybrid Josephson junctions with Co doped Ba-122
International Nuclear Information System (INIS)
Josephson junctions are a strong tool to investigate fundamental superconducting properties, such as gap behaviour, dependencies from external fields and the order parameter symmetry. Finding secure values enables the possibility of theoretical descriptions to understand the physical processes within the new iron-based superconductors. Based on Co-doped BaFe2As2 (Ba-122) layers produced via pulsed laser deposition (PLD) on (La,Sr)(Al,Ta)O3 substrates, we manufactured superconductor-normal conductor-superconductor (S-N-S) junctions structures by using photolithography, ion beam etching as well as insulating SiO2 layers. We present working Ba-122/Au/PbIn thin film Josephson junctions with different contact areas and barrier thicknesses, their temperature dependence and response to microwave irradiation. The calculated IcRN product is in the range of a couple of microvolts.
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.
Josephson current and multiple Andreev reflections in graphene SNS junctions
Du, Xu; Skachko, Ivan; Andrei, Eva Y.
2008-05-01
The Josephson effect and superconducting proximity effect were observed in superconductor-graphene-superconductor (SGS) Josephson junctions with coherence lengths comparable to the distance between the superconducting leads. By comparing the measured gate dependence of the proximity induced subgap features (multiple Andreev reflections) and of the supercurrent to theoretical predictions, we find that the diffusive junction model yields close quantitative agreement with the results. By contrast, predictions of the ballistic SGS model are inconsistent with the data. We show that all SGS devices reported so far, our own as well as those of other groups, fall in the diffusive junction category. This is attributed to substrate induced potential fluctuations due to trapped charges and to the invasiveness of the metallic leads.
Flux flow in high-Tc Josephson junctions
DEFF Research Database (Denmark)
Filatrella, G.; Pedersen, Niels Falsig
1993-01-01
The possibility of achieving fluxon nucleation in nonhysteretic high-T(c) Josephson junctions due to the presence of inhomogeneities is investigated numerically. For a large range of parameters the I- V characteristics in presence of such discontinuities show a strong similarity with those obtained...... experimentally. The spatial inhomogeneities considered are on the scale of the Josephson penetration depth (mum). It is demonstrated that the topic is of interest for the construction of amplifiers. Thus when fluxons are generated the resulting flux flow regime proves to be much more sensitive than the uniform...
Experimental observation of subharmonic gap structures in long Josephson junctions
DEFF Research Database (Denmark)
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...
Triplet supercurrent in ferromagnetic Josephson junctions by spin injection
Mal'shukov, A. G.; Brataas, Arne
2012-09-01
We show that injecting nonequilibrium spins into the superconducting leads strongly enhances the stationary Josephson current through a superconductor-ferromagnet-superconductor junction. The resulting long-range supercurrent through a ferromagnet is carried by triplet Cooper pairs that are formed in s-wave superconductors by the combined effects of spin injection and exchange interaction. We quantify the exchange interaction in terms of Landau Fermi-liquid factors. The magnitude and direction of the long-range Josephson current can be manipulated by varying the angles of the injected polarizations with respect to the magnetization in the ferromagnet.
Vortex dynamics in Josephson ladders with II-junctions
DEFF Research Database (Denmark)
Kornev, Victor K.; Klenov, N. V.; Oboznov, V.A.; Feofanov, A.K.; Bolginov, V.V.; Ryazanov, V.V.; Pedersen, Niels Falsig
2004-01-01
Both experimental and numerical studies of a self-frustrated triangular array of pi-junctions are reported. The array of SFS Josephson junctions shows a transition to the pi-state and self-frustration with a decrease in temperature. This manifests itself in a half-period shift of the bias critical...... current versus applied magnetic field. At temperatures close to the 0-pi transition this dependence shows a doubling of its periodicity frequency that can be explained by 0-pi bistability of the SFS junctions. The change in the array behaviour with number of unit cells has been studied by means of...
Vortex dynamics in Josephson ladders with π-junctions
International Nuclear Information System (INIS)
Both experimental and numerical studies of a self-frustrated triangular array of π-junctions are reported. The array of SFS Josephson junctions shows a transition to the π-state and self-frustration with a decrease in temperature. This manifests itself in a half-period shift of the bias critical current versus applied magnetic field. At temperatures close to the 0-π transition this dependence shows a doubling of its periodicity frequency that can be explained by 0-π bistability of the SFS junctions. The change in the array behaviour with number of unit cells has been studied by means of numerical simulation
Scanning SQUID microscopy of SFS π-Josephson junction arrays
Stoutimore, M. J. A.; Oboznov, V. A.
2005-03-01
We use a Scanning SQUID Microscope to image the magnetic flux distribution in arrays of SFS (superconductor-ferromagnet-superconductor) Josephson junctions. The junctions are fabricated with barrier thickness such that they undergo a transition to a π-junction state at a temperature Tπ 2-4 K. In arrays with cells that have an odd number of π-junctions, we observe spontaneously generated magnetic flux in zero applied magnetic field. We image both fully-frustrated arrays and arrays with non-uniform frustration created by varying the number of π-junctions in the cells. By monitoring the onset of spontaneous flux as a function of temperature near Tπ,^ we estimate the uniformity of the junction critical currents.
International Nuclear Information System (INIS)
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
Studies of static and dynamic properties of multilayered (stacked) Josephson junctions
International Nuclear Information System (INIS)
The authors have studied the static I-V characteristics and vortex dynamics in stacked Nb/AlOxNb Josephson junctions. In Josephson junction stacks consisting of two junctions having identical maximum Josephson supercurrent Ic, Ic vs. H characteristics of deviating from the Fraunhofer pattern have been observed, implying that a structural phase transformation to a triangular vortex lattice occurs with increasing H. Interjunction coupling leads to splitting of the Swihart mode; which manifests itself as Fisk steps with different voltage spacings. When subjected to microwave radiation, the I-V curves of the stacked Josephson junctions exhibit new features which are absent in single junctions
Measurement of Quantum Phase-Slips in Josephson Junction Chains
Guichard, Wiebke
2011-03-01
Quantum phase-slip dynamics in Josephson junction chains could provide the basis for the realization of a new type of topologically protected qubit or for the implementation of a new current standard. I will present measurements of the effect of quantum phase-slips on the ground state of a Josephson junction chain. We can tune in situ the strength of the phase-slips. These phase-slips are the result of fluctuations induced by the finite charging energy of each junction in the chain. Our measurements demonstrate that a Josephson junction chain under phase bias constraint behaves in a collective way. I will also show evidence of coherent phase-slip interference, the so called Aharonov-Casher effect. This phenomenon is the dual of the well known Aharonov-Bohm interference. In collaboration with I.M. Pop, Institut Neel, C.N.R.S. and Universite Joseph Fourier, BP 166, 38042 Grenoble, France; I. Protopopov, L. D. Landau Institute for Theoretical Physics, Kosygin str. 2, Moscow 119334, Russia and Institut fuer Nanotechnologie, Karlsruher Institut fuer Technologie, 76021 Karlsruhe, Germany; and F. Lecocq, Z. Peng, B. Pannetier, O. Buisson, Institut Neel, C.N.R.S. and Universite Joseph Fourier. European STREP MIDAS, ANR QUANTJO.
Supercurrent reversal in Josephson junctions based on bilayer graphene flakes
Rameshti, Babak Zare; Zareyan, Malek; Moghaddam, Ali G.
2015-08-01
We investigate the Josephson effect in a bilayer graphene flake contacted by two monolayer sheets deposited by superconducting electrodes. It is found that when the electrodes are attached to the different layers of the bilayer, the Josephson current is in a π state, if the bilayer region is undoped and there is no vertical bias. Applying doping or bias to the junction reveals π -0 transitions which can be controlled by varying the temperature and the junction length. The supercurrent reversal here is very different from the ferromagnetic Josephson junctions where the spin degree of freedom plays the key role. We argue that the scattering processes accompanied by layer and sublattice index change give rise to the scattering phases, the effect of which varies with doping and bias. Such scattering phases are responsible for the π -0 transitions. On the other hand, if both of the electrodes are coupled to the same layer of the flake or the flake has AA stacking instead of common AB, the junction will be always in 0 state since the layer or sublattice index is not changed.
Energy Technology Data Exchange (ETDEWEB)
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.)
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).
Subgap Structures in High-Tc Intrinsic Josephson Junctions
Müller, Paul
1998-03-01
Due to their extremely short coherence length many high-Tc superconductors form natural superconducting multilayers. Adjacent superconducting layers are weakly coupled by the Josephson effect. As a result single crystals act intrinsically as vertical stacks of hundreds of Josephson junctions. We start by summarizing our present state of knowledge, including recent observations of Cherenkov radiation from moving fluxons (G. Hechtfischer, R. Kleiner, A.V. Ustinov, P. Müller, Phys. Rev. Lett. 79, 1365 (1997), and this conference.), and the direct measurement of the (collective) Josephson plasma frequency. We then report on pronounced structures in the current-voltage characteristics of Bi_2Sr_2CaCu_2O8 single crystals, and of Tl_2Ba_2Ca_2Cu_3O_10 thin films. These structures appear well below the superconducting gap, independent on magnetic field and temperatures up to 0.5 T_c(K. Schlenga, G. Hechtfischer, R. Kleiner, W. Walkenhorst, P. Müller, Phys. Rev. Lett. 76, 4943 (1996).). We explain these features by coupling between c-axis phonons and Josephson oscillations(Ch. Helm, Ch. Preis, F. Forsthofer, J. Keller, K. Schlenga, R. Kleiner, P. Müller, Phys. Rev. Lett. 79, 737 (1997).). C-axis lattice vibrations between adjacent superconducting layers are exited by the rf Josephson currents in the resistive state. Our results correspond well to the frequencies of longitudinal c-axis phonons.
Two coupled Josephson junctions: dc voltage controlled by biharmonic current
International Nuclear Information System (INIS)
We study transport properties of two Josephson junctions coupled by an external shunt resistance. One of the junctions (say, the first) is driven by an unbiased ac current consisting of two harmonics. The device can rectify the ac current yielding a dc voltage across the first junction. For some values of coupling strength, controlled by an external shunt resistance, a dc voltage across the second junction can be generated. By variation of system parameters such as the relative phase or frequency of two harmonics, one can conveniently manipulate both voltages with high efficiency, e.g. changing the dc voltages across the first and second junctions from positive to negative values and vice versa. (paper)
Dynamics of fractional vortices in long Josephson junctions
International Nuclear Information System (INIS)
In this thesis static and dynamic properties of fractional vortices in long Josephson junctions are investigated. Fractional vortices are circulating supercurrents similar to the well-known Josephson fluxons. Yet, they show the distinguishing property of carrying only a fraction of the magnetic flux quantum. Fractional vortices are interesting non-linear objects. They spontaneously appear and are pinned at the phase discontinuity points of so called 0-κ junctions but can be bend or flipped by external forces like bias currents or magnetic fields. 0-κ junctions and fractional vortices are generalizations of the well-known 0-π junctions and semifluxons, where not only phase jumps of pi but arbitrary values denoted by kappa are considered. By using so-called artificial 0-κ junctions that are based on standard Nb-AlOx-Nb technology the classical dynamics of fractional vortices has been investigated experimentally for the very first time. Here, half-integer zero field steps could be observed. These voltage steps on the junction's current-voltage characteristics correspond to the periodic flipping/hopping of fractional vortices. In addition, the oscillatory eigenmodes of fractional vortices were investigated. In contrast to fluxons fractional vortices have an oscillatory eigenmode with a frequency within the plasma gap. Using resonance spectroscopy the dependence of the eigenmode frequency on the flux carried by the vortex and an applied bias current was determined. (orig.)
Characteristics of the Surface-Intrinsic Josephson Junction
Institute of Scientific and Technical Information of China (English)
YANG Li; XU Wei-wei; YE Su-li; GUO Da-yuan; YOU Li-xing; WU Pei-heng
2006-01-01
During the fabrication of intrinsic Josephson junctions (IJJs) with Bi2Sr2CaCu2O8+δ(BSCCO) single crystals,the superconductivity of the surface Cu-O layer is degraded because of a deposited metal film on top of the stack.Thus,the characteristics of the surface junction consisting of the surface Cu-O double layers remarkably differ from those of the junctions deep in the stack,which will be referred to as ordinary IJJs.The electrical transport characteristics of the surface junction,such as I-V,I'c-T,and R-T,show that the critical temperature T'c of the surface junction is always lower than that of ordinary IJJs,and that the change of its critical current I'c with temperature is different from that of ordinary IIJs.Furthermore,by shunting! the surface junction resistively,we are able to observe the AC Josephson effect at 3-mm waveband.
Semiclassical Quantization of Spinning Quasiparticles in Ballistic Josephson Junctions
Konschelle, François; Bergeret, F. Sebastián; Tokatly, Ilya V.
2016-06-01
A Josephson junction made of a generic magnetic material sandwiched between two conventional superconductors is studied in the ballistic semiclassic limit. The spectrum of Andreev bound states is obtained from the single valuedness of a particle-hole spinor over closed orbits generated by electron-hole reflections at the interfaces between superconducting and normal materials. The semiclassical quantization condition is shown to depend only on the angle mismatch between initial and final spin directions along such closed trajectories. For the demonstration, an Andreev-Wilson loop in the composite position-particle-hole-spin space is constructed and shown to depend on only two parameters, namely, a magnetic phase shift and a local precession axis for the spin. The details of the Andreev-Wilson loop can be extracted via measuring the spin-resolved density of states. A Josephson junction can thus be viewed as an analog computer of closed-path-ordered exponentials.
Electron Transport Through Josephson Junction Containing a Dimeric Structure
Val'kov, V. V.; Aksenov, S. V.
2016-02-01
The dc Josephson effect in a superconductor/dimeric molecule/superconductor junction has been investigated by means of the nonequilibrium Green's function method and the Keldysh diagram technique. The application of the atomic representation has allowed to simplify considerably the computation of the supercurrent and occupation numbers and receive the general expressions which take into account all processes of the Andreev reflection in the loopless approach. It is significant that the expressions for the current and occupation numbers are valid for different multilevel structures in the Josephson junction. The sf-exchange interaction between the electron spin and the spins of the dimer leads to the suppression of the critical current due to a new set of Andreev bound states.
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
International Nuclear Information System (INIS)
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
Energy Technology Data Exchange (ETDEWEB)
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.
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.
DYNAMICAL BEHAVIOUR OF THE SUPERCURRENT IN MESOSCOPIC JOSEPHSON JUNCTIONS
Institute of Scientific and Technical Information of China (English)
YU KAI-ZHI; ZOU JIAN; SHAO BIN
2001-01-01
In this paper we use a numerical method to study the quantum effect of dynamical localization on the supercurrent in a mesoscopic Josephson junction driven by a periodically external electromagnetic field. We find that the charge is localized effectively when the ratio of the field magnitude and the field frequency equal some critical values, and in these cases the amplitude of the oscillation of the supercurrent will remain constant.
Suppression of timing errors in short overdamped Josephson junctions
Pankratov, Andrey L.; Spagnolo, Bernardo
2004-01-01
The influence of fluctuations and periodical driving on temporal characteristics of short overdamped Josephson junction is analyzed. We obtain the standard deviation of the switching time in the presence of a dichotomous driving force for arbitrary noise intensity and in the frequency range of practical interest. For sinusoidal driving the resonant activation effect has been observed. The mean switching time and its standard deviation have a minimum as a function of driving frequency. As a co...
Suspended InAs nanowire Josephson junctions assembled via dielectrophoresis
Montemurro, Domenico; Stornaiuolo, Daniela; Massarotti, Davide; Ercolani, Daniele; Sorba, Lucia; Beltram, Fabio; Tafuri, Francesco; Roddaro, Stefano
2016-01-01
We present a novel technique for the realization of suspended Josephson junctions based on InAs semiconductor nanowires. The devices are assembled using a technique of drop-casting guided by dielectrophoresis that allows to finely align the nanostructures on top of the electrodes. The proposed architecture removes the interaction between the nanowire and the substrate which is known to influence disorder and the orientation of the Rashba vector. The relevance of this approach in view of the i...
Niobium nitride Josephson junctions: Experiment and computer simulations
International Nuclear Information System (INIS)
Highly asymmetric Josephson NbN-NbN*-Nb oxide-Pb junctions have been fabricated. A prominent feature, known as a 'knee', has been observed in the energy-gap region of quasiparticle current-voltage curves. It is discussed and explained within a conventional scattering approach to the phase-coherent charge transport in a quasiballistic double-barrier S1-I1-N-I2-S2 heterostructure with an extremely great difference between the two barrier transparencies
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...
Topological order in the insulating Josephson junction array
Douçot, B.; Feigel'Man, M.V.; Ioffe, L. B.
2002-01-01
We propose a Josephson junction array which can be tuned into an unconventional insulating state by varying external magnetic field. This insulating state retains a gap to half vortices; as a consequence, such array with non-trivial global geometry exhibits a ground state degeneracy. This degeneracy is protected from the effects of external noise. We compute the gaps separating higher energy states from the degenerate ground state and we discuss experiments probing the unusual properties of t...
Measurements of quantum noise in resistively shunted Josephson junctions
International Nuclear Information System (INIS)
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
Multiple frequency generation by bunched solitons in Josephson tunnel junctions
DEFF Research Database (Denmark)
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....
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...
Phase diffusion in graphene-based Josephson junctions
Borzenets, I. V.; Coskun, U. C.; Jones, S. J.; Finkelstein, G
2011-01-01
We report on graphene-based Josephson junctions with contacts made from lead. The high transition temperature of this superconductor allows us to observe the supercurrent branch at temperatures up to $\\sim 2$ K, at which point we can detect a small, but non-zero, resistance. We attribute this resistance to the phase diffusion mechanism, which has not been yet identified in graphene. By measuring the resistance as a function of temperature and gate voltage, we can further characterize the natu...
Ballistic Josephson junctions in edge-contacted graphene
Calado, Victor E.; Goswami, Srijit; Nanda, Gaurav; Diez, Mathias; Akhmerov, Anton R.; Watanabe, Kenji; Taniguchi, Takashi; Klapwijk, Teun M.; Vandersypen, Lieven M. K.
2015-01-01
Hybrid graphene-superconductor devices have attracted much attention since the early days of graphene research. So far, these studies have been limited to the case of diffusive transport through graphene with poorly defined and modest quality graphene-superconductor interfaces, usually combined with small critical magnetic fields of the superconducting electrodes. Here we report graphene based Josephson junctions with one-dimensional edge contacts of Molybdenum Rhenium. The contacts exhibit a...
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.
Planar intrinsic Josephson junctions fabricated on Bi-2212 LPE films
Yasuda, Takashi; Kawae, Takeshi; Yamashita, Tsutomu; Taka, Chihiro; Nishida, Akihiko; Takano, Shuzo
2003-05-01
Planar design of intrinsic Josephson junctions (IJJs) is studied using Bi2Sr2CaCu2Ox (Bi-2212) films prepared by liquid phase epitaxy. Step-type IJJ stacks fabricated on step-patterned MgO substrates exhibit multibranched current-voltage characteristics inherent in Bi-2212 single crystals. This behavior is found to be limited to films on small-angle steps, suggesting the incorporation of defects near the steep steps of substrates.
Resonantly phase-matched Josephson junction traveling wave parametric amplifier
O'Brien, Kevin; Macklin, Chris; Siddiqi, Irfan; Zhang, Xiang
2014-01-01
We develop a technique to overcome phase-mismatch in Josephson-junction traveling wave parametric amplifiers in order to achieve high gain over a broad bandwidth. Using "resonant phase matching," we design a compact superconducting device consisting of a transmission line with subwavelength resonant inclusions that simultaneously achieves a gain of 20 dB, an instantaneous bandwidth of 3 GHz, and a saturation power of -98 dBm. Such an amplifier is well-suited to cryogenic broadband microwave m...
Quantum phases in intrinsic Josephson junctions: Quantum magnetism analogy
Energy Technology Data Exchange (ETDEWEB)
Machida, Masahiko, E-mail: machida.masahiko@jaea.go.jp [CCSE, Japan Atomic Energy 6-9-3 Agency, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8587 (Japan); Kobayashi, Keita [CCSE, Japan Atomic Energy 6-9-3 Agency, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8587 (Japan); Koyama, Tomio [IMR, Tohouku University, 2-1-1 Katahira Aoba-ku, Sendai 980-0072 (Japan)
2013-08-15
Highlights: ► Quantum phases in intrinsic Josephson junctions are explored via magnetism analogy. ► The magnetism analogy is available when the capacitive coupling dominates. ► The effective Hamiltonian of the phase is equivalent with 1-D interacting spin model. ► The correspondent model is that of 1-D ferromagnetically-interacting spins. ► The magnetism analogy clarifies synchronous features in quantum phase dynamics. -- Abstract: We explore quantum phases in intrinsic Josephson junction (IJJ) stacks, whose in-plane area is so small that the capacitive coupling has a dominant role in the superconducting phase dynamics. In such cases, the effective Hamiltonian for the superconducting phase can be mapped onto that of one-dimensional ferromagnetically-interacting spin model, whose spin length S depends on the magnitude of the on-site Coulomb repulsion. The ferromagnetic model for IJJ’s prefers synchronized quantum features in contrast to the antiferromagnetically-interacting model in the conventional Josephson junction arrays.
Three-dimensional Josephson-junction arrays: Static magnetic response
International Nuclear Information System (INIS)
In this work we present a simple three-dimensional Josephson-junction array model: a cube with twelve junctions, one on each edge. The low-field magnetic response of the system is studied numerically for arbitrary directions of the applied field. In this model the magnetic energy of the circulating currents is taken into account by introducing an effective mutual inductance matrix. The lower threshold field for flux penetration is determined in a closed analytic form for field directions perpendicular to one cube side. copyright 1998 The American Physical Society
Nonlocality in mesoscopic Josephson junctions with strip geometry
Ledermann, Urs; Fauchere, Alban L.; Blatter, Gianni
1999-01-01
We study the current in a clean superconductor-normal-metal-superconductor junction of length d and width w in the presence of an applied magnetic field H. We show that both the geometrical pattern of the current density and the critical current as a function of the total flux in the junction, depend on the ratio of the Josephson vortex distance a_0 and the range r of the nonlocal electrodynamics. In particular, the critical current has the periodicity of the superconducting flux quantum only...
Manifestation of resonance-related chaos in coupled Josephson junctions
International Nuclear Information System (INIS)
Manifestation of chaos in the temporal dependence of the electric charge is demonstrated through the calculation of the maximal Lyapunov exponent, phase–charge and charge–charge Lissajous diagrams and correlation functions. It is found that the number of junctions in the stack strongly influences the fine structure in the current–voltage characteristics and a strong proximity effect results from the nonperiodic boundary conditions. The observed resonance-related chaos exhibits intermittency. The criteria for a breakpoint region with no chaos are obtained. Such criteria could clarify recent experimental observations of variations in the power output from intrinsic Josephson junctions in high temperature superconductors.
Single intrinsic Josephson junction with double-sided fabrication technique
You, L. X.; Torstensson, M.; Yurgens, A.; Winkler, D.; Lin, C. T.; Liang, B.
2006-05-01
We make stacks of intrinsic Josephson junctions (IJJs) embedded in the bulk of very thin (d⩽100nm) Bi2Sr2CaCu2O8+x single crystals. By precisely controlling the etching depth during the double-sided fabrication process, the stacks can be reproducibly tailor-made to be of any microscopic height (0-9nmIJJ (0-6), including the important case of a single junction. We discuss reproducible gaplike features in the current-voltage characteristics of the samples at high bias.
Spin-triplet supercurrent in planar geometry ferromagnetic Josephson junctions
Martinez, William M.; Pratt, W. P., Jr.; Birge, Norman O.
2013-03-01
The spin-triplet supercurrent in ferromagnetic Josephson junctions is obtained by surrounding the central ferromagnet with noncollinear ferromagnetic layers, F'. In metallic ferromagnets, the long-range nature of the spin-triplet supercurrent has only been tested to lengths of a few tens of nm. In this work, we are fabricating and measuring S/F'/F/F'/S junctions where the central F layer has a lateral geometry with lengths up to a few hundred nm. We will report on our recent progress. Supported by the DOE under grant DE-FG-02-06ER46341.
Interference pattern of a long diffusive Josephson junction
Montambaux, Gilles
2007-01-01
We calculate the modulation by a magnetic field of the critical current of a long disordered Josephson junction in the diffusive limit, i.e. when the dimensions of the junction are larger that the elastic mean free path, and when the length $L$ is much larger than the width $w$. Due to the averaging of the gauge invariant phase factor over diffusive trajectories, the well-known oscillations of the Fraunhofer pattern are smoothed out and replaced by an exponential decay at large field. The pre...
Q factor and resonance amplitude of Josephson tunnel junctions
International Nuclear Information System (INIS)
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
Thermally assisted vortex motion in intrinsic Josephson junctions
Irie, A.; Oya, G.
2008-02-01
The vortex dynamics in intrinsic Josephson junctions (IJJs) at finite temperatures has been investigated numerically by taking into account the thermal fluctuations. Our simulations based on the perturbed, coupled sine-Gordon model successfully reproduce the experimental results associated with the Josephson-vortex flow resistance (JVFR) at low bias currents. Depending on the junction length, bias current, and temperature, the JVFR oscillation is changed from the period of half flux quantum per junction to the period of one flux quantum per junction. It is shown that the oscillation is essentially due to the field dependence of the critical current. At currents slightly exceeding the critical current the stationary vortex lattice structure becomes unstable and an irregular vortex flow can be induced by thermal fluctuations in different junctions. Our simulation results strongly suggest that the triangular lattice of vorticies in the dynamical state is more stable rather than the rectangular one even in a submicrometer IJJ stack when IJJs are biased at a low current.
Spin and charge transport in hybrid triplet Josephson junctions
International Nuclear Information System (INIS)
We report a theoretical study on the spin and charge transport in hybrid triplet Josephson junctions, of which the triplet pair potentials could have both different orbital symmetries and spin states. Based on a lattice model and a Hamiltonian method, we find that the spin/charge supercurrent is proportional to sin2ψ with ψ being the macroscopic superconducting phase, coming from the second-order Josephson effect, when the orbital symmetries of pair potentials in the two triplet superconductors are orthogonal to each other. A dissipationless transverse spin current is also found flowing at the interface of the junction and its polarization points along the cross-product of two d vectors, which arises from the combined effect of the orthogonal orbital symmetries and misalignment of d vectors. In a special hybrid junction, where the zero-energy states are absent at the interface of the junction, there is no net spin supercurrent flowing through the junction although two d vectors can be perpendicular to each other, whereas a mode-resolved spin supercurrent is flowing in the system instead.
International Nuclear Information System (INIS)
A two-dimensional NXN array of coupled Josephson junctions, each of size tau0 and Josephson length lambdasub(JO)>>tau0, is shown to exhibit macroscopic weak superconductivity. The Josephson phase coherence here extends across the array, vanishing discontinuously at the Kosterlitz-Thouless transition temperature. The transverse size Ntau0 must be smaller than a few times the effective Josephson screening length lambdasub(J)sup(eff) proportional to lambdasub(JO), for a sharp transition to be seen. (author)
Yokoyama, Takehito
2011-01-01
We investigate transverse charge and spin dc Josephson current in superconductor/ferromagnet/superconductor junction where the ferromagnet has inhomogeneous magnetic structure. The transverse Josephson effect arises from non-trivial structure of the magnetization. The magnetic structure manifested in the transverse charge Josephson effect is essentially different from that discussed in the context of anomalous Hall effect, reflecting the disspationless nature of Josephson current. Possible ca...
Manipulating Josephson junctions in thin-films by nearby vortices
International Nuclear Information System (INIS)
Highlights: • Vortex located in a bank of a planar Josephson junction changes its character. • Vortex located at some discreet positions in thin strip bank suppresses to zero the zero-field current. • The number of these positions is equal to the number of vortices trapped. • Critical current-field patterns are strongly affected by the vortex position. - Abstract: It is shown that a vortex trapped in one of the banks of a planar edge-type Josephson junction in a narrow thin-film superconducting strip can change drastically the dependence of the junction critical current on the applied field, Ic(H). When the vortex is placed at certain discrete positions in the strip middle, the pattern Ic(H) has zero at H=0 instead of the traditional maximum of ‘0-type’ junctions. The number of these positions is equal to the number of vortices trapped at the same location. When the junction–vortex separation exceeds ∼W, the strip width, Ic(H) is no longer sensitive to the vortex presence. The same is true for any separation if the vortex approaches the strip edges
High reliability Pb-alloy Josephson junctions for integrated circuits
International Nuclear Information System (INIS)
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.)
Gürlich, C.; Scharinger, S.; Weides, M.; Kohlstedt, H.; Mints, R. G.; Goldobin, E.; Koelle, D.; Kleiner, R.
2009-01-01
Josephson junctions with ferromagnetic barrier can have positive or negative critical current depending on the thickness $d_F$ of the ferromagnetic layer. Accordingly, the Josephson phase in the ground state is equal to 0 (a conventional or 0 junction) or to $\\pi$ ($\\pi$ junction). When 0 and $\\pi$ segments are joined to form a "0-$\\pi$ junction", spontaneous supercurrents around the 0-$\\pi$ boundary can appear. Here we report on the visualization of supercurrents in superconductor-insulator-...
Gürlich, C.; Scharinger, S.; Weides, M.; Kohlstedt, H.; Mints, R. G.; Goldobin, E.; Koelle, D.; Kleiner, R.
2010-01-01
Josephson junctions with ferromagnetic barrier can have positive or negative critical current depending on the thickness d(F) of the ferromagnetic layer. Accordingly, the Josephson phase in the ground state is equal to 0 (a conventional or 0 junction) or to pi (pi junction). When 0 and pi segments are joined to form a "0-pi junction," spontaneous supercurrents around the 0-pi boundary can appear. Here we report on the visualization of supercurrents in superconductor-insulator-ferromagnet-supe...
Zueco D.; Mazo J.J.; Solano E.; Garcia-Ripoll J.J.
2012-01-01
We study different architectures for a photonic crystal in the microwave regime based on superconducting transmission lines interrupted by Josephson junctions, both in one and two dimensions. A study of the scattering properties of a single junction in the line shows that the junction behaves as a perfect mirror when the photon frequency matches the Josephson plasma frequency. We generalize our calculations to periodic arrangements of junctions, demonstrating that they can be used for tunable...
Influence of noise and near-resonant perturbations on bifurcations in Josephson junctions
DEFF Research Database (Denmark)
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...
Two-particle structures in high quality Nb/AlOx/Nb Josephson tunnel junctions
International Nuclear Information System (INIS)
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.)
High-Tc SNS Junctions: A New Generation of Proximity-Coupled Josephson Devices
Kleinsasser, A. W.
1997-01-01
This paper reviews this evolution of proximity - coupled Josephson jucntion from the early investigations on low temperature superconductor-normal -superconductor junctions through the introduction of hybrid superconductor-semiconductor devices and the resulting interest in mesoscopic Josephson junctions, to the recent development of high temperature devices.
Institute of Scientific and Technical Information of China (English)
Zhan You-Bang
2004-01-01
We have investigated the reduced fluctuation properties in a mesoscopic Josephson junction with the squeezed state at a finite temperature. It is shown that the fluctuations increase with increasing temperature and the mesoscopic Josephson junction subsystem can exhibit squeezing behaviour at an appropriately low temperature.
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
Phase dynamics of low critical current density YBCO Josephson junctions
International Nuclear Information System (INIS)
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
Tunable ground states in helical p-wave Josephson junctions
Cheng, Qiang; Zhang, Kunhua; Yu, Dongyang; Chen, Chongju; Zhang, Yinhan; Jin, Biao
2016-07-01
We study new types of Josephson junctions composed of helical p-wave superconductors with {k}x\\hat{x}+/- {k}y\\hat{y} and {k}y\\hat{x}+/- {k}x\\hat{y}-pairing symmetries using quasi-classical Green’s functions with generalized Riccati parametrization. The junctions can host rich ground states: π phase, 0 + π phase, φ 0 phase and φ phase. The phase transition can be tuned by rotating the magnetization in the ferromagnetic interface. We present the phase diagrams in the parameter space formed by the orientation of the magnetization or by the magnitude of the interfacial potentials. The selection rules for the lowest order current which are responsible for the formation of the rich phases are summarized from the current-phase relations based on the numerical calculation. We construct a Ginzburg–Landau type of free energy for the junctions with d-vectors and the magnetization, which not only reveals the interaction forms of spin-triplet superconductivity and ferromagnetism, but can also directly lead to the selection rules. In addition, the energies of the Andreev bound states and the novel symmetries in the current-phase relations are also investigated. Our results are helpful both in the prediction of novel Josephson phases and in the design of quantum circuits.
International Nuclear Information System (INIS)
Superconductor/normal conductor/superconductor (SNS) Josephson junction series arrays are the subject of research for the realization of a Josephson arbitrary waveform synthesizer (JAWS) based on pulse-driven Josephson junctions. Lumped arrays of SNS Josephson junctions are investigated for this application at the Physikalisch-Technische Bundesanstalt (PTB). The series arrays consisting of Nb/HfTi/Nb SNS junctions are embedded in the center line of a coplanar waveguide transmission line. To increase the ac output voltage, the Josephson junction series array is designed as a meander-like structure. A broadband response of the arrays is required for the complex pulse operation of the JAWS. The arrays are investigated by dc measurements and for test purposes under continuous microwave irradiation at different frequencies. Flat Shapiro steps were measured for meander-like series arrays with 21 parallel lines containing up to 10 752 junctions. A sine wave with a frequency of 2.5 kHz and a peak voltage of 214 mVPeak was synthesized under pulse mode operation
Resonant Phase Matching of Josephson Junction Traveling Wave Parametric Amplifiers
O'Brien, Kevin; Macklin, Chris; Siddiqi, Irfan; Zhang, Xiang
2014-10-01
We propose a technique to overcome phase mismatch in Josephson-junction traveling wave parametric amplifiers in order to achieve high gain over a broad bandwidth. Using "resonant phase matching," we design a compact superconducting device consisting of a transmission line with subwavelength resonant inclusions that simultaneously achieves a gain of 20 dB, an instantaneous bandwidth of 3 GHz, and a saturation power of -98 dBm. Such an amplifier is well suited to cryogenic broadband microwave measurements such as the multiplexed readout of quantum coherent circuits based on superconducting, semiconducting, or nanomechanical elements, as well as traditional astronomical detectors.
Critical dynamics and plastic flow in disordered Josephson junction arrays
International Nuclear Information System (INIS)
We present numerical simulations of Josephson junction arrays with positional disorder. We study their IV characteristics and vortex dynamics as a function of disorder. We find that above the critical current ic there is a plastic flow of vortices and antivortices through channels, characterized by strong fluctuations of the total vorticity. For large currents there is a crossover to homogeneous flow without vortex fluctuations. We also study the dynamical critical behaviour close to ic in the gauge glass mode, calculating critical exponents for the voltage onset and voltage fluctuations. (author). 20 refs, 3 figs
HTS ion damage Josephson junction technology for SQUID arrays
International Nuclear Information System (INIS)
The high temperature superconducting (HTS) Josephson Junction (JJ) ion damage technology we are developing is well suited for making large SQUID arrays. We have studied arrays of similar SQUIDs together with large SQIFs (Superconducting Quantum Interference Filter) with 2000 SQUIDs of different loop areas. Magnetic field sensitivity has been measured in both types of devices as a function of bias current and temperature. The effects of the barrier thickness (from 20 to 80 nm) and JJ length (2 or 5 μm) on characteristics have been investigated.
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...
Phase Diffusion in Graphene-Based Josephson Junctions
Borzenets, I. V.; Coskun, U. C.; Jones, S. J.; Finkelstein, G.
2011-09-01
We report on graphene-based Josephson junctions with contacts made from lead. The high transition temperature of this superconductor allows us to observe the supercurrent branch at temperatures up to ˜2K, at which point we can detect a small, but nonzero, resistance. We attribute this resistance to the phase diffusion mechanism, which has not been yet identified in graphene. By measuring the resistance as a function of temperature and gate voltage, we can further characterize the nature of the electromagnetic environment and dissipation in our samples.
Perturbed period-doubling bifurcation. II. Experiments on Josephson junctions
DEFF Research Database (Denmark)
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....
Resonant phase matching of Josephson junction traveling wave parametric amplifiers.
O'Brien, Kevin; Macklin, Chris; Siddiqi, Irfan; Zhang, Xiang
2014-10-10
We propose a technique to overcome phase mismatch in Josephson-junction traveling wave parametric amplifiers in order to achieve high gain over a broad bandwidth. Using "resonant phase matching," we design a compact superconducting device consisting of a transmission line with subwavelength resonant inclusions that simultaneously achieves a gain of 20 dB, an instantaneous bandwidth of 3 GHz, and a saturation power of -98 dBm. Such an amplifier is well suited to cryogenic broadband microwave measurements such as the multiplexed readout of quantum coherent circuits based on superconducting, semiconducting, or nanomechanical elements, as well as traditional astronomical detectors. PMID:25375734
An influence of the curvature on the kink dynamics in the spherical Josephson junction
Directory of Open Access Journals (Sweden)
T. Dobrowolski
2009-10-01
Full Text Available area Josephson junction.Design/methodology/approach: The effective Lagrangian method is used in order to obtain the dynamics of the sine-Gordon kink on a curved manifold.Findings: The main finding of this article is an effective potential that describes the influence of the curvature on the kink motion in the spherical Josephson junction.Research limitations/implications: The paper is limited to the description of the dynamics of kinks that move with non relativistic speeds in narrow Josephson junctions.Practical implications: It seems that junctions with appropriate geometry will find applications in future electronic devices. It is expected that curved Josephson junctions can be used in order to store a binary data.Originality/value: The main idea of the paper is to use a Riemann geometry in order to describe the influence of the curvature on the kink motion in the spherical junction.
Theory of phase dynamics in intrinsic Josephson junctions with multigap superconducting layers
International Nuclear Information System (INIS)
We study intrinsic Josephson junction stacks with multigap superconductors. The theory predicts this system has two longitudinal collective excitations. Their remarkable properties are illustrated via linear analyses. We reveal that the electric or magnetic imbalance induces their mixing effects. We construct a theory of dynamical behavior in intrinsic Josephson junction stacks with multigap superconducting layers. The theory predicts the existence of two kinds of phase modes, one of which is the Josephson-plasma mode and other of which is the Leggett's mode. We discuss a cooperative phenomena induced by inter-band Josephson coupling in addition to capacitive and inductive couplings between the superconducting layers.
Theory of phase dynamics in intrinsic Josephson junctions with multigap superconducting layers
Energy Technology Data Exchange (ETDEWEB)
Ota, Y., E-mail: yota@alice.math.kindai.ac.jp [CCSE, Japan Atomic Energy Agency, 6-9-3 Higashi-Ueno, Taito-ku, Tokyo 110-0015 (Japan)] [CREST (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Machida, M. [CCSE, Japan Atomic Energy Agency, 6-9-3 Higashi-Ueno, Taito-ku, Tokyo 110-0015 (Japan)] [CREST (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)] [JST-TRIP, 5 Sanbancho Chiyoda-ku, Tokyo 102-0075 (Japan); Koyama, T. [Institute for Materials Research, Tohoku University, 2-1-1 Katahira Aoba-ku, Sendai 980-8577 (Japan)] [CREST (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)
2011-11-15
We study intrinsic Josephson junction stacks with multigap superconductors. The theory predicts this system has two longitudinal collective excitations. Their remarkable properties are illustrated via linear analyses. We reveal that the electric or magnetic imbalance induces their mixing effects. We construct a theory of dynamical behavior in intrinsic Josephson junction stacks with multigap superconducting layers. The theory predicts the existence of two kinds of phase modes, one of which is the Josephson-plasma mode and other of which is the Leggett's mode. We discuss a cooperative phenomena induced by inter-band Josephson coupling in addition to capacitive and inductive couplings between the superconducting layers.
Josephson effect in SIFS junctions at arbitrary scattering
International Nuclear Information System (INIS)
Full text: The interplay between dirty and clean limits in Superconductor-Ferromagnet-Superconductor (SFS) Josephson junctions is a subject of intensive theoretical studies. SIFS junctions, containing an additional insulator (I) barrier are interesting as potential logic elements in superconducting circuits, since their critical current Ic can be tuned over a wide range, still keeping a high IcRN product, where RN is the normal resistance of the junction. They are also a convenient model system for a comparative study of the 0-π transitions for arbitrary relations between characteristic lengths of the F-layer: the layer thickness d, the mean free path l, the magnetic length ξH=vF/2H, and the nonmagnetic coherence length ξ0=vF/2πT, where vF is the Fermi velocity, H is the exchange magnetic energy, and T is the temperature. The spatial variations of the order parameter are described by the complex coherent length in the ferromagnet ξF-1 = ξ1-1+ iξ2-1. It is well known, that in the dirty limit (l1,2) described by the Usadel equations both ξ12= ξ22= vFl/3H. In this work the spatial distribution of the anomalous Green's functions and the Josephson current in the SIFS junction are calculated. The linearized Eilenberger equations are solved together with the Zaitsev boundary conditions. This allows comparing the dirty and the clean limits, investigating a moderate disorder, and establishing the applicability limits of the Usadel equations for such structures. We demonstrate that for an arbitrary relation between l, ξH, and d the spatial distribution of the anomalous Green's function can be approximated by a single exponent with reasonable accuracy, and we find its effective decay length and oscillation period for several values of ξH, l and d. The role of different types of the FS interface is analyzed. The applicability range of the Usadel equation is established. The results of calculations have been applied to the interpretation of experimental data obtained
Computer simulations of the anisotropic Josephson junction arrays
International Nuclear Information System (INIS)
Using complementary methods, we numerically investigate the anisotropic Josephson junction arrays (AJJAs). For various anisotropic strengths (λ), the Monte Carlo simulation gives a precise measurement of specific heat, magnetization, and magnetic susceptibility; while the resistively shunted-junction dynamical simulation produces the current-voltage characteristics. The critical temperatures obtained from the two approaches are well consistent with each other. We find that, except for the anisotropic limit (λ=0), the quasi-long-range order is always established at a finite temperature. Further, the algebraically decaying spin-spin correlations in the low-temperature region are analyzed in detail. Finally, the full phase diagram of the AJJAs, which sheds some lights to the crossover of the XY model from one dimension to two, is constructed. These predictions are to be confronted with future experiments.
Computer simulations of the anisotropic Josephson junction arrays
Energy Technology Data Exchange (ETDEWEB)
Lv Jianping, E-mail: phys.lv@gmail.com [Department of Physics, China University of Mining and Technology, Xuzhou 221116 (China); Zhu Shujing [Department of Physics, Zhejiang University, Hangzhou 310027 (China)
2012-12-15
Using complementary methods, we numerically investigate the anisotropic Josephson junction arrays (AJJAs). For various anisotropic strengths ({lambda}), the Monte Carlo simulation gives a precise measurement of specific heat, magnetization, and magnetic susceptibility; while the resistively shunted-junction dynamical simulation produces the current-voltage characteristics. The critical temperatures obtained from the two approaches are well consistent with each other. We find that, except for the anisotropic limit ({lambda}=0), the quasi-long-range order is always established at a finite temperature. Further, the algebraically decaying spin-spin correlations in the low-temperature region are analyzed in detail. Finally, the full phase diagram of the AJJAs, which sheds some lights to the crossover of the XY model from one dimension to two, is constructed. These predictions are to be confronted with future experiments.
Dispersive Thermometry with a Josephson Junction Coupled to a Resonator
Saira, O.-P.; Zgirski, M.; Viisanen, K. L.; Golubev, D. S.; Pekola, J. P.
2016-08-01
We embed a small Josephson junction in a microwave resonator that allows simultaneous dc biasing and dispersive readout. Thermal fluctuations drive the junction into phase diffusion and induce a temperature-dependent shift in the resonance frequency. By sensing the thermal noise of a remote resistor in this manner, we demonstrate primary thermometry in the range of 300 mK to below 100 mK, and high-bandwidth (7.5 MHz) operation with a noise-equivalent temperature of better than 10 μ K /√{Hz } . At a finite bias voltage close to a Fiske resonance, amplification of the microwave probe signal is observed. We develop an accurate theoretical model of our device based on the theory of dynamical Coulomb blockade.
Characterization of escape times of Josephson Junctions for signal detection
Addesso, Paolo; Pierro, Vincenzo
2011-01-01
The measurement of the escape time of a Josephson junction might be used to detect the presence of a sinusoidal signal embedded in noise when standard signal processing tools can be prohibitive. We show that the prescriptions for the experimental set-up and some physical behaviors depend on the detection strategy. More specifically, by exploiting the sample mean of escape times to perform detection, two resonant regions are identified. At low frequencies there is a stochastic resonance/activation phenomenon, while near the plasma frequency a geometric resonance appears. The naive sample mean detector is outperformed, in terms of error probability, by the optimal likelihood ratio test. The latter exhibits only geometric resonance, showing monotonically increasing performance as the bias current approaches the junction critical current. In this regime the escape times are vanishingly small and therefore performance are essentially limited by measurement electronics. The behavior of the likelihood ratio and samp...
Soliton oscillations in Josephson junctions and deoxyribonucleic acid
International Nuclear Information System (INIS)
This paper discusses two seemingly disparate subjects: i) anharmonic oscillations on finite segments of the Josephson transmission line (JTL) which are governed by a sine-Gordon equation (SGE) and ii) anharmonic oscillations on finite segments of deocyribonucleic acid (DNA) which are governed by a Boussinesq equation (BE). In the SGE description of JTL, phi is the pair phase difference across the junction, ω/sub o/ is the junction plasma frequency, and c-bar is a velocity that is a few percent of the velocity of light. In the SGE description of DNA, Q is longitudinal strain, c/sup --/ is the velocity of longitudinal acoustic waves, ξ is a dispersive parameter and δ is an anharmonic parameter
Flicker (1/f) noise in Josephson tunnel junctions
International Nuclear Information System (INIS)
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
Ballistic Josephson junctions in edge-contacted graphene
Calado, V. E.; Goswami, S.; Nanda, G.; Diez, M.; Akhmerov, A. R.; Watanabe, K.; Taniguchi, T.; Klapwijk, T. M.; Vandersypen, L. M. K.
2015-09-01
Hybrid graphene-superconductor devices have attracted much attention since the early days of graphene research. So far, these studies have been limited to the case of diffusive transport through graphene with poorly defined and modest-quality graphene/superconductor interfaces, usually combined with small critical magnetic fields of the superconducting electrodes. Here, we report graphene-based Josephson junctions with one-dimensional edge contacts of molybdenum rhenium. The contacts exhibit a well-defined, transparent interface to the graphene, have a critical magnetic field of 8 T at 4 K, and the graphene has a high quality due to its encapsulation in hexagonal boron nitride. This allows us to study and exploit graphene Josephson junctions in a new regime, characterized by ballistic transport. We find that the critical current oscillates with the carrier density due to phase-coherent interference of the electrons and holes that carry the supercurrent caused by the formation of a Fabry-Pérot cavity. Furthermore, relatively large supercurrents are observed over unprecedented long distances of up to 1.5 μm. Finally, in the quantum Hall regime we observe broken symmetry states while the contacts remain superconducting. These achievements open up new avenues to exploit the Dirac nature of graphene in interaction with the superconducting state.
Generation and Detection of THz Radiation Using Intrinsic Josephson Junctions
Irie, Akinobu; Oikawa, Dai; Oya, Gin-ichiro
We present the generation and detection of terahertz radiation using intrinsic Josephson junctions (IJJs) in Bi2Sr2CaCu2Oy single crystals. This approach allows us to detect THz radiation from large stacks consisting of a few hundred intrinsic Josephson junctions. The lateral dimensions of the fabricated IJJ oscillator mesa range from 290×50 to 290×90 μm2 and the number of IJJs which constitute the mesas is between 100 and 450, while the small mesa with the lateral dimensions of 5 × 5 μm2 is used as the high sensitive THz detector. The largest emission is always observed when the oscillator is biased at the negative resistance region of the current-voltage characteristics. We find that the emission frequency cor-responds to the second harmonics of the in-phase cavity resonance mode. This is consistent with the emission condition of the case of thick IJJ stacks reported previously.
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.
Spin-triplet supercurrent in Co-based Josephson junctions
International Nuclear Information System (INIS)
In the past year several groups have reported experimental evidence for spin-triplet supercurrents in Josephson junctions containing strong ferromagnetic materials. In this paper we present several new experimental results that follow up on our previous work. We study Josephson junctions of the form S/X/N/SAF/N/X/S, where S is a superconductor (Nb), N is a normal metal, SAF is a synthetic antiferromagnet of the form Co/Ru/Co and X is an ferromagnetic layer necessary to induce spin-triplet correlations in the structure. Our work is distinguished by the fact that the generation of spin-triplet correlations is tuned by the type and thickness of the X layers. The most important new result reported here is the discovery that a conventional, strong ferromagnetic material, Ni, performs well as the X layer, if it is sufficiently thin. This discovery rules out our earlier hypothesis that out-of-plane magnetocrystalline anisotropy is an important attribute of the X layers. These results suggest that the spin-triplet correlations are most likely induced by noncollinear magnetization between the X layers and adjacent Co layers.
Spin-triplet supercurrent in Co-based Josephson junctions
Energy Technology Data Exchange (ETDEWEB)
Khasawneh, Mazin A; Khaire, Trupti S; Klose, Carolin; Pratt, William P Jr; Birge, Norman O, E-mail: birge@pa.msu.edu [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-2320 (United States)
2011-02-15
In the past year several groups have reported experimental evidence for spin-triplet supercurrents in Josephson junctions containing strong ferromagnetic materials. In this paper we present several new experimental results that follow up on our previous work. We study Josephson junctions of the form S/X/N/SAF/N/X/S, where S is a superconductor (Nb), N is a normal metal, SAF is a synthetic antiferromagnet of the form Co/Ru/Co and X is an ferromagnetic layer necessary to induce spin-triplet correlations in the structure. Our work is distinguished by the fact that the generation of spin-triplet correlations is tuned by the type and thickness of the X layers. The most important new result reported here is the discovery that a conventional, strong ferromagnetic material, Ni, performs well as the X layer, if it is sufficiently thin. This discovery rules out our earlier hypothesis that out-of-plane magnetocrystalline anisotropy is an important attribute of the X layers. These results suggest that the spin-triplet correlations are most likely induced by noncollinear magnetization between the X layers and adjacent Co layers.
Spin-triplet supercurrent in Co-based Josephson junctions
Khasawneh, Mazin A.; Khaire, Trupti S.; Klose, Carolin; Pratt, William P., Jr.; Birge, Norman O.
2011-02-01
In the past year several groups have reported experimental evidence for spin-triplet supercurrents in Josephson junctions containing strong ferromagnetic materials. In this paper we present several new experimental results that follow up on our previous work. We study Josephson junctions of the form S/X/N/SAF/N/X/S, where S is a superconductor (Nb), N is a normal metal, SAF is a synthetic antiferromagnet of the form Co/Ru/Co and X is an ferromagnetic layer necessary to induce spin-triplet correlations in the structure. Our work is distinguished by the fact that the generation of spin-triplet correlations is tuned by the type and thickness of the X layers. The most important new result reported here is the discovery that a conventional, strong ferromagnetic material, Ni, performs well as the X layer, if it is sufficiently thin. This discovery rules out our earlier hypothesis that out-of-plane magnetocrystalline anisotropy is an important attribute of the X layers. These results suggest that the spin-triplet correlations are most likely induced by noncollinear magnetization between the X layers and adjacent Co layers.
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...
Guarcello, Claudio; Valenti, Davide; Spagnolo, Bernardo
2014-01-01
In this work we study by numerical methods the phase dynamics in ballistic graphene-based short Josephson junctions. The supercurrent through a graphene junction shows a non-sinusoidal phase-dependence, unlike a conventional junction ruled by the well-known d.c. Josephson relation. A superconductor-graphene-superconductor system exhibits superconductive quantum metastable states similar to those present in normal current-biased JJs. We explore the effects of thermal and correlated fluctuation...
International Nuclear Information System (INIS)
This paper theoretically studies Josephson spin current through triplet superconductor/ferromagnet/triplet superconductor junctions. At the ferromagnet/superconductor interfaces, the ferromagnetic scattering potential gives rise to coupling between the Andreev bound states and lifts their spin degeneracy. These spin-split Andreev states carry the Josephson spin current through the junctions. The generated spin supercurrent can be controlled by the magnetization of a ferromagnetic thin layer and bias voltage across the junctions. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Black-Schaffer, Annica M.; Doniach, Sebastian
2008-01-01
Using the self-consistent tight-binding Bogoliubov-de Gennes formalism we have studied the effect of nearest neighbor spin-singlet bond (SB) correlations on Josephson coupling and proximity effect in graphene SNS Josephson junctions with conventional s-wave superconducting contacts. Despite the s-wave superconducting state in the contacts, the SB pairing state inside the junction has d-wave symmetry and clean, sharp interface junctions resemble a 'bulk-meets-bulk' situation with very little i...
Josephson oscillation linewidth of ion-irradiated YBa2Cu3O7 junctions
Sharafiev, A.; Malnou, M.; Feuillet-Palma, C.; Ulysse, C.; Febvre, P.; Lesueur, J.; Bergeal, N.
2016-07-01
We report on the noise properties of ion-irradiated YBa2Cu3O7 Josephson junctions. This work aims at investigating the linewidth of the Josephson oscillation with a detector response experiment at ≃132 GHz. Experimental results are compared with a simple analytical model based on the Likharev–Semenov equation and the de Gennes dirty limit approximation. We show that the main source of low-frequency fluctuations in these junctions is the broadband Johnson noise and that the excess ≤ft(\\tfrac{1}{f}\\right) noise contribution does not prevail in the temperature range of interest, as reported in some other types of high-T c superconducting Josephson junctions. Finally, we discuss the interest of ion-irradiated junctions to implement frequency-tunable oscillators consisting of synchronized arrays of Josephson junctions.
Simultaneous quasiparticle and Josephson tunneling in BSCCO-2212 break junctions.
Energy Technology Data Exchange (ETDEWEB)
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
International Nuclear Information System (INIS)
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
Theory of phase dynamics in intrinsic Josephson junctions with multigap superconducting layers
Ota, Y.; Machida, M.; Koyama, T.
2011-11-01
We construct a theory of dynamical behavior in intrinsic Josephson junction stacks with multigap superconducting layers. The theory predicts the existence of two kinds of phase modes, one of which is the Josephson-plasma mode and other of which is the Leggett’s mode. We discuss a cooperative phenomena induced by inter-band Josephson coupling in addition to capacitive and inductive couplings between the superconducting layers.
Repulsive fluxons in a stack of Josephson junctions perturbed by a cavity
DEFF Research Database (Denmark)
Madsen, Søren; Pedersen, Niels Falsig; Christiansen, Peter Leth
The BSCCO type intrinsic Josephson junction has been modeled as a stack of inductively coupled long Josephson junctions, which were described by a system of coupled sine-Gordon equations. In a system of 10 long Josephson junctions coupled to a linear cavity, we numerically investigate how the cav...... of the inductive coupling strength, we investigate the cavity current, fluxon phase difference, and current–voltage characteristic. The stack-cavity system with in-phase fluxon motion may be utilized as a THz oscillator.......The BSCCO type intrinsic Josephson junction has been modeled as a stack of inductively coupled long Josephson junctions, which were described by a system of coupled sine-Gordon equations. In a system of 10 long Josephson junctions coupled to a linear cavity, we numerically investigate how the...... cavity perturbs fluxon motion in the junctions. Fluxons in neighboring junctions are repulsive leading to anti-phase motion. The cavity provides a force which perturbs this anti-phase motion, and may even force the fluxons to build a square lattice, i.e. to perform in-phase motion. For different values...
Search for the in-phase Flux Flow mode in stacked Josephson junctions
DEFF Research Database (Denmark)
Pedersen, Niels Falsig; Madsen, Søren Peder
2006-01-01
Josephson vortex flux flow states in stacked Josephson junctions are investigated numerically. The aim of the work is to understand the mechanisms behind the formation of triangular (anti-phase) and square (in-phase) vortex lattices, and is motivated by recent experiments on layered BSCCO type high...
Microwave receiver system with quantum superconducting Josephson junctions based on LTSC and HTSC
Energy Technology Data Exchange (ETDEWEB)
Anischenko, S.E.; Larkin, S.Y.; Khabayev, P.V. (State Research Center Fonon, Kiev (Ukraine))
1993-03-01
The paper is concerned with the methods for frequency measurement in millimeter and submillimeter wave ranges using AC Josephson effect. Basing on the method the Microwave Superconductive Receiver System was designed. The main results obtained for niobium Josephson junctions and bridges made of HTSC, as a measurement element are presented. 7 refs., 4 figs.
SQUID microscope read-out on a Josephson junction array
International Nuclear Information System (INIS)
LTC Josephson junction arrays (JJA) have recently gained interest as a model for the study of magnetization in superconductor materials. The presence of paramagnetic Meissner effect in such devices when field-cooled makes them an excellent candidate to discriminate between the different explanations given for such phenomenon. On the other hand, the understanding of the JJA physics is not simple due to the interplay between the non-linear behaviour of Josephson devices and the mutual induction effects in large JJA. The use of a SQUID microscope (SSM) to catch the magnetic image of the array is a distinctive feature of the experiment. So a study of SQUID read-out based on the actual JJA magnetic behaviour is needed in order to have a correct picture of what is going on. In this paper, using a simple way to reconstruct the complex array far-field viewed by the SQUID, we study how the flux read-out is dependent on array resolution, distance, tilting and noise for the typical situations in which arrays are found. (author)
Strained graphene Josephson junction with anisotropic d-wave superconductivity
Goudarzi, H.; Khezerlou, M.; Kamalipour, H.
2015-07-01
Effect of proximity-induced superconductivity in the new two-dimensional structures, as graphene and topological insulator on the Andreev bound states (ABSs) and Josephson supercurrent has attracted much efforts. Motivated by this subject, we study, in particular, the influence of anisotropic Fermi velocity and unconventional d-wave pairing in a strained graphene-based superconductor/normal/ superconductor junction. Strain is applied in the zigzag direction of graphene sheet. In this process, effect of zero energy states and Fermi wavevector mismatch are investigated. It is shown, that strain up to 22% in graphene lattice differently affects Josephson currents in parallel and perpendicular directions of strain. Strain causes to exponentially decrease the supercurrent in the strain direction, whereas increase for other direction. We find that, in one hand, the ABSs strongly depend on strain and, on the other hand, a gap opens in the states with respect to non-zero incidence angle of quasiparticles, where a period of 2 π is obtained for Andreev states. Moreover, we observe no gap for θs ≠ 0 , when the zero energy states (ZESs) occur in α = π / 4 due to anisotropic superconducting gap. In this case, ABSs have a period of 4 π .S
Fluxons in a superlattice of Josephson junctions: dynamics and radiation
Gaididei, Y; Flytzanis, N
2003-01-01
We study the dynamics of a homopolar coherent array of fluxons in a planar superlattice of long Josephson junctions coupled through lateral idle regions. These regions introduce dispersion, which in effect destroys the Lorentz invariance of the usual sine-Gordon equation. Thus, the system is described by an effectively non-local equation. We use a collective coordinate approach to determine the fluxon width resulting uniform coherent fluxon motion, as well as the fluttering frequency as a function of the momentum, which is an integral of the motion. At relatively high fluxon velocities Cherenkov radiation appears as oscillations following the propagating fluxon. We obtained analytical formulae for the wavevector, frequency, amplitude and form of the emitted radiation. The analytical results are in fair agreement with numerical simulations. At very high fluxon velocities, the radiation strongly modifies the I-v characteristics leading to resonant structures, known as Cherenkov steps. The coherency of the emitt...
Supersymmetric phase transition in Josephson-tunnel-junction arrays
Energy Technology Data Exchange (ETDEWEB)
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.
Scattering to different vortex polarity in coupled long Josephson junctions
Wustmann, Waltraut; Osborn, Kevin D.
We theoretically study the motion of flux vortices (fluxons) in structures made from discrete long Josephson junctions (DLJJs) which may have applications in the fields of reversible and low-power computing. We investigate the scattering of fluxons at specially designed interfaces where multiple DLJJs meet. Once fluxons approach the interface, flux oscillations at the interface can be temporarily excited before the fluxons continue along to another DLJJ. Under some conditions the fluxons will change their polarity (to antifluxons) and in other cases the fluxon continues without a change in polarity. We explain the dynamics through the resonant interaction of the soliton with bound states at the interface. We also study a controlled polarity gate, where the polarity of the target fluxon depends on a control fluxon which enters and exits the interface through separate DLJJs.
Thermal analysis of Josephson junctions array in cryocooler
Durandetto, P; Trinchera, B; Lolli, L; Serazio, D; Fretto, M; Sosso, A
2016-01-01
Complex cryogenics is still a strong limitation to the spread of quantum voltage standards and cryogen-free operation is then particularly interesting for Josephson standards. The main difficulties in He-free refrigeration are related to chip thermalization. We tested different solutions and interface materials between the chip and the cooling surface, to improve thermal conduction. Some junctions were chosen as elements to dissipate electrical power, while some others were operated as on-chip temperature sensors. Indium foil between chip and Cu support was demonstrated to provide a good thermal interface suitable for programmable voltage standard operation. However, thermal conduction can be further increased by thermal contacting the chip at the top. Finally, general physical constraints in vacuum thermal contacts are analyzed in terms of known properties of thermal interfaces at cryogenics temperatures.
High-performance passive microwave survey on Josephson junctions
International Nuclear Information System (INIS)
The quasi-optical generations of image of objects with their internal structure in millimeter (MM) and submillimeter (SMM) bands is one of the prime problems of modern radioelectronics. The main advantage of passive MM imaging systems in comparison with visible and infrared (IR) systems is small attenuation of signals in fog, cloud, smoke, dust and other obscurants. However at a panoramic scanning of space the observation time lengthens and thereby the information processing rate becomes restricted. So that single-channel system cannot image in real time. Therefore we must use many radiometers in parallel to reduce the observation time. Such system must contain receiving sensors as pixels in multibeam antenna. The use of Josephson Junctions (JJ) for this purpose together with the cryoelectronic devices like GaAs FET or SQUIDS for signal amplifications after JJ is of particular interest in this case
A supersymmetric phase transition in Josephson-tunnel-junction arrays
International Nuclear Information System (INIS)
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
DEFF Research Database (Denmark)
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....
Optimization of Spin-Triplet Supercurrent in Ferromagnetic Josephson Junctions
Klose, Carolin; Khaire, Trupti S.; Wang, Yixing; Pratt, W. P., Jr.; Birge, Norman O.; McMorran, B. J.; Ginley, T. P.; Borchers, J. A.; Kirby, B. J.; Maranville, B. B.; Unguris, J.
2012-03-01
We have observed long-range spin-triplet supercurrents in Josephson junctions containing ferromagnetic (F) materials, which are generated by noncollinear magnetizations between a central Co/Ru/Co synthetic antiferromagnet and two outer thin F layers. Here we show that the spin-triplet supercurrent is enhanced up to 20 times after our samples are subject to a large in-plane field. This occurs because the synthetic antiferromagnet undergoes a “spin-flop” transition, whereby the two Co layer magnetizations end up nearly perpendicular to the magnetizations of the two thin F layers. We report direct experimental evidence for the spin-flop transition from scanning electron microscopy with polarization analysis and from spin-polarized neutron reflectometry. These results represent a first step toward experimental control of spin-triplet supercurrents.
High-performance passive microwave survey on Josephson junctions
Energy Technology Data Exchange (ETDEWEB)
Denisov, A.G.; Radzikhovsky, V.N.; Kudeliya, A.M. [State Research Center of Superconductive Radioelectronics, Kiev (Ukraine)
1994-12-31
The quasi-optical generations of image of objects with their internal structure in millimeter (MM) and submillimeter (SMM) bands is one of the prime problems of modern radioelectronics. The main advantage of passive MM imaging systems in comparison with visible and infrared (IR) systems is small attenuation of signals in fog, cloud, smoke, dust and other obscurants. However at a panoramic scanning of space the observation time lengthens and thereby the information processing rate becomes restricted. So that single-channel system cannot image in real time. Therefore we must use many radiometers in parallel to reduce the observation time. Such system must contain receiving sensors as pixels in multibeam antenna. The use of Josephson Junctions (JJ) for this purpose together with the cryoelectronic devices like GaAs FET or SQUIDS for signal amplifications after JJ is of particular interest in this case.
Maximum supercurrent in two Josephson-junction stacks: Theory and experiment
DEFF Research Database (Denmark)
Carapella, G; Costabile, G; Sakai, S; Pedersen, Niels Falsig
1998-01-01
The interaction between two long Josephson junctions in a stack is investigated experimentally in the absence of applied magnetic field. Mutual interaction is observed when both junctions or only one junction in the stack is in the zero voltage state. To account for the observed phenomena we...
Resonant tunneling in small current-biased Josephson Junctions
Energy Technology Data Exchange (ETDEWEB)
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.
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
International Nuclear Information System (INIS)
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.
Influence of length on the noise delayed switching of long Josephson junctions
Federov, K. G.; Pankratov, A. L.; Spagnolo, B.
2008-01-01
The transient dynamics of long overlap Josephson junctions in the frame of the sine-Gordon model with a white noise source is investigated. The effect of noise delayed decay is observed for the case of overdamped sine-Gordon equation. It is shown that this noise induced effect, in the range of small noise intensities, vanishes for junctions lengths greater than several Josephson penetration length.
Supercurrent distribution and flux penetration in high-Tc edge Josephson junctions
International Nuclear Information System (INIS)
The spatial distribution of supercurrent in high-Tc Josephson junction devices has been studied extensively using field modulation measurements of the critical current and microwave absorption. The devices are edge junctions composed of YBa2Cu3O7-YBa2Co0.21Cu2.79O7-YBa2Cu3O7. The Ic(H) patterns allow a quantitative Fourier transform analysis to obtain a self-consistent spatial supercurrent density distribution, Js(x). These junctions are found to be more homogeneous than in most other high-Tc Josephson junctions reported to date
Coherent current states in mesoscopic four-terminal Josephson junction
International Nuclear Information System (INIS)
A theory is offered for the ballistic 4-terminal Josephson junction. The studied system consist of a mesoscopic two-dimensional normal rectangular layer which is attached on each side to the bulk superconducting banks (terminals). A relation is obtained between the currents through the different terminals, that is valid for arbitrary temperatures and junction sizes. The nonlocal coupling of the supercurrent leads to a new effect, specific for the mesoscopic weak link between two superconducting rings; an applied magnetic flux through one of the rings produces a magnetic flux in the other ring even in the absence of an external flux through the other one. The phase dependent distributions of the local density of Andreev states, of the supercurrents and of the induced order parameter are obtained. The 'interference pattern' for the anomalous average inside the two-dimensional region cam be regulated by the applied magnetic fluxes or the transport currents. For some values of the phase differences between the terminals, the current vortex state and two-dimensional phase slip center appear
International Nuclear Information System (INIS)
This paper examines the quantization of mesoscopic circuit including Josephson junctions. Following Feynman's assumption, via the Hamilton dynamic approach and by virtue of the entangled state representation, it constructs Hamiltonian operator for the double-Josephson-junction mesoscopic circuit coupled by a capacitor. Then it uses the Heisenberg equation of motion to derive the induction voltage across each Josephson junction. The result manifestly shows how the voltage is affected by the capacitance coupling
Josephson Junctions Made of YBa2Cu3O7-x Superconducting Nanofilms
Chesca, Boris
Conventional Josephson junctions are used to build superconducting quantum interference devices (SQUIDs) which are the most sensitive magnetic field sensors known. Today, SQUIDS are widely used in many different areas like medical and biological research and diagnostics, geophysics, non-destructive evaluation of materials and structures, or fundamental physics research. In recent years the highly anisotropic and unique intrinsic properties of YBa2Cu3O7- x superconducting nano-films allowed fabrication of a special type of Josephson junctions, so-called π-junctions, which are excellent candidates as building block for fast, low-dissipative superconducting digital electronics or quantum computation. For those reasons fabricating high quality and reliably Josephson junctions has been one of the priority areas of research in superconductivity. There are several well-established technologies to fabricate Josephson junctions made of YBa2Cu3O7-x superconducting nano-films. Here I will briefly describe two of the most important ones used to fabricate both conventional Josephson junctions and π-junctions.
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.
DEFF Research Database (Denmark)
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...
SFS Josephson Junctions using PdNi alloy
Khaire, Trupti; Pratt, William P., Jr.; Birge, Norman O.
2009-03-01
We have studied the variation of critical current in Superconductor/Ferromagnet/Superconductor (S/F/S) Josephson Junctions as a function of ferromagnet thickness (dF) using a weakly ferromagnetic alloy, Pd82Ni12. The critical current density oscillates and decays over five orders of magnitude as dF is increased from 32 to 100 nm. These oscillations are indicative of 0-π transitions in S/F/S junctions. We find the characteristic length of oscillation (ξF2) to be 4.3 ± 0.1 nm and the characteristic length of decay (ξF1) to be 7.9 ± 0.4 nm. Earlier studies [1] using a similar PdNi alloy in S/I/F/S junctions found ξF1 ξF2 2.81ptnm, however, those measurements were performed for dF between 4.5 and 14 nm. In our experiment, ξF1>ξF2, indicating that our samples are in the regime Eexτ> [2, 3], where Eex is the exchange energy and τ is the mean free time between electron collisions in the ferromagnet. In spite of covering this wide range, we see no evidence of a crossover to a slower decay, which, if present, would be indicative of long-range spin triplet correlations [4]. [1] T. Kontos et al.,Phys. Rev. Lett. 89, 137007 (2002). [2] F. S. Bergeret, et al., Phys. Rev. B, 64, 134506 (2001) [3] Kashuba, et al., Phys. Rev. B. 75, 132502 (2007). [4] F.S. Bergeret, et al., Rev. Mod. Phys. 77, 1321 (2005). [This work is supported by US-DOE grant, DE-FG02-06ER46341.
Directed transport in coupled noisy Josephson junctions controlled via ac signals
Machura, L.; Spiechowicz, J.; Luczka, J.
2012-01-01
Transport properties of two coupled Josephson junctions driven by ac currents and thermal fluctuations are studied with the purpose of determining dc voltage characteristics. It is a physical realization of directed transport induced by a non-biased zero averaged external signal. The ac current is applied either to (A) only one junction as a biharmonic current or (B) is split into two simple harmonic components and separately applied to respective junctions. We identify regimes where junction...
Neighbor-junction state effect on the fluxon motion in a Josephson stack
Goldobin, E.; Ustinov, A. V.
1999-01-01
We study experimentally and theoretically the influence of phase-whirling (resistive) state in one junction of a two-fold Josephson stack on the fluxon motion in the other junction. In experiment, we measure the fluxon velocity versus current in one junction as a function of the state (Meissner or resistive) of the neighboring junction. The analysis, made for the limit of high fluxon density, shows that the interaction with the resistive state results in an increase of the effective damping f...
Perturbation treatment of boundary conditions for fluxon motion in long Josephson junctions
DEFF Research Database (Denmark)
Olsen, O. H.; Pedersen, Niels Falsig; Samuelsen, Mogens Rugholm; Svensmark, Henrik; Welner, D.
1986-01-01
The sine-Gordon equation governing the motion of fluxons in the long Josephson junction is investigated by transforming it into a relativistic-particle equation of motion and using a perturbational approach. The effects of a finite junction length, an external magnetic field, as well as the effects...
One-third (period three) harmonic generation in microwave-driven Josephson tunnel junctions
DEFF Research Database (Denmark)
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...
Remanent effects and granular Josephson tunnelling in 1:2:3 micro-bridge junctions
International Nuclear Information System (INIS)
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
DEFF Research Database (Denmark)
Krasnov, V.M.; Oboznov, V.A.; Pedersen, Niels Falsig
1997-01-01
self-energy (from the cold to the hot end of the junction). A phenomenon, the ''zero crossing flux flow step'' (ZCFFS) with a nonzero voltage at a zero applied current, was observed in nonuniform long Josephson junctions. The phenomenon is due to the existence of a preferential direction for the...
Superposition of Coherent States in a Mesoscopic Josephson Junction with Dissipation
Institute of Scientific and Technical Information of China (English)
ZOU Jian; SHAO Bin; SU Wen-Yong
2001-01-01
A mesoscopic Josephson junction with dissipation is considered. Usually the dissipation in the system is described as a consequence of its coupling to a reservoir. By solving the master equation we show that the state of the junction can evolve in a quantum superposition of two coherent states even when the dissipation is present.``
Negative Differential Resistance due to Nonlinearities in Single and Stacked Josephson Junctions
DEFF Research Database (Denmark)
Filatrella, Giovanni; Pierro, Vincenzo; Pedersen, Niels Falsig;
2014-01-01
Josephson junction systems with a negative differential resistance (NDR) play an essential role for applications. As a well-known example, long Josephson junctions of the BSCCO type have been considered as a source of terahertz radiation in recent experiments. Numerical results for the dynamics of...... the fluxon system have demonstrated that a cavity induced NDR plays a crucial role for the emission of electromagnetic radiation. We consider the case of an NDR region in the McCumber curve itself of a single junction and found that it has an effect on the emission of electromagnetic radiation. Two...
A single flux quantum circuit with a ferromagnet-based Josephson π-junction
International Nuclear Information System (INIS)
We report on the functionality of a Nb-based superconducting single flux quantum (SFQ) toggle flip-flop (TFF) circuit, comprising a complementary superconductor-ferromagnet-superconductor (SFS) Josephson π-junction. The SFS junction was used as a phase shifting element inserted in the storage loop of the TFF. The fabricated circuits demonstrated correct functionality with the operation parameter ranges of ± 20%. The application of SFS π-junctions makes the SFQ circuits very compact, may substantially improve their stability, and may also be suitable for integration with Josephson quantum circuits (qubits).
Closed form solutions for the self-resonances in a short Josephson junction
International Nuclear Information System (INIS)
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.
Direct measurements of the current-phase relation in graphene Josephson junctions
English, Christopher; Hamilton, David; van Harlingen, Dale; Mason, Nadya
2013-03-01
The current-phase relation (CPR) of a Josephson junction can provide key information about the microscopic processes and symmetries that control the supercurrent. In this talk, we present CPR measurements on Josephson junctions incorporating single-layer graphene as a weak link between Al superconducting electrodes with spacing supercurrent amplitude and phase as a function of temperature and electrostatic doping (gate voltage). As the critical current is varied, we observe a crossover from forward skewing in the CPR that arises from the low density of discrete electronic states in the junction to backward skewing induced by noise-rounding in the CPR measurement. We compare our results to theoretical models.
Energy Technology Data Exchange (ETDEWEB)
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.
Fluxons in a triangular set of coupled long Josephson junctions
Energy Technology Data Exchange (ETDEWEB)
Yukon, Stanford P., E-mail: yukon@alum.mit.edu [Air Force Research Laboratory (United States); Malomed, Boris A. [Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel)
2015-09-15
We report results of an analysis of the dynamics of magnetic flux solitons in the system of three long Josephson junctions between three bulk superconductors that form a prism. The system is modeled by coupled sine-Gordon equations for the phases of the junctions. The Aharonov-Bohm constraint takes into account the axial magnetic flux enclosed by the prism and reduces the system from three independent phases to two. The equations of motion for the phases include dissipative terms, and a control parameter δ which accounts for the deviation of the enclosed flux from half a quantum. Analyzing the effective potential of the coupled equations, we identify different species of topological and non-topological phase solitons (fluxons) in this system. In particular, subkinks with fractional topological charges ±1/3 and ±2/3, confined inside integer-charge fluxons, may be mapped onto the root diagrams for mesons and baryons in the original quark model of hadrons. Solutions for straight-line kinks and for two types of non-topological solitons are obtained in an explicit analytical form. Numerical tests demonstrate that the former species is unstable against breakup into pairs of separating single-fluxon kinks. The non-topological kinks feature metastability, eventually breaking up into fluxon-antifluxon pairs. Free fractional-fluxon kinks, that connect different potential minima and are, accordingly, pulled by the potential difference, are also considered. Using the momentum-balance method, we predict the velocity at which these kinks should move in the presence of the dissipation. Numerical tests demonstrate that the analysis predicts the velocity quite closely. Higher-energy static solutions for all of the stable kink types mentioned above, as well as kinks connecting false vacua, are found by means of the shooting method. Inelastic collisions among the stable fractional and single-fluxon kinks are investigated numerically.
Fluxons in a triangular set of coupled long Josephson junctions
Yukon, Stanford P.; Malomed, Boris A.
2015-09-01
We report results of an analysis of the dynamics of magnetic flux solitons in the system of three long Josephson junctions between three bulk superconductors that form a prism. The system is modeled by coupled sine-Gordon equations for the phases of the junctions. The Aharonov-Bohm constraint takes into account the axial magnetic flux enclosed by the prism and reduces the system from three independent phases to two. The equations of motion for the phases include dissipative terms, and a control parameter δ which accounts for the deviation of the enclosed flux from half a quantum. Analyzing the effective potential of the coupled equations, we identify different species of topological and non-topological phase solitons (fluxons) in this system. In particular, subkinks with fractional topological charges ±1/3 and ±2/3, confined inside integer-charge fluxons, may be mapped onto the root diagrams for mesons and baryons in the original quark model of hadrons. Solutions for straight-line kinks and for two types of non-topological solitons are obtained in an explicit analytical form. Numerical tests demonstrate that the former species is unstable against breakup into pairs of separating single-fluxon kinks. The non-topological kinks feature metastability, eventually breaking up into fluxon-antifluxon pairs. Free fractional-fluxon kinks, that connect different potential minima and are, accordingly, pulled by the potential difference, are also considered. Using the momentum-balance method, we predict the velocity at which these kinks should move in the presence of the dissipation. Numerical tests demonstrate that the analysis predicts the velocity quite closely. Higher-energy static solutions for all of the stable kink types mentioned above, as well as kinks connecting false vacua, are found by means of the shooting method. Inelastic collisions among the stable fractional and single-fluxon kinks are investigated numerically.
Multiwall carbon nanotube Josephson junctions with niobium contacts
International Nuclear Information System (INIS)
The main goal of this thesis is the investigation of dissipationless supercurrent in multiwall carbon nanotubes embedded in a controlled environment. The experimental observation of a dissipationless supercurrent in gated carbon nanotubes remains challenging because of its extreme sensitivity to the environment and to noise fluctuations. We address these issues by choosing niobium as a superconductor and by designing an optimized on chip electromagnetic environment. The environment is meant to reduce the suppression of the supercurrent and allows to disentangle the effects of thermal fluctuations from the intrinsic behavior of the junction. This is crucial for the extraction of the value critical current from the measured data. When the transparency of the contacts is high enough we observed a fully developed supercurrent and we found that it depends on the gate voltage in a resonant manner. In average the critical current increases when the gate is tuned more negative, reflecting the increase of the transparency of the contacts, while the resonant behavior is due to quantum interference effects. We measured the temperature dependence of the switching current and we analyzed the data with an extended RCSJ model that allow to extract the critical current from the experimental data. The measured critical currents are very high with respect to previous reports on gated devices. At positive gate voltage the contacts transparency is lowered and Coulomb blockade is observed. This allows to use Coulomb blockade measurements to further characterize the nanotube and to study the physics of a quantum dot coupled to superconducting leads. The last part of this thesis is dedicated to the measurements of a carbon nanotube Josephson junction in the Coulomb blockade regime. (orig.)
Fluxons in a triangular set of coupled long Josephson junctions
International Nuclear Information System (INIS)
We report results of an analysis of the dynamics of magnetic flux solitons in the system of three long Josephson junctions between three bulk superconductors that form a prism. The system is modeled by coupled sine-Gordon equations for the phases of the junctions. The Aharonov-Bohm constraint takes into account the axial magnetic flux enclosed by the prism and reduces the system from three independent phases to two. The equations of motion for the phases include dissipative terms, and a control parameter δ which accounts for the deviation of the enclosed flux from half a quantum. Analyzing the effective potential of the coupled equations, we identify different species of topological and non-topological phase solitons (fluxons) in this system. In particular, subkinks with fractional topological charges ±1/3 and ±2/3, confined inside integer-charge fluxons, may be mapped onto the root diagrams for mesons and baryons in the original quark model of hadrons. Solutions for straight-line kinks and for two types of non-topological solitons are obtained in an explicit analytical form. Numerical tests demonstrate that the former species is unstable against breakup into pairs of separating single-fluxon kinks. The non-topological kinks feature metastability, eventually breaking up into fluxon-antifluxon pairs. Free fractional-fluxon kinks, that connect different potential minima and are, accordingly, pulled by the potential difference, are also considered. Using the momentum-balance method, we predict the velocity at which these kinks should move in the presence of the dissipation. Numerical tests demonstrate that the analysis predicts the velocity quite closely. Higher-energy static solutions for all of the stable kink types mentioned above, as well as kinks connecting false vacua, are found by means of the shooting method. Inelastic collisions among the stable fractional and single-fluxon kinks are investigated numerically
Multiwall carbon nanotube Josephson junctions with niobium contacts
Energy Technology Data Exchange (ETDEWEB)
Pallecchi, Emiliano
2009-02-17
The main goal of this thesis is the investigation of dissipationless supercurrent in multiwall carbon nanotubes embedded in a controlled environment. The experimental observation of a dissipationless supercurrent in gated carbon nanotubes remains challenging because of its extreme sensitivity to the environment and to noise fluctuations. We address these issues by choosing niobium as a superconductor and by designing an optimized on chip electromagnetic environment. The environment is meant to reduce the suppression of the supercurrent and allows to disentangle the effects of thermal fluctuations from the intrinsic behavior of the junction. This is crucial for the extraction of the value critical current from the measured data. When the transparency of the contacts is high enough we observed a fully developed supercurrent and we found that it depends on the gate voltage in a resonant manner. In average the critical current increases when the gate is tuned more negative, reflecting the increase of the transparency of the contacts, while the resonant behavior is due to quantum interference effects. We measured the temperature dependence of the switching current and we analyzed the data with an extended RCSJ model that allow to extract the critical current from the experimental data. The measured critical currents are very high with respect to previous reports on gated devices. At positive gate voltage the contacts transparency is lowered and Coulomb blockade is observed. This allows to use Coulomb blockade measurements to further characterize the nanotube and to study the physics of a quantum dot coupled to superconducting leads. The last part of this thesis is dedicated to the measurements of a carbon nanotube Josephson junction in the Coulomb blockade regime. (orig.)
Nonergodic metallic and insulating phases of Josephson junction chains.
Pino, Manuel; Ioffe, Lev B; Altshuler, Boris L
2016-01-19
Strictly speaking, the laws of the conventional statistical physics, based on the equipartition postulate [Gibbs J W (1902) Elementary Principles in Statistical Mechanics, developed with especial reference to the rational foundation of thermodynamics] and ergodicity hypothesis [Boltzmann L (1964) Lectures on Gas Theory], apply only in the presence of a heat bath. Until recently this restriction was believed to be not important for real physical systems because a weak coupling to the bath was assumed to be sufficient. However, this belief was not examined seriously until recently when the progress in both quantum gases and solid-state coherent quantum devices allowed one to study the systems with dramatically reduced coupling to the bath. To describe such systems properly one should revisit the very foundations of statistical mechanics. We examine this general problem for the case of the Josephson junction chain that can be implemented in the laboratory and show that it displays a novel high-temperature nonergodic phase with finite resistance. With further increase of the temperature the system undergoes a transition to the fully localized state characterized by infinite resistance and exponentially long relaxation. PMID:26719416
Structured chaos in a devil's staircase of the Josephson junction
Shukrinov, Yu. M.; Botha, A. E.; Medvedeva, S. Yu.; Kolahchi, M. R.; Irie, A.
2014-09-01
The phase dynamics of Josephson junctions (JJs) under external electromagnetic radiation is studied through numerical simulations. Current-voltage characteristics, Lyapunov exponents, and Poincaré sections are analyzed in detail. It is found that the subharmonic Shapiro steps at certain parameters are separated by structured chaotic windows. By performing a linear regression on the linear part of the data, a fractal dimension of D = 0.868 is obtained, with an uncertainty of ±0.012. The chaotic regions exhibit scaling similarity, and it is shown that the devil's staircase of the system can form a backbone that unifies and explains the highly correlated and structured chaotic behavior. These features suggest a system possessing multiple complete devil's staircases. The onset of chaos for subharmonic steps occurs through the Feigenbaum period doubling scenario. Universality in the sequence of periodic windows is also demonstrated. Finally, the influence of the radiation and JJ parameters on the structured chaos is investigated, and it is concluded that the structured chaos is a stable formation over a wide range of parameter values.
Tailored Josephson phase: 0, π and 0-π SIFS Josephson junctions
International Nuclear Information System (INIS)
In superconducting/ferromagnet (S/F) systems the superconducting wave function extends into the ferromagnet with a damped oscillatory behavior. This results in novel and interesting physics, such as the possibility to realize a π Josephson junction (JJ) - a JJ with the phase drop of π in the ground state. Recently, we fabricated Nb/Al2O3/NiCu/Nb JJs with uniform as well as step-like ferromagnetic layer to obtain 0, π and 0-π JJs. Here we present our recent results on planar SIFS JJs with F-layer made of Ni, and compare them with the theory in the clean/dirty limit and with experiments by other groups. The critical current density in the π state is larger and the order parameter decay is weaker than for π JJs made using weak ferromagnetic alloys, e.g. NiCu. The 0-π boundary in JJs with a step-like F-layer thickness may give rise to a pinned spontaneous vortex of supercurrent with magnetic flux ≤Φ0/2. Latest experiments on short and long stepped SIFS JJs (0-π, 0-π-0 etc.) are discussed
Tailored Josephson phase: 0, {pi} and 0-{pi} SIFS Josephson junctions
Energy Technology Data Exchange (ETDEWEB)
Weides, Martin; Bannykh, Alexey; Peralagu, Uthayasankaran [Institute for Solid State Research, Research Centre Juelich (Germany); Pfeiffer, Judith; Kemmler, Matthias; Koelle, Dieter; Kleiner, Reinhold; Goldobin, Edward [Physikalisches Institut - Experimentalphysik II, (Germany)
2008-07-01
In superconducting/ferromagnet (S/F) systems the superconducting wave function extends into the ferromagnet with a damped oscillatory behavior. This results in novel and interesting physics, such as the possibility to realize a {pi} Josephson junction (JJ) - a JJ with the phase drop of {pi} in the ground state. Recently, we fabricated Nb/Al{sub 2}O{sub 3}/NiCu/Nb JJs with uniform as well as step-like ferromagnetic layer to obtain 0, {pi} and 0-{pi} JJs. Here we present our recent results on planar SIFS JJs with F-layer made of Ni, and compare them with the theory in the clean/dirty limit and with experiments by other groups. The critical current density in the {pi} state is larger and the order parameter decay is weaker than for {pi} JJs made using weak ferromagnetic alloys, e.g. NiCu. The 0-{pi} boundary in JJs with a step-like F-layer thickness may give rise to a pinned spontaneous vortex of supercurrent with magnetic flux {<=}{phi}{sub 0}/2. Latest experiments on short and long stepped SIFS JJs (0-{pi}, 0-{pi}-0 etc.) are discussed.
0-π Transition Driven by Magnetic Proximity Effect in a Josephson Junction
Hikino, Shin-ichi; Yunoki, Seiji
2015-02-01
We theoretically study the Josephson effect in a superconductor/normal metal/superconductor (S/N/S) Josephson junction composed of s-wave Ss with N which is sandwiched by two ferromagnetic insulators (Fs), forming a spin valve, in the vertical direction of the junction. We show that the 0-π transition of the Josephson critical current occurs with increasing the thickness of N along the junction. This transition is due to the magnetic proximity effect (MPE) which induces ferromagnetic magnetization in the N. Moreover, we find that, even for fixed thickness of N, the proposed Josephson junction with the spin valve can be switched from π to 0 states and vice versa by varying the magnetization configuration (parallel or antiparallel) of two Fs. We also examine the effect of spin-orbit scattering on the Josephson critical current and argue that the 0-π transition found here can be experimentally observed within the current nanofabrication techniques, thus indicating a promising potential of this junction as a 0-π switching device operated reversibly with varying the magnetic configuration in the spin valve by, e.g., applying an external magnetic field. Our results not only provide possible applications in superconducting electronics but also suggest the importance of a fundamental concept of MPE in nanostructures of multilayer N/F systems.
Josephson Current in Superconductor-Ferromagnet/Insulator/d-Wave Superconductor Junctions
Institute of Scientific and Technical Information of China (English)
LI Xiao-Wei; DONG Zheng-Chao
2005-01-01
Solving the Bogoliubov-de Gennes equation, the energy levels of bound states are obtained in the ferromagnetic superconductor. The Josephson currents in a ferromagnetic superconductor/Insulator/d-wave superconductor junction are calculated as a function of the exchange field, temperature, and insulating barrier strength. It is found that the Josephson critical current is always suppressed by the presence of exchange field h and depends on crystalline axis orientation of d-wave superconductor.
Intense terahertz emission from intrinsic Josephson junctions by external heat control
Asai, Hidehiro; Kawabata, Shiro
2014-01-01
A practical method for realizing intense terahertz (THz) emission from intrinsic Josephson junctions (IJJs) by utilizing external local-heating is proposed and demonstrated theoretically. An artificial temperature distribution induced by local heating strongly excites Josephson plasma waves inside IJJs. Accordingly, the emission power of the THz wave is enhanced drastically, and it can reach the order of mW. Our result indicates that the use of local heat control is a powerful method to reali...
Possibility to enhance teraherz emission from intrinsic Josephson junction by external local heating
Asai, Hidehiro; Kawabata, Shiro
2014-01-01
We theoretically propose a practical method for realizing intense terahertz (THz) emission from intrinsic Josephson junctions (IJJs) using an external heat source. An artificial inhomogeneous temperature distribution by the local heating strongly excites the Josephson plasma wave inside IJJs and enhances THz emission power. We show optimum heating conditions for achieving high power THz emission. Our result indicates that local heat control is a powerful method to realize practical solid-stat...
Above-gap Conductance Anomaly Studied in Superconductor-graphene-superconductor Josephson Junctions
Choi, Jae-Hyun; Lee, Hu-Jong; Doh, Yong-Joo
2011-01-01
We investigated the electrical transport properties of superconductor-graphene-superconductor (SGS) Josephson junctions. In low voltage bias, we observed conventional proximity-coupled Josephson effect, such as the supercurrent flow through the graphene, sub-gap structure of differential conductance due to Andreev reflection, and periodic modulation of the critical current Ic with perpendicular magnetic field H to the graphene. In high bias above the superconducting gap voltage, however, we a...
High-Tc Josephson junctions fabricated by focused ion beam direct milling
International Nuclear Information System (INIS)
High-Tc Josephson junctions were successfully fabricated by focused ion beam (FIB) direct milling. The characteristics of the junction barrier were carefully controlled by tuning the thickness of the link region. The optimal remaining thickness for the YBCO is about 70–80 nm even though the YBCO thicknesses are different. The temperature-dependence of the critical current provides good evidence of the superconductor–normal–superconductor weak link of the junctions. Although the flux-flow behavior increasingly dominates at lower temperatures, the voltage–current shows resistively shunted junction-like characteristics at temperatures close to Tc. The Shapiro steps of a single junction irradiated with microwaves were measured, revealing strong Josephson effects in ion-damaged junctions. This method will be of great benefit to nanoSQUIDs for the detection of spin systems. (paper)
Flux qubit with a large loop size and tunable Josephson junctions
Institute of Scientific and Technical Information of China (English)
Deng Hui; Yu Hai-Feng; Xue Guang-Ming; Tian Ye; Ren Jian-Kun; Wu Yu-Lin; Huang Ke-Qiang; Zhao Shi-Ping; Zheng Dong-Ning
2012-01-01
We present the design of a superconducting flux qubit with a large loop inductance.The large loop inductance is desirable for coupling between qubits.The loop is configured into a gradiometer form that could reduce the interference from environmental magnetic noise.A combined Josephson junction,i.e.,a DC-SQUID is used to replace the small Josephson junction in the usual 3-JJ (Josephaon junction) flux qubit,leading to a tunable energy gap by using an independent external flux line.We perform numerical calculations to investigate the dependence of the energy gap on qubit parameters such as junction capacitance,critical current,loop inductance,and the ratio of junction energy between small and large junctions in the flux qubit.We suggest a range of values for the parameters.
Linewidth of Josephson oscillations in YBa2Cu3O7-x grain-boundary junctions
DEFF Research Database (Denmark)
Divin, Yu. Ya.; Mygind, Jesper; Pedersen, Niels Falsig;
1993-01-01
The AC Josephson effect in YBa2Cu3O7-x grain-boundary junctions (GBJs) was studied in the temperature range from 4 K to 90 K. The temperature dependence of the linewidth of millimeter-wave Josephson oscillations was measured, and it is shown that the derived effective noise temperature of GBJ might...... 72 GHz Josephson oscillations observed at 77 K was equal to 380 MHz, which demonstrates the applicability of GBJ, particularly in the field of radiation spectroscopy, even at liquid nitrogen temperatures...
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.
Paik, Hanhee; Schuster, D. I.; Bishop, Lev S.; Kirchmair, G.; Catelani, G.; Sears, A. P.; Johnson, B. R.; Reagor, M. J.; Frunzio, L.; Glazman, L.; Girvin, S.M.; Devoret, M. H.; Schoelkopf, R. J.
2011-01-01
Superconducting quantum circuits based on Josephson junctions have made rapid progress in demonstrating quantum behavior and scalability. However, the future prospects ultimately depend upon the intrinsic coherence of Josephson junctions, and whether superconducting qubits can be adequately isolated from their environment. We introduce a new architecture for superconducting quantum circuits employing a three dimensional resonator that suppresses qubit decoherence while maintaining sufficient ...
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}}...
DeFeo, M. P.; Bhupathi, P.; K. Yu; Heitmann, T. W.; Song, C.; McDermott, R; Plourde, B. L. T.
2010-01-01
We present measurements of an amplifier based on a dc superconducting quantum interference device (SQUID) with submicron Al-AlOx-Al Josephson junctions. The small junction size reduces their self-capacitance and allows for the use of relatively large resistive shunts while maintaining nonhysteretic operation. This leads to an enhancement of the SQUID transfer function compared to SQUIDs with micron-scale junctions. The device layout is modified from that of a conventional SQUID to allow for c...
Shunt-capacitor-assisted synchronization of oscillations in intrinsic Josephson junctions stack
Martin, I.; Halász, Gábor B.; Bulaevskii, L. N.; Koshelev, A. E.
2010-01-01
We show that shunt capacitor stabilizes synchronized oscillations in intrinsic Josephson junction stacks biased by DC current. This synchronization mechanism has an effect similar to the previously discussed radiative coupling between junctions, however, it is not defined by the geometry of the stack. It is particularly important in crystals with smaller number of junctions, where radiation coupling is week, and is comparable with the effect of strong super-radiation in crystal with many junc...
Josephson Current and Noise at a Superconductor-Quantum Spin Hall Insulator-Superconductor Junction
Fu, Liang; Kane, C. L.
2008-01-01
We study junctions between superconductors mediated by the edge states of a quantum spin Hall insulator. We show that such junctions exhibit a fractional Josephson effect, in which the current phase relation has a 4\\pi, rather than a 2\\pi periodicity. This effect is a consequence of the conservation of fermion parity - the number of electrons modulo 2 - in a superconducting junction, and is closely related to the Z_2 topological structure of the quantum spin Hall insulator. Inelastic processe...
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.
Niobium nitride-niobium Josephson tunnel junctions with sputtered amorphous silicon barriers
International Nuclear Information System (INIS)
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
Synchronization of a Josephson junction array in terms of global variables
Vlasov, Vladimir; Pikovsky, Arkady
2013-01-01
We consider an array of Josephson junctions with a common LCR-load. Application of the Watanabe-Strogatz approach [Physica D, v. 74, p. 197 (1994)] allows us to formulate the dynamics of the array via the global variables only. For identical junctions this is a finite set of equations, analysis of which reveals the regions of bistability of the synchronous and asynchronous states. For disordered arrays with distributed parameters of the junctions, the problem is formulated as an integro-diffe...
Serdyukova, S. I.
2014-07-01
We prove that, in the case of non-periodic (with γ = 1) boundary conditions, the calculation of the current-voltage characteristic (IVC) for a stack of n intrinsic Josephson junctions reduces to solving a system of [( n + 1)/2] non-linear differential equations instead of the n original ones. The current voltage characteristic V( I) has the shape of a hysteresis loop. On the back branch of the loop V( I) decreases to zero rapidly near the breakpoint I b . We succeeded to derive an algorithm determining the approximate breakpoint location and to improve simultaneously the mixed numerical-analytical algorithm of IVC calculation for a stack of Josephson junctions developed by us before. The efficiency of the improved algorithm is shown by the calculations of IVC for stacks consisting of various numbers of intrinsic Josephson junctions.
Synchronization dynamics on the picosecond timescale in coupled Josephson junction neurons
Segall, Ken; Kaplan, Steven; Svitelskiy, Oleksiy; Khadka, Shreeya; Crotty, Patrick; Schult, Daniel
2016-01-01
Conventional digital computation is rapidly approaching physical limits for speed and energy dissipation. Here we fabricate and test a simple neuromorphic circuit that models neuronal somas, axons and synapses with superconducting Josephson junctions. Similar to biological neurons, two mutually-coupled Josephson junction neurons synchronize in one of two states, symmetric (in-phase) or anti-symmetric (anti-phase). The experimental alteration of the delay and strength of the connecting synapses can toggle the system back and forth in a collective behavior known as a phase-flip bifurcation. Firing synchronization states are calculated >70,000 times faster than conventional digital approaches. With their speed and very low energy dissipation (10-17 Joules/spike), Josephson junction neurons are now established as a viable approach for vast improvements in neuronal computation as well as applications in neuromorphic computing.
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.
High temperature superconductor step-edge Josephson junctions using Ti-Ca-Ba-Cu-O
Ginley, David S.; Hietala, Vincent M.; Hohenwarter, Gert K. G.; Martens, Jon S.; Plut, Thomas A.; Tigges, Chris P.; Vawter, Gregory A.; Zipperian, Thomas E.
1994-10-25
A process for formulating non-hysteretic and hysteretic Josephson junctions using HTS materials which results in junctions having the ability to operate at high temperatures while maintaining high uniformity and quality. The non-hysteretic Josephson junction is formed by step-etching a LaAlO.sub.3 crystal substrate and then depositing a thin film of TlCaBaCuO on the substrate, covering the step, and forming a grain boundary at the step and a subsequent Josephson junction. Once the non-hysteretic junction is formed the next step to form the hysteretic Josephson junction is to add capacitance to the system. In the current embodiment, this is accomplished by adding a thin dielectric layer, LaA1O.sub.3, followed by a cap layer of a normal metal where the cap layer is formed by first depositing a thin layer of titanium (Ti) followed by a layer of gold (Au). The dielectric layer and the normal metal cap are patterned to the desired geometry.
Fabrication of a quasi-three-dimensional Josephson-junction array
International Nuclear Information System (INIS)
In a first step towards fabricating a truly 3-dimensional (3-d) Josephson-junction array, we have fabricated a quasi-3-d one, i.e. an array consisting of two 2-d arrays stacked on top of and capacitively- and inductively-coupled to one another. We discuss in detail the fabrication techniques we have employed to create this novel type of an array. Such techniques include alignment using topological markers, electron-beam lithography, shadow evaporation, and planarization. We have fabricated different samples whose 2-d arrays consist of underdamped Al-Al2O3-Al junctions in which either the Josephson-coupling energy EJ=hic/2e, where ic is the junction critical current, dominates the single-junction charging energy Ec=e2/2C, where C is the junction capacitance, or vice versa. With these arrays, we plan to study the interaction between vortices and/or charges. (orig.)
Nanometer-scale patterning of high-Tc superconductors for Josephson junction-based digital circuits
International Nuclear Information System (INIS)
A straightforward method for nanometer-scale patterning of high-Tc superconductor thin films is discussed. The technique combines direct-write electron beam lithography with well-controlled aqueous etches and is applied to the fabrication of Josephson junction nanobridges in high-quality, epitaxial thin-film YBa2Cu3O7. We present the results of our studies of the dimensions, yield, uniformity, and mechanism of the junctions along with the performance of a representative digital circuit based on these junctions. Direct current junction parameter statistics measured at 77 K show critical currents of 27.5 μA±13% for a sample set of 220 junctions. The Josephson behavior of the nanobridge is believed to arise from the aggregation of oxygen vacancies in the nanometer-scale bridge
A low-noise series-array Josephson junction parametric amplifier
Yurke, B.; Roukes, M. L.; Movshovich, R.; Pargellis, A. N.
1996-01-01
We have obtained parametric gain at 19 GHz from a distributed Josephson junction parametric amplifier whose active gain medium consists of a series array of 1000 Josephson junctions embedded in a coplanar waveguide. When cooled to 1.7 K the amplifier provides 16 dB gain in a mode where the internally generated double sideband noise referred to input is 0.5 ± 0.1 K. This noise is consistent with Nyquist noise generated from the losses. An instantaneous bandwidth of 125 MHz has been observed wi...
Dissipative Josephson junction of an optical soliton and a surface plasmon
Ekşioğlu, Yasa; Müstecaplıoğlu, Özgür E.; Güven, Kaan
2013-01-01
PHYSICAL REVIEW A 87, 023823 (2013) Dissipative Josephson junction of an optical soliton and a surface plasmon Yasa Eks¸iog˘lu,* O¨ zgu¨r E. Mu¨stecaplıog˘lu, and Kaan Gu¨ven Department of Physics, Koc¸ University, Istanbul 34450, Turkey (Received 4 October 2012; published 20 February 2013) We examine the dynamics of a dissipative photonic Josephson junction formed by the weak coupling of an optical soliton in a nonlinear dielectric waveguide and a co-propagating surface pla...
International Nuclear Information System (INIS)
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
Double-side fabrication process and millimeter wave response of intrinsic Josephson junctions
Institute of Scientific and Technical Information of China (English)
WU JingBo; YI DongChao; GU ZhengHao; KANG Lin; XU WeiWei; CHEN Jian; WU PeiHeng
2009-01-01
We adopted double-side fabrication process to prepare intrinsic Josephson junctions (IJJs) based on Bi2Sr2CaCu2O8-x(BSCCO) single crystals. Using crystal cleavage and double-side argon ion milling, we have successfully fabricated very uniform IJJs with the thickness of single crystal slice less than 200 nm. Using quasi-optical system, the response of the IJJs to millimeter wave radiation was studied. With applied magnetic field perpendicular to a-b plane, we have observed Shapiro steps under millimeter wave radiation, and the Josephson oscillation of each junction was phase-locking.
Analog simulation on enhanced ac Josephson effect for junction driven by pulse train current
International Nuclear Information System (INIS)
The enhanced ac Josephson effect is studied based on an analog simulation when the junction is driven by an rf-signal source. On the basis of the resistively shunted Josephson junction model driven by a pulse train current, larger rf-induced current step-heights in the current-voltage characteristics were obtained in comparison with those obtained by a monochromatic sinusoidal drive. This result is considered to be originated by the harmonics of the rf-signal. In addition, the maximum value of the step-height is independent on the step number. (orig.)
DEFF Research Database (Denmark)
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....
Modulated microwave absorption spectra from Josephson junctions on a scratched niobium wire
International Nuclear Information System (INIS)
Modulated microwave absorption (MMA) spectra from Josephson junction formations on a scratched Nb wire have been studied at 9.3 GHz and 4 K. The peak-to-peak separation, δH of the Josephson lines was found to vary linearly with P1/2, where P is the applied microwave power, in contrast to a recent interpretation of junction formation in pressed lead pieces by Rubins, Drumheller, and Trybula. The interpretation of the MMA data on Nb are given in terms of the theory of Vichery, Beuneu, and Lejay for superconducting loops containing weak links. copyright 1997 The American Physical Society
Effective model for a short Josephson junction with a phase discontinuity
Goldobin, E.; Mironov, S.; Buzdin, A.; Mints, R. G.; Koelle, D.; Kleiner, R.
2016-04-01
We consider a short Josephson junction with a phase discontinuity κ created, e.g., by a pair of tiny current injectors, at some point x0 along the width of the junction. We derive the effective current-phase relation (CPR) for the system as a whole, i.e., reduce it to an effective pointlike junction. From the effective CPR we obtain the ground state of the system and predict the dependence of its critical current on κ . We show that in a large range of κ values the effective junction behaves as a φ0 Josephson junction, i.e., has a unique ground state phase φ0 within each 2 π interval. For κ ≈π and x0 near the middle of the junction one obtains a φ0±φ junction, i.e., a Josephson junction with degenerate ground state phase φ0±φ within each 2 π interval. Further, in view of possible escape experiments especially in the quantum domain, we investigate the scaling of the energy barrier and eigenfrequency close to the critical currents and predict the behavior of the escape histogram width σ (κ ) in the regime of the macroscopic quantum tunneling.
In-phase electrodynamics and terahertz wave emission in extended intrinsic Josephson junctions
Koyama, Tomio; Matsumoto, Hideki; Machida, Masahiko; Kadowaki, Kazuo
2009-03-01
Strong emission of subterahertz electromagnetic (EM) waves has been observed recently in the high Tc superconductor Bi2Sr2CaCu2O8 intrinsic Josephson junctions (IJJ’s). We investigate numerically the dynamics of the EM fields both inside and outside the IJJ’s emitting terahertz EM waves under a constant bias current, using two-dimensional models composed of IJJ’s and the space surrounding them: (1) xy model and (2) xz model. In the xy model we investigate the EM modes excited in the rectangular junctions. In the voltage state the Josephson oscillation generates the oscillating EM field having nodes inside the junctions. The number of nodes depends on the DC voltage appearing in the junctions, and their direction is parallel to the shorter side of the junctions. The EM field shows a complex distribution pattern in the near field region. In the region far from the junctions we have only the expanding EM wave oscillating with the Josephson frequency. In the xz model we study the EM waves emitted in the xz plane from the junctions covered with normal electrodes. It is shown that the power of the emitted EM waves has distribution similar to that in the dipole emission in the system where electrodes of the same size are attached on top and bottom junctions. In the asymmetric system where the lower electrode is larger than the upper one the power distribution of emitted EM wave deviates from that in the dipole emission.
Gapped graphene-based Josephson junction with d-wave pair coupling
Energy Technology Data Exchange (ETDEWEB)
Goudarzi, H., E-mail: h.goudarzi@urmia.ac.ir; Khezerlou, M., E-mail: m.khezerlou@urmia.ac.ir; Dezhaloud, T.
2013-06-15
Highlights: • We aim to study the influence of the Josephson current passing through a d-wave S/I/S gapped graphene-based junction. • We investigate how the Andreev bound states and the Josephson current are affected by characteristic of d-wave pairing asymmetry. • It is shown that the Josephson current for special range of phase vanishes and the position of the maximum current depends on the mass gap of graphene. -- Abstract: The Josephson current passing through a S/I/S gapped graphene-based junction, where superconductivity in the S region is induced by depositing unconventional d-wave superconductor is investigated. The energy levels of massive Dirac fermions are exactly found for Andreev bound states. We illustrate the effect of characteristic of d-wave pairing symmetry on the Andreev bound states and the Josephson current. It is shown that the Josephson current vanishes for special range of superconductivity phase, φ = φ{sub 1} − φ{sub 2} and the position of the maximum current depends on the mass gap of graphene. The critical supercurrent varies in an oscillatory manner as function of the barrier strength, so that the period of oscillations does not change by increasing the effective mass of quasiparticles.
Gapped graphene-based Josephson junction with d-wave pair coupling
International Nuclear Information System (INIS)
Highlights: • We aim to study the influence of the Josephson current passing through a d-wave S/I/S gapped graphene-based junction. • We investigate how the Andreev bound states and the Josephson current are affected by characteristic of d-wave pairing asymmetry. • It is shown that the Josephson current for special range of phase vanishes and the position of the maximum current depends on the mass gap of graphene. -- Abstract: The Josephson current passing through a S/I/S gapped graphene-based junction, where superconductivity in the S region is induced by depositing unconventional d-wave superconductor is investigated. The energy levels of massive Dirac fermions are exactly found for Andreev bound states. We illustrate the effect of characteristic of d-wave pairing symmetry on the Andreev bound states and the Josephson current. It is shown that the Josephson current vanishes for special range of superconductivity phase, φ = φ1 − φ2 and the position of the maximum current depends on the mass gap of graphene. The critical supercurrent varies in an oscillatory manner as function of the barrier strength, so that the period of oscillations does not change by increasing the effective mass of quasiparticles
Josephson junction spectrum analyzer for millimeter and submillimeter wavelengths
Energy Technology Data Exchange (ETDEWEB)
Larkin, S.Y.; Anischenko, S.E.; Khabayev, P.V. [State Research Center, Kiev (Ukraine)
1994-12-31
A prototype of the Josephson-effect spectrum analyzer developed for the millimeter-wave band is described. The measurement results for spectra obtained in the frequency band from 50 to 250 GHz are presented.
Institute of Scientific and Technical Information of China (English)
Liang Bao-Long; Wang Ji-Suo; Fan Hong-Yi
2008-01-01
This paper examines the quantization of mesoscopic circuit including Josephson junctions.Following Feynman's assumption,via the Hamilton dynamic approach and by virtue of the entangled state representation,it constructs Hamiltonian operator for the double-Jceephson-junction mesoscopic circuit coupled by a capacitor.Then it uses the Heisenberg equation of motion to derive the induction voltage across each Josephson junction.The result manifestly shows how the voltage is affected by the capacitance coupling.
An effect of temperature distribution on terahertz phase dynamics in intrinsic Josephson junctions
Energy Technology Data Exchange (ETDEWEB)
Asai, Hidehiro, E-mail: hd-asai@aist.go.jp; Kawabata, Shiro
2013-11-15
Highlights: •We calculate the temperature distribution in intrinsic Josephson junctions (IJJs). •We investigate the effect of temperature distribution on THz radiation from IJJs. •The Joule heating in the IJJs makes inhomogeneous temperature distribution. •The inhomogeneous temperature distribution strongly excites THz emission. -- Abstract: In this study, we numerically calculate the temperature distribution and the THz phase dynamics in the mesa-structured intrinsic Josephson junctions (IJJs) using the thermal diffusion equation and the Sine–Gordon equation. We observe that the temperature distribution has a broad peak around the center region of the IJJ mesa. Under a high external current, a “hot spot” where the temperature is locally higher than the superconducting critical temperature appears around this region. The transverse Josephson plasma wave is strongly excited by the inhomogeneous temperature distribution in the mesa. This gives rise to intense THz emission.
RF impedance of intrinsic Josephson junction in flux-flow state with a periodic pinning potential
Yamada, Y.; Nakajima, K.; Nakajima, K.
2008-09-01
We have investigated the dynamics of Josephson vortices interacting with electromagnetic waves in Bi 2Sr 2CaCu 2O 8+ y intrinsic Josephson junction (IJJ) stacks by means of millimeter wave irradiation and numerical simulations based on coupled sine-Gordon equations while taking into account a sinusoidal form of the periodic pinning potential. The numerical simulation results for the influence of the electromagnetic waves on the flux-flow properties reveal that the periodic pinning potential induces the in-phase motion of Josephson vortices over the junctions. In order to prove from another viewpoint, we investigate RF impedance of IJJ in flux-flow state in this study. A remarkable negative real part region appears at 1st harmonic step, it means that the IJJ in flux-flow state acts as an oscillator at the negative real part region.
Reentrant superconducting behavior of the Josephson SFS junction. Evidence for the π-phase state
Ryazanov, V. V.; Veretennikov, A. V.; Oboznov, V. A.; Rusanov, A. Yu.; Larkin, V. A.; Golubov, A. A.; Aarts, J.
2000-11-01
Critical supercurrents, Ic in Nbsbnd Cu1- xNixsbnd Nb Josephson SFS junctions with F-layers prepared from ferromagnetic Cu1- xNix alloys have been studied. For value x=0.52 and particular F-layer thickness we have observed Ic( T) oscillations with Ic vanishing for some values of T. We associate this reentrant superconducting behavior with a crossover of the SFS junction from ‘0’- to ‘π’-state that is related to temperature dependence of spatial oscillation period of induced superconducting order parameter in the weak ferromagnet. We argue this is the first experimental evidence of the π-behavior of a Josephson junction, that is the special feature of superconducting pair flow through a ferromagnet predicted for SFS junctions by Bulaevskii, Buzdin et al [1].
Transport properties of Nb/PdNi bilayers and Nb/PdNi/Nb Josephson junctions
International Nuclear Information System (INIS)
The superconducting proximity effect was examined in both Nb/PdNi (SF) bilayer films and Nb/PdNi/Nb (SFS) Josephson junctions. In Nb/PdNi bilayer films, nonmonotonic behavior of Tc was observed as a function of PdNi thickness dF. The effective exchange energy Eex extracted from the data was about 13 meV. In Nb/PdNi/Nb (SFS) Josephson junctions, the existence of a crossover between the 0 state and the π state was confirmed in the PdNi thickness dependence of Ic. For the junction with dF = 9 nm, such a crossover was observed in the temperature dependence of Ic. Eex estimated from the junctions characteristics was about 19 meV. These behaviors can be interpreted from the view point of a damped oscillatory superconducting order parameter induced at the SF interface.
Design of a scanning Josephson junction microscope for submicron-resolution magnetic imaging
International Nuclear Information System (INIS)
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
Amplitude Control of the Spin-Triplet Supercurrent in S /F /S Josephson Junctions
Martinez, William M.; Pratt, W. P.; Birge, Norman O.
2016-02-01
Josephson junctions made with conventional s -wave superconductors and containing multiple layers of ferromagnetic materials can carry spin-triplet supercurrent in the presence of certain types of magnetic inhomogeneity. In junctions containing three ferromagnetic layers, the triplet supercurrent is predicted to be maximal when the magnetizations of the adjacent layers are orthogonal, and zero when the magnetizations of any two adjacent layers are parallel. Here we demonstrate on-off control of the spin-triplet supercurrent in such junctions, achieved by rotating the magnetization direction of one of the three layers by 90°. We obtain "on-off" ratios of 5, 7, and 19 for the supercurrent in the three samples that have been studied so far. These observations directly confirm one of the most salient predictions of the theory, and they pave the way for applications of spin-triplet Josephson junctions in the nascent area of "superconducting spintronics".
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.
Characteristics of Off-Chip Millimeter-Wave Radiation from Serial Josephson Junction Arrays
Institute of Scientific and Technical Information of China (English)
WANG Zheng; FAN Bin; ZHAO Xin-Jie; YUE Hong-Wei; HE Ming; JI Lu; YAN Shao-Lin; FANG Lan; Klushin A. M.
2011-01-01
@@ We investigate the self-emissions from serial high-temperature superconductor bicrystal Josephson junction ar- rays embedded in a quasi-optical resonator.A bicrystal substrate is used as a dielectric resonator antenna, which increases the coupling strength between the junction array and the electromagnetic (EM) wave.Both three-dimension (3D) electromagnetic simulations and experiments are performed.Strong ofT-chip radiations axe measured from the junction array at 78 GHz and 78 K.The proposed method and the experimental results are important for millimeter wave applications in junction arrays.
DEFF Research Database (Denmark)
Shukrinov, Yu M.; Mahfouzi, F.; Pedersen, Niels Falsig
2007-01-01
We study the breakpoint region on the outermost branch of current-voltage characteristics of the stacks with di_erent number of intrinsic Josephson junctions. E_ect of the boundary conditions on the breakpoint region is demonstrated. At periodic boundary conditions the breakpoint region is absent...... for stacks with even number of junctions. For stacks with odd number of junctions and for stacks with nonperiodic boundary conditions the breakpoint current is increased with number of junctions and saturated at the value corresponding to the periodic boundary conditions. The region of saturation and...
Moor, Andreas; Volkov, Anatoly F.; Efetov, Konstantin B.
2016-03-01
On the basis of the Usadel equation we study a multiterminal Josephson junction. This junction is composed by "magnetic" superconductors Sm, which have singlet pairing and are separated from the normal n wire by spin filters so that the Josephson coupling is caused only by fully polarized triplet components. We show that there is no interaction between triplet Cooper pairs with antiparallel total spin orientations. The presence of an additional singlet superconductor S attached to the n wire leads to a finite Josephson current IQ with an unusual current-phase relation. The density of states in the n wire for different orientations of spins of Cooper pairs is calculated. We derive a general formula for the current IQ in a multiterminal Josephson contact and apply this formula for analysis of two four-terminal Josephson junctions of different structures. It is shown in particular that both the "nematic" and the "magnetic" cases can be realized in these junctions. In a two-terminal structure with parallel filter orientations and in a three-terminal structure with antiparallel filter orientations of the "magnetic" superconductors with attached additional singlet superconductor, we find a nonmonotonic temperature dependence of the critical current. Also, in these structures, the critical current shows a Riedel peak like dependence on the exchange field in the "magnetic" superconductors. Although there is no current through the S/n interface due to orthogonality of the singlet and triplet components, the phase of the order parameter in the superconuctor S is shown to affect the Josephson current in a multiterminal structure.
Planar S-F-S Josephson junctions made by focused ion beam etching
International Nuclear Information System (INIS)
Superconductor-ferromagnet-superconductor (S-F-S) Josephson junctions were fabricated by making a narrow cut through a S-F double layer using direct writing by focused ion beam (FIB). Due to a high resolution (spot size smaller than 10 nm) of FIB, junctions with a small separation between superconducting electrodes (cRn product ranging from 0.5 mV to ∼1 μV were fabricated
Amado, M.; Fornieri, A.; Carillo, F.; Biasiol, G; Sorba, L.; Pellegrini, V.; F. Giazotto
2013-01-01
The magneto-electrostatic tailoring of the supercurrent in quantum point contact ballistic Josephson junctions is demonstrated. An etched InAs-based heterostructure is laterally contacted to superconducting niobium leads and the existence of two etched side gates permits, in combination with the application of a perpendicular magnetic field, to modify continuously the magnetic interference pattern by depleting the weak link. For wider junctions the supercurrent presents a Fraunhofer-like inte...
Experimental demonstration of Aharonov-Casher interference in a Josephson junction circuit
Pop, I. M.; Douçot, B.; Ioffe, L.; Protopopov, I.; Lecocq, F.; Matei, I.; Buisson, O.; Guichard, W.
2011-01-01
A neutral quantum particle with magnetic moment encircling a static electric charge acquires a quantum mechanical phase (Aharonov-Casher effect). In superconducting electronics the neutral particle becomes a fluxon that moves around superconducting islands connected by Josephson junctions. The full understanding of this effect in systems of many junctions is crucial for the design of novel quantum circuits. Here we present measurements and quantitative analysis of fluxon interference patterns...
Tafuri, F.; Carillo, F.; Lombardi, F.; Granozio, F. Miletto; Ricci, F; di Uccio, U. Scotti; Barone, A.; Testa, G.; E. Sarnelli; Kirtley, J. R.
2000-01-01
We present various concepts and experimental procedures to produce biepitaxial YBaCuO grain boundary Josephson junctions. The device properties have an interesting phenomenology related in part to the possible influence of "pai loops". The performance of our junctions and Superconducting Quantum Interference Devices indicates significant improvement in the biepitaxial technique. Further, we propose methods for fabricating circuits in which "0-" and "pai-loops" are controllably located on the ...
Gate-controlled supercurrent reversal in MoS$_2$-based Josephson junctions
Rameshti, Babak Zare; Moghaddam, Ali G.; Zareyan, Malek
2014-01-01
Motivated by recent experiments revealing superconductivity in MoS$_2$, we investigate the Josephson effect in the monolayer MoS$_2$ at the presence of an exchange splitting. We show that the supercurrent reversal known as $0-\\pi$ transition can occur by varying the doping via gate voltages. This is in contrast to common superconductor/ferromagnet/superconductor junctions in which successive $0-\\pi$ transition take place with the variation of junction length or temperature. In fact for the ca...
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...
Fluxon modes in stacked Josephson junctions: The role of linear modes
DEFF Research Database (Denmark)
Madsen, Søren Peder; Pedersen, Niels Falsig
2004-01-01
Plasma modes in stacked Josephson junctions are easily understood analytically from a linearization of the coupled sine-Gordon equation describing the system. We demonstrate here by numerical methods that the analytically derived symmetries of the plasma modes are carried over to the fluxon modes...
Kink propagation and trapping in a two-dimensional curved Josephson junction
DEFF Research Database (Denmark)
Gorria, Carlos; Gaididei, Yuri Borisovich; Sørensen, Mads Peter;
2004-01-01
for Josephson junctions of overlap type. A collective variable approach based on the kink position and the kink width depending on the transversal coordinate is developed. The latter allows to take into account both longitudinal and centrifugal forces which act on the nonlinear excitation moving in a region...
International Nuclear Information System (INIS)
The dependence of the mean value of the voltage of a Josephson junction on temperature and current is obtained for low viscosity. No resonant response to high-frequency-driven force exists in the mean value of the voltage when the frequency is close to the distances between levels at quasilocalized states
Parameter dependence of homoclinic solutions in a single long Josephson junction
Berg, van den J.B.; Gils, van S.A.; Visser, T.P.P.
2003-01-01
For a model of the long Josephson junction one can calculate for which parameter values there exists a homoclinic solution (fluxon solution). These parameter values appear to lie on a spiral. We show that this is a consequence of the presence of a heteroclinic solution, which lies at the centre of t
Noise properties in an rf-biased Josephson junction noise thermometer
International Nuclear Information System (INIS)
Frequency fluctuation in an rf-biased R-SQUID noise thermometer operating in an nonhysteretic mode is examined. The noise sources caused by the shunt resistor and by the dissipative elements in the tank circuit are included in the model. The results demonstrate that the noise in the tank circuit has a significant influence on the accuracy of the Josephson junction noise thermometer
On the transmission of binary bits in discrete Josephson-junction arrays
Energy Technology Data Exchange (ETDEWEB)
Macias-Diaz, J.E. [Departamento de Matematicas y Fisica, Universidad Autonoma de Aguascalientes, Avenida Universidad 940, Colonia Ciudad Universitaria, Aguascalientes, Ags. 20100 (Mexico)], E-mail: jemacias@correo.uaa.mx; Puri, A. [Department of Physics, University of New Orleans, 2000 Lake Shore Dr., New Orleans, LA 70148 (United States)], E-mail: apuri@uno.edu
2008-07-21
In this work, we use supratransmission and infratransmission in the mathematical modeling of the propagation of digital signals in weakly damped, discrete Josephson-junction arrays, using energy-based detection criteria. Our results show an efficient and reliable transmission of binary information.
Schäpers, Th.; Guzenko, V.A.; Müller, R.P.; Golubov, A.A.; Brinkman, A.; Crecelius, G.; Kaluza, A.; Lüth, H.
2003-01-01
We study the suppression of the critical current in a multi-terminal superconductor/two-dimensional electron gas/superconductor Josephson junction by means of hot carrier injection. As a superconductor Nb is used, while the two-dimensional electron gas is located in a strained InGaAs/InP heterostruc
X-band singly degenerate parametric amplification in a Josephson tunnel junction
DEFF Research Database (Denmark)
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...
Aspects of stochastic resonance in Josephson junction, bimodal maps and coupled map lattice
Indian Academy of Sciences (India)
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.
Criteria for fluxon generation in long Josephson junctions by current pulses
Sakai, S.; Samuelsen, Mogens Rugholm
1987-01-01
In recent measurements in the time domain on the fluxon shape in long Josephson junctions the fluxons were generated by a current pulse injected into one end. We present here a perturbation treatment of the fluxon generation which we compare with numerical experiments. The agreement turns out to be excellent. Applied Physics Letters is copyrighted by The American Institute of Physics.
Edge-type Josephson junctions in narrow thin-film strips
Moshe, Maayan; Kogan, V. G.; Mints, R. G.
2008-07-01
We study the field dependence of the maximum current Im(H) in narrow edge-type thin-film Josephson junctions. We calculate Im(H) within nonlocal Josephson electrodynamics taking into account the stray fields. These fields affect the difference of phases of the order parameter 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, i.e., it is universal. An explicit formula for this universal function is derived and used to calculate Im(H) . It is shown that the maxima of Im(H)∝1/H and the zeros of Im(H) are equidistant only in high fields. We find that the spacing between the zeros is proportional to 1/w2 , where w is the width of the junction. The general approach is applied to calculate Im(H) for a superconducting quantum interference device (SQUID) with two narrow edge-type junctions.
Blackburn, James A.; Cirillo, Matteo; Grønbech-Jensen, Niels
2016-02-01
For decades following its introduction in 1968, the resistively and capacitively shunted junction (RCSJ) model, sometimes referred to as the Stewart-McCumber model, was successfully applied to study the dynamics of Josephson junctions embedded in a variety of superconducting circuits. In 1980 a theoretical conjecture by A.J. Leggett suggested a possible new and quite different behavior for Josephson junctions at very low temperatures. A number of experiments seemed to confirm this prediction and soon it was taken as given that junctions at tens of millikelvins should be regarded as macroscopic quantum entities. As such, they would possess discrete levels in their effective potential wells, and would escape from those wells (with the appearance of a finite junction voltage) via a macroscopic quantum tunneling process. A zeal to pursue this new physics led to a virtual abandonment of the RCSJ model in this low temperature regime. In this paper we consider a selection of essentially prototypical experiments that were carried out with the intention of confirming aspects of anticipated macroscopic quantum behavior in Josephson junctions. We address two questions: (1) How successful is the non-quantum theory (RCSJ model) in replicating those experiments? (2) How strong is the evidence that data from these same experiments does indeed reflect macroscopic quantum behavior?
New type of zero-field steps in the I-V curve of a Josephson junction of intermediate length
DEFF Research Database (Denmark)
Hansen, Jørn Bindslev; Mygind, Jesper
1985-01-01
We report on the observation of a new type of high-order zero-field steps in the I-V curve of a Josephson transmission line of intermediate length l=L/λJ≊5, where λJ is the Josephson penetration length. On such steps, deviations from the generalized Josephson relation Vdc=N(h/2e)νdet relating the...... measured dc voltage to the frequency of the radiation emitted from the junction are observed....
New type of zero-field steps in the I-V curve of a Josephson junction of intermediate length
Hansen, Jørn Bindslev; Mygind, Jesper
1985-01-01
We report on the observation of a new type of high-order zero-field steps in the I-V curve of a Josephson transmission line of intermediate length l=L/λJ≊5, where λJ is the Josephson penetration length. On such steps, deviations from the generalized Josephson relation Vdc=N(h/2e)νdet relating the measured dc voltage to the frequency of the radiation emitted from the junction are observed.
Properties of Josephson tunnel junction with trapped Abrikosov vortices
International Nuclear Information System (INIS)
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
Two-dimensional macroscopic quantum tunneling in multi-gap superconductor Josephson junctions
International Nuclear Information System (INIS)
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
Non-sinusoidal current-phase relations in SFS pi-Josephson junctions
van Harlingen, Dale J.
2010-03-01
We report the direct observation of a sin(2φ) component in the current-phase relation (CPR) of Superconductor-Ferromagnet-Superconductor (SFS) Josephson junctions. The deviation from a sinusoidal CPR is most evident near the crossover between the 0-junction to π-junction states reached by tuning the thickness of the ferromagnet barrier and the temperature. We measure the CPR in Nb-CuNi-Nb junctions using a phase-sensitive Josephson interferometer technique in which the junctions are incorporated into a superconducting loop coupled to a dc SQUID. We correlate the CPR data with measurements of subharmonic Shapiro steps and anomalous critical current diffraction patterns that have previously been cited as evidence for higher-order Josephson tunneling components. We will discuss possible origins and implications for the non-sinusoidal component. In collaboration with M.J.A. Stoutimore (University of Illinois at Urbana-Champaign) and A.Yu. Rusanov, V.A. Oboznov, V.V. Bolginov, A.N. Rossolenko, and V.V. Ryazanov (Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Russia).
Semifluxons in 0–π–0 infinitely long Josephson junctions
International Nuclear Information System (INIS)
We investigate both analytically and numerically an infinitely long Josephson junction with two π-discontinuities in the phase characterized by a jump of π in the phase difference of the junction, i.e. a 0–π–0 long Josephson junction on an infinite domain. The dynamics of the system is described by a modified one-dimensional perturbed sine-Gordon equation. We investigate an instability region of the trivial zero solution in which semifluxons are spontaneously generated. A perturbation technique is used to show that the existence of static semifluxons depends on the length of the junction, the facet length, and the applied bias current. Numerical simulations are presented accompanying our analytical results. - Highlights: • A 0–π–0 long Josephson junction on infinite domain is studied. • The stability of the uniform solutions in terms of facet length is discussed. • We show that in the instability region the ground states solutions are non-uniform. • The effect of bias current on the ground state is studied. • The critical current about the zero state is calculated analytically
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.
Charge-transport in Josephson-junctions with ferromagnetic Ni3Al-interlayer
International Nuclear Information System (INIS)
The present dissertation reports on experimental studies about superconducting coupling through a thin Ni76Al24 film. A new patterning process has been developed, which allows in combination with the wedge shaped deposition technique the in situ deposition of 20 single Nb/Al/Al2O3/Ni3Al/Nb multilayers, each with its own well defined Ni3Al thickness. Every single multilayer consists of 10 different sized Josephson junctions, showing a high reproducibility and scaling with its junction area. Up to six damped oscillations of the critical current density against F-layer thickness were observed, revealing three single 0-π-transitions in the ground state of Josephson junctions. Contrary to former experimental studies, the exponential decay length is one magnitude larger than the oscillation period defining decay length. The theoretical predictions based on linearised Eilenberger equations results in excellent agreement of theory and experimental results. (orig.)
Energy scales in YBaCuO grain boundary biepitaxial Josephson junctions
International Nuclear Information System (INIS)
Self-assembled nanoscale channels may naturally arise in the growth process of grain boundaries (GBs) in high critical temperature superconductor (HTS) systems, and deeply influence the transport properties of the GB Josephson junctions (JJs). By isolating nano-channels in YBCO biepitaxial JJs and studying their properties, we sort out specific fingerprints of the mesoscopic nature of the contacts. The size of the channels combined to the characteristic properties of HTS favors a special regime of the proximity effect, where normal state coherence prevails on the superconducting coherence in the barrier region. Resistance oscillations from the current-voltage characteristic encode mesoscopic information on the junction and more specifically on the minigap induced in the barrier. Thouless energy emerges as a characteristic energy of these types of Josephson junctions. Possible implications on the understanding of coherent transport of quasiparticles in HTS and of the dissipation mechanisms are discussed, along with elements to take into account when designing HTS nanostructures.
Turbulence, chaos and thermal noise in globally coupled Josephson junction arrays
International Nuclear Information System (INIS)
We discuss the effects of thermal noise in underdamped Josephson junction series arrays that are globally coupled through a resistive load and driven by an rf current. We study the breakdown of the law of large numbers in the turbulent phase of the Josephson arrays. This corresponds to a saturation of the broad band noise S0 for a large number N of junctions. We find that this phenomenon is stable against thermal fluctuations below a critical temperature Tcl. The behaviour of S0 vs. T, for large N, shows three different regimes. For 0 cl, S0 decreases when increasing T, and there is turbulence and the breakdown of the law of large numbers. For Tcl c2, S0 is constant and the dynamics is dominated by the chaos of the individual junctions. Finally for T > Tc2, S0 in mainly due to thermal fluctuations, since it increases linearly with T. (author). 23 refs, 6 figs
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.
Experimental and theoretical investigation on high-Tc superconducting intrinsic Josephson junctions
Grib, Alexander; Shukrinov, Yury; Schmidl, Frank; Seidel, Paul
2010-11-01
Within the last years many groups have realized and investigated different types of intrinsic Josephson junction (IJJ) arrays out of high-temperature superconducting single crystals or thin films. We tried to improve the synchronization between the junctions by external shunts. Mesa structures as well as microbridges on vicinal cut substrates showed multi-branch behaviour in their IV characteristics and random switching between branches. Theoretical modelling was done investigating phase dynamics and stability numerically as well as analytically. Branch structure in current voltage characteristics of IJJ is studied in the framework of different models, particularly, in capacitevely coupled Josephson junctions (CCJJ) model and CCJJ model with diffusion current. Results of modelling of return current in IV characteristics for stacks with different number of IJJ are presented. We discussed the possible mechanisms of synchronization and the ranges of stability. Conclusions with respect to application of such arrays such as radiation sources were given.
A search for the coherently radiating fluxon state in stacks of long intrinsic Josephson junctions
Lee, H J; Bae, M H; Wang, H; Yamashita, T
2002-01-01
We studied the motion of fluxons in a stack of intrinsic Josephson junctions (IJJs) of Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 sub + subdelta single crystals in a long junction limit. Driven by the tunnelling bias, current Josephson fluxons excite plasma oscillations and move in resonance with the plasma propagation modes. We examined two types of samples in this study; mesa structure (UD1) and a stack of junctions sandwiched between normal-metallic electrodes (DSC1). In a high magnetic field, the hysteresis in the I-V characteristics of both-types of samples vanished. The resulting single I-V curve exhibited a cusp structure at characteristic bias voltages which were believed to be boundaries of different moving fluxon configurations. We studied the sample-geometry dependence of the cusp characteristics by comparing the results from the two types of samples.
Cryogenic small-signal conversion with relaxation oscillations in Josephson junctions
Furlan, M
2006-01-01
Broadband detection of small electronic signals from cryogenic devices, with the option of simple implementation for multiplexing, is often a highly desired, although non-trivial task. We investigate and demonstrate a small-signal analog-to-frequency conversion system based on relaxation oscillations in a single Josephson junction. Operation and stability conditions are derived, with special emphasis on noise analysis, showing the dominant noise sources to originate from fluctuation processes in the junction. At optimum conditions the circuit is found to deliver excellent noise performance over a broad dynamic range. Our simple models successfully apply within the regime of classical Josephson junction and circuit dynamics, which we confirm by experimental results. A discussion on possible applications includes a measurement of the response to a cryogenic radiation detector.
International Nuclear Information System (INIS)
In terms of nonlocal electrodynamics of the Josephson junction in a finite thickness plate one investigated into modulation instability of the Josephson frequency oscillating homogeneous plane finite amplitude waves with nonlinear shift of frequency. One derived dispersion equation for increment of intensification of small amplitude perturbations. For the mentioned type of the waves one determined the regions of modulation instability development. Modulation instability of waves is shown to develop for long-wave amplitude perturbations in the finite range of O B(A, D, L) wave vectors, while for Q ≥ QB(A, D, L) waves are stable ones
Nonlocal magnetic configuration controlling realized in a triple-quantum-dot Josephson junction
Yi, Guang-Yu; Wang, Xiao-Qi; Wu, Hai-Na; Gong, Wei-Jiang
2016-07-01
We investigate the Josephson effect in a superconductor/triple-quantum-dot/superconductor junction in which the central dot is coupled to the superconductors. It is found that the supercurrent exhibits rich 0-π phase translations due to the interplay between interdot spin and electron correlations. Moreover, when the side dots are half-occupied, the nonlocal spin correlation between them, i.e., ferromagnetic or antiferromagnetic, coincides well with the supercurrent phase. We thus consider such a system to be a promising candidate for controlling the nonlocal magnetic configuration based on the Josephson effect.
Anomalous Josephson Effect in Junctions with Rashba Spin-Orbit Coupling
Nesterov, Konstantin; Houzet, Manuel; Meyer, Julia
2015-03-01
We study two-dimensional double-barrier SINIS Josephson junctions in which the inversion symmetry in the normal part is broken by Rashba spin-orbit coupling. In the presence of a suitably oriented Zeeman field in the normal part, the system displays the anomalous Josephson effect: the current is nonzero even at zero phase difference between two superconductors. We investigate this effect by means of the Ginzburg-Landau formalism and microscopic Green's functions approach in the clean limit. This work was supported in part by the Grants No. ANR-12-BS04-0016-03 and an EU-FP7 Marie Curie IRG.
An effect of temperature distribution on terahertz phase dynamics in intrinsic Josephson junctions
Asai, Hidehiro; Kawabata, Shiro
2013-11-01
In this study, we numerically calculate the temperature distribution and the THz phase dynamics in the mesa-structured intrinsic Josephson junctions (IJJs) using the thermal diffusion equation and the Sine-Gordon equation. We observe that the temperature distribution has a broad peak around the center region of the IJJ mesa. Under a high external current, a “hot spot” where the temperature is locally higher than the superconducting critical temperature appears around this region. The transverse Josephson plasma wave is strongly excited by the inhomogeneous temperature distribution in the mesa. This gives rise to intense THz emission.
International Nuclear Information System (INIS)
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)
Shukrinov, Yu. M.; Rahmonov, I. R.; Plecenik, A.; Streltsova, O. I.; Zuev, M. I.; Ososkov, G. A.
2016-02-01
The current-voltage (IV) characteristics of the intrinsic Josephson junctions in high temperature superconductors under external electromagnetic radiation are calculated numerically in the parametric resonance region. We discuss a numerical method for calculation of the Shapiro step width on the amplitude of radiation. In order to accelerate computations we used parallelization by task parameter via Simple Linux Utility for Resource Management (SLURM) arrays and tested it in the case of a single junction. An analysis of the junction transitions between rotating and oscillating states in the branching region of IV-characteristics is presented.
Vortex penetration and self-resonant effects in large Josephson tunnel junction
International Nuclear Information System (INIS)
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
Observation of supercurrent in PbIn-graphene-PbIn Josephson junction
Jeong, Dongchan; Choi, Jae-Hyun; Lee, Gil-Ho; Jo, Sanghyun; Doh, Yong-Joo; Lee, Hu-Jong
2011-03-01
Superconductor-graphene-superconductor (SGS) junction provides a unique platform to study relativistic electrodynamics of Dirac fermions in graphene combined with proximity-induced superconductivity. We report the observation of the Josephson effect in proximity-coupled superconducting junctions of graphene in contact with Pb1-xInx (x=0.07) electrodes for temperatures as high as T = 4.8 K, with a large value of IcRN (~255 μ V). This demonstrates that Pb1-xInx SGS junction would facilitate the development of the superconducting quantum information devices and superconductor-enhanced phase-coherent transport of graphene.
Observation of Supercurrent in PbIn-Graphene-PbIn Josephson Junction
Jeong, Dongchan; Choi, Jae-Hyun; Lee, Gil-Ho; Jo, Sanghyun; Doh, Yong-Joo; Lee, Hu-Jong
2011-01-01
Superconductor-graphene-superconductor (SGS) junction provides a unique platform to study relativistic electrodynamics of Dirac fermions combined with proximity-induced superconductivity. We report observation of the Josephson effect in proximity-coupled superconducting junctions of graphene in contact with Pb1-xInx (x=0.07) electrodes for temperatures as high as T = 4.8K, with a large IcRn (~ 255 microV). This demonstrates that Pb1-xInx SGS junction would facilitate the development of the su...
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.
Wang, Huabing; Wu, Peiheng; Yamashita, Tsutomu
2001-10-01
Using a newly developed double-side fabrication method, an IJJ stack plus a bow-tie antenna and chokes were integrated in a slice 200 nm thick and singled out from inside a bulk Bi2Sr2CaCu2O8+x (BSCCO) single crystal. The junctions in the fabricated stack were very uniform, and the number of junctions involved was rather controllable. In addition to this method, which can be used to fabricate integrated circuits based on intrinsic Josephson junctions in high temperature (Tc) superconductors, also reported will be terahertz responses of IJJs, and the possible applications in quantum voltage standard, spectroscopy, and so on.
Gapped graphene-based Josephson junction with d-wave pair coupling
Goudarzi, H.; Khezerlou, M.; Dezhaloud, T.
2013-06-01
The Josephson current passing through a S/I/S gapped graphene-based junction, where superconductivity in the S region is induced by depositing unconventional d-wave superconductor is investigated. The energy levels of massive Dirac fermions are exactly found for Andreev bound states. We illustrate the effect of characteristic of d-wave pairing symmetry on the Andreev bound states and the Josephson current. It is shown that the Josephson current vanishes for special range of superconductivity phase, φ = φ1 - φ2 and the position of the maximum current depends on the mass gap of graphene. The critical supercurrent varies in an oscillatory manner as function of the barrier strength, so that the period of oscillations does not change by increasing the effective mass of quasiparticles.
Long-range spin-triplet proximity effect in Josephson junctions with multilayered ferromagnets
International Nuclear Information System (INIS)
We study theoretically the Josephson effect and pairing correlations in planar SF1F2S junctions that consist of conventional superconductors (S) connected through two metallic monodomain ferromagnets (F1 and F2) with transparent interfaces. We solve self-consistently the Eilenberger equations for arbitrary orientation of in-plane magnetizations in the clean limit and for moderate disorder in ferromagnets. Both singlet and triplet pair amplitudes and the Josephson current-phase relations are calculated numerically. It is shown that for equally thick ferromagnetic layers (symmetric junctions) the long-range spin-triplet correlations are not dominant: For thin ferromagnetic layers all amplitudes are equally large, while for thick layers the long range triplet amplitude is very small. It is shown that for noncollinear magnetizations the long-range proximity effect can be dominant in highly non-symmetric SF1F2S junctions with particularly thin F1 and thick F2 ferromagnetic layers. We find that dominant triplet correlations in Josephson junctions with ferromagnetic bilayer always give dominant second harmonics in current-phase relations at low temperatures.
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
Long-range spin-triplet proximity effect in Josephson junctions with multilayered ferromagnets
Energy Technology Data Exchange (ETDEWEB)
Trifunovic, Luka [Department of Physics, University of Belgrade (RS); Department of Physics, University of Basel (Switzerland); Radovic, Zoran [Department of Physics, University of Belgrade (RS)
2011-07-01
We study theoretically the Josephson effect and pairing correlations in planar SF{sub 1}F{sub 2}S junctions that consist of conventional superconductors (S) connected through two metallic monodomain ferromagnets (F{sub 1} and F{sub 2}) with transparent interfaces. We solve self-consistently the Eilenberger equations for arbitrary orientation of in-plane magnetizations in the clean limit and for moderate disorder in ferromagnets. Both singlet and triplet pair amplitudes and the Josephson current-phase relations are calculated numerically. It is shown that for equally thick ferromagnetic layers (symmetric junctions) the long-range spin-triplet correlations are not dominant: For thin ferromagnetic layers all amplitudes are equally large, while for thick layers the long range triplet amplitude is very small. It is shown that for noncollinear magnetizations the long-range proximity effect can be dominant in highly non-symmetric SF{sub 1}F{sub 2}S junctions with particularly thin F{sub 1} and thick F{sub 2} ferromagnetic layers. We find that dominant triplet correlations in Josephson junctions with ferromagnetic bilayer always give dominant second harmonics in current-phase relations at low temperatures.
Vertically-stacked interface-treated Josephson junctions fabricated by new in situ process
International Nuclear Information System (INIS)
We have developed a new in situ preparation process for trilayer structures of vertically-stacked Josephson junctions. We adopted YBa2Cu3O7-x (YBCO) as a base electrode, and YbBa2Cu3O7-x (YbBCO) as a counter electrode in these junctions. The barrier was formed by sputtering in a reduced total gas pressure and subsequent annealing. As the gas pressure decreases, the mean free path of the negative ions increases, which results in the bombardment of higher energy ions to the substrate and in etching the base electrode surface. The critical current Ic of the obtained junction was modulated up to 50% by applying an external magnetic field. The difference of the characteristics between the junctions fabricated by this new technique and conventional interface-treated junctions would be attributed to the difference in the species and their energy distributions of the particles incident to the sample during the barrier formation
R.F. self-field depression of microwave induced currents steps in Josephson tunnel junction
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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
Energy Technology Data Exchange (ETDEWEB)
Gaber, Tobias
2007-07-01
In this thesis static and dynamic properties of fractional vortices in long Josephson junctions are investigated. Fractional vortices are circulating supercurrents similar to the well-known Josephson fluxons. Yet, they show the distinguishing property of carrying only a fraction of the magnetic flux quantum. Fractional vortices are interesting non-linear objects. They spontaneously appear and are pinned at the phase discontinuity points of so called 0-{kappa} junctions but can be bend or flipped by external forces like bias currents or magnetic fields. 0-{kappa} junctions and fractional vortices are generalizations of the well-known 0-{pi} junctions and semifluxons, where not only phase jumps of pi but arbitrary values denoted by kappa are considered. By using so-called artificial 0-{kappa} junctions that are based on standard Nb-AlO{sub x}-Nb technology the classical dynamics of fractional vortices has been investigated experimentally for the very first time. Here, half-integer zero field steps could be observed. These voltage steps on the junction's current-voltage characteristics correspond to the periodic flipping/hopping of fractional vortices. In addition, the oscillatory eigenmodes of fractional vortices were investigated. In contrast to fluxons fractional vortices have an oscillatory eigenmode with a frequency within the plasma gap. Using resonance spectroscopy the dependence of the eigenmode frequency on the flux carried by the vortex and an applied bias current was determined. (orig.)
Temperature behavior of SNS-like Nb/Al-AlO x/Nb Josephson junctions
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Overdamped Nb/Al-AlO x/Nb Josephson junctions are an intermediate state between the SIS and SNS Josephson junctions. Stable and reproducible non-hysteretic current-voltage characteristics have been obtained with a proper choice of the fabrication parameters, featuring critical current densities J c up to 25 kA/cm2 and characteristic voltages up to 450 μV. While these values make the junctions interesting for RSFQ electronic circuits, their response to an RF signal at 70 GHz has demonstrated their suitability for both programmable and ac voltage standard. In these work we analyse the temperature behavior of these junctions up to T/T c = 1, T c being the niobium critical temperature, which gives relevant information on the junction structure and, especially, on the oxide insulator/metallic film barrier, which is the key for the reproducible transition from an hysteretic to a non-hysteretic behavior. The results are also compared with other data of hysteretic and overdamped junctions
Phase-flip bifurcation in a coupled Josephson junction neuron system
Segall, Kenneth; Guo, Siyang; Crotty, Patrick; Schult, Dan; Miller, Max
2014-12-01
Aiming to understand group behaviors and dynamics of neural networks, we have previously proposed the Josephson junction neuron (JJ neuron) as a fast analog model that mimics a biological neuron using superconducting Josephson junctions. In this study, we further analyze the dynamics of the JJ neuron numerically by coupling one JJ neuron to another. In this coupled system we observe a phase-flip bifurcation, where the neurons synchronize out-of-phase at weak coupling and in-phase at strong coupling. We verify this by simulation of the circuit equations and construct a bifurcation diagram for varying coupling strength using the phase response curve and spike phase difference map. The phase-flip bifurcation could be observed experimentally using standard digital superconducting circuitry.
Critical current in semiconductor nanowire Josephson junctions in the presence of magnetic field
International Nuclear Information System (INIS)
We study theoretically the critical current in semiconductor nanowire Josephson junction with strong spin-orbit interaction. The critical current oscillates with an external magnetic field. We reveal that the oscillation of critical current depends on the orientation of magnetic field in the presence of spin-orbit interaction. We perform a numerical simulation using a tight-binding model. The Andreev levels are calculated as a function of phase difference ψ between two superconductors. The DC Josephson current is evaluated from the Andreev levels in the case of short junctions. The spin-orbit interaction induces the effective magnetic field. When the external field is parallel with the effective one, the critical current oscillates accompanying the 0-π like transition at the cusp of critical current. The distance of cusps increases gradually with increasing of the angle between the external and effective fields. The magnetic anisotropy of critical current is attributed to the spin precession due to the spin-orbit interaction
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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.
Phase-flip bifurcation in a coupled Josephson junction neuron system
Energy Technology Data Exchange (ETDEWEB)
Segall, Kenneth, E-mail: ksegall@colgate.edu [Department of Physics and Astronomy, Colgate University, Hamilton, NY 13346 (United States); Guo, Siyang; Crotty, Patrick [Department of Physics and Astronomy, Colgate University, Hamilton, NY 13346 (United States); Schult, Dan [Department of Mathematics, Colgate University, Hamilton, NY 13346 (United States); Miller, Max [Department of Physics and Astronomy, Colgate University, Hamilton, NY 13346 (United States)
2014-12-15
Aiming to understand group behaviors and dynamics of neural networks, we have previously proposed the Josephson junction neuron (JJ neuron) as a fast analog model that mimics a biological neuron using superconducting Josephson junctions. In this study, we further analyze the dynamics of the JJ neuron numerically by coupling one JJ neuron to another. In this coupled system we observe a phase-flip bifurcation, where the neurons synchronize out-of-phase at weak coupling and in-phase at strong coupling. We verify this by simulation of the circuit equations and construct a bifurcation diagram for varying coupling strength using the phase response curve and spike phase difference map. The phase-flip bifurcation could be observed experimentally using standard digital superconducting circuitry.
Above-gap conductance anomaly studied in superconductor-graphene-superconductor Josephson junctions
Energy Technology Data Exchange (ETDEWEB)
Choi, Jae-Hyun; Lee, Hu-Jong [Pohang University of Science and Technology, Pohang (Korea, Republic of); Doh, Yong-Joo [Korea University, Yeongigun (Korea, Republic of)
2010-07-15
We investigated the electrical transport properties of superconductor-graphene-superconductor (SGS) Josephson junctions. At low voltage bias, we observed the conventional proximity-coupled Josephson effect, such as supercurrent flow through graphene, a sub-gap structure of differential conductance due to Andreev reflection, and a periodic modulation of the critical current I{sub c} when a perpendicular magnetic field H is applied to the graphene. For high bias above the superconducting gap voltage, however, we observed an anomalous jump of the differential conductance, the voltage position of which is sensitive to the backgate voltage V{sub g}. Our extensive study with varying V{sub g}, temperature, and H reveals that the above-gap structure takes place at a characteristic power P{sup *}, irrespective of V{sub g}, for a given junction. The temperature and the H dependences of P{sup *} are well explained by an increase in the electron temperature in graphene.
Above-gap conductance anomaly studied in superconductor-graphene-superconductor Josephson junctions
International Nuclear Information System (INIS)
We investigated the electrical transport properties of superconductor-graphene-superconductor (SGS) Josephson junctions. At low voltage bias, we observed the conventional proximity-coupled Josephson effect, such as supercurrent flow through graphene, a sub-gap structure of differential conductance due to Andreev reflection, and a periodic modulation of the critical current Ic when a perpendicular magnetic field H is applied to the graphene. For high bias above the superconducting gap voltage, however, we observed an anomalous jump of the differential conductance, the voltage position of which is sensitive to the backgate voltage Vg. Our extensive study with varying Vg, temperature, and H reveals that the above-gap structure takes place at a characteristic power P*, irrespective of Vg, for a given junction. The temperature and the H dependences of P* are well explained by an increase in the electron temperature in graphene.
Numerical study for electromagnetic wave emission in thin samples of intrinsic Josephson junctions
Koyama, T.; Matsumoto, H.; Ohta, Y.; Machida, M.
2011-11-01
Emission of THz electromagnetic waves from thin samples of intrinsic Josephson junctions (IJJ’s) is numerically studied, using the xz-model. We show that the spatial symmetry of the electromagnetic excitations corresponding to the π-cavity mode is different from that of the 2 π-cavity mode in the IJJ’s where the junction parameters such as the Josephson critical current are weakly inhomogeneous. In such IJJ’s the emission in the [0 0 1] direction, which is forbidden in the dipole emission, appears at the π-cavity mode resonance, whereas it is not observed in the 2 π-cavity mode resonance. It is also shown that the strong emission occurs when the transition between branches in the I- V characteristics takes place.
Charge creation and nucleation of the longitudinal plasma wave in coupled Josephson junctions
Shukrinov, Yu. M.; Hamdipour, M.
2010-11-01
We study the phase dynamics in coupled Josephson junctions described by a system of nonlinear differential equations. Results of detailed numerical simulations of charge creation in the superconducting layers and the longitudinal plasma wave (LPW) nucleation are presented. We demonstrate the different time stages in the development of the LPW and present the results of FFT analysis at different values of bias current. The correspondence between the breakpoint position on the outermost branch of current voltage characteristics (CVC) and the growing region in time dependence of the electric charge in the superconducting layer is established. The effects of noise in the bias current and the external microwave radiation on the charge dynamics of the coupled Josephson junctions are found. These effects introduce a way to regulate the process of LPW nucleation in the stack of IJJ.
Nonideal Quantum Measurement Effects on the Switching Currents Distribution of Josephson Junctions
Pierro, Vincenzo
2016-01-01
The quantum character of Josephson junctions is ordinarily revealed through the analysis of the switching currents, i.e. the current at which a finite voltage appears: A sharp rise of the voltage signals the passage (tunnel) from a trapped state (the zero voltage solution) to a running state (the finite voltage solution). In this context, we investigate the probability distribution of the Josephson junctions switching current taking into account the effect of the bias sweeping rate and introducing a simple nonideal quantum measurements scheme. The measurements are modelled as repeated voltage samplings at discrete time intervals, that is with repeated projections of the time dependent quantum solutions on the static or the running states, to retrieve the probability distribution of the switching currents. The distribution appears to be immune of the quantum Zeno effect, and it is close to, but distinguishable from, the Wentzel-Kramers-Brillouin approximation. For energy barriers comparable to the quantum fund...
Internal resonances in periodically modulated long Josephson junctions
DEFF Research Database (Denmark)
Larsen, Britt Hvolbæk; Mygind, Jesper; Ustinov, Alexey V.
1995-01-01
Fiske modes in the sub-junctions formed between the inhomogeneities. The voltage positions of the resonant steps oscillate as function of the applied magnetic field with a period corresponding to the inclusion of one magnetic flux quantum, Φ0=h/2e, per sub-junction. A qualitative explanation that takes...
Fluxon propagation in long Josephson junctions with external magnetic field
DEFF Research Database (Denmark)
Olsen, O.H.; Samuelsen, Mogens Rugholm
1981-01-01
The reflection of a single fluxon propagating in a Josephson line cavity influenced by an external magnetic field is examined numerically. We find a single reflected fluxon, an antifluxon, collapse of the incident fluxon, fission into a higher number of antifluxons or fluxons, and formation...... of breather-like waves depending on the velocity of the incident fluxon and the magnitude of the external magnetic field. Approximations based on energy analysis describing the border lines between regions of different processes are presented. Journal of Applied Physics is copyrighted by The American...
Nonlinear Phase Dynamics in a Driven Bosonic Josephson Junction
International Nuclear Information System (INIS)
We study the collective dynamics of a driven two-mode Bose-Hubbard model in the Josephson interaction regime. The classical phase space is mixed, with chaotic and regular components, which determine the dynamical nature of the fringe visibility. For a weak off-resonant drive, where the chaotic component is small, the many-body dynamics corresponds to that of a Kapitza pendulum, with the relative phase φ between the condensates playing the role of the pendulum angle. Using a master equation approach we show that the modulation of the intersite potential barrier stabilizes the φ=π 'inverted pendulum' coherent state, and protects the fringe visibility.
Mobile fluxon qubits in a long superconductor-ferromagnet-superconductor Josephson junction
International Nuclear Information System (INIS)
We propose a new type of mobile qubit that utilizes a bound pair of half fluxons in a long superconductor-ferromagnet-superconductor (SFS) Josephson junction. The qubit states are composed of the lowest two levels of the quantized nonlinear internal oscillation of the bound pair. The energy levels are estimated by the numerical quantization based on a collective coordinate method. The qubit operation scheme is discussed, showing an estimate of the interaction strength between a bound pair and a microcircuit
Chaos and catastrophe near the plasma frequency in the rf-biased Josephson junction
International Nuclear Information System (INIS)
At bias frequencies much higher than the plasma frequency, the zero-voltage state of the rf-biased Josephson junction is known to span a range of dc bias proportional to the zero-order Bessel function of the rf amplitude. This pattern is modified at frequencies near the plasma frequency by the onset of chaotic instabilities and by the presence of cusp catastrophes
DEFF Research Database (Denmark)
Filatrella, G; Pedersen, Niels Falsig
1999-01-01
We have numerically investigated the behavior of stacks of long Josephson junctions considering a nonuniform bias profile. In the presence of a microwave field the nonuniform bias, which favors the formation of fluxons, can give rise to a change of the sequence of radio-frequency induced steps. The...... amplitude of the steps is enhanced when the external frequency matches the fluxon shuttling regime. ©1999 American Institute of Physics....
Serdyukova, S. I.
2013-05-01
We prove that in the case of periodic and nonperiodic (with γ = 0) boundary conditions, the calculation of the current-voltage characteristic for a stack of n intrinsic Josephson junctions reduces to solving a unique equation. The current-voltage characteristic V( I) has the shape of a hysteresis loop. On the back branch of the loop, V( I) rapidly decreases to zero near the breakpoint I b . We succeeded to derive an equation determining the approximate breakpoint location.
dc Conductivity of an array of Josephson junctions in the insulating state
Syzranov, S. V.; Efetov, K. B.; Altshuler, B. L.
2009-01-01
We consider microscopically low-temperature transport in weakly disordered arrays of Josephson junctions in the Coulomb blockade regime. We demonstrate that at sufficiently low temperatures the main contribution to the dc conductivity comes from the motion of single-Cooper-pair excitations, scattered by irregularities in the array. Being proportional to the concentration of the excitations, the conductivity is exponentially small in temperature with the activation energy close to the charging...
Majorana boundary modes in Josephson junctions arrays with gapless bulk excitations
Pino, M.; A.M. Tsvelik; Ioffe, L. B.
2015-01-01
The search for Majorana bound states in solid-state physics has been limited to materials which display a gap in their bulk spectrum. We show that such unpaired states appear in certain quasi-one-dimensional Josephson junctions arrays with gapless bulk excitations. The bulk modes mediate a coupling between Majorana bound states via the Ruderman-Kittel-Yosida-Kasuya mechanism. As a consequence, the lowest energy doublet acquires a finite energy difference. For realistic set of parameters this ...
A single intrinsic Josephson junction with double-sided fabrication technique
You, L. X.; M.; Torstensson; Yurgens, A.; Winkler, D.; Lin, C T; Liang, B
2006-01-01
We make stacks of intrinsic Josephson junctions (IJJs) imbedded in the bulk of very thin ($d\\leq 100$~nm) $\\mathrm{Bi_2Sr_2CaCu_2O_{8+x}}$ single crystals. By precisely controlling the etching depth during the double-sided fabrication process, the stacks can be reproducibly tailor-made to be of any microscopic height ($0-9 \\mathrm{nm}
Vortex detection and quantum transport in mesoscopic graphene Josephson junction arrays
Richardson, C. L.; Edkins, S. D.; Berdiyorov, G. R.; Chua, C. J.; Griffiths, J. P.; Jones, G. A. C.; Buitelaar, M.R.; Narayan, V; Sfigakis, F.; Smith, C. G.; Covaci, L.; Connolly, M. R.
2015-01-01
We investigate mesoscopic Josephson junction arrays created by patterning superconducting disks on monolayer graphene, concentrating on the high-$T/T_c$ regime of these devices and the phenomena which contribute to the superconducting glass state in diffusive arrays. We observe features in the magnetoconductance at rational fractions of flux quanta per array unit cell, which we attribute to the formation of flux-quantized vortices. The applied fields at which the features occur are well descr...
Coherent Charge Transport in Ballistic InSb Nanowire Josephson Junctions
Li, S.; Kang, N; Fan, D. X.; L. B. Wang; Huang, Y. Q.; Caroff, P.; Xu, H. Q.
2016-01-01
Hybrid InSb nanowire-superconductor devices are promising for investigating Majorana modes and topological quantum computation in solid-state devices. An experimental realisation of ballistic, phase-coherent superconductor-nanowire hybrid devices is a necessary step towards engineering topological superconducting electronics. Here, we report on a low-temperature transport study of Josephson junction devices fabricated from InSb nanowires grown by molecular-beam epitaxy and provide a clear evi...
Warp of the Invariant Circle and Onset of Chaos in Josephson Junction Equation
Institute of Scientific and Technical Information of China (English)
QIAN Min; WANG Jia-Zeng
2007-01-01
The dynamics of the dc and ac driving Josephson junction equation is studied in terms of the tvo-dimensional Poincaré map. The smooth invariant circle on the phase cylinder in over-damped case α ＞ 2 loses smoothness as α decreases and becomes a strange attractor eventually. This triggers two kinds of chaos, one occurs in the regions between two Arnold tongues and the other occurs within the tongues.
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.
Superconducting current and proximity effect in ABA and ABC multilayer graphene Josephson junctions
Munoz, W. A.; Covaci, L.; Peeters, F. M.
2013-01-01
Using a numerical tight-binding approach based on the Chebyshev-Bogoliubov-de Gennes method we describe Josephson junctions made of multilayer graphene contacted by top superconducting gates. Both Bernal (ABA) and rhombohedral (ABC) stacking are considered and we find that the type of stacking has a strong effect on the proximity effect and the supercurrent flow. For both cases the pair amplitude shows a polarization between dimer and non-dimer atoms, being more pronounced for rhombohedral st...
Analysis of Possible Quantum Metastable States in Ballistic Graphene-based Josephson Junctions
Lambert, Joseph G.; Carabello, Steven; Ramos, Roberto C.
2009-01-01
Graphene is a relatively new material (2004) made of atomic layers of carbon arranged in a honeycomb lattice. Josephson junction devices are made from graphene by depositing two parallel superconducting leads on a graphene flake. These devices have hysteretic current-voltage characteristics with a supercurrent branch and Shapiro steps appear when irradiated with microwaves. These properties motivate us to investigate the presence of quantum metastable states similar to those found in conventi...
International Nuclear Information System (INIS)
We experimentally studied current-voltage characteristics of superconductor/thin graphite film/superconductor Josephson junctions. A reentrant behavior in the differential conductance was observed at low bias voltages just above the structure due to supercurrent. The gate voltage dependence of the conductance peak shows that the origin of the reentrant behavior is different from that for the conventional reentrant behavior seen in a disordered normal metal coupled to a superconductor
The electric field effect and electromagnetic wave emission in intrinsic Josephson junctions
Koyama, T.
2013-04-01
We formulate a theory for the electric field effect in intrinsic Josephson junctions (IJJs). The coupled dynamical equations for the phase differences are derived in the presence of both a bias current and an applied electric field on the basis of the capacitively-coupled IJJ model. It is shown that the current-voltage characteristics of the IJJs sensitively depend on the applied electric field. The dipole emission originating from the electric field effect is also predicted.
Study of charge-phase diagrams for coupled system of Josephson junctions
Hamdipour, M.; Shukrinov, Y. U. M.
2010-11-01
Dynamics of stacked intrinsic Josephson junctions (IJJ) in the high-Tc superconductors is theoretically investigated. We calculate the current-voltage characteristics (CVC) of IJJ and study the breakpoint region on the outermost branch of the CVC for the stacks with 9 IJJ. A method for investigation of the fine structure in CVC of IJJ based on the recording the "phase-charge" diagrams is suggested. It is demonstrated that this method reflects the main features of the breakpoint region.
Koyama, T.; Matsumoto, H.; Ota, Y.; Machida, M.
2013-08-01
Electromagnetic (EM) wave emission from the intrinsic Josephson junction stacks (IJJ’s) covered with a thin dielectric medium is numerically investigated, using the multi-scale simulation method developed in our previous paper. It is shown that the power of emitted EM waves is considerably increased in the IJJ’s with a dielectric cover. The emission from the n = 2 resonance mode is greatly enhanced. The enhancement is caused by the excitation of a solitonic mode.
Study of charge-phase diagrams for coupled system of Josephson junctions
Hamdipour, M.; Shukrinov, Yu M.
2010-01-01
Dynamics of stacked intrinsic Josephson junctions (IJJ) in the high-Tc superconductors is theoretically investigated. We calculate the current-voltage characteristics (CVC) of IJJ and study the breakpoint region on the outermost branch of the CVC for the stacks with 9 IJJ. A method for investigation of the fine structure in CVC of IJJ based on the recording the "phase-charge" diagrams is suggested. It is demonstrated that this method reflects the main features of the breakpoint region.
Zero vorticity condition in calculation of ground state energy of Josephson junction lattices
Azizi, Y.
2010-01-01
We employ the charge neutrality condition in the form of zero vorticity for a Josephson junction lattice in calculating its ground state. We consider a Fibonacci ladder and the Penrose lattice to test our method. We also compare the results with those of the model that treats the plaquettes independently. We show that the zero vorticity condition improves on the results of the independent plaquette model.
Josephson SFS π-junctions. Potential Applications in Computing
Ryazanov, Valeriy; Oboznov, Vladimir; Bolginov, Vitalii; Feofanov, Alexey
2006-09-01
Novel superconducting weak links, `π-junctions', were realized recently. An origin of the π-state in a Superconductor - Ferromagnet - Superconductor (SFS) junction is an oscillating and sign-reversing superconducting order parameter induced in the ferromagnet close to the SF-interface. The π-behavior in SFS sandwiches was first observed by our group in 2000. Our recent result was a detection of transitions into π-state and back into 0-state, i.e. a nonmonotonic (with two nodes) behavior of the junction critical current vs. F-layer thickness, π-junctions with critical current density up to 2000 A/cm2 were achieved that are suitable for applications in future superconducting digital and quantum electronics. Our junctions are based on a niobium thin film technology so they can be incorporated directly into existing architectures of the superconducting electronics.
Zeeman effects on Josephson current in d-wave superconductor/d-wave superconductor junctions
Institute of Scientific and Technical Information of China (English)
Liao Yan-Hua; Dong Zheng-Chao; Yin Zai-Feng; Fu Hao
2008-01-01
This paper solves a self-consistent equation for the d-wave superconducting gap and the effective exchange field in the mean-field approximation,and studies the Zeeman effects on the d-wave superconducting gap and thermodynamic potential.The Josephson currents in the d-wave superconductor(S)/insulating layer(I)/d-wave S junctions are calculated as a function of the temperature,exchange field,and insulating barrier strength under a Zeeman magnetic field on the two d-wave Ss.It is found that the Josephson critical currents in d-wave S/d-wave S junction to a great extent depend on the relative orientation of the effective exchange field of the two S electrodes,and the crystal orientation of the d-wave S.The exchange field under certain conditions can enhance the Josephson critical current in a d-wave S/I/d-wave S junction.
Precise tuning of the kink width in the long Josephson junction
Directory of Open Access Journals (Sweden)
T. Dobrowolski
2008-10-01
Full Text Available Purpose: The purpose of this report is to present how the external magnetic field can be employed in order to precise control the kink width in the long Josephson junction.Design/methodology/approach: In this paper we concentrate on construction of the analytical kink solutions of the sine-Gordon model with the profile modified by the external magnetic field.Findings: The main findings of this article are exact solutions of the sine-Gordon model which describe the squeezed or stretched kinks.Research limitations/implications: The paper is limited to the description of the dynamics of the long Josephson junctions which are one dimensional systems with stable kink structures.Practical implications: It is expected that the possibility of control the width of the kink will find applications in future electronic devices.Originality/value: The main idea of the paper is to use some special magnetic field configurations to modulate (precisely the properties of the Josephson junction.
Katz, Andrew Steven
The 1986 discovery of high temperature superconductivity in copper oxide perovskite compounds (a.k.a., cuprates) set off an avalanche of research with the twin goals of understanding the origin of the superconducting state and of developing practical superconducting technologies. Proponents of superconducting technology were renewed with the possibility of achieving devices with cheaper, simpler coolants such as liquid nitrogen rather than the more expensive and exotic liquid helium. While the underlying origin of the superconducting state in the cuprates is still elusive, great strides towards applications of the new superconductors have been made over the past decade. The primary element in active superconducting electronics is the Josephson junction. In the case of the cuprates, numerous techniques have been tried to produce Josephson junctions for use in superconducting electronics. Each has some advantages and some limitations. None to date, however, have been reliable enough to imagine manufacturing devices with more than a few Josephson elements. High temperature superconducting electronics of the future will require the reliable and reproducible fabrication of dozens and even hundreds of Josephson elements on a single chip. This dissertation attempts to address this problem by presenting a technique for fabricating reliable, reproducible, controllable, and manufacturable Josephson junctions in the superconductor YBasb2Cusb3CuOsb{7-delta}. A process has been developed to fabricate planar high-Tsb{c} Josephson junctions using nanolithography and a 200 keV ion implanter. Conduction occurs in the ab-plane and is interface free. Devices may be tuned to operate at temperatures between 1 K and the Tsb{c} of the undamaged superconducting material by varying the length of the weak link and by changing the amount of ion damage. The normal state and superconducting state properties of these films have been examined and analyzed in the contexts of a de Gennes dirty
Temporal stability of Y Ba Cu O nano Josephson junctions from ion irradiation
Energy Technology Data Exchange (ETDEWEB)
Cybart, Shane A.; Roediger, Peter; Chen, Ke; Parker, J. M.; Cho, Ethan Y.; Wong, Travis J.; Dynes, R. C.
2012-11-29
We investigate the temporal stability of YBa2Cu3O7 Josephson junctions created by ion irradiation through a nano-scale implant mask fabricated using electron beam lithography and reactive ion etching. A comparison of current-voltage characteristics measured for junctions after fabrication and eight years of storage at room temperature show a slight decrease in critical current and increase in normal state resistance consistent with broadening of the weaklink from diffusion of defects. Shapiro step measurements performed 8 years after fabrication reveal that device uniformity is maintained and is strong evidence that these devices have excellent temporal stability for applications.
External noise-induced transitions in a current-biased Josephson junction
Directory of Open Access Journals (Sweden)
Qiongwei Huang
2016-01-01
Full Text Available We investigate noise-induced transitions in a current-biased and weakly damped Josephson junction in the presence of multiplicative noise. By using the stochastic averaging procedure, the averaged amplitude equation describing dynamic evolution near a constant phase difference is derived. Numerical results show that a stochastic Hopf bifurcation between an absorbing and an oscillatory state occurs. This means the external controllable noise triggers a transition into the non-zero junction voltage state. With the increase of noise intensity, the stationary probability distribution peak shifts and is characterised by increased width and reduced height. And the different transition rates are shown for large and small bias currents.
Interfacial spin Hall current in a Josephson junction with Rashba spin-orbit coupling
Institute of Scientific and Technical Information of China (English)
Yang Zhi-Hong; Yang Yong-Hong; Wang Jun
2012-01-01
We theoretically investigate the spin transport properties of the Cooper pairs in a conventional Josephson junction with Rashba spin orbit coupling considered in one of the superconducting leads.It is found that an angle-resolved spin supercurrent flows through the junction and a nonzero interfacial spin Hall current driven by the superconducting phase difference also appears at the interface.The physical origin of this is that the Rashba spin-orbit coupling can indnce a triplet order parameter in the s-wave superconductor.The interfacial spin Hall current dependences on the system parameters are also discussed.
A low noise dc-SQUID based on Nb/Al-AlOx/Nb Josephson junctions
International Nuclear Information System (INIS)
Low noise dc SQUIDs based on a Nb/Al-AlOx/Nb Josephson junction technology have been developed. The design has been optimized for improved control of the resonances. An eight-level process has been used for device fabrication. Flux noise levels of 2.8x10-7Φ0/√Hz at 1 kHz and 1.5x10-6Φ0/√Hz at 1 Hz have been measured for an integrated SQUID magnetometer having 3 μm2 junctions, a 12-turn input coil, and a dc SQUID inductance Ldc = 11 pH. (orig.)
Josephson junctions with centered step and local variation of critical current density
Weides, M.
2009-01-01
Superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson tunnel junctions based on Nb\\Al2O3\\Ni\\Cu\\Nb stacks with a thickness step in the metallic NiCu interlayer were fabricated. The step height of a few 0.1 nm was defined by optical lithography and controlled etching of both Nb and NiCu layers. Experimentally determined junction parameters by current-voltage characteristics and Fraunhofer pattern indicate a uniform NiCu thickness and similar interface transparencies for etched an...
Order and turbulence in rf-driven Josephson junction series arrays
International Nuclear Information System (INIS)
We study underdamped Josephson junction series arrays that are globally coupled through a resistive shunting load and driven by an rf bias current. We find coherent, ordered, partially ordered and turbulent regimes in the IV characteristics. The ordered regime corresponds to giant Shapiro steps. In the turbulent regime there is a saturation of the broad band noise for a large number of junctions. This corresponds to a breaking of the law of large numbers already seen in globally coupled maps. Coexisting with this, we find an emergence of novel pseudo-steps in the IV characteristics. (author). 18 refs, 3 figs
Effects of spin-orbit coupling and spatial symmetries on the Josephson current in SNS junctions
Rasmussen, Asbjørn; Danon, Jeroen; Suominen, Henri; Nichele, Fabrizio; Kjaergaard, Morten; Flensberg, Karsten
2016-04-01
We present an analysis of the symmetries of the interference pattern of critical currents through a two-dimensional superconductor-semiconductor-superconductor junction, taking into account Rashba and Dresselhaus spin-orbit interaction, an arbitrarily oriented magnetic field, disorder, and structural asymmetries. We relate the symmetries of the pattern to the absence or presence of symmetries in the Hamiltonian, which provides a qualitative connection between easily measurable quantities and the spin-orbit coupling and other symmetries of the junction. We support our analysis with numerical calculations of the Josephson current based on a perturbative expansion up to eighth order in tunnel coupling between the normal region and the superconductors.
Spatio-temporal effects in a perturbed Sine-Gordan system: A long Josephson junction
International Nuclear Information System (INIS)
A collective coordinate approach is applied to study chaotic responses induced by an applied driven signal on the long Josephson junction influenced by a constant dc-driven field. We derive a nonlinear equation for a collective variable of the breather and the Melnikov method is then used to demonstrate the existence of irregular behavior in breather-fluxon-antifluxon pair transitions. Additionally, numerical simulations show that the theoretical predictions are well reproduced. Results obtained using these perturbative analysis are in good agreement with numerical simulations of the dynamics of the junction. (author)
Diluted Josephson-Junction arrays in a magnetic field: Phase coherence and vortex glass thresholds
International Nuclear Information System (INIS)
The effects of random dilution of junctions on a two-dimensional Josephson-junction array in a magnetic field are considered. For rational values of the average flux quantum per plaquette f, the superconducting transition temperature vanishes, for increasing dilution at a critical value xs(f), while the vortex ordering remains stable up to xVL > XS, much below the value xp corresponding to the geometric percolation threshold. For xVL p, the array behaves as a zero-temperature vortex-glass. Numerical results for f = 1/2 from defect energy calculations are presented which are consistent with this scenario. (author)
Strain-induced 0-π transition in a zigzag graphene nanoribbon Josephson junction
Zou, Jianfei; Jin, Guojun
2011-03-01
We study theoretically the supercurrent through a superconductor/ferromagnetic zigzag graphene nanoribbon/superconductor junction by the Matsubara Green function method. The transformation of the supercurrent between the 0 and π states is remarkably realized in this Josephson junction by the combination of the uniaxial strain and gate-controlled barrier potential. Such strain-induced 0-π transition is found to result from the dependence of the effective Fermi velocity on the uniaxial strain in the graphene nanoribbon modulated by mechanical approaches.
Mathematical modeling of intrinsic Josephson junctions with capacitive and inductive couplings
Rahmonov, I. R.; Shukrinov, Yu M.; Zemlyanaya, E. V.; Sarhadov, I.; Andreeva, O.
2012-11-01
We investigate the current voltage characteristics (CVC) of intrinsic Josephson junctions (IJJ) with two types of couplings between junctions: capacitive and inductive. The IJJ model is described by a system of coupled sine-Gordon equations which is solved numerically by the 4th order Runge-Kutta method. The method of numerical simulation and numerical results are presented. The magnetic field distribution is calculated as the function of coordinate and time at different values of the bias current. The influence of model parameters on the CVC is studied. The behavior of the IJJ in dependence on coupling parameters is discussed.
Interfacial spin Hall current in a Josephson junction with Rashba spin—orbit coupling
International Nuclear Information System (INIS)
We theoretically investigate the spin transport properties of the Cooper pairs in a conventional Josephson junction with Rashba spin—orbit coupling considered in one of the superconducting leads. It is found that an angle-resolved spin supercurrent flows through the junction and a nonzero interfacial spin Hall current driven by the superconducting phase difference also appears at the interface. The physical origin of this is that the Rashba spin—orbit coupling can induce a triplet order parameter in the s-wave superconductor. The interfacial spin Hall current dependences on the system parameters are also discussed. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
External noise-induced transitions in a current-biased Josephson junction
International Nuclear Information System (INIS)
We investigate noise-induced transitions in a current-biased and weakly damped Josephson junction in the presence of multiplicative noise. By using the stochastic averaging procedure, the averaged amplitude equation describing dynamic evolution near a constant phase difference is derived. Numerical results show that a stochastic Hopf bifurcation between an absorbing and an oscillatory state occurs. This means the external controllable noise triggers a transition into the non-zero junction voltage state. With the increase of noise intensity, the stationary probability distribution peak shifts and is characterised by increased width and reduced height. And the different transition rates are shown for large and small bias currents
External noise-induced transitions in a current-biased Josephson junction
Energy Technology Data Exchange (ETDEWEB)
Huang, Qiongwei; Xue, Changfeng, E-mail: cfxue@163.com [School of Mathematics and Physics, Yancheng Institute of Technology, Yancheng 224051 (China); Tang, Jiashi [College of Mechanical and Vehicle Engineering, Hunan University, Changsha 410082 (China)
2016-01-15
We investigate noise-induced transitions in a current-biased and weakly damped Josephson junction in the presence of multiplicative noise. By using the stochastic averaging procedure, the averaged amplitude equation describing dynamic evolution near a constant phase difference is derived. Numerical results show that a stochastic Hopf bifurcation between an absorbing and an oscillatory state occurs. This means the external controllable noise triggers a transition into the non-zero junction voltage state. With the increase of noise intensity, the stationary probability distribution peak shifts and is characterised by increased width and reduced height. And the different transition rates are shown for large and small bias currents.
Shunted-Josephson-junction model. II. The nonautonomous case
DEFF Research Database (Denmark)
Belykh, V. N.; Pedersen, Niels Falsig; Sørensen, O. H.
1977-01-01
. The mathematical discussion makes use of the phase-space representation of the solutions to the differential equation. The behavior of the trajectories in phase space is described for different characteristic regions in parameter space and the associated features of the junction IV curve to be...... expected are pointed out. The main objective is to provide a qualitative understanding of the junction behavior, to clarify which kinds of properties may be derived from the shunted-junction model, and to specify the relative arrangement of the important domains in the parameter-space decomposition....
Yamada, Y.; Nakajima, K.; Nakajima, K.
2009-10-01
We reported dynamics of Josephson vortices interacting with electromagnetic waves in strongly coupled long Josephson junctions stack, such as an intrinsic Josephson junction (IJJ), by numerical simulations based on coupled sine-Gordon equations considering a periodic pinning potential of sinusoidal form. The numerical simulation results for the influence of the electromagnetic waves on flux-flow properties show that the periodic pinning potential induces an in-phase motion of Josephson vortices over the junction stacks, which achieve high performances of IJJ flux-flow oscillator. In order to prove it from another viewpoint, we calculate RF impedance of long Josephson junction stacks in flux-flow state. A remarkable negative real part region of RF impedance appears at 1st harmonic step, it means that the long Josephson junction stacks in flux-flow state acts as an oscillator at the negative real part region. In this study, we evaluate the optimum condition for RF radiation with the periodic pinning potential.
Ramp-type Josephson junctions with YBa2Cu3O7 and Nb electrodes
International Nuclear Information System (INIS)
We present our status of the development of an improved ramp-type Josephson junction technology for fabrication of all-high Tc junctions with YBa2Cu3O7 (YBCO) electrodes and PbBa2Cu3O7 (PBCO) barrier, and hybrid YBCO/Au/Nb junctions. The fabrication is done in a UHV cluster tool for the deposition of oxide thin films by pulsed laser deposition (PLD) using in-situ high-pressure RHEED for monitoring the thin film growth. Deposition of Nb and Au thin films is done by dc magnetron sputtering and electron beam evaporation, respectively, in two separate processing chambers. A milling chamber equipped with a high-frequency inductively-coupled plasma source allows surface cleaning and etching with argon and/or oxygen, reactive ion etching with SF6 and removal of resist structures in an oxygen plasma. The substrate holder in the milling chamber allows in-situ adjustment and variation of the milling angle and additional rotation of the substrate about its normal axis, in order to realize an isotropic milling process, which is essential for the fabrication of 2-dimensional arrays of Josephson junctions. Initial results on the properties of fabricated ramp junctions will be shown.
Gate-Tunable Superconductor-Insulator Transition in Bilayer-Graphene Josephson Junctions
Jeong, Dongchan; Lee, Gil-Ho; Doh, Yong-Joo; Lee, Hu-Jong
2012-02-01
Bilayer graphene shows opening of electric-field-induced band gap, the size of which is proportional to the intensity of the electric field. We report electronic transport measurements on superconducting proximity effect in planar dual-gated bilayer-graphene Josephson junction with Pb0.93In0.07 (PbIn) electrodes (δPbIn ˜ 1.1meV, Tc = 7.0 K). The junction resistance along the charge-neutral point (CNP) increases as we modulate top- and back-gate voltages away from the zero-gap CNP. The resistive state near the CNP shows a variable-range-hopping-type insulating behavior in R-T curve with lowering temperature crossing the superconducting transition of PbIn electrodes. However, a highly doped regime shows metallic R-T behavior and junction becomes superconducting below Tc. Moreover, magnetic-field-induced Fraunhofer supercurrent modulation, microwave-induced Shapiro steps, and multiple Andreev reflection (MAR) are observed, which indicate the formation of genuine Josephson coupling across the planar junctions below Tc with sufficiently transparent superconductor-bilayer graphene interface. The separatrix of the superconductor-insulator transition corresponds to the square junction conductance of Gsq˜ 6-8e^2/h.
Preparation and properties of two types of submicron high-Tc Josephson junctions
International Nuclear Information System (INIS)
There is a variety of different types of high-Tc Josephson junctions corresponding to the short coherence length, high anisotropy and some interface problems of the oxide superconductors. Using submicron technologies nanobridges and bridges modified by ion beams in a hundred nanometer region can be fabricated. Depending on preparation parameters the ion beam influence causes implantation, sputtering or a modification of the lattice changing the superconducting properties. The case of modification is discussed in details. It is shown how parameters of the preparation process influence the physical properties of these junctions. The application of such junctions is shown for DC-SQUIDs and gradiometers including a comparison to other junction types like bicrystal or step-edge junctions. Submicron technology is useful for preparation of intrinsic stacked junctions out of thin films. In this case the single junction dimension is determined by the coupling of two copper oxide planes in an atomic scale. A mesa structure acts as a series connection of a number of single junctions corresponding to the stack height. Preparation and physical properties of these types of junction arrays are given in detail. The possible application of such new kind of devices as radiation sources or voltage standard will be discussed
Area-dependence of spin-triplet supercurrent in ferromagnetic Josephson junctions
International Nuclear Information System (INIS)
In 2010, several experimental groups obtained compelling evidence for spin-triplet supercurrent in Josephson junctions containing strong ferromagnetic materials. Our own best results were obtained from large-area junctions containing a thick central Co/Ru/Co “synthetic antiferromagnet” and two thin outer layers made of Ni or PdNi alloy. Because the ferromagnetic layers in our samples are multi-domain, one would expect the sign of the local current-phase relation inside the junctions to vary randomly as a function of lateral position. Here we report measurements of the area dependence of the critical current in several samples, where we find some evidence for those random sign variations. When the samples are magnetized, however, the critical current becomes clearly proportional to the area, indicating that the current-phase relation has the same sign across the entire area of the junctions.
Area-dependence of spin-triplet supercurrent in ferromagnetic Josephson junctions
Wang, Yixing; Pratt, W. P., Jr.; Birge, Norman O.
2012-12-01
In 2010, several experimental groups obtained compelling evidence for spin-triplet supercurrent in Josephson junctions containing strong ferromagnetic materials. Our own best results were obtained from large-area junctions containing a thick central Co/Ru/Co “synthetic antiferromagnet” and two thin outer layers made of Ni or PdNi alloy. Because the ferromagnetic layers in our samples are multi-domain, one would expect the sign of the local current-phase relation inside the junctions to vary randomly as a function of lateral position. Here we report measurements of the area dependence of the critical current in several samples, where we find some evidence for those random sign variations. When the samples are magnetized, however, the critical current becomes clearly proportional to the area, indicating that the current-phase relation has the same sign across the entire area of the junctions.
Stability of fluxon motion in long Josephson junctions at high bias
DEFF Research Database (Denmark)
Pagano, S.; Sørensen, Mads Peter; Christiansen, Peter Leth; Parmentier, R. D.
1988-01-01
on by numerical integration of the model equation, the perturbed sine-Gordon equation, simulating junctions of overlap and annular geometry. A detailed description of the mechanism for the switching from the top of the zero-field step for both geometries is reported. Moreover, the effect of the...... various dissipations and of the junction length on the switching-current value is investigated. A simple boundary model is able to describe, for junctions of overlap geometry, the qualitative dependence of the switching current on the system parameters....
Direct measurements of the current-phase relation in long-range spin-triplet SFS Josephson junctions
Hamilton, David; van Harlingen, Dale; Wang, Yixing; Birge, Norman
2015-03-01
We present direct measurements of the current-phase relation (CPR) of Josephson junctions which use multiple ferromagnetic layers to generate long-range spin-triplet pair correlations. Using a phase-sensitive Josephson interferometry technique, we obtain the phase and temperature dependence of this spin-triplet supercurrent. We also demonstrate the use of an inductive shunt to enhance this technique at higher critical currents. Our data suggest that the current-phase relation of these junctions is harmonic in character. Further measurements are planned in order to determine the ground state phase shift of these junctions.
Holographic model of hybrid and coexisting s-wave and p-wave Josephson junction
Energy Technology Data Exchange (ETDEWEB)
Liu, Shuai; Wang, Yong-Qiang [Lanzhou University, Institute of Theoretical Physics, Lanzhou (China)
2015-10-15
In this paper the holographic model for a hybrid and coexisting s-wave and p-wave Josephson junction is constructed by a triplet charged scalar field coupled with a non-Abelian SU(2) gauge field in (3+1)-dimensional AdS spacetime. Depending on the value of chemical potential μ, one can show that there are four types of junctions (s+p-N-s+p, s+p-N-s, s+p-N-p and s-N-p). We show that the DC currents of all the hybrid and coexisting s-wave and p-wave junctions are proportional to the sine of the phase difference across the junction. In addition, the maximum current and the total condensation decay with the width of junction exponentially, respectively. For the s+p-N-s and s-N-p junctions, the maximum current decreases with growing temperature. Moreover, we find that the maximum current increases with growing temperature for the s+p-N-s+p and s+p-N-p junctions, which is different from the behavior of the s+p-N-s and s-N-p junctions. (orig.)
Microwave phase locking of Josephson-junction fluxon oscillators
DEFF Research Database (Denmark)
Salerno, M.; Samuelsen, Mogens Rugholm; Filatrella, G.; Pagano, S.; Parmentier, R. D.
1990-01-01
-dimensional functional map. Phase-locked states correspond to fixed points of the map. For junctions of in-line geometry, the existence and stability of such fixed points can be studied analytically. Study of overlap-geometry junctions requires the numerical inversion of a functional equation, but the results are...... qualitatively very similar. The map predicts significantly different behaviors for locking at odd and even subharmonic frequencies and at superharmonic frequencies. It also gives indications regarding hysteresis in the current-voltage characteristic, the existence of zero-crossing steps, and a description of...
Josephson Effects in superconducting conventional/unconventional tunnel junctions and weak-links
International Nuclear Information System (INIS)
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.
Superconducting-to-Normal State Switching Experiments using Graphene-based Josephson Junctions
Lambert, Joseph; Carabello, Steven; Ramos, Roberto
2011-03-01
We report results of ongoing superconductor-to-normal state switching experiments using graphene-based Josephson junctions. These devices consist of a single-layer graphene flake contacted by two superconducting parallel leads separated by a few hundred nanometers. Through the proximity effect, the superconducting state is induced in the graphene region below the leads and the Josephson supercurrent is mediated through the normal graphene region by multiple Andreev reflections. The Josephson effect has been firmly demonstrated in these devices, where supercurrents in the hysteretic current-voltage characteristic, Shapiro steps, the Fraunhofer-like diffraction pattern in the critical current versus external magnetic field, and the current-phase relationship have been observed. We report on work in progress, in measuring I-V characteristics, thermal activation and microwave resonant activation in graphene-based junctions, at various temperatures below 1 Kelvin. We modulate the density of charge carriers using a back-gate voltage, which tunes the critical current. This provides another knob for studying these state switching properties.
Noise performance of superconductive magnetometers based on long Josephson tunnel junctions
International Nuclear Information System (INIS)
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)
The current-phase relation of graphene-based Josephson junctions
Chialvo, Cesar Eduardo
The current-phase relation (CPR) of a Josephson junction reveals valuable information about the microscopic processes and symmetries that influence the supercurrent. For the work described in this thesis, we have studied the CPR of graphene-based Josephson junctions, inspired by previous theoretical predictions of a departure from the usual sinusoidal functionality, or skewness, of the CPR. The experimental data was obtained by incorporating the junction into an rf SQUID geometry coupled to a dc SQUID magnetometer, a technique usually referred to as phase-sensitive SQUID interferometry, which allows for the direct measurement of the phase difference across the junction. While some of the predictions from theory---like the departure of the CPR from sinusoidal behavior, its symmetry with carrier nature and the de-skewing with increasing temperature---were qualitatively observed, others were inconsistent with the experimental data. Perhaps the most important disparity was that of the functionality of the skewing, which we found to vary linearly with critical current (Ic), independent of the carrier density/temperature combination used to attain Ic. It is worth mentioning that our measurements have prompted renewed theoretical interest in this system, culminating in the modification of the original model to include the effects of temperature, and a recent publication venturing an explanation for the observed linearity of the CPR skewness with Ic.
Traveling wave parametric amplifier with Josephson junctions using minimal resonator phase matching
International Nuclear Information System (INIS)
Josephson parametric amplifiers have become a critical tool in superconducting device physics due to their high gain and quantum-limited noise. Traveling wave parametric amplifiers (TWPAs) promise similar noise performance, while allowing for significant increases in both bandwidth and dynamic range. We present a TWPA device based on an LC-ladder transmission line of Josephson junctions and parallel plate capacitors using low-loss amorphous silicon dielectric. Crucially, we have inserted λ/4 resonators at regular intervals along the transmission line in order to maintain the phase matching condition between pump, signal, and idler and increase gain. We achieve an average gain of 12 dB across a 4 GHz span, along with an average saturation power of −92 dBm with noise approaching the quantum limit
Energy Technology Data Exchange (ETDEWEB)
Yokoyama, Tomohiro; Eto, Mikio [Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); Nazarov, Yuli V. [Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands (Netherlands)
2013-12-04
We theoretically study the current-phase relation in semiconductor nanowire Josephson junction in the presence of spin-orbit interaction. In the nanowire, the impurity scattering with strong SO interaction is taken into account using the random matrix theory. In the absence of magnetic field, the Josephson current I and phase difference φ between the superconductors satisfy the relation of I(φ) = –I(–φ). In the presence of magnetic field along the nanowire, the interplay between the SO interaction and Zeeman effect breaks the current-phase relation of I(φ) = –I(–φ). In this case, we show that the critical current depends on the current direction, which qualitatively agrees with recent experimental findings.
Josephson junction at the onset of chaos: A complete devil's staircase
International Nuclear Information System (INIS)
By analog computer calculations of the resistively and capacitively shunted Josephson junction model, I-V characteristics are measured for several choices of the parameters in the Josephson equation. The points, where hysteresis sets in, are related to cubic inflection points in the return map. For different values of the amplitude and the frequency of the imposed ac field the critical line is determined in the (I,G) space, where I is the dc current and G is the damping factor. Furthermore, the subharmonic steps along the critical line form a complete devil's staircase with a fractal dimension Dapprox.0.87 and a decay exponent for the (1/Q)-steps deltaapprox.3. Besides the hysteresis which gives occasion for a chaotic behavior everywhere below a certain critical voltage, hysteresis also turns up locally. It is suggested that the critical points where local hysteresis occurs can be found by use of a local approximation
The in-phase states of Josephson junctions stacks as attractors
International Nuclear Information System (INIS)
The aim of this investigation is to show that the coherent, in-phase states of intrinsic Josephson junctions stacks are attractors of the stacks' states when the applied external magnetic field he and the external current γ vary within certain domains. Mathematically the problem is to find the solutions of the system of perturbed sine-Gordon equations for fixed other parameters and zero or random initial conditions. We determine the region in the plane (he, γ), where the in-phase states are attractors of the stack's states for arbitrary initial perturbations. This is important, because the in-phase states are required for achieving terahertz radiation from the Josephson stacks
Josephson frequency singularity in the noise of normal-metal-superconductor junctions
Lesovik, Gordey B.; Martin, Thierry; Torrès, Julien
1999-11-01
A singularity at the Josephson frequency in the noise spectral density of a disordered normal-metal-superconductor junction is predicted for bias voltages below the superconducting gap. The nonstationary Aharonov-Bohm effect, recently introduced for normal metals [G. B. Lesovik and L. S. Levitov, Phys. Rev. Lett. 72, 538 (1994)], is proposed as a tool for detecting this singularity. In the presence of a harmonic external field, the derivative of the noise with respect to the voltage bias reveals jumps when the applied frequency is commensurate with the Josephson frequency associated with this bias. The height of these jumps is nonmonotonic in the amplitude of the periodic field. The superconducting flux quantum enters this dependence. Additional singularities in the frequency dependent noise are predicted above gap.
Induced change of critical current density profile in Nb/Al-AlOx/Nb Josephson junctions
International Nuclear Information System (INIS)
A technique to induce spatial modulation of critical current density in niobium based Josephson devices by using a selective thermal annealing is reported. By depositing a carbon film onto selected region of the Josephson element it is possible to induce a localized heating, with a spatial resolution less than 1 μm, exploiting the much higher absorbance coefficient of carbon than the niobium one. The effectiveness of such technique is demonstrated by experimental measurement of the critical current vs. magnetic field, measured at T = 4.2 K, showing that the change of critical current density occurs only in the region corresponding to the absorber film area. Furthermore, the theoretical behaviour, by modelling a suitable step-like junction barrier shape, has been carried out to fit the experimental data in order to verify the selective modulation of critical current. This technique can be very useful in view of quantum computing experiments, Majorana fermions detection and superconducting magnetic sensors.
International Nuclear Information System (INIS)
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
High temperature superconducting step-edge SNS Josephson junctions on silicon substrates
International Nuclear Information System (INIS)
The authors have fabricated and tested YBCO step-edge SNS Josephson junctions on silicon substrates. The silicon step edges were patterned photolithographically and reactively ion etched using an SF6 plasma. The structures were fabricated through sequential angled pulsed laser deposition of yttria stabilized zirconia, YBCO, and gold layers, followed by photolithographic patterning and ion milling. The completed devices showed resistively shunted junction (RSJ)-like current voltage characteristics and microwave induced Shapiro Steps. Critical currents as large as 84 microA and resistances of order 0.5 Ω were obtained. Measurable critical currents were observed up to 76 K. The authors report on the fabrication and properties of these junctions
Experimental study of noise and Josephson oscillation linewidths in bicrystal YBCO junctions
DEFF Research Database (Denmark)
Constatinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.; Pogosyan, N.G.; Hakuhoumian, A.A.; Yagoubov, P.; Mygind, J.; Pedersen, Niels Falsig
range up to voltages V = 2 mV in connection with low-voltage noise rise. Both the features observed, the linewidth broadening and the excess noise over the noise level of thermal fluctuations, are discussed in terms of multiple Andreev reflection, giving rise to a nonequilibrium shot noise-the case...... which may take place in the d-wave superconducting junctions. Experimental results on noise performance are also compared with the qualitatively similar dependences of the current noise, known for the s-superconducting ballistic point-like or diffusive-type SNS junctions, where the excess low......-voltage noise is manifested due to multiple Andreev reflections. Increasing the operating temperature, the thermal (equilibrium) fluctuations were found to predominate, resulting in a decrease of ratio Deltaf(J)/Deltaf(RSJ). The characteristics of the ac Josephson effect in FITS junctions measured at submm...
DEFF Research Database (Denmark)
Holm, Jesper; Mygind, Jesper
1995-01-01
measurements on different oscillator samples, performed with a novel Cryogenic Scanning Laser Microscope (CSLM) having a spatial resolution of less than ±2.5 μm over a 500 μm×50 μm wide scanning area in the temperature range 2 K-300 K. Even though the dynamical states are extremely sensitive to external noise...... tunnel current is one of the most important internal junction parameters which together with the boundary conditions determine the dynamics, it is of vital importance to experimentally determine the current density throughout the entire junction with high spatial resolution. Here we report on...... this microscope enables us to make stable in-situ measurements on operating Josephson junctions. Recent results are presented and discussed....
Spin-triplet supercurrent in Co/Ni multilayer Josephson junctions with perpendicular anisotropy
Gingrich, E. C.; Quarterman, P.; Wang, Yixing; Loloee, R.; Pratt, W. P., Jr.; Birge, Norman O.
2012-12-01
We have measured spin-triplet supercurrent in Josephson junctions of the form S/F'/F/F'/S, where S is superconducting Nb, F' is a thin Ni layer with in-plane magnetization, and F is a Ni/[Co/Ni]n multilayer with out-of-plane magnetization. The supercurrent in these junctions decays very slowly with F-layer thickness and is much larger than in similar junctions not containing the two F' layers. Those two features are the characteristic signatures of spin-triplet supercurrent, which is maximized by the orthogonality of the magnetizations in the F and F' layers. Magnetic measurements confirm the out-of-plane anisotropy of the Co/Ni multilayers. These samples have their critical current optimized in the as-prepared state, which will be useful for future applications.
Two-dimensional Josephson junction arrays coupled through a high-Q cavity
DEFF Research Database (Denmark)
Filatrella, G.; Pedersen, Niels Falsig; Wiesenfeld, K.
2001-01-01
The problem of disordered two-dimensional arrays of underdamped Josephson junctions is addressed. Our simulations show that when coupled to a high-Q cavity, the array exhibits synchronized behavior, and the power emitted can be considerably increased once enough junctions are activated to pump the...... cavity. The highly resonant cavity induces synchronized behavior, which is qualitatively different than what is familiar from other studies on nonlinear oscillator arrays, for example the Kuramoto model. We also address the effects of disorder, as well as the role of detuning between the spontaneous...... emission frequency of the junctions and the cavity resonant frequency. We show with a simple argument that we can predict the scaling behavior of disorder with the size of the array. The consequences for the design of microwave oscillators in the Gigahertz region are discussed...
Gaussian tunneling model of c-axis twist Josephson junctions
International Nuclear Information System (INIS)
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.
S–I–S Josephson junction with a correlated insulator below its S–I transition
Energy Technology Data Exchange (ETDEWEB)
Porter, C.D. [Department of Physics, The Ohio State University, Columbus, OH 43210 (United States); Kim, Kwangmoo [Department of Physics, The Ohio State University, Columbus, OH 43210 (United States); School of Physics, Korea Institute for Advanced Study, Seoul 130-722 (Korea, Republic of); Stroud, D., E-mail: stroud@mps.ohio-state.edu [Department of Physics, The Ohio State University, Columbus, OH 43210 (United States)
2014-03-15
Highlights: • We model an S–I–S junction, whose insulating layer is actually a superconductor below its S–I transition. • We demonstrate that such a structure indeed behaves like a single Josephson junction. • The coherence length diverges as the insulating layer approaches its S–I transition • The model may describe so-called Cooper pair insulators studied in some experiments. - Abstract: We consider a Josephson junction composed of two superconducting (S) regions separated by an insulating (I) region, but with the special property that the S and the I regions are superconducting films respectively above and below the superconducting–insulating (S–I) transition. To calculate the properties of this junction, we describe the system using an inhomogeneous quantum rotor Hamiltonian with a coupling energy J and spatially varying charging energy U. The ratio J/U is chosen so that it is above the critical value for an S–I transition in the two superconducting regions, but below it in the insulating regime. Using both mean-field theory and perturbation theory, we show that the phase order parameter is finite in the S region and decays exponentially into the I region. Thus, the order parameter, which would be zero in the I region in isolation, is instead rendered nonzero by the adjacent S region, because of a proximity effect. As a result, there is a nonzero coupling energy between the two S regions. We show, using both mean-field theory and a quantum Monte Carlo calculation, that the phase stiffness constant, or helicity modulus, of this junction is nonzero, and falls off exponentially with separation of the two superconductors. We also analytically estimate the dependence of the coupling energy on the properties of the S and I regions, and suggest an analogy with conventional S–N–S junctions. Our results support the conclusion that this S–I–S sandwich structure, with a correlated insulating region, can be viewed as a single effective
International Nuclear Information System (INIS)
Taking advantage of a New Wave 213 nm laser system, equipped with high-precision submicron resolution sample mosaic navigation, we are able to laser-etch and fabricate planar submicron-size Josephson junctions on YBa2Cu3O7-x thin films successfully. The entire process of laser etching and sample navigation is software controlled. The widths were measured by atomic force microscopy (AFM), and they range from 0.7 to 1.4 μm. We report on the observed I-V characteristics and Shapiro steps, which confirm the Josephson effect in these junctions. The measured critical current dependence on temperature shows a linear relationship for micron-size constrictions. In the case of submicron constrictions, the dependence is an exponential decay type, consistent with diffusive long S-N-S junction behaviour. It is believed that the observed behaviour can be ascribed to laser heating of the constriction material, changing the superconducting phase to the normal one
Josephson junction-embedded transmission-line resonators: from Kerr medium to in-line transmon
Bourassa, J; Gambetta, Jay M; Blais, A
2012-01-01
We provide a general method to find the Hamiltonian of a linear circuit in the presence of a nonlinearity. Focussing on the case of a Josephson junction embedded in a transmission-line resonator, we solve for the normal modes of the system by taking into account exactly the effect of the quadratic (i.e. inductive) part of the Josephson potential. The nonlinearity is then found to lead to self and cross-Kerr effect, as well as beam-splitter type interactions between modes. By adjusting the parameters of the circuit, the Kerr coefficient K can be made to reach values that are weak (K \\kappa) or even very strong (K >> \\kappa) with respect to the photon-loss rate \\kappa. In the latter case, the resonator+junction circuit corresponds to an in-line version of the transmon. By replacing the single junction by a SQUID, the Kerr coefficient can be tuned in-situ, allowing for example the fast generation of Schr\\"odinger cat states of microwave light. Finally, we explore the maximal strength of qubit-resonator coupling...
Experimental study of noise and Josephson oscillation linewidths in bicrystal YBCO junctions
DEFF Research Database (Denmark)
Constatinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.;
2001-01-01
which may take place in the d-wave superconducting junctions. Experimental results on noise performance are also compared with the qualitatively similar dependences of the current noise, known for the s-superconducting ballistic point-like or diffusive-type SNS junctions, where the excess low......The intensities of the noise in a bicrystal high-T-c (HTS) Josephson junction have been precision-measured at 1-2 GHz frequency band at bias voltages up to 50 mV at T = 4.2 K. At large bias voltages, V > 30 mV, the dependence of current noise density was found exactly coinciding with the Schottky...... shot noise asymptote 2eI. At relatively low voltages, V <4 mV, a noticeable noise rise has been registered. The broadening of Josephson oscillation linewidths fJ over the values Deltaf(RSJ) predicted by the RSJ model has been experimentally studied at different frequencies in the nim and submm wave...
Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions
Rakyta, Péter; Kormányos, Andor; Cserti, József
2016-06-01
We study the Josephson current in long ballistic superconductor-monolayer graphene-superconductor junctions. As a first step, we have developed an efficient computational approach to calculate the Josephson current in tight-binding systems. This approach can be particularly useful in the long-junction limit, which has hitherto attracted less theoretical interest but has recently become experimentally relevant. We use this computational approach to study the dependence of the critical current on the junction geometry, doping level, and an applied perpendicular magnetic field B . In zero magnetic field we find a good qualitative agreement with the recent experiment of M. Ben Shalom et al. [Nat. Phys. 12, 318 (2016), 10.1038/nphys3592] for the length dependence of the critical current. For highly doped samples our numerical calculations show a broad agreement with the results of the quasiclassical formalism. In this case the critical current exhibits Fraunhofer-like oscillations as a function of B . However, for lower doping levels, where the cyclotron orbit becomes comparable to the characteristic geometrical length scales of the system, deviations from the results of the quasiclassical formalism appear. We argue that due to the exceptional tunability and long mean free path of graphene systems a new regime can be explored where geometrical and dynamical effects are equally important to understand the magnetic field dependence of the critical current.
Multi-terminal Josephson junctions with ferromagnetic elements
International Nuclear Information System (INIS)
The interplay between magnetism and superconductivity in heterostructures has attracted considerable interest since the discovery of the 0-π transition in superconductor-ferromagnet (SF) contacts. Here we investigate the supercurrent in systems of multiple tunnel junctions in the framework of the quantum circuit theory. The considered network consists of two superconducting and two ferromagnetic reservoirs with non-collinear magnetization direction connected by tunnel contacts to a normal metal. We find and interesting interplay between the superconducting phase difference and the relative magnetization angle, which manifests itself in the current phase relation and the critical current
Quantum Phase Diffusion in a Small Underdamped Josephson Junction
Yu, H. F.; Zhu, X. B.; Peng, Z. H.; Tian, Ye; Cui, D. J.; Chen, G. H.; Zheng, D. N.; Jing, X. N.; Lu, Li; Zhao, S. P.; Han, Siyuan
2011-08-01
Quantum phase diffusion in a small underdamped Nb/AlOx/Nb junction (˜0.4μm2) is demonstrated in a wide temperature range of 25-140 mK where macroscopic quantum tunneling (MQT) is the dominant escape mechanism. We propose a two-step transition model to describe the switching process in which the escape rate out of the potential well and the transition rate from phase diffusion to the running state are considered. The transition rate extracted from the experimental switching current distribution follows the predicted Arrhenius law in the thermal regime but is greatly enhanced when MQT becomes dominant.
The gravity-induced phase shift detected by high-Tc Josephson junctions
Institute of Scientific and Technical Information of China (English)
HE Jian-e
2007-01-01
We derive from the Kaluza-Klein theory a formula for the gravity-induced phase shift around a circuit loop,which amounts to the order of 10-6 We propose experiments to detect this phase shift by using the high-Tc d-wave Josephson junction,which is included in a cuprate superconductor circuit loop.By rotating the loop around the horizontal axis,the gravity-induced phase shift can be detected as a frequency shift.These settings can also be used in turn to determine the gravitational constant.This method will be sensitive and accurate.
Decoherence in Josephson-junction qubits due to critical current fluctuations
Van Harlingen, D. J.; Robertson, T. L.; Plourde, B. L. T.; Reichardt, P. A.; Crane, T.A.; Clarke, John
2004-01-01
We compute the decoherence caused by $1/f$ fluctuations at low frequency $f$ in the critical current $I_0$ of Josephson junctions incorporated into flux, phase, charge and hybrid flux-charge superconducting quantum bits (qubits). The dephasing time $\\tau_{\\phi}$ scales as $I_0/ \\Omega \\Lambda S_{I_0}^{1/2}(1$ Hz$)$, where $\\Omega / 2\\pi$ is the energy level splitting frequency, $S_{I_0}(1$ Hz$)$ is the spectral density of the critical current noise at 1 Hz, and $\\Lambda \\equiv |I_0 d \\Omega /...
Influence of substrate on coupling of high temperature superconducting Josephson junction arrays
International Nuclear Information System (INIS)
High temperature superconducting (HTS) Josephson junction arrays (JJAs) fabricated on bicrystal substrate were embedded in a Fabry-Pérot (F-P) resonator. We detected the radiation from the JJAs at about 74.08 GHz. By investigating the Current-Voltage (I-V) characteristics of the JJAs, the influence of the substrate on height of the Shapiro steps was studied. The result showed that the JJAs located at different positions of the substrate had different coupling strength. Also, the influence of the substrate was explored by presenting the comparison of radiation at different frequencies. Electromagnetic simulation was used to explain the experiment results.
Richardson, C. L.; Edkins, S. D.; Berdiyorov, G. R.; Chua, C. J.; Griffiths, J. P.; Jones, G. A. C.; Buitelaar, M.R.; Narayan, V; Sfigakis, F.; Smith, C. G.; Covaci, L.; Connolly, M. R.
2015-01-01
The files listed below are raw experimental data from 'Vortex detection and quantum transport in mesoscopic graphene Josephson-junction arrays' by C. L. Richardson et al., to appear in Phys. Rev. B. The three-part files (filename, filenameHdr and filenameSD) are in tab-separated .txt format, produced by CryoMeas (written by C. J. B. Ford). Only a subset of the Fig. 6 dataset is included. 20130514-040 (device A, Fig. 2(a) and 3) 20130515-041 (device A, Fig. 2(a) and 3) 20130809-066 (...
Low-noise parametric amplification at 35 GHz in a single Josephson tunnel junction
DEFF Research Database (Denmark)
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....
Influence of substrate on coupling of high temperature superconducting Josephson junction arrays
Energy Technology Data Exchange (ETDEWEB)
Wang, P. [Department of Electronics, Nankai University, Tianjin 300071 (China); Wang, Zh. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China); Fan, B. [Department of Electronics, Nankai University, Tianjin 300071 (China); Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48823 (United States); Xie, W.; Liu, W.; Zhao, X.J.; Zhang, X. [Department of Electronics, Nankai University, Tianjin 300071 (China); Ji, L., E-mail: luji@nankai.edu.cn [Department of Electronics, Nankai University, Tianjin 300071 (China); He, M.; Fang, L.; Yan, S.L. [Department of Electronics, Nankai University, Tianjin 300071 (China)
2012-12-14
High temperature superconducting (HTS) Josephson junction arrays (JJAs) fabricated on bicrystal substrate were embedded in a Fabry-Perot (F-P) resonator. We detected the radiation from the JJAs at about 74.08 GHz. By investigating the Current-Voltage (I-V) characteristics of the JJAs, the influence of the substrate on height of the Shapiro steps was studied. The result showed that the JJAs located at different positions of the substrate had different coupling strength. Also, the influence of the substrate was explored by presenting the comparison of radiation at different frequencies. Electromagnetic simulation was used to explain the experiment results.
Atomic delocalization as a microscopic origin of two-level defects in Josephson junctions
International Nuclear Information System (INIS)
Identifying the microscopic origins of decoherence sources prevalent in Josephson junction (JJ) based circuits is central to their use as functional quantum devices. Focussing on so called ‘strongly coupled’ two-level defects, we construct a theoretical model using the atomic position of the oxygen which is spatially delocalized in the oxide forming the JJ barrier. Using this model, we investigate which atomic configurations give rise to two-level behaviour of the type seen in experiments. We compute experimentally observable parameters for phase qubits and examine defect response under the effects of applied electric field and strain. (paper)
Fabrication of submicron La2-xSrxCuO4 intrinsic Josephson junction stacks
Kubo, Yuimaru; Takahide, Yamaguchi; Tanaka, Takayoshi; Ueda, Shinya; Ishii, Satoshi; Tsuda, Shunsuke; Islam, ATM Nazmul; Tanaka, Isao; Takano, Yoshihiko
2011-02-01
Intrinsic Josephson junction (IJJ) stacks of cuprate superconductors have potential to be implemented as intrinsic phase qubits working at relatively high temperatures. We report success in fabricating submicron La2-xSrxCuO4 (LSCO) IJJ stacks carved out of single crystals. We also show a new fabrication method in which argon ion etching is performed after focused ion beam etching. As a result, we obtained an LSCO IJJ stack in which resistive multibranches appeared. It may be possible to control the number of stacked IJJs with an accuracy of a single IJJ by developing this method.
Fabrication of submicron La$_{2-x}$Sr$_{x}$CuO$_{4}$ intrinsic Josephson junction stacks
Kubo, Yuimaru; Takahide, Yamaguchi; Tanaka, Takayoshi; Ueda, Shinya; Ishii, Satoshi; Tsuda, Shunsuke; Islam, A. T. M. Nazmul; Tanaka, Isao; Takano, Yoshihiko
2011-01-01
Intrinsic Josephson junction (IJJ) stacks of cuprate superconductors have potential to be implemented as intrinsic phase qubits working at relatively high temperatures. We report success in fabricating submicron La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO) IJJ stacks carved out of single crystals. We also show a new fabrication method in which argon ion etching is performed after focused ion beam etching. As a result, we obtained an LSCO IJJ stack in which resistive multi-branches appeared. It may be p...
Current-induced in-plane superconducting transition in intrinsic Josephson junctions
You, L. X.; Yurgens, A.; Winkler, D.; Torstensson, M.; Kajiki, K.; Tanaka, I.
2006-05-01
In stacks of intrinsic Josephson junctions (IJJs) with lateral sizes of several microns, the current is non-uniform in many cases. In certain geometries a significant part of the current flows along the superconducting planes and can reach the critical value. The current-driven superconductivity breakdown within a single Cu2O4 plane can be seen as an extra branch structure of the c-axis current-voltage characteristics. This allows us to deduce the sheet critical current of a single Cu2O4 plane in different measurement configurations. The conditions for the observation of such a current-induced transition in different IJJ geometries are discussed.
An IR focal plane array employing superconducting Josephson junction thermal detectors
Osterman, D. P.; Yao, C.-T.; Dang, H.; Cohen, C.; Radparvar, M.
1990-07-01
Thin-film superconductors invite the single-process/single-substrate fabrication of IR detector arrays and their associated processing circuitry. In place of the bolometric thermal-detection principle typical of previous superconductor-employing schemes, the temperature-dependence of the current-voltage relation in a current-biased Josephson tunnel junction is used in the present device; this yields very low intrinsic detector noise, as well as clearly-defined 'on' and 'off' states. Superconducting processing circuitry encompassing addressing and decoding circuits, analog amplifiers, and ADC has been tested for an 8 x 8 prototype array.
Triplet supercurrent due to spin-active zones in a Josephson junction
Linder, Jacob; Sudbø, Asle
2010-07-01
Motivated by a recent experiment evidencing triplet superconductivity in a ferromagnetic Josephson junction with a Cu2MnAl -Heusler barrier, we construct a theoretical model accounting for this observation. The key ingredients in our model which generate the triplet supercurrent are spin-active zones, characterized by an effective canted interface magnetic moment. Using a numerical solution of the quasiclassical equations of superconductivity with spin-active boundary conditions, we find qualitatively very good agreement with the experimentally observed supercurrent. Further experimental implications of the spin-active zones are discussed.
Charge representation of a small two-dimensional Josephson-junction array in the quantum regime
International Nuclear Information System (INIS)
Using the charge representation, we calculate the ground state energy and the critical current of a small two-dimensional Josephson junction array subject to both charge and magnetic frustration. In the quantum regime the ground state of the array is a superposition of charge states, allowing a supercurrent to flow through the circuit. Both the ground state energy and the critical current can be tuned by the two frustrations. We show that the notion of a vortex is compatible with a charge representation of the array. copyright 1996 The American Physical Society
Simulation studies of radiation linewidth in circular Josephson-junction fluxon oscillators
DEFF Research Database (Denmark)
If, F.; Christiansen, Peter Leth; Parmentier, R. D.;
1985-01-01
Detailed simulation studies of the dynamics of fluxons in long circular Josephson tunnel junctions under the influence of external microwave radiation and internal thermal noise are presented. The simulation algorithm uses a pseudospectral method well adapted to vector processors (CRAY-1-S), which...... gives a speed-up factor in computing time of typically 22 in comparison to conventional high-speed computers, and also provides results with a relative accuracy of less than 10-8 thereby making possible the study of the very narrow radiation linewidth of such oscillators. Comparison of calculated...
Weak coupling Josephson junction as a current probe: effect of dissipation on escape dynamics
International Nuclear Information System (INIS)
We have studied the temperature dependence of escape phenomena in various underdamped Josephson junctions (JJs). The junctions had different Josephson coupling energies EJ which were relatively small, but larger than the charging energy EC. Upon increasing the temperature T, we first observe the usual cross-over between macroscopic quantum tunnelling and thermally activated (TA) behaviour at temperatures kBT ∼ ℎωp, where ωp is the plasma frequency of the junction. Increasing T further, the width of the switching current distribution has, counterintuitively, a non-monotonic temperature dependence. This can be explained by the novel cross-over from TA behaviour to underdamped phase diffusion. We show that this cross-over is expected to occur at temperatures such that kBT ∼ EJ(1 - 4/πQ)3/2, where Q is the quality factor of the junction at the plasma frequency, in agreement with experiment. Our findings can be compared with detailed model calculations which take into account dissipation and level quantization in a metastable well. Particular attention is paid to the sample with the smallest EJ, which shows extensive phase diffusion even at the lowest temperatures. This sample consists of a dc-SQUID and a single JJ close to each other, such that the SQUID acts as a tunable inductive protection for the single junction from fluctuations of a dissipative environment. By varying the flux through the dc-SQUID, we present, for the first time, experimental evidence of the escape of a JJ from the phase diffusion regime to the free running state in a tunable environment. We also show that in the zero voltage state the losses mainly occur at frequencies near the plasma resonance
Multi-terminal Josephson junctions as topological matter
Riwar, Roman-Pascal; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
2016-04-01
Topological materials and their unusual transport properties are now at the focus of modern experimental and theoretical research. Their topological properties arise from the bandstructure determined by the atomic composition of a material and as such are difficult to tune and naturally restricted to =4, the Andreev subgap spectrum of the junction can accommodate Weyl singularities in the space of the n-1 independent superconducting phases, which play the role of bandstructure quasimomenta. The presence of these Weyl singularities enables topological transitions that are manifested experimentally as changes of the quantized transconductance between two voltage-biased leads, the quantization unit being 4e2/h, where e is the electric charge and h is the Planck constant.
Temperature dependence of submillimeter wave response in the point-contact Josephson junction
International Nuclear Information System (INIS)
The authors have measured the magnitude of the first Shapiro step in both bridge-type (Ta-Ta and Ta-Sn) and tunneltype (Ta-SnOx-Sn) point-contact Josephson junctions in the SMMW (Submillimeter Wave) region. By varying the temperature continuously with the frequency of the SMMW fixed (ω=2π/lambda, lambda=699, 570 and 469 μm), we determined I1 /SUP MAX/ /I /SUB c/ minutely as a function of the normalized frequency ω/ω /SUB g/ (T), where I1 /SUP MAX/ is the maximum (half) height of the first Shapiro step as a function of the ac field power, I /SUB c/ is the critical current, and ω /SUB g/ (T)=4Δ /SUB Ta/ (T)/h or 2(Δ /SUB Ta/ (T)+Δ /SUB Sn/ (T))/h. By fitting the shape of the Riedel peak at ω/ω /SUB g/ (T)=1 with the theory of the tunnel junction, we have determined the damping factor delta. They obtained delta=0.02 for the Ta-SnOx-Sn tunnel - type junction, and delta=0.05 for both the Ta-Sn and Ta-Ta bridge - type junctions, respectively. At ω/ω /SUB g/ (T)>1.5, we have found that I1 /SUP MAX/ /I /SUB c/ tends to saturate in both the tunnel-type and the bridge-type junctions as ω/ω /SUB g/ (T) increases. For the tunnel-type junction, this agrees with the very slow decrease predicted by the theory of the tunnel junction. But for the bridge-type junction, this slow decrease is in marked contrast to the very rapid decrease found from the previous experiments, where the Shapiro step was measured for a number of frequencies at a fixed temperature
Numerical Study of a System of Long Josephson Junctions with Inductive and Capacitive Couplings
Rahmonov, I. R.; Shukrinov, Yu. M.; Plecenik, A.; Zemlyanaya, E. V.; Bashashin, M. V.
2016-02-01
The phase dynamics of the stacked long Josephson junctions is investigated taking into account the inductive and capacitive couplings between junctions and the diffusion current. The simulation of the current-voltage characteristics is based on the numerical solution of a system of nonlinear partial differential equations by a fourth order Runge-Kutta method and finite-difference approximation. A parallel implementation is based on the MPI technique. The effectiveness of the MPI/C++ code is confirmed by calculations on the multi-processor cluster CICC (LIT JINR, Dubna). We demonstrate the appearance of the charge traveling wave (CTW) at the boundary of the zero field step. Based on this fact, we conclude that the CTW and the fluxons coexist.
Linear and nonlinear excitations in two stacks of parallel arrays of long Josephson junctions
DEFF Research Database (Denmark)
Carapella, G.; Constabile, Giovanni; Latempa, R.;
2000-01-01
known from continuous and discrete systems as well as the excitation of a new state exhibiting synchronization in two dimensions are inferred from the mathematical model of the system. The stable nonlinear solution of the coupled sine-Gordon equations describing the system is found to consist of a......We investigate a structure consisting of two parallel arrays of long Josephson junctions sharing a common electrode that allows inductive coupling between the arrays. A model for this structure is derived starting from the description of its continuous limit. The excitation of linear cavity modes...... fluxon-antifluxon string. This is a two-dimensional phase-locked solitonic mode. Both linear and nonlinear excitations are numerically investigated and experimentally demonstrated in two stacks of five-junction arrays....
Tunneling transport properties in (La,Sr)2CuO4 grain boundary Josephson junctions
International Nuclear Information System (INIS)
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
Park, Sunghun; Recher, Patrik
2015-12-11
A phase from an adiabatic exchange of Majorana bound states (MBS) reveals their exotic anyonic nature. For detecting this exchange phase, we propose an experimental setup consisting of a Corbino geometry Josephson junction on the surface of a topological insulator, in which two MBS at zero energy can be created and rotated. We find that if a metallic tip is weakly coupled to a point on the junction, the time-averaged differential conductance of the tip-Majorana coupling shows peaks at the tip voltages eV=±(α-2πl)ℏ/T_{J}, where α=π/2 is the exchange phase of the two circulating MBS, T_{J} is the half rotation time of MBS, and l an integer. This result constitutes a clear experimental signature of Majorana fermion exchange. PMID:26705644
Crystal engineering of oxide films in the fabrication of high-Tc Josephson tunnel junction
International Nuclear Information System (INIS)
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
Planar intrinsic Josephson junctions with in-plane aligned YBCO films
Zhang, L; Kobayashi, T; Goto, T; Mukaida, M
2002-01-01
Planar type devices were fabricated by patterning in-plane aligned YBa sub 2 Cu sub 3 O sub 7 sub - subdelta (YBCO) films. The current-voltage characteristics along the c-axis at various temperatures and oxygen contents were measured. The current voltage curves showing supercurrent and hysteresis were obtained for the samples annealed at an oxygen pressure of 1.3 x 10 sup 4 Pa, while the supercurrent and hysteresis became smaller and even disappeared as the oxygen pressure decreased. The relationships between the critical currents and temperatures are similar to those of d-wave superconducting tunnel junctions. These results indicate the formation of stacks of intrinsic Josephson junctions, which are useful for developing high-frequency electron devices.
Suwannasit, Tatnatchai; Tang, I.-Ming; Hoonsawat, Rassmidara; Soodchomshom, Bumned
2011-10-01
The Josephson effect in a gapped graphene-based superconductor/barrier/superconductor junction is studied. The superconductivity in gapped graphene may be achieved by depositing conventional superconductor on the top of the gapped graphene such as graphene grown on SiC substrate. In gapped graphene system, the carriers exhibit massive Dirac fermions. We focus on the effect of pseudo-Dirac-like mass on the supercurrent. In contrast to that in the gapless graphene superconductor/barrier/superconductor junction, we find that the supercurrent exhibits dependency of the Fermi energy. Also, the massive supercurrent anomalously oscillates as a function of the gate potential. This novel behavior is due to the effect of electrons acquiring mass in gapped graphene.
Possible method to observe the breathing mode of a magnetic domain wall in the Josephson junction
International Nuclear Information System (INIS)
A magnetic domain wall (DW) behaves as a massive particle with elasticity. Sliding and oscillation of the DW have been observed experimentally, whereas vibration of a width in the DW, ‘breathing mode’, has not been measured so far. We theoretically propose how to observe the breathing mode by the Josephson junction having a ferromagnetic layer between superconducting electrodes. The current-voltage (I-V) curve is calculated by an equivalent circuit of the resistively shunted junction model. The breathing mode is identified by stepwise structures in the I-V curve, which appear at the voltages V = n (ℏ/2e)ω with the fundamental constant ℏ/e, integer number n and the frequency of the breathing mode ω. (paper)
International Nuclear Information System (INIS)
We consider Josephson junctions on surfaces of three dimensional topological insulator nanowires. We find that in the presence of a parallel magnetic field, short junctions on nanowires show signatures of a perfectly transmitted mode capable of supporting Majorana fermions. Such signatures appear in the current-phase relation in the presence or absence of the fermion parity anomaly, and are most striking when considering the critical current as a function of flux Φ, which exhibits a peak at Φ=h/2e. The peak sharpens in the presence of disorder at low but finite chemical potentials, and can be easily disentangled from weak-anti-localization effects. The peak also survives at small but finite temperatures, and represents a realistic and robust hallmark for perfect transmission and the emergence of Majorana physics inside the wire
Simulation of I-V curves of small Josephson tunnel junctions with finite capacitance
International Nuclear Information System (INIS)
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