Wendt, J.R.; Plut, T.A.; Martens, J.S.
1995-05-02
A novel method for fabricating nanometer geometry electronic devices is described. Such Josephson junctions can be accurately and reproducibly manufactured employing photolithographic and direct write electron beam lithography techniques in combination with aqueous etchants. In particular, a method is described for manufacturing planar Josephson junctions from high temperature superconducting material. 10 figs.
Wendt, Joel R.; Plut, Thomas A.; Martens, Jon S.
1995-01-01
A novel method for fabricating nanometer geometry electronic devices is described. Such Josephson junctions can be accurately and reproducibly manufactured employing photolithographic and direct write electron beam lithography techniques in combination with aqueous etchants. In particular, a method is described for manufacturing planar Josephson junctions from high temperature superconducting material.
NASA Astrophysics Data System (ADS)
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.
Mathematical modeling of intrinsic Josephson junctions with capacitive and inductive couplings
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Antonenko, Daniil S.; Skvortsov, Mikhail A.
2015-12-01
A nondissipative supercurrent state of a Josephson junction is metastable with respect to the formation of a finite-resistance state. This transition is driven by fluctuations, thermal at high temperatures and quantum at low temperatures. We evaluate the lifetime of such a state due to quantum fluctuations in the limit when the supercurrent is approaching the critical current. The decay probability is determined by the instanton action for the superconducting phase difference across the junction. At low temperatures, the dynamics of the phase is massive and is determined by the effective capacitance, which is a sum of the geometric and intrinsic capacitance of the junction. We model the central part of the Josephson junction either by an arbitrary short mesoscopic conductor described by the set of its transmission coefficients, or by a diffusive wire of an arbitrary length. The intrinsic capacitance can generally be estimated as C*˜G /Eg , where G is the normal-state conductance of the junction and Eg is the proximity minigap in its normal part. The obtained capacitance is sufficiently large to qualitatively explain the hysteretic behavior of the current-voltage characteristic even in the absence of overheating.
Modeling of LC-shunted intrinsic Josephson junctions in high-T c superconductors
NASA Astrophysics Data System (ADS)
Shukrinov, Yu M.; Rahmonov, I. R.; Kulikov, K. V.; Botha, A. E.; Plecenik, A.; Seidel, P.; Nawrocki, W.
2017-02-01
Resonance phenomena in a model of intrinsic Josephson junctions shunted by LC-elements (L-inductance, C-capacitance) are studied. The phase dynamics and IV-characteristics are investigated in detail when the Josephson frequency approaches the frequency of the resonance circuit. A realization of parametric resonance through the excitation of a longitudinal plasma wave, within the bias current interval corresponding to the resonance circuit branch, is demonstrated. It is found that the temporal dependence of the total voltage of the stack, and the voltage measured across the shunt capacitor, reflect the charging of superconducting layers, a phenomenon which might be useful as a means of detecting such charging experimentally. Thus, based on the voltage dynamics, a novel method for the determination of charging in the superconducting layers of coupled Josephson junctions is proposed. A demonstration and discussion of the influence of external electromagnetic radiation on the IV-characteristics and charge-time dependence is given. Over certain parameter ranges the radiation causes an interesting new type of temporal splitting in the charge-time oscillations within the superconducting layers.
Enhancement of the critical current of intrinsic Josephson junctions by carrier injection
NASA Astrophysics Data System (ADS)
Kizilaslan, O.; Simsek, Y.; Aksan, M. A.; Koval, Y.; Müller, P.
2015-08-01
We present a study of the doping effect by carrier injection of high-Tc superconducting Bi-based whiskers. The current was injected in the c-axis direction, i.e., perpendicular to the superconducting planes. Superconducting properties were investigated systematically as a function of the doping level. The doping level of one and the same sample was changed by current injection in very small steps from an underdoped state up to a slightly overdoped state. We have observed that Tc versus log (jc) exhibits a dome-shaped characteristic, which can be fitted by a parabola. As Tc versus carrier concentration has a parabolic form, too, it can be concluded that the critical current density jc increases exponentially with the doping level. The electron-trapping mechanism is interpreted in the framework of Phillips’ microscopic theory. In addition, the Joule heating effect in the intrinsic Josephson junction (IJJ) was controlled by carrier injection, and the effect of the non-equilibrium quasiparticle on the I-V curves of the IJJs was also discussed.
Stability of the kink state in a stack of intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Lin, Shi-Zeng; Hu, Xiao
2010-12-01
A new dynamic state characterized by (2ml+1)π static phase kink with integers {ml} is proposed recently in a stack of inductively coupled Josephson junctions. In the present paper, the stability of the phase kink state is investigated against various perturbations and it is shown that the kink state is stable. It is also discussed that the suppression of the amplitude of superconducting order parameter caused by the kink is weak.
NASA Astrophysics Data System (ADS)
Kashiwagi, T.; Nakade, K.; Saiwai, Y.; Minami, H.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y.; Tsujimoto, M.; Yamamoto, T.; Marković, B.; Mirković, J.; Klemm, R. A.; Kadowaki, K.
2014-02-01
A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-Tc superconductor Bi2Sr2CaCu2O8+δ was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.
NASA Astrophysics Data System (ADS)
Kizilaslan, O.; Rudau, F.; Wieland, R.; Hampp, J. S.; Zhou, X. J.; Ji, M.; Kiselev, O.; Kinev, N.; Huang, Y.; Hao, L. Y.; Ishii, A.; Aksan, M. A.; Hatano, T.; Koshelets, V. P.; Wu, P. H.; Wang, H. B.; Koelle, D.; Kleiner, R.
2017-03-01
We report on doping and undoping experiments of terahertz (THz) emitting intrinsic Josephson junction stacks, where the change in charge carrier concentration is achieved by heavy current injection. The experiments were performed on stand-alone structures fabricated from a Bi2Sr2CaCu2O{}8+δ single crystal near optimal doping. The stacks contained about 930 intrinsic Josephson junctions. On purpose, the doping and undoping experiments were performed over only a modest range of charge carrier concentrations, changing the critical temperature of the stack by less than 1 K. We show that both undoping and doping is feasible also for the large intrinsic Josephson junction stacks used for THz generation. Even moderate changes in doping introduce large changes in the THz emission properties of the stacks. The highest emission power was achieved after doping a pristine sample.
Signatures of topological Josephson junctions
NASA Astrophysics Data System (ADS)
Peng, Yang; Pientka, Falko; Berg, Erez; Oreg, Yuval; von Oppen, Felix
2016-08-01
Quasiparticle poisoning and diabatic transitions may significantly narrow the window for the experimental observation of the 4 π -periodic dc Josephson effect predicted for topological Josephson junctions. Here, we show that switching-current measurements provide accessible and robust signatures for topological superconductivity which persist in the presence of quasiparticle poisoning processes. Such measurements provide access to the phase-dependent subgap spectrum and Josephson currents of the topological junction when incorporating it into an asymmetric SQUID together with a conventional Josephson junction with large critical current. We also argue that pump-probe experiments with multiple current pulses can be used to measure the quasiparticle poisoning rates of the topological junction. The proposed signatures are particularly robust, even in the presence of Zeeman fields and spin-orbit coupling, when focusing on short Josephson junctions. Finally, we also consider microwave excitations of short topological Josephson junctions which may complement switching-current measurements.
Fabrication of submicron La{sub 2-x}Sr{sub x}CuO{sub 4} intrinsic Josephson junction stacks
Kubo, Yuimaru; Takano, Yoshihiko; Takahide, Yamaguchi; Ueda, Shinya; Ishii, Satoshi; Tsuda, Shunsuke; Tanaka, Takayoshi; Islam, ATM Nazmul; Tanaka, Isao
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 La{sub 2-x}Sr{sub x}CuO{sub 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 multibranches appeared. It may be possible to control the number of stacked IJJs with an accuracy of a single IJJ by developing this method.
Clarke, J.; Hilbert, C.; Hahn, E.L.; Sleator, T.
1986-03-25
An automatic Q-spoiler comprising at least one Josephson tunnel junction connected in an LC circuit for flow of resonant current therethrough. When in use in a system for detecting the magnetic resonance of a gyromagnetic particle system, a high energy pulse of high frequency energy irradiating the particle system will cause the critical current through the Josephson tunnel junctions to be exceeded, causing the tunnel junctions to act as resistors and thereby damp the ringing of the high-Q detection circuit after the pulse. When the current has damped to below the critical current, the Josephson tunnel junctions revert to their zero-resistance state, restoring the Q of the detection circuit and enabling the low energy magnetic resonance signals to be detected.
Clarke, John; Hilbert, Claude; Hahn, Erwin L.; Sleator, Tycho
1988-01-01
An automatic Q-spoiler comprising at least one Josephson tunnel junction connected in an LC circuit for flow of resonant current therethrough. When in use in a system for detecting the magnetic resonance of a gyromagnetic particle system, a high energy pulse of high frequency energy irradiating the particle system will cause the critical current through the Josephson tunnel junctions to be exceeded, causing the tunnel junctions to act as resistors and thereby damp the ringing of the high-Q detection circuit after the pulse. When the current has damped to below the critical current, the Josephson tunnel junctions revert to their zero-resistance state, restoring the Q of the detection circuit and enabling the low energy magnetic resonance signals to be detected.
Simple Electronic Analog of a Josephson Junction.
ERIC Educational Resources Information Center
Henry, R. W.; And Others
1981-01-01
Demonstrates that an electronic Josephson junction analog constructed from three integrated circuits plus an external reference oscillator can exhibit many of the circuit phenomena of a real Josephson junction. Includes computer and other applications of the analog. (Author/SK)
Kashiwagi, T. Minami, H.; Kadowaki, K.; Nakade, K.; Saiwai, Y.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y.; Tsujimoto, M.; Yamamoto, T.; Marković, B.; Mirković, J.; Klemm, R. A.
2014-02-24
A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-T{sub c} superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.
Squeezed States in Josephson Junctions.
NASA Astrophysics Data System (ADS)
Hu, X.; Nori, F.
1996-03-01
We have studied quantum fluctuation properties of Josephson junctions in the limit of large Josephson coupling energy and small charging energy, when the eigenstates of the system can be treated as being nearly localized. We have considered(X. Hu and F. Nori, preprints.) a Josephson junction in a variety of situations, e.g., coupled to one or several of the following elements: a capacitor, an inductor (in a superconducting ring), and an applied current source. By solving an effective Shrödinger equation, we have obtained squeezed vacuum (coherent) states as the ground states of a ``free-oscillating'' (linearly-driven) Josephson junction, and calculated the uncertainties of its canonical momentum, charge, and coordinate, phase. We have also shown that the excited states of the various systems we consider are similar to the number states of a simple harmonic oscillator but with different fluctuation properties. Furthermore, we have obtained the time-evolution operators for these systems. These operators can make it easier to calculate the time-dependence of the expectation values and fluctuations of various quantities starting from an arbitrary initial state.
NASA Astrophysics Data System (ADS)
Delfanazari, Kaveh; Asai, Hidehiro; Tsujimoto, Manabu; Kashiwagi, Takanari; Kitamura, Takeo; Yamamoto, Takashi; Sawamura, Masashi; Ishida, Kazuya; Tachiki, Masashi; Klemm, Richard A.; Hattori, Toshiaki; Kadowaki, Kazuo
2013-08-01
We report on intense and coherent terahertz (THz) electromagnetic (EM) waves emitted from equilateral triangular mesa structures of the intrinsic Josephson junctions (IJJs) in single crystalline high-Tc superconducting Bi2Sr2CaCu2O8+δ. The focused ion beam milling technique is used for mesa fabrication. THz radiation is observed when the emission frequency is in the vicinity of the primary cavity resonance frequency determined by the mesa geometry. We also investigated numerically the THz radiation from such mesas using the finite difference time domain method. We found an apparent EM mode similar to the known TM(1, 0) = TM(0, 1) cavity mode during the THz emission.
NASA Astrophysics Data System (ADS)
Kakizaki, Yoshihiro; Koyama, Junpei; Yamaguchi, Ayami; Umegai, Shunpei; Ayukawa, Shin-ya; Kitano, Haruhisa
2017-04-01
We report a transmission electron microscopy (TEM) study on the damage produced by the focused ion beam (FIB) etching for small Bi2Sr2CaCu2O y (Bi2212) intrinsic Josephson junctions (IJJs). The selected area diffraction patterns of TEM images demonstrate that the FIB damage causes the formation of an amorphous layer. The thickness of FIB damage is at least 30 nm for the Ga+ ion beam emitted at 50 pA and 30 kV, independent of the incident direction of the Ga+ ion beam. We also confirmed that the damage or the redeposition due to the FIB etching was effectively removed by the additional irradiation of Ar ions after the FIB etching. This suggests the advantage of the combinatorial method of the FIB and Ar-ion etchings in the successful fabrication of small and high-quality IJJs.
YBCO Josephson Junction Arrays
1993-07-14
Also, CaRuO 3 is chemically compatible with YBa2Cu30 7 and its conductivity does not appear to be strongly dependent on doping or oxygen concentration...barrier conductivity is quite high. The first YBa2Cu30 7 layer and the SrTiO3 layer are deposited first and then patterned with ion milling (to help form...the edge junction will dominate any leakage through the SrTiO3 , thus the integrity of that dielectric will not be a concern here. The integrity of the
Quantum dynamics in the bosonic Josephson junction
Chuchem, Maya; Cohen, Doron; Smith-Mannschott, Katrina; Hiller, Moritz; Kottos, Tsampikos; Vardi, Amichay
2010-11-15
We employ a semiclassical picture to study dynamics in a bosonic Josephson junction with various initial conditions. Phase diffusion of coherent preparations in the Josephson regime is shown to depend on the initial relative phase between the two condensates. For initially incoherent condensates, we find a universal value for the buildup of coherence in the Josephson regime. In addition, we contrast two seemingly similar on-separatrix coherent preparations, finding striking differences in their convergence to classicality as the number of particles increases.
NASA Astrophysics Data System (ADS)
Gross, B.; Rudau, F.; Kinev, N.; Tsujimoto, M.; Yuan, J.; Huang, Y.; Ji, M.; Zhou, X. J.; Y An, D.; Ishii, A.; Wu, P. H.; Hatano, T.; Koelle, D.; Wang, H. B.; Koshelets, V. P.; Kleiner, R.
2015-05-01
We report on the investigation of the electrothermal behavior and the terahertz (THz) emission properties of two nearby Bi2Sr2CaCu2O8+δ (BSCCO) intrinsic Josephson junction stacks, using a combination of electric transport and THz emission measurements plus low temperature scanning laser microscopy. We start with a compact BSCCO stack (placed in a z-shaped structure between two BSCCO electrodes) with lateral dimensions of 330× 60 μ {{m}2} and 0.7 μ m height, consisting of about 480 junctions. After characterization, a 200 nm wide slit was introduced by focused ion beam milling, splitting the stack into two halves connected by continuous superconducting electrodes. In a third step, the upper electrode was also split, leading to a structure where the two stacks can be biased separately. In all configurations hot-spot formation was observed. Despite the separation into two stacks only a single hot spot formed, which, depending on the bias condition, could either be located in one of the stacks or extend into both stacks with its center in the slit. In none of the structures it was possible to achieve mutual synchronization of the two stacks, indicating that additional synchronizing elements or the presence of a base crystal as for mesa structures may be necessary for the operation of parallel array structures.
Instability of Driven Josephson Vortices in Long Underdamped Junctions
NASA Astrophysics Data System (ADS)
Sheikhzada, Ahmad; Gurevich, Alex
We show that a Josephson vortex driven by a dc current can become unstable due to strong Cherenkov radiation resulting from intrinsic nonlocal electrodynamics of long underdamped Josephson junctions. This instability is not captured by the conventional sine-Gordon equation but is described by a more general integro-differential equation for the phase difference, θ (x , t) . Our numerical simulations of this nonlinear dynamic equation for different junction geometries have shown that, as the vortex reaches a critical velocity, it triggers a cascade of expanding vortex-antivortex pairs. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. Our results suggest that a rapidly moving Josephson vortex can destroy the superconducting long-range order in a way that is similar to the crack propagation in solids. This work was supported by DOE under Grant No. DE-SC0010081.
Hot Spot and THz Wave Generation in Bi2Sr2CaCu2O8 Intrinsic Josephson Junction Stacks
NASA Astrophysics Data System (ADS)
Kleiner, Reinhold
2013-03-01
Stacks of intrinsic Josephson junctions made of the high temperature superconductor Bi2Sr2CaCu2O8 have been shown to emit coherent radiation at THz frequencies. Emission is observed both in a low bias regime and a high bias regime. While at low bias the temperature of the stack is close to the bath temperature, at high bias a hot spot and a standing wave, formed in the ``cold'' part of the stack, coexist. THz radiation is very stable in this regime, exhibiting a linewidth which is much smaller than expected from a purely cavity-induced synchronization mechanism. We investigate the interaction of hot spots and THz waves using a combination of transport measurement, direct electromagnetic wave detection and low temperature scanning laser microscopy (LTSLM). In this talk recent developments will be presented, with a focus on the mechanism of hot spot formation. In collaboration with B. Gross, S. Guénon, M. Y. Li, J. Yuan, N. Kinev, J. Li, A. Ishii, K. Hirata, T. Hatano, R. G. Mints, D. Koelle, V. P. Koshelets, H. B. Wang and P. H. Wu.
NASA Astrophysics Data System (ADS)
Liu, X.; Wang, P.; Xie, W.; Ma, L. J.; Zhao, X. J.; He, M.; Ji, L.; Zhang, X.
2015-12-01
An intrinsic Josephson junctions (IJJs) microbridge with planar equiangular spiral antenna (PESA) is proposed and studied by simulation and experiment. This IJJs circuit is simulated firstly to obtain the minimum of reflection coefficient and pattern. Secondly, IJJs with PESA are fabricated on misaligned Tl2Ba2CaCu2O8 superconducting film. The millimeter wave characteristics are investigated by a Febry-Pérot resonator, which consists of a spherical mirror antenna and a plane mirror. At 37.4 GHz, the IJJs and the millimeter wave show an optimum coupling, which deviate from the simulation for only 0.004 GHz. In addition, the extent of the coupling between IJJs and the resonator is discussed at different angle for the polarization direction of the spherical mirror antenna with the microbridge. The result shows that the strongest coupling is obtained at 0-30° angle. Good conformance of measurements and simulations illustrate the effectiveness of our design in strong coupling between sample and resonator.
Statistics of voltage fluctuations in resistively shunted Josephson junctions
NASA Astrophysics Data System (ADS)
Marthaler, Michael; Golubev, Dmitry; Utsumi, Yasuhiro; Schön, Gerd
2011-03-01
The intrinsic nonlinearity of Josephson junctions converts Gaussian current noise in the input into non-Gaussian voltage noise in the output. For a resistively shunted Josephson junction with white input noise we determine numerically exactly the properties of the few lowest cumulants of the voltage fluctuations, and we derive analytical expressions for these cumulants in several important limits. The statistics of the voltage fluctuations is found to be Gaussian at bias currents well above the Josephson critical current, but Poissonian at currents below the critical value. In the transition region close to the critical current the higher-order cumulants oscillate and the voltage noise is strongly non-Gaussian. For coloured input noise we determine the third cumulant of the voltage.
Statistics of voltage fluctuations in resistively shunted Josephson junctions
NASA Astrophysics Data System (ADS)
Golubev, D. S.; Marthaler, M.; Utsumi, Y.; Schön, Gerd
2010-05-01
The intrinsic nonlinearity of Josephson junctions converts Gaussian current noise in the input into non-Gaussian voltage noise in the output. For a resistively shunted Josephson junction with white input noise we determine numerically exactly the properties of the few lowest cumulants of the voltage fluctuations, and we derive analytical expressions for these cumulants in several important limits. The statistics of the voltage fluctuations is found to be Gaussian at bias currents well above the Josephson critical current but Poissonian at currents below the critical value. In the transition region close to the critical current the higher-order cumulants oscillate and the voltage noise is strongly non-Gaussian. For colored input noise we determine the third cumulant of the voltage.
Dressed fluxon in a Josephson window junction
NASA Astrophysics Data System (ADS)
Caputo, Jean Guy; Flytzanis, Nikos; Devoret, Michel
1994-09-01
The static fluxon solutions of a Josephson window junction have been studied numerically. We show that the effect of the idle region surrounding the junction is to ``dress'' the fluxon causing its energy to increase. This effect can be predicted accurately by a simple model.
Numerical Investigation of Josephson Junction Structures
Hristov, I.; Dimova, S.; Boyadjiev, T.
2009-10-29
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.
Soft nanostructuring of YBCO Josephson junctions by phase separation.
Gustafsson, D; Pettersson, H; Iandolo, B; Olsson, E; Bauch, T; Lombardi, F
2010-12-08
We have developed a new method to fabricate biepitaxial YBa2 Cu3 O7-δ (YBCO) Josephson junctions at the nanoscale, allowing junctions widths down to 100 nm and simultaneously avoiding the typical damage in grain boundary interfaces due to conventional patterning procedures. By using the competition between the superconducting YBCO and the insulating Y2 BaCuO5 phases during film growth, we formed nanometer sized grain boundary junctions in the insulating Y2 BaCuO5 matrix as confirmed by high-resolution transmission electron microscopy. Electrical transport measurements give clear indications that we are close to probing the intrinsic properties of the grain boundaries.
Josephson junctions with alternating critical current density
Mints, R.G.; Kogan, V.G.
1997-04-01
The magnetic-field dependence of the critical current I{sub c}(H) is considered for a short Josephson junction with the critical current density j{sub c} alternating along the tunnel contact. Two model cases, periodic and randomly alternating j{sub c}, are treated in detail. Recent experimental data on I{sub c}(H) for grain-boundary Josephson junctions in YBa{sub 2}Cu{sub 3}O{sub x} are discussed. {copyright} {ital 1997} {ital The American Physical Society}
Demonstration of an ac Josephson junction laser
NASA Astrophysics Data System (ADS)
Cassidy, M. C.; Bruno, A.; Rubbert, S.; Irfan, M.; Kammhuber, J.; Schouten, R. N.; Akhmerov, A. R.; Kouwenhoven, L. P.
2017-03-01
Superconducting electronic devices have reemerged as contenders for both classical and quantum computing due to their fast operation speeds, low dissipation, and long coherence times. An ultimate demonstration of coherence is lasing. We use one of the fundamental aspects of superconductivity, the ac Josephson effect, to demonstrate a laser made from a Josephson junction strongly coupled to a multimode superconducting cavity. A dc voltage bias applied across the junction provides a source of microwave photons, and the circuit’s nonlinearity allows for efficient down-conversion of higher-order Josephson frequencies to the cavity’s fundamental mode. The simple fabrication and operation allows for easy integration with a range of quantum devices, allowing for efficient on-chip generation of coherent microwave photons at low temperatures.
Axion mass estimates from resonant Josephson junctions
NASA Astrophysics Data System (ADS)
Beck, Christian
2015-03-01
Recently it has been proposed that dark matter axions from the galactic halo can produce a small Shapiro step-like signal in Josephson junctions whose Josephson frequency resonates with the axion mass (Beck, 2013). Here we show that the axion field equations in a voltage-driven Josephson junction environment allow for a nontrivial solution where the axion-induced electrical current manifests itself as an oscillating supercurrent. The linear change of phase associated with this nontrivial solution implies the formal existence of a large magnetic field in a tiny surface area of the weak link region of the junction which makes incoming axions decay into microwave photons. We derive a condition for the design of Josephson junction experiments so that they can act as optimum axion detectors. Four independent recent experiments are discussed in this context. The observed Shapiro step anomalies of all four experiments consistently point towards an axion mass of (110±2) μeV. This mass value is compatible with the recent BICEP2 results and implies that Peccei-Quinn symmetry breaking was taking place after inflation.
Josephson instantons and Josephson monopoles in a non-Abelian Josephson junction
NASA Astrophysics Data System (ADS)
Nitta, Muneto
2015-08-01
The non-Abelian Josephson junction is a junction of non-Abelian color superconductors sandwiching an insulator, or a non-Abelian domain wall if flexible, whose low-energy dynamics is described by a U (N ) principal chiral model with the conventional pion mass. A non-Abelian Josephson vortex is a non-Abelian vortex (color magnetic flux tube) residing inside the junction, that is described as a non-Abelian sine-Gordon soliton. In this paper, we propose Josephson instantons and Josephson monopoles, that is, Yang-Mills instantons and monopoles inside a non-Abelian Josephson junction, respectively, and show that they are described as S U (N ) Skyrmions and U (1 )N -1 vortices in the U (N ) principal chiral model without and with a twisted-mass term, respectively. Instantons with a twisted boundary condition are reduced (or T-dual) to monopoles, implying that C PN -1 lumps are T-dual to C PN -1 kinks inside a vortex. Here we find S U (N ) Skyrmions are T-dual to U (1 )N-1 vortices inside a wall. Our configurations suggest a yet another duality between C PN -1 lumps and S U (N ) Skyrmions as well as that between C PN -1 kinks and U (1 )N-1 vortices, viewed from different host solitons. They also suggest a duality between fractional instantons and bions in the C PN -1 model and those in the S U (N ) principal chiral model.
Radiation comb generation with extended Josephson junctions
Solinas, P.; Bosisio, R.; Giazotto, F.
2015-09-21
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.
Defect formation in long Josephson junctions
Gordeeva, Anna V.; Pankratov, Andrey L.
2010-06-01
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 to the power law with the exponent of either 0.25 or 0.5 depending on the temperature variation in the critical current density.
Josephson junction microwave modulators for qubit control
NASA Astrophysics Data System (ADS)
Naaman, O.; Strong, J. A.; Ferguson, D. G.; Egan, J.; Bailey, N.; Hinkey, R. T.
2017-02-01
We demonstrate Josephson junction based double-balanced mixer and phase shifter circuits operating at 6-10 GHz and integrate these components to implement both a monolithic amplitude/phase vector modulator and an I/Q quadrature mixer. The devices are actuated by flux signals, dissipate no power on chip, exhibit input saturation powers in excess of 1 nW, and provide cryogenic microwave modulation solutions for integrated control of superconducting qubits.
Josephson junction in a thin film
Kogan, V. G.; Dobrovitski, V. V.; Clem, J. R.; Mawatari, Yasunori; Mints, R. G.
2001-04-01
The phase difference {phi}(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 {phi}'(y)/2{pi}. We study the integral equation for {phi}(y) and show that the phase is sensitive to the ratio l/{Lambda}, where l={lambda}{sub J}{sup 2}/{lambda}{sub L}, {Lambda}=2{lambda}{sub L}{sup 2}/d, {lambda}{sub L}, and {lambda}{sub J} are the London and Josephson penetration depths, and d is the film thickness. For l<<{Lambda}, the vortex ''core'' of the size l is nearly temperature independent, while the phase ''tail'' scales as l{Lambda}/y{sup 2}={lambda}{sub J}2{lambda}{sub L}/d/y{sup 2}; i.e., it diverges as T{yields}T{sub c}. For l>>{Lambda}, both the core and the tail have nearly the same characteristic length l{Lambda}.
Edge currents in frustrated Josephson junction ladders
NASA Astrophysics Data System (ADS)
Marques, A. M.; Santos, F. D. R.; Dias, R. G.
2016-09-01
We present a numerical study of quasi-1D frustrated Josephson junction ladders with diagonal couplings and open boundary conditions, in the large capacitance limit. We derive a correspondence between the energy of this Josephson junction ladder and the expectation value of the Hamiltonian of an analogous tight-binding model, and show how the overall superconducting state of the chain is equivalent to the minimum energy state of the tight-binding model in the subspace of one-particle states with uniform density. To satisfy the constraint of uniform density, the superconducting state of the ladder is written as a linear combination of the allowed k-states of the tight-binding model with open boundaries. Above a critical value of the parameter t (ratio between the intra-rung and inter-rung Josephson couplings) the ladder spontaneously develops currents at the edges, which spread to the bulk as t is increased until complete coverage is reached. Above a certain value of t, which varies with ladder size (t = 1 for an infinite-sized ladder), the edge currents are destroyed. The value t = 1 corresponds, in the tight-binding model, to the opening of a gap between two bands. We argue that the disappearance of the edge currents with this gap opening is not coincidental, and that this points to a topological origin for these edge current states.
Work fluctuations in bosonic Josephson junctions
NASA Astrophysics Data System (ADS)
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.
Quantum Phase Transition in Josephson Junction Arrays
NASA Astrophysics Data System (ADS)
Moon, K.; Girvin, S. M.
1997-03-01
One-dimensional Josephson junction arrays of SQUIDS exhibit a novel superconductor-insulator phase transition. The critical regime can be accessed by tuning the effective Josephson coupling energy using a weak magnetic field applied to the SQUIDS. The role of instantons induced by quantum fluctuations will be discussed. One novel feature of these systems which can be explained in terms of quantum phase slips is that in some regimes, the array resistance decreases with increasing length of the array. We calculate the finite temperature crossover function for the array resistance and compare our theoretical results with the recent experiments by D. Haviland and P. Delsing at Chalmers. This work is supported by DOE grant #DE-FG02-90ER45427 and by NSF DMR-9502555.
Josephson effect in a Weyl SNS junction
NASA Astrophysics Data System (ADS)
Madsen, Kevin A.; Bergholtz, Emil J.; Brouwer, Piet W.
2017-02-01
We calculate the Josephson current density j (ϕ ) for a Weyl superconductor-normal-metal-superconductor junction for which the outer terminals are superconducting Weyl metals and the normal layer is a Weyl (semi)metal. We describe the Weyl (semi)metal using a simple model with two Weyl points. The model has broken time-reversal symmetry, but inversion symmetry is present. We calculate the Josephson current for both zero and finite temperature for the two pairing mechanisms inside the superconductors that have been proposed in the literature, zero-momentum BCS-like pairing and finite-momentum FFLO-like pairing, and assuming the short-junction limit. For both pairing types we find that the current is proportional to the normal-state junction conductivity, with a proportionality coefficient that shows quantitative differences between the two pairing mechanisms. The current for the BCS-like pairing is found to be independent of the chemical potential, whereas the current for the FFLO-like pairing is not.
NASA Astrophysics Data System (ADS)
Kato, Takahiro; Ishida, Hiroki; Suematsu, Hisayuki; Yasui, Kanji; Hamasaki, Katsuyoshi
2012-07-01
We have developed a new double-sided patterning (DSP) process that employs dilute acid (pH = 1.65) to fabricate Bi2Sr2CaCu2O8+x (Bi-2212) stacks of intrinsic Josephson junctions. These stacks, which were fabricated from a single crystal of Bi-2212, were surrounded by an acid-treated product. The critical aspect of this process is that the Bi-2212 surrounding the photoresist pattern was converted into a transparent material, BiOCl, which was connected with the Bi-2212 crystal. Consequently, this process provides a simple way to achieve DSP of the surfaces of Bi-2212 crystals. This new DSP process realizes a remarkably improved reproducibility in fabricating Bi-2212 stacks that exhibit good current-voltage characteristics with a large hysteresis and multiple branches at T = 77 K.
NASA Astrophysics Data System (ADS)
Konschelle, François; Tokatly, Ilya V.; Bergeret, F. Sebastián
2015-09-01
Due to the spin-orbit coupling (SOC) an electric current flowing in a normal metal or semiconductor can induce a bulk magnetic moment. This effect is known as the Edelstein (EE) or magnetoelectric effect. Similarly, in a bulk superconductor a phase gradient may create a finite spin density. The inverse effect, also known as the spin-galvanic effect, corresponds to the creation of a supercurrent by an equilibrium spin polarization. Here, by exploiting the analogy between a linear-in-momentum SOC and a background SU(2) gauge field, we develop a quasiclassical transport theory to deal with magnetoelectric effects in superconducting structures. For bulk superconductors this approach allows us to easily reproduce and generalize a number of previously known results. For Josephson junctions we establish a direct connection between the inverse EE and the appearance of an anomalous phase shift φ0 in the current-phase relation. In particular we show that φ0 is proportional to the equilibrium spin current in the weak link. We also argue that our results are valid generically, beyond the particular case of linear-in-momentum SOC. The magnetoelectric effects discussed in this study may find applications in the emerging field of coherent spintronics with superconductors.
NASA Astrophysics Data System (ADS)
Motzkau, H.; Katterwe, S. O.; Rydh, A.; Krasnov, V. M.
2013-08-01
Bi2Sr2CaCu2O8+x single crystals represent natural stacks of atomic scale intrinsic Josephson junctions, formed between metallic CuO2-Ca-CuO2 and ionic insulating SrO-2BiO-SrO layers. Electrostriction effect in the insulating layers leads to excitation of c-axis phonons by the ac-Josephson effect. Here we study experimentally the interplay between and velocity matching (Eck) electromagnetic resonances in the flux-flow state of small mesa structures with c-axis optical phonons. A very strong interaction is reported, which leads to formation of phonon-polaritons with infrared and Raman-active transverse optical phonons. A special focus in this work is made on analysis of the angular dependence of the resonances. We describe an accurate sample alignment procedure that prevents intrusion of Abrikosov vortices in fields up to 17 T, which is essential for achieving high-quality resonances at record high frequencies up to 13 THz.
Coherent diffraction of thermal currents in long Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Guarcello, Claudio; Giazotto, Francesco; Solinas, Paolo
2016-08-01
We discuss heat transport in thermally-biased long Josephson tunnel junctions in the presence of an in-plane magnetic field. In full analogy with the Josephson critical current, the phase-dependent component of the heat current through the junction displays coherent diffraction. Thermal transport is analyzed as a function of both the length and the damping of the junction, highlighting deviations from the standard "Fraunhofer" pattern characteristic of short junctions. The heat current diffraction patterns show features strongly related to the formation and penetration of Josephson vortices, i.e., solitons. We show that a dynamical treatment of the system is crucial for the realistic description of the Josephson junction, and it leads to peculiar results. In fact, hysteretic behaviors in the diffraction patterns when the field is swept up and down are observed, corresponding to the trapping of vortices in the junction.
Quantum computing with Josephson junction circuits
NASA Astrophysics Data System (ADS)
Xu, Huizhong
This work concerns the study of Josephson junction circuits in the context of their usability for quantum computing. The zero-voltage state of a current-biased Josephson junction has a set of metastable quantum energy levels. If a junction is well isolated from its environment, it will be possible to use the two lowest states as a qubit in a quantum computer. I first examine the meaning of isolation theoretically. Using a master equation, I analyzed the effect of dissipation on escape rates and suggested a simple method, population depletion technique, to measure the relaxation time (T1). Using a stochastic Bloch equation to analyze the dependence of microwave resonance peak width on current noise, I found decoherence due to current noise depends on the noise spectrum. For high frequency noise with a cutoff frequency fc much larger than 1/T1, I found decoherence due to noise can be described by a dephasing rate that is proportional to the noise spectral density. However, for low frequency noise such that its cutoff frequency fc is much smaller than 1/T 1, decoherence due to noise depends on the total rms current noise. I then analyze and test a few qubit isolation schemes, including resistive isolation, inductor-capacitor (LC) isolation, half-wavelength resonant isolation and inductor-junction (LJ) isolation. I found the resistive isolation scheme has a severe heating problem. Macroscopic quantum tunneling and energy level quantization were observed in the LC isolated Nb/AlOx/Nb and AL/ALOx/Al junction qubits at 25 mK. Relaxation times of 4--12 ns and spectroscopic coherence times of 1--3 ns were obtained for these LC isolated qubits. I found the half-wavelength isolated junction qubit has a relaxation time of about 20 ns measured by the population-depletion techniques, but no energy levels were observed in this qubit. Experimental results suggest the LJ isolated qubit has a longer relaxation and coherence times than all my previously examined samples. Using a
MAR current of Josephson junctions with topological superconducting nanowires
NASA Astrophysics Data System (ADS)
Aguado, Ramon; San-Jose, Pablo; Prada, Elsa; Cayao, Jorge Luis
2013-03-01
We study Josephson junctions made with topological superconducting nanowires hosting Majorana bound states (MBS). We show that, despite the absence of a fractional Josephson effect in the steady state limit [1], the dissipative multiple Andreev reflection (MAR) current contains nontrivial features owing to the presence of MBS. In particular, the MAR steps appear at voltages eVP = Δ / q
Target attractor tracking of relative phase in Bosonic Josephson junction
NASA Astrophysics Data System (ADS)
Borisenok, Sergey
2016-06-01
The relative phase of Bosonic Josephson junction in the Josephson regime of Bose-Hubbard model is tracked via the target attractor (`synergetic') feedback algorithm with the inter-well coupling parameter presented as a control function. The efficiency of our approach is demonstrated numerically for Gaussian and harmonic types of target phases.
Josephson junctions with tunable weak links.
Schön, J H; Kloc, C; Hwang, H Y; Batlogg, B
2001-04-13
The electrical properties of organic molecular crystals, such as polyacenes or C60, can be tuned from insulating to superconducting by application of an electric field. By structuring the gate electrode of such a field-effect switch, the charge carrier density, and therefore also the superfluid density, can be modulated. Hence, weak links that behave like Josephson junctions can be fabricated between two superconducting regions. The coupling between the superconducting regions can be tuned and controlled over a wide range by the applied gate bias. Such devices might be used in superconducting circuits, and they are a useful scientific tool to study superconducting material parameters, such as the superconducting gap, as a function of carrier concentration or transition temperature.
Flux Cloning Anomalities in Josephson Nano-Junctions
NASA Astrophysics Data System (ADS)
Hassan, Hanaa Farhan; Kusmartsev, Feo V.
2010-12-01
The propagation of single flux quanta in T-shaped Josephson junctions gives rise to the flux cloning phenomenon. We have studied numerically the dynamics of flux cloning in cases of extended Josephson junctions. The changing thicknesses of T-junctions lead to new and interesting effects in terms of their dynamics. We have found out that when an additional Josephson transmission line is larger than the main Josephson transmission line, numerical simulations do not show the cloning phenomenon and soliton is reflected when it approaches the T junction. This strange result may be happened because the soliton losses more energy in the sharp edge. Although the vortex is moving very highly and it has huge energy but it still does not give birth to a new vortex. We have investigated conditions at which flux cloning occurs when both widths, W and W0, are changing.
Flux Cloning Anomalities in Josephson Nano-Junctions
NASA Astrophysics Data System (ADS)
Hassan, Hanaa Farhan; Kusmartsev, Feo V.
The propagation of single flux quanta in T-shaped Josephson junctions gives rise to the flux cloning phenomenon. We have studied numerically the dynamics of flux cloning in cases of extended Josephson junctions. The changing thicknesses of T-junctions lead to new and interesting effects in terms of their dynamics. We have found out that when an additional Josephson transmission line is larger than the main Josephson transmission line, numerical simulations do not show the cloning phenomenon and soliton is reflected when it approaches the T junction. This strange result may be happened because the soliton losses more energy in the sharp edge. Although the vortex is moving very highly and it has huge energy but it still does not give birth to a new vortex. We have investigated conditions at which flux cloning occurs when both widths, W and W0, are changing.
High-performance DC SQUIDs with submicrometer niobium Josephson junctions
de Waal, V.J.; Klapwijk, T.M.; van den Hamer, P.
1983-11-01
We report on the fabrication and performance of low-noise, all-niobium, thin-film planar dc SQUIDs with submicrometer Josephson junctions. The junctions are evaporated obliquely through a metal shadow evaporation mask, which is made using optical lithography with 0.5 ..mu..m tolerance. The Josephson junction barrier is formed by evaporating a thin silicon film and with a subsequent oxidation in a glow discharge. The junction parameters can be reproduced within a factor of two. Typical critical currents of the SQUIDs are about 3 ..mu..A and the resistances are about 100 ..cap omega... With SQUIDs having an inductance of 1 nH the voltage modulation is a least 60 ..mu..V. An intrinsic energy resolution of 4 x 10/sup -32/ J/Hz has been reached. The SQUIDs are coupled to wire-wound input coils or with thin-film input coils. The thin-film input coil consists of a niobium spiral of 20 turns on a separate substrate. In both cases the coil is glued onto a 2-nH SQUID with a coupling efficiency of at least 0.5. Referred to the thin-film input coil, the best coupled energy resolution achieved is 1.2 x 10/sup -30/ J/Hz measured in a flux-locked loop at frequencies above 10 Hz. As far as we know, this is the best figure achieved with an all-refractory-metal thin-film SQUID. The fabrication technique used is suited for making circuits with SQUID and pickup coil on the same substrate. We describe a compact, planar, first-order gradiometer integrated with a SQUID on a single substrate. The gradient noise of this device is 3 x 10/sup -12/ Tm/sup -1/. The gradiometer has a size of 12 mm x 17 mm, is simple to fabricate, an is suitable for biomedical applications.
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 I; Girvin, S M; Devoret, M H; Schoelkopf, R J
2011-12-09
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 coupling to the control signal. With the new architecture, we demonstrate that Josephson junction qubits are highly coherent, with T2 ∼ 10 to 20 μs without the use of spin echo, and highly stable, showing no evidence for 1/f critical current noise. These results suggest that the overall quality of Josephson junctions in these qubits will allow error rates of a few 10(-4), approaching the error correction threshold.
Effect of current injection into thin-film Josephson junctions
Kogan, V. G.; Mints, R. G.
2014-11-11
New thin-film Josephson junctions have recently been tested in which the current injected into one of the junction banks governs Josephson phenomena. One thus can continuously manage the phase distribution at the junction by changing the injected current. Our method of calculating the distribution of injected currents is also proposed for a half-infinite thin-film strip with source-sink points at arbitrary positions at the film edges. The strip width W is assumed small relative to Λ=2λ2/d;λ is the bulk London penetration depth of the film material and d is the film thickness.
Effect of current injection into thin-film Josephson junctions
Kogan, V. G.; Mints, R. G.
2014-11-11
New thin-film Josephson junctions have recently been tested in which the current injected into one of the junction banks governs Josephson phenomena. One thus can continuously manage the phase distribution at the junction by changing the injected current. Our method of calculating the distribution of injected currents is also proposed for a half-infinite thin-film strip with source-sink points at arbitrary positions at the film edges. The strip width W is assumed small relative to Λ=2λ^{2}/d;λ is the bulk London penetration depth of the film material and d is the film thickness.
Quantum interference in topological insulator Josephson junctions
NASA Astrophysics Data System (ADS)
Song, Juntao; Liu, Haiwen; Liu, Jie; Li, Yu-Xian; Joynt, Robert; Sun, Qing-feng; Xie, X. C.
2016-05-01
Using nonequilibrium Green's functions, we studied numerically the transport properties of a Josephson junction, superconductor-topological insulator-superconductor hybrid system. Our numerical calculation shows first that proximity-induced superconductivity is indeed observed in the edge states of a topological insulator adjoining two superconducting leads and second that the special characteristics of topological insulators endow the edge states with an enhanced proximity effect with a superconductor but do not forbid the bulk states to do the same. In a size-dependent analysis of the local current, it was found that a few residual bulk states can lead to measurable resistance, whereas because these bulk states spread over the whole sample, their contribution to the interference pattern is insignificant when the sample size is in the micrometer range. Based on these numerical results, it is concluded that the apparent disappearance of residual bulk states in the superconducting interference process as described by Hart et al. [Nat. Phys. 10, 638 (2014), 10.1038/nphys3036] is just due to the effects of size: the contribution of the topological edge states outweighs that of the residual bulk states.
Superconducting qubits with semiconductor nanowire Josephson junctions
NASA Astrophysics Data System (ADS)
Petersson, K. D.; Larsen, T. W.; Kuemmeth, F.; Jespersen, T. S.; Krogstrup, P.; Nygård, J.; Marcus, C. M.
2015-03-01
Superconducting transmon qubits are a promising basis for a scalable quantum information processor. The recent development of semiconducting InAs nanowires with in situ molecular beam epitaxy-grown Al contacts presents new possibilities for building hybrid superconductor/semiconductor devices using precise bottom up fabrication techniques. Here, we take advantage of these high quality materials to develop superconducting qubits with superconductor-normal-superconductor Josephson junctions (JJs) where the normal element is an InAs semiconductor nanowire. We have fabricated transmon qubits in which the conventional Al-Al2O3-Al JJs are replaced by a single gate-tunable nanowire JJ. Using spectroscopy to probe the qubit we observe fluctuations in its level splitting with gate voltage that are consistent with universal conductance fluctuations in the nanowire's normal state conductance. Our gate-tunable nanowire transmons may enable new means of control for large scale qubit architectures and hybrid topological quantum computing schemes. Research supported by Microsoft Station Q, Danish National Research Foundation, Villum Foundation, Lundbeck Foundation and the European Commission.
Macroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions.
Massarotti, D; Pal, A; Rotoli, G; Longobardi, L; Blamire, M G; Tafuri, F
2015-06-09
The interfacial coupling of two materials with different ordered phases, such as a superconductor (S) and a ferromagnet (F), is driving new fundamental physics and innovative applications. For example, the creation of spin-filter Josephson junctions and the demonstration of triplet supercurrents have suggested the potential of a dissipationless version of spintronics based on unconventional superconductivity. Here we demonstrate evidence for active quantum applications of S-F-S junctions, through the observation of macroscopic quantum tunnelling in Josephson junctions with GdN ferromagnetic insulator barriers. We show a clear transition from thermal to quantum regime at a crossover temperature of about 100 mK at zero magnetic field in junctions, which present clear signatures of unconventional superconductivity. Following previous demonstration of passive S-F-S phase shifters in a phase qubit, our result paves the way to the active use of spin filter Josephson systems in quantum hybrid circuits.
Macroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions
Massarotti, D.; Pal, A.; Rotoli, G.; Longobardi, L.; Blamire, M. G.; Tafuri, F.
2015-01-01
The interfacial coupling of two materials with different ordered phases, such as a superconductor (S) and a ferromagnet (F), is driving new fundamental physics and innovative applications. For example, the creation of spin-filter Josephson junctions and the demonstration of triplet supercurrents have suggested the potential of a dissipationless version of spintronics based on unconventional superconductivity. Here we demonstrate evidence for active quantum applications of S-F-S junctions, through the observation of macroscopic quantum tunnelling in Josephson junctions with GdN ferromagnetic insulator barriers. We show a clear transition from thermal to quantum regime at a crossover temperature of about 100 mK at zero magnetic field in junctions, which present clear signatures of unconventional superconductivity. Following previous demonstration of passive S-F-S phase shifters in a phase qubit, our result paves the way to the active use of spin filter Josephson systems in quantum hybrid circuits. PMID:26054495
Memory cell operation based on small Josephson junctions arrays
NASA Astrophysics Data System (ADS)
Braiman, Y.; Nair, N.; Rezac, J.; Imam, N.
2016-12-01
In this paper we analyze a cryogenic memory cell circuit based on a small coupled array of Josephson junctions. All the basic memory operations (e.g., write, read, and reset) are implemented on the same circuit and different junctions in the array can in principle be utilized for these operations. The presented memory operation paradigm is fundamentally different from conventional single quantum flux operation logics (SFQ). As an example, we demonstrate memory operation driven by a SFQ pulse employing an inductively coupled array of three Josephson junctions. We have chosen realistic Josephson junction parameters based on state-of-the-art fabrication capabilities and have calculated access times and access energies for basic memory cell operations. We also implemented an optimization procedure based on the simulated annealing algorithm to calculate the optimized and typical values of access times and access energies.
Conditions for synchronization in Josephson-junction arrays
Chernikov, A.A.; Schmidt, G.
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.
Processing of Superconductor-Normal-Superconductor Josephson Edge Junctions
NASA Technical Reports Server (NTRS)
Kleinsasser, A. W.; Barner, J. B.
1997-01-01
The electrical behavior of epitaxial superconductor-normal-superconductor (SNS) Josephson edge junctions is strongly affected by processing conditions. Ex-situ processes, utilizing photoresist and polyimide/photoresist mask layers, are employed for ion milling edges for junctions with Yttrium-Barium-Copper-Oxide (YBCO) electrodes and primarily Co-doped YBCO interlayers.
Josephson junctions in high-T/sub c/ superconductors
Falco, C.M.; Lee, T.W.
1981-01-14
The invention includes a high T/sub c/ Josephson sperconducting junction as well as the method and apparatus which provides the junction by application of a closely controlled and monitored electrical discharge to a microbridge region connecting two portions of a superconducting film.
Revealing topological superconductivity in extended quantum spin Hall Josephson junctions.
Lee, Shu-Ping; Michaeli, Karen; Alicea, Jason; Yacoby, Amir
2014-11-07
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 fingerprints of topological superconductivity-even when noise spoils parity conservation.
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.
Novel all-high Tc epitaxial Josephson junction
NASA Astrophysics Data System (ADS)
Chin, D. K.; van Duzer, T.
1991-02-01
Josephson junctions are essential components in high-temperature superconductive integrated circuits. YBaCuO/Nb-doped SrTiO3/YBaCuO epitaxial Josephson junctions have been designed, fabricated, and tested. The YBaCuO and Nb-doped SrTiO3 films were deposited by off-axis sputtering. Both dc and ac Josephson effects have been observed and the supercurrent persists up to 80 K. The critical current density is an exponential function of the barrier layer thickness. The product of critical current and normal resistance is between one and three millivolts. A superconducting quantum interference device made of the junctions displays magnetic field modulation of critical current.
HTS step-edge Josephson junction terahertz harmonic mixer
NASA Astrophysics Data System (ADS)
Du, Jia; Weily, Andrew R.; Gao, Xiang; Zhang, Ting; Foley, Cathy P.; Guo, Yingjie Jay
2017-02-01
A high-temperature superconducting (HTS) terahertz (THz) frequency down-converter or mixer based on a thin-film ring-slot antenna coupled YBa2Cu3O7-x (YBCO)/MgO step-edge Josephson junction is reported. The frequency down-conversion was achieved using higher order harmonics of an applied lower frequency (19-40 GHz) local oscillator signal in the Josephson junction mixing with a THz signal of over 600 GHz, producing a 1-3 GHz intermediate frequency signal. Up to 31st order of harmonic mixing was obtained and the mixer operated stably at temperatures up to 77 K. The design details of the antenna, HTS Josephson junction mixer, the matching and isolation circuits, and the DC and RF performance evaluation are described in this paper.
Micromagnetic modeling of critical current oscillations in magnetic Josephson junctions
NASA Astrophysics Data System (ADS)
Golovchanskiy, I. A.; Bol'ginov, V. V.; Stolyarov, V. S.; Abramov, N. N.; Ben Hamida, A.; Emelyanova, O. V.; Stolyarov, B. S.; Kupriyanov, M. Yu.; Golubov, A. A.; Ryazanov, V. V.
2016-12-01
In this work we propose and explore an effective numerical approach for investigation of critical current dependence on applied magnetic field for magnetic Josephson junctions with in-plane magnetization orientation. This approach is based on micromagnetic simulation of the magnetization reversal process in the ferromagnetic layer with introduced internal magnetic stiffness and subsequent reconstruction of the critical current value using total flux or reconstructed actual phase difference distribution. The approach is flexible and shows good agreement with experimental data obtained on Josephson junctions with ferromagnetic barriers. Based on this approach we have obtained a critical current dependence on applied magnetic field for rectangular magnetic Josephson junctions with high size aspect ratio. We have shown that the rectangular magnetic Josephson junctions can be considered for application as an effective Josephson magnetic memory element with the value of critical current defined by the orientation of magnetic moment at zero magnetic field. An impact of shape magnetic anisotropy on critical current is revealed and discussed. Finally, we have considered a curling magnetic state in the ferromagnetic layer and demonstrated its impact on critical current.
Vortex States in Intrinsic Josephson Junctions of B2Sr2CaCu2O8+δ in High Parallel Magnetic Fields
NASA Astrophysics Data System (ADS)
Mirkovic, Jovan; Takashi, Saito; Kubo, Yuimaru; Kakeya, Itsuhiro; Oral, Ahmed; Yamamoto, Takashi; Kadowaki, Kazuo
2009-03-01
The Ic-axis resistivity measurements were performed in the vicinity of the ab-plane in order to investigate the interaction between Josephson vortices (JVs) and pancake vortices (PVs) in B2Sr2CaCu2O8+δ mesoscopic single crystals. It was found that the vortex lock-in transition becomes considerably broad in high magnetic fields, while the angular dependence of resistance exhibits the sharp lock-in features in low magnetic field region. The magnetic field dependence of the resistance exhibits the non-monotonic behavior probing the different vortex phases in tilted magnetic fields. Sharp dips and steps in the c-axis resistance were observed accompanied by penetration of quantized pancake vortices by tilting external fields from the ab-plane.
Resonant Phase Matching of Josephson Junction Traveling Wave Parametric Amplifiers
2014-10-06
Resonant Phase Matching of Josephson Junction Traveling Wave Parametric Amplifiers Kevin O’Brien,1 Chris Macklin,2 Irfan Siddiqi,2 and Xiang Zhang1,3...overcome phase mismatch in Josephson-junction traveling wave parametric amplifiers in order to achieve high gain over a broad bandwidth. Using “resonant...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
Field theoretical model of multilayered Josephson junction and dynamics of Josephson vortices
NASA Astrophysics Data System (ADS)
Fujimori, Toshiaki; Iida, Hideaki; Nitta, Muneto
2016-09-01
Multilayered 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, where one of the complex scalar fields has a gap. 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 an effective theory in which 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 (the width of superconductors). On the other hand, when two neighboring superconductors tend to have π -phase differences, the ground state has a phase transition depending on the positions of domain walls; when the two walls are close to each other (one superconductor is thin), frustration occurs because of the coupling between the two superconductors besides the thin superconductor. Focusing on the case of three superconductors separated by two insulators, we find for the former case that the interaction between two Josephson vortices on different insulators changes its nature, i.e., attractive or repulsive, depending on the positions of the domain walls. In the latter case, there emerges fractional Josephson vortices when two degenerate ground states appear due to spontaneous charge-symmetry breaking, and the number of the Josephson vortices varies with the position of the domain walls. Our predictions should be verified in multilayered Josephson junctions.
Thin-film Josephson junctions with alternating critical current density
NASA Astrophysics Data System (ADS)
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.
Josephson radiation from InSb-nanowire junction
NASA Astrophysics Data System (ADS)
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.
Evidence for nonlocal electrodynamics in planar Josephson junctions.
Boris, A A; Rydh, A; Golod, T; Motzkau, H; Klushin, A M; Krasnov, V M
2013-09-13
We study the temperature dependence of the critical current modulation I(c)(H) for two types of planar Josephson junctions: a low-Tc Nb/CuNi/Nb and a high-Tc YBa2Cu3O(7-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 I(c)(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.
Dayem bridge Josephson junctions. [for millimeter wave mixer
NASA Technical Reports Server (NTRS)
Barr, D. W.; Mattauch, R. J.
1977-01-01
The Josephson junction shows great promise as a millimeter wave mixer element. This paper discusses the physical mixing process from a first-order mathematical approach. Design and fabrication of such structures tailored for use in a 80-120 GHz mixer application is presented. Testing of the structures and a discussion of their interpretation is presented.
Josephson Junction Arrays with Positional Disorder: Experiments and Simulations
1988-02-01
Caislinuo an loe*@*. old* it no.ee.q Aid taoncitI y IOcA flMwb~wJ Josephson junctions Positional disorder Monta Carlo simulations 20. AUSTRACT (Conoidiie an...both experiments and Monte Carlo siimulations. We have fabricated 50 x 50 arrays of Pb/Cu proximity-effect junctions, with controlled positional...However, our experiments show no evidence for the predicted reentrant phase transition. Our Monte Carlo simulations of XY spin systems with positional
Evidence for a minigap in YBCO grain boundary Josephson junctions.
Lucignano, P; Stornaiuolo, D; Tafuri, F; Altshuler, B L; Tagliacozzo, A
2010-10-01
Self-assembled YBaCuO diffusive grain boundary submicron Josephson junctions offer a realization of 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. Their persistence at large voltages is evidence of the long lifetime of the antinodal (high energy) quasiparticles.
Mesoscopic Josephson junctions with switchable current-phase relation
NASA Astrophysics Data System (ADS)
Strambini, E.; Bergeret, F. S.; Giazotto, F.
2015-10-01
We propose and analyze a mesoscopic Josephson junction consisting of two ferromagnetic insulator-superconductors (FI-Ss) coupled through a normal metal (N) layer. The Josephson current of the junction is non-trivially affected by the spin-splitting field induced by the FIs in the two superconductors. In particular, it shows sizeable enhancement by increasing the amplitude of the exchange field (hex) and displays a switchable current-phase relation which depends on the relative orientation of h ex in the FIs. In a realistic EuS/Al-based setup this junction can be exploited as a high-resolution threshold sensor for the magnetic field as well as an on-demand tunable kinetic inductor.
Quantum Phase Slips in Topological Josephson Junction Rings
NASA Astrophysics Data System (ADS)
Rodriguez Mota, Rosa; Vishveshwara, Smitha; Pereg-Barnea, Tami
We study quantum phase slip processes (QPS) in a ring of N topological superconducting islands joined by Josephson junctions and threaded by magnetic flux. In this array, neighboring islands interact through the usual charge 2e Josephson tunneling and the Majorana assisted charge e tunneling. When the charging energy associated with the island's capacitance is zero, the energy vs. flux relation of the system is characterized by parabolas centered around even or odd multiples of the superconducting flux quantum, depending on the parity of the system. For small but non-zero charging energy, quantum fluctuations can lead to tunneling between these classical states. In this work, we calculate the amplitude of these tunneling processes, commonly known as quantum phase slips. We also add gate voltages to our system and study how the amplitude of QPS in these topological Josephson array is modified by Aharanov-Casher interference effects.
Cooper pair splitting in parallel quantum dot Josephson junctions
Deacon, R. S.; Oiwa, A.; Sailer, J.; Baba, S.; Kanai, Y.; Shibata, K.; Hirakawa, K.; Tarucha, S.
2015-01-01
Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair. PMID:26130172
Josephson Coupling in Nb/SmB6/Nb Junctions
NASA Astrophysics Data System (ADS)
Zhang, Xiaohang; Lee, Seunghun; Drisko, Jasper; Cumings, John; Greene, Richard; Takeuchi, Ichiro
Josephson coupling of superconductors through a topological surface has attracted considerable attention because it may provide device applications of topological insulators with implications for Majorana fermions. However, the results of previous Josephson junction studies on topological insulators have not been fully understood due to complications arising from the conducting bulk and the non-pristine nature of the surfaces/interfaces of the topological insulator materials used. In this work, SmB6 thin films with a highly insulating bulk were adopted to minimize the influence of the bulk carriers while in-situ deposition of Nb film on SmB6 surface was used to ensure the interface quality. The bilayer structure was then patterned into Nb/SmB6/Nb lateral junctions by e-beam lithography and ion milling. The Nb electrodes in our junctions had a typical width of ~1 μm and the gap between the two Nb electrodes was varied from 50 nm to 200 nm. A critical current up to 40 μA has been observed in junctions with a gap around 50 nm at 2.0 K. In this talk, I will discuss the implication of our results to the desired Josephson coupling through topological surface states. This work was supported by NSF under Grant No. DMR-1410665 and conducted at CNAM and at the Maryland NanoCenter.
Measurement of Quantum Phase-Slips in Josephson Junction Chains
NASA Astrophysics Data System (ADS)
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.
Quantum Dynamics of a d-wave Josephson Junction
NASA Astrophysics Data System (ADS)
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).
Cleland, A.N.
1991-04-01
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 {approx} 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.
Effects of the environment on the switching current in graphene-based Josephson Junctions
NASA Astrophysics Data System (ADS)
Borzenets, Ivan; Ke, Chung-Ting; Amet, Francois; Tso Wei, Ming; Yamamoto, Michihisa; Bomze, Yuriy; Tarucha, Seigo; Finkelstein, Gleb
The nature of the switching current and hysteresis (difference between switching and retrapping currents) in graphene-based Josephson junctions depends greatly on the interaction with the environment. Conventional devices result in underdamped Josephson junctions making the true critical current inaccessible. On the other hand, heavily isolating the Josephson junctions places them in the microscopic quantum tunneling regime even at high temperatures, also masking the critical current. We study the critical current, and the switching statistics in graphene Josephson junctions while varying the effects of the environment. Proper isolation of graphene Josephson junctions is necessary to measure the true critical current, especially so for the cases of small currents around the Dirac point. This is true for the case of conventional diffusive as well as the novel ballistic Josephson junctions.
Dissipation in a simple model of a topological Josephson junction.
Matthews, Paul; Ribeiro, Pedro; García-García, Antonio M
2014-06-20
The topological features of low-dimensional superconductors have created a lot of excitement recently because of their broad range of applications in quantum information and their potential to reveal novel phases of quantum matter. A potential problem for practical applications is the presence of phase slips that break phase coherence. Dissipation in nontopological superconductors suppresses phase slips and can restore long-range order. Here, we investigate the role of dissipation in a topological Josephson junction. We show that the combined effects of topology and dissipation keep phase and antiphase slips strongly correlated so that the device is superconducting even under conditions where a nontopological device would be resistive. The resistive transition occurs at a critical value of the dissipation that is 4 times smaller than that expected for a conventional Josephson junction. We propose that this difference could be employed as a robust experimental signature of topological superconductivity.
The current-phase relation in HTS Josephson junctions
NASA Astrophysics Data System (ADS)
Il'ichev, E.; Zakosarenko, V.; Ijsselsteijn, R. P. J.; Schultze, V.; Meyer, H.-G.; Hoenig, H. E.
The current-phase relation of YBa2Cu3O7-x step-edge as well as 24° and 45° grain boundary Josephson junctions has been investigated experimentally. The junctions were incorporated into a washer-shaped superconducting ring with inductance L≈80-300 pH. The ring was inductively coupled to a tank circuit with a resonance frequency 9…40 MHz. The current-phase relation was obtained from the measurement of the impedance of the phase-biased junction. It is shown, that experimentally observed deviations from harmonic behavior of the apparent current-phase relation for step-edge and 24° grain boundary junctions can be explained by the influence of thermal noise. The current-phase relation of 45° grain boundary junctions was found to be extremely non-harmonic. The reasons of this unusual behavior are discussed.
Quasi-optical Josephson-junction oscillator arrays
NASA Technical Reports Server (NTRS)
Stern, J. A.; Leduc, H. G.; Zmuidzinas, J.
1993-01-01
Josephson junctions are natural voltage-controlled oscillators capable of generating submillimeter-wavelength radiation, but a single junction usually can produce only 100 nW of power and often has a broad spectral linewidth. The authors are investigating 2D quasi-optical power combining arrays of 103 and 104 NbN/MgO/NbN and Nb/Al-AlO(x)/Nb junctions to overcome these limitations. The junctions are dc-biased in parallel and are distributed along interdigitated lines. The arrays couple to a resonant mode of a Fabry-Perot cavity to achieve mutual phase-locking. The array configuration has a relatively low impedance, which should allow the capacitance of the junctions to be tuned out at the oscillation frequency.
Identification of the periodic processes in Josephson junctions p
Zagrodzinski, J.
1984-02-01
It is shown that different forms of the same quasiperiodic solution of the sine-Gordon equation can be obtained by applying to the Riemann-theta function a transformation determined by a matrix belonging to a certain subgroup of the symplectic group Sp(g,Z). A few examples important for classification of the processes occurring in the Josephson junction illustrate the essential statement.
Engineering double-well potentials with variable-width annular Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Monaco, Roberto
2016-11-01
Long Josephson tunnel junctions are non-linear transmission lines that allow propagation of current vortices (fluxons) and electromagnetic waves and are used in various applications within superconductive electronics. Recently, the Josephson vortex has been proposed as a new superconducting qubit. We describe a simple method to create a double-well potential for an individual fluxon trapped in a long elliptic annular Josephson tunnel junction characterized by an intrinsic non-uniform width. The distance between the potential wells and the height of the inter-well potential barrier are controlled by the strength of an in-plane magnetic field. The manipulation of the vortex states can be achieved by applying a proper current ramp across the junction. The read-out of the state is accomplished by measuring the vortex depinning current in a small magnetic field. An accurate one-dimensional sine-Gordon model for this strongly non-linear system is presented, from which we calculate the position-dependent fluxon rest-mass, its Hamiltonian density and the corresponding trajectories in the phase space. We examine the dependence of the potential properties on the annulus eccentricity and its electrical parameters and address the requirements for observing quantum-mechanical effects, as discrete energy levels and tunneling, in this two-state system.
Engineering double-well potentials with variable-width annular Josephson tunnel junctions.
Monaco, Roberto
2016-11-09
Long Josephson tunnel junctions are non-linear transmission lines that allow propagation of current vortices (fluxons) and electromagnetic waves and are used in various applications within superconductive electronics. Recently, the Josephson vortex has been proposed as a new superconducting qubit. We describe a simple method to create a double-well potential for an individual fluxon trapped in a long elliptic annular Josephson tunnel junction characterized by an intrinsic non-uniform width. The distance between the potential wells and the height of the inter-well potential barrier are controlled by the strength of an in-plane magnetic field. The manipulation of the vortex states can be achieved by applying a proper current ramp across the junction. The read-out of the state is accomplished by measuring the vortex depinning current in a small magnetic field. An accurate one-dimensional sine-Gordon model for this strongly non-linear system is presented, from which we calculate the position-dependent fluxon rest-mass, its Hamiltonian density and the corresponding trajectories in the phase space. We examine the dependence of the potential properties on the annulus eccentricity and its electrical parameters and address the requirements for observing quantum-mechanical effects, as discrete energy levels and tunneling, in this two-state system.
Model for large arrays of Josephson junctions with unconventional superconductors
NASA Astrophysics Data System (ADS)
Khveshchenko, D. V.; Crooks, R.
2011-10-01
We study large arrays of mesoscopic junctions made out of gapless unconventional superconductors where the tunneling processes of both particle-hole and Cooper pairs give rise to a strongly retarded effective action which, contrary to the standard case, cannot be readily characterized in terms of a local Josephson energy. This action can be relevant, for example, to grain boundary and c-axis junctions in layered high-Tc superconductors. By using a particular functional representation, we describe emergent collective phenomena in this system, ascertain its phase diagram, and compute electrical conductivity.
Fabrication and measurement of multi-terminal mesoscopic Josephson junctions
NASA Astrophysics Data System (ADS)
Solovyeva, Natalya; Tetsuya, Mishima; Santos, Michael; Shabani, Javad; Manucharyan, Vladimir
We present fabrication and characterization of 3- and 4-terminal mesoscopic Josephson junctions involving InAs quantum well heterostructures and superconducting Al contacts. A cross-shaped nanowire junction region with dimensions of order a few 100 nm is dry-etched in the 2DEG, followed by deposition of superconducting contacts and gating electrodes. These novel 0D devices have been recently predicted to have topological features in their Andreev spectra and finite-bias transport; they may also be useful in efforts towards observation and braiding of Majorana fermions in the solid state. // This material is based upon work supported by the NSF under Grant No. DMR-1207537.
dc properties of series-parallel arrays of Josephson junctions in an external magnetic field
Lewandowski, S.J. )
1991-04-01
A detailed dc theory of superconducting multijunction interferometers has previously been developed by several authors for the case of parallel junction arrays. The theory is now extended to cover the case of a loop containing several junctions connected in series. The problem is closely associated with high-{ital T}{sub {ital c}} superconductors and their clusters of intrinsic Josephson junctions. These materials exhibit spontaneous interferometric effects, and there is no reason to assume that the intrinsic junctions form only parallel arrays. A simple formalism of phase states is developed in order to express the superconducting phase differences across the junctions forming a series array as functions of the phase difference across the weakest junction of the system, and to relate the differences in critical currents of the junctions to gaps in the allowed ranges of their phase functions. This formalism is used to investigate the energy states of the array, which in the case of different junctions are split and separated by energy barriers of height depending on the phase gaps. Modifications of the washboard model of a single junction are shown. Next a superconducting inductive loop containing a series array of two junctions is considered, and this model is used to demonstrate the transitions between phase states and the associated instabilities. Finally, the critical current of a parallel connection of two series arrays is analyzed and shown to be a multivalued function of the externally applied magnetic flux. The instabilities caused by the presence of intrinsic serial junctions in granular high-{ital T}{sub {ital c}} materials are pointed out as a potential source of additional noise.
Ballistic Graphene Josephson Junctions from the Short to the Long Junction Regimes
NASA Astrophysics Data System (ADS)
Borzenets, I. V.; Amet, F.; Ke, C. T.; Draelos, A. W.; Wei, M. T.; Seredinski, A.; Watanabe, K.; Taniguchi, T.; Bomze, Y.; Yamamoto, M.; Tarucha, S.; Finkelstein, G.
2016-12-01
We investigate the critical current IC of ballistic Josephson junctions made of encapsulated graphene-boron-nitride heterostructures. We observe a crossover from the short to the long junction regimes as the length of the device increases. In long ballistic junctions, IC is found to scale as ∝exp (-kBT /δ E ). The extracted energies δ E are independent of the carrier density and proportional to the level spacing of the ballistic cavity. As T →0 the critical current of a long (or short) junction saturates at a level determined by the product of δ E (or Δ ) and the number of the junction's transversal modes.
Manipulating Josephson junctions in thin-films by nearby vortices
Kogan, V G; Mints, R G
2014-07-01
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, I-c(H). When the vortex is placed at certain discrete positions in the strip middle, the pattern I-c(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 similar to W, the strip width, I-c(H) is no longer sensitive to the vortex presence. The same is true for any separation if the vortex approaches the strip edges. (C) 2014 Elsevier B.V. All rights reserved.
High-efficiency thermal switch based on topological Josephson junctions
NASA Astrophysics Data System (ADS)
Sothmann, Björn; Giazotto, Francesco; Hankiewicz, Ewelina M.
2017-02-01
We propose theoretically a thermal switch operating by the magnetic-flux controlled diffraction of phase-coherent heat currents in a thermally biased Josephson junction based on a two-dimensional topological insulator. For short junctions, the system shows a sharp switching behavior while for long junctions the switching is smooth. Physically, the switching arises from the Doppler shift of the superconducting condensate due to screening currents induced by a magnetic flux. We suggest a possible experimental realization that exhibits a relative temperature change of 40% between the on and off state for realistic parameters. This is a factor of two larger than in recently realized thermal modulators based on conventional superconducting tunnel junctions.
Lin, Shi-Zeng; Hu, Xiao
2011-04-01
The nano-scale intrinsic Josephson junctions in highly anisotropic cuprate superconductors have potential for generation of terahertz electromagnetic waves. When the thickness of a superconductor sample is much smaller than the wavelength of electromagnetic waves in vacuum, the superconductor renders itself as a cavity. Unlike conventional lasers, the presence of the cavity does not guarantee a coherent emission because of the internal degree of freedom of the superconductivity phase in long junctions. We study the excitation of terahertz wave by solitons in a stack of intrinsic Josephson junctions, especially for relatively short junctions. Coherent emission requires a rectangular configuration of solitons. However such a configuration is unstable against weak fluctuations, contrarily solitons favor a triangular lattice corresponding to an out-phase oscillation of electromagnetic waves. To utilize the cavity, we propose to use an array of stacks of short intrinsic Josephson junctions to generate powerful terahertz electromagnetic waves. The cavity synchronizes the plasma oscillation in different stacks and the emission intensity is predicted to be proportional to the number of stacks squared.
Fluctuation of heat current in Josephson junctions
Virtanen, P.; Giazotto, F.
2015-02-15
We discuss the statistics of heat current between two superconductors at different temperatures connected by a generic weak link. As the electronic heat in superconductors is carried by Bogoliubov quasiparticles, the heat transport fluctuations follow the Levitov–Lesovik relation. We identify the energy-dependent quasiparticle transmission probabilities and discuss the resulting probability density and fluctuation relations of the heat current. We consider multichannel junctions, and find that heat transport in diffusive junctions is unique in that its statistics is independent of the phase difference between the superconductors.
Coexistence of tunneling magnetoresistance and Josephson effects in SFIFS junctions
NASA Astrophysics Data System (ADS)
Vávra, O.; Soni, R.; Petraru, A.; Himmel, N.; Vávra, I.; Fabian, J.; Kohlstedt, H.; Strunk, Ch.
2017-02-01
We demonstrate an integration of tunneling magnetoresistance and the Josephson effects within one tunneling junction. Several sets of Nb-Fe-Al-Al2O3-Fe-Nb wafers with varying Al and Fe layers thickness were prepared to systematically explore the competition of TMR and Josephson effects. A coexistence of the critical current IC(dFe) and the tunneling magnetoresistance ratio T M R(dFe) is observed for iron layer dFe thickness range 1.9 and 2.9 nm. Further optimization such as thinner Al2O3 layer leads to an enhancement of the critical current and thus to an extension of the coexistence regime up to dFe≃3.9 nm Fe.
Noise performance of superconductive magnetometers based on long Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
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.
Characteristics of strong ferromagnetic Josephson junctions with epitaxial barriers
NASA Astrophysics Data System (ADS)
Bell, C.; Loloee, R.; Burnell, G.; Blamire, M. G.
2005-05-01
We present the measurement of superconductor/ferromagnetic Josephson junctions, based on an epitaxial Nb bottom electrode and epitaxial Fe20Ni80 barrier. Uniform junctions have been fabricated with a barrier thicknesses in the range 2-12nm . The maximum critical current density ˜2.4±0.2×109Am-2 was found for a device with a 3-nm -thick barrier at 4.2K , corresponding to an average characteristic voltage ICRN˜16μV . The ICRN showed a nonmonotonic behavior with Fe20Ni80 thickness. The variation of the resistance of a unit area ARN , of the junctions with barrier thickness gave a Nb/Py specific interface resistance of 6.0±0.5fΩm2 and Fe20Ni80 resistivity of 174±50nΩm , consistent with other studies in polycrystalline samples.
Controllable 0–π Josephson junctions containing a ferromagnetic spin valve
Gingrich, E. C.; Niedzielski, Bethany M.; Glick, Joseph A.; ...
2016-03-14
Superconductivity and ferromagnetism are antagonistic forms of order, and rarely coexist. Many interesting new phenomena occur, however, in hybrid superconducting/ferromagnetic systems. For example, a Josephson junction containing a ferromagnetic material can exhibit an intrinsic phase shift of π in its ground state for certain thicknesses of the material. Such ‘π-junctions’ were first realized experimentally in 2001, and have been proposed as circuit elements for both high-speed classical superconducting computing and for quantum computing. Here we demonstrate experimentally that the phase state of a Josephson junction containing two ferromagnetic layers can be toggled between 0 and pi by changing the relativemore » orientation of the two magnetizations. These controllable 0–π junctions have immediate applications in cryogenic memory, where they serve as a necessary component to an ultralow power superconducting computer. Such a fully superconducting computer is estimated to be orders of magnitude more energy-efficient than current semiconductor-based supercomputers. Here, phase-controllable junctions also open up new possibilities for superconducting circuit elements such as superconducting ‘programmable logic’, where they could function in superconducting analogues to field-programmable gate arrays.« less
Controllable 0–π Josephson junctions containing a ferromagnetic spin valve
Gingrich, E. C.; Niedzielski, Bethany M.; Glick, Joseph A.; Wang, Yixing; Miller, D. L.; Loloee, Reza; Pratt, Jr., W. P.; Birge, Norman O.
2016-03-14
Superconductivity and ferromagnetism are antagonistic forms of order, and rarely coexist. Many interesting new phenomena occur, however, in hybrid superconducting/ferromagnetic systems. For example, a Josephson junction containing a ferromagnetic material can exhibit an intrinsic phase shift of π in its ground state for certain thicknesses of the material. Such ‘π-junctions’ were first realized experimentally in 2001, and have been proposed as circuit elements for both high-speed classical superconducting computing and for quantum computing. Here we demonstrate experimentally that the phase state of a Josephson junction containing two ferromagnetic layers can be toggled between 0 and pi by changing the relative orientation of the two magnetizations. These controllable 0–π junctions have immediate applications in cryogenic memory, where they serve as a necessary component to an ultralow power superconducting computer. Such a fully superconducting computer is estimated to be orders of magnitude more energy-efficient than current semiconductor-based supercomputers. Here, phase-controllable junctions also open up new possibilities for superconducting circuit elements such as superconducting ‘programmable logic’, where they could function in superconducting analogues to field-programmable gate arrays.
Detection of Weak Microwave Fields with an Underdamped Josephson Junction
NASA Astrophysics Data System (ADS)
Oelsner, G.; Andersen, C. K.; Rehák, M.; Schmelz, M.; Anders, S.; Grajcar, M.; Hübner, U.; Mølmer, K.; Il'ichev, E.
2017-01-01
We construct a microwave detector based on the voltage switching of an underdamped Josephson junction that is positioned at a current antinode of a λ /4 coplanar waveguide resonator. By measuring the switching current and the transmission through a waveguide capacitively coupled to the resonator at different drive frequencies and temperatures, we are able to fully characterize the system and assess its detection efficiency and sensitivity. Testing the detector by applying a classical microwave field with the strength of a single photon yields a sensitivity parameter of 0.5, in qualitative agreement with theoretical calculations.
Precise Heater Controller with rf-Biased Josephson Junctions
NASA Technical Reports Server (NTRS)
Green, Colin J.; Sergatskov, Dmitri A.; Duncan, R. V.
2003-01-01
Paramagnetic susceptibility thermometers used in fundamental physics experiments are capable of measuring temperature changes with a precision of a part in 2 x 10(exp 10). However, heater controllers are only able to control open-loop power dissipation to about a part in 10(exp 5). We used an array of rf-biased Josephson junctions to precisely control the electrical power dissipation in a heater resistor mounted on a thermally isolated cryogenic platform. Theoretically, this method is capable of controlling the electrical power dissipation to better than a part in 10(exp 12). However, this level has not yet been demonstrated experimentally. The experiment consists of a liquid helium cell that also functions as a high-resolution PdMn thermometer, with a heater resistor mounted on it. The cell is thermally connected to a temperature-controlled cooling stage via a weak thermal link. The heater resistor is electrically connected to the array of Josephson junctions using superconducting wire. An rf-biased array of capacitively shunted Josephson junctions drives the voltage across the heater. The quantized voltage across the resistor is Vn = nf(h/2e), where h is Planck's constant, f is the array biasing frequency, e is the charge of an electron, and n is the integer quantum state of the Josephson array. This results in an electrical power dissipation on the cell of Pn = (Vn)(sup 2/R), where R is the heater resistance. The change of the quantum state of the array changes the power dissipated in the heater, which in turn, results in the change of the cell temperature. This temperature change is compared to the expected values based on the known thermal standoff resistance of the cell from the cooling stage. We will present our initial experimental results and discuss future improvements. This work has been funded by the Fundamental Physics Discipline of the Microgravity Science Office of NASA, and supported by a no-cost equipment loan from Sandia National Laboratories.
In-phase motion of Josephson vortices in stacked SNS Josephson junctions: effect of ordered pinning
NASA Astrophysics Data System (ADS)
Berdiyorov, G. R.; Savel'ev, S. E.; Kusmartsev, F. V.; Peeters, F. M.
2013-12-01
The dynamics of Josephson vortices (fluxons) in artificial stacks of superconducting-normal-superconducting Josephson junctions is investigated using the anisotropic time-dependent Ginzburg-Landau theory in the presence of a square/rectangular array of pinning centers (holes). For small values of the applied drive, fluxons in different junctions move out of phase, forming a periodic triangular lattice. A rectangular lattice of moving fluxons is observed at larger currents, which is in agreement with previous theoretical predictions (Koshelev and Aranson 2000 Phys. Rev. Lett. 85 3938). This ‘superradiant’ flux-flow state is found to be stable in a wide region of applied current. The stability range of this ordered state is considerably larger than the one obtained for the pinning-free sample. Clear commensurability features are observed in the current-voltage characteristics of the system with pronounced peaks in the critical current at (fractional) matching fields. The effect of density and strength of the pinning centers on the stability of the rectangular fluxon lattice is discussed. Predicted synchronized motion of fluxons in the presence of ordered pinning can be detected experimentally using the rf response of the system, where enhancement of the Shapiro-like steps is expected due to the synchronization.
4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions
Wiedenmann, J.; Bocquillon, E.; Deacon, R. S.; Hartinger, S.; Herrmann, O.; Klapwijk, T. M.; Maier, L.; 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 deeply influences the properties of the supercurrent. In recent years, considerable efforts have focused on the coupling of superconductors to the surface states of a three-dimensional topological insulator. In such a material, an unconventional induced p-wave superconductivity should occur, with a doublet of topologically protected gapless Andreev bound states, whose energies vary 4π-periodically with the superconducting phase difference across the junction. In this article, we report the observation of an anomalous response to rf irradiation in a Josephson junction made of a HgTe weak link. The response is understood as due to a 4π-periodic contribution to the supercurrent, and its amplitude is compatible with the expected contribution of a gapless Andreev doublet. Our work opens the way to more elaborate experiments to investigate the induced superconductivity in a three-dimensional insulator. PMID:26792013
Dispersive Thermometry with a Josephson Junction Coupled to a Resonator
NASA Astrophysics Data System (ADS)
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.
Multi-terminal Josephson junctions as topological matter
Riwar, Roman-Pascal; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
2016-01-01
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 ≤3 dimensions. Here we demonstrate that n-terminal Josephson junctions with conventional superconductors may provide novel realizations of topology in n−1 dimensions, which have similarities, but also marked differences with existing 2D or 3D topological materials. For n≥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. PMID:27040917
All-MgB2 Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Ueda, K.; Saito, S.; Semba, K.; Makimoto, T.; Naito, M.
2005-04-01
Sandwich-type all-MgB2 Josephson tunnel junctions (MgB2/AlOx/MgB2) have been fabricated with as-grown MgB2 films formed by molecular-beam epitaxy. The junctions exhibit substantial superconducting current (IcRN product ˜0.8mV at 4.2 K), a well-defined superconducting gap (Δ=2.2-2.3mV), and clear Fraunhofer patterns. The superconducting gap voltage of Δ agrees well with the smaller gap in the multigap scenario. The results demonstrate that MgB2 has great promise for superconducting electronics that can be operated at T ˜20K.
Observation of the Bloch oscillations in an ultrasmall Josephson junction
Kuzmin, L.S.; Haviland, D.B. Laboratory of Cryoelectronics, Physics Department, Moscow State University, Moscow 119 899 GSP )
1991-11-11
We have studied the low-temperature behavior of lead-alloy Josephson tunnel junctions with area {ital S}{approx}0.01 {mu}m{sup 2}, isolated from their electromagnetic environment by high-resistance metallic resistors inserted into the current and voltage leads. Under irradiation with microwaves frequencies, {ital f}=3.5--10 GHz, the dc differential resistance {ital dV}/{ital dI}, as a function of the dc current {ital I}, showed peaks at {ital I}={plus minus}2{ital ef}. This effect, and other observations, arises due to the periodic electrical recharging of the junction by discrete Cooper pairs, and can be explained by the orthodox'' theory of Bloch oscillations.
Multi-terminal Josephson junctions as topological matter
NASA Astrophysics Data System (ADS)
Riwar, Roman-Pascal; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
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 <= 3 dimensions. Here we demonstrate that n-terminal Josephson junctions with conventional superconductors may provide novel realizations of topology in n - 1 dimensions, which have similarities, but also marked differences with existing 2D or 3D topological materials. For n >= 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 .
Multi-terminal Josephson junctions as topological matter
NASA Astrophysics Data System (ADS)
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 <=3 dimensions. Here we demonstrate that n-terminal Josephson junctions with conventional superconductors may provide novel realizations of topology in n-1 dimensions, which have similarities, but also marked differences with existing 2D or 3D topological materials. For n>=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.
Parallel arrays of Josephson junctions for submillimeter local oscillators
NASA Technical Reports Server (NTRS)
Pance, Aleksandar; Wengler, Michael J.
1992-01-01
In this paper we discuss the influence of the DC biasing circuit on operation of parallel biased quasioptical Josephson junction oscillator arrays. Because of nonuniform distribution of the DC biasing current along the length of the bias lines, there is a nonuniform distribution of magnetic flux in superconducting loops connecting every two junctions of the array. These DC self-field effects determine the state of the array. We present analysis and time-domain numerical simulations of these states for four biasing configurations. We find conditions for the in-phase states with maximum power output. We compare arrays with small and large inductances and determine the low inductance limit for nearly-in-phase array operation. We show how arrays can be steered in H-plane using the externally applied DC magnetic field.
Josephson junction detectors for Majorana modes and Dirac fermions
NASA Astrophysics Data System (ADS)
Maiti, M.; Kulikov, K. M.; Sengupta, K.; Shukrinov, Yu. M.
2015-12-01
We demonstrate that the current-voltage (I -V ) characteristics of resistively and capacitively shunted Josephson junctions (RCSJs) hosting localized subgap Majorana states provide a phase-sensitive method for their detection. The I -V characteristics of such RCSJs, in contrast to their resistively shunted counterparts, exhibit subharmonic odd Shapiro steps. These steps, owing to their subharmonic nature, exhibit qualitatively different properties compared to harmonic odd steps of conventional junctions. In addition, the RCSJs hosting Majorana bound states also display an additional sequence of steps in the devil's staircase structure seen in their I -V characteristics; such a sequence of steps makes their I -V characteristics qualitatively distinct from that of their conventional counterparts. A similar study for RCSJs with graphene superconducting junctions hosting Dirac-like quasiparticles reveals that the Shapiro step width in their I -V curves bears a signature of the transmission resonance phenomenon of their underlying Dirac quasiparticles; consequently, these step widths exhibit a π periodic oscillatory behavior with variation of the junction barrier potential. We discuss experiments which can test our theory.
Chaos and related nonlinear noise phenomena in Josephson tunnel junctions
Miracky, R.F.
1984-07-01
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 10/sup 6/ 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 10/sup 3/ 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 ..omega../sub p/ and a mode at the half harmonic ..omega../sub p//2. The hopping is induced by thermal noise associated with the shunt resistance. 71 references.
Topological transconductance quantization in a four-terminal Josephson junction
NASA Astrophysics Data System (ADS)
Eriksson, Erik; Riwar, Roman-Pascal; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
2017-02-01
Recently we predicted that the Andreev bound-state spectrum of four-terminal Josephson junctions may possess topologically protected zero-energy Weyl singularities, which manifest themselves in a quantized transconductance in units of 4 e2/h when two of the terminals are voltage biased [R.-P. Riwar, M. Houzet, J. S. Meyer, and Y. V. Nazarov, Nature Commun. 7, 11167 (2016), 10.1038/ncomms11167]. Here, using the Landauer-Büttiker scattering theory, we compute numerically the currents flowing through such a structure in order to assess the conditions for observing this effect. We show that the voltage below which the transconductance becomes quantized is determined by the interplay of nonadiabatic transitions between Andreev bound states and inelastic relaxation processes. We demonstrate that the topological quantization of the transconductance can be observed at voltages of the order of 10-2Δ /e ,Δ being the the superconducting gap in the leads.
High-performance passive microwave survey on Josephson junctions
Denisov, A.G.; Radzikhovsky, V.N.; Kudeliya, A.M.
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.
High-performance passive microwave survey on Josephson Junctions
NASA Technical Reports Server (NTRS)
Denisov, A. G.; Radzikhovsky, V. N.; Kudeliya, A. M.
1995-01-01
The quasi-optical generations of images of objects with their internal structure in millimeter (MM) and submillimeter (SMM) bands is one of 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 (field effect transistors) or SQUIDS for signal amplifications after JJ is of particular interest in this case.
Optimal control of quantum superpositions in a bosonic Josephson junction
NASA Astrophysics Data System (ADS)
Lapert, M.; Ferrini, G.; Sugny, D.
2012-02-01
We show how to optimally control the creation of quantum superpositions in a bosonic Josephson junction within the two-site Bose-Hubbard-model framework. Both geometric and purely numerical optimal-control approaches are used, the former providing a generalization of the proposal of Micheli [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.67.013607 67, 013607 (2003)]. While this method is shown not to lead to significant improvements in terms of time of formation and fidelity of the superposition, a numerical optimal-control approach appears more promising, as it allows creation of an almost perfect superposition, within a time short compared to other existing protocols. We analyze the robustness of the optimal solution against atom-number variations. Finally, we discuss the extent to which these optimal solutions could be implemented with state-of-the-art technology.
Resonant tunneling in small current-biased Josephson Junctions
Schmidt, John Mark
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.
Controlled dynamics of sine-Gordon breather in long Josephson junctions
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Gaifullin, M. B.; Kusmartsev, F. V.
2012-01-01
We describe a method of controlled creation and detection of breathers in long Josephson Junctions. We show how a breather can be detected and investigated by measuring switching of the current biased Josephson junction to a resistive state. The complete theoretical description of the switching events associated with the decay of a breather into a fluxon-antifluxon pair is developed. Eventually, we propose several designs of the systems where breathers can be observed.
Octavio, M. ); Free, J.U. Physics Department, Harvard University, Cambridge, Massachusetts ); Benz, S.P. ); Newrock, R.S.; Mast, D.B. ); Lobb, C.J. )
1991-09-01
We present simulations of two-dimensional Josephson-junction arrays to study giant Shapiro steps in these arrays. The amplitude and frequency dependence of the step widths is found to be more complex than in single junctions. The fractional step widths are found to decrease more rapidly with increasing frequency or rf current than conventional steps in single junctions. The washboard model of single junctions is extended to arrays to explain these differences between arrays and single junctions.
Statistics of avalanches in the self-organized criticality state of a Josephson junction
Matizen, E. V.; Martynets, V. G. Bezverkhii, P. P.
2010-08-15
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 {lambda} 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.
Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio; Matsumoto, Hideki
2009-06-12
Using the functional integral method, we construct a theory of heterotic superconductor-insulator-superconductor Josephson junctions between one- and two-gap superconductors. The theory predicts the presence of in-phase and out-of-phase collective oscillation modes of superconducting phases. The former corresponds to the Josephson plasma mode whose frequency is drastically reduced for +/- s-wave symmetry, and the latter is a counterpart of Leggett's mode in Josephson junctions. We also reveal that the critical current and the Fraunhofer pattern strongly depend on the symmetry type of the two-gap superconductor.
Phase dynamics of low critical current density YBCO Josephson junctions
NASA Astrophysics Data System (ADS)
Massarotti, D.; Stornaiuolo, D.; Rotoli, G.; Carillo, F.; Galletti, L.; Longobardi, L.; Beltram, F.; Tafuri, F.
2014-08-01
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.
Diffusion current in a system of coupled Josephson junctions
Shukrinov, Yu. M. Rahmonov, I. R.
2012-08-15
The role of a diffusion current in the phase dynamics of a system of coupled Josephson junctions (JJs) has been analyzed. It is shown that, by studying the temporal dependences of the superconducting, quasi-particle, diffusion, and displacement currents and the dependences of average values of these currents on the total current, it is possible to explain the main features of the current-voltage characteristic (CVC) of the system. The effect of a diffusion current on the character of CVC branching in the vicinity of a critical current and in the region of hysteresis, as well as on the part of CVC branch corresponding to a parametric resonance in the system is demonstrated. A clear interpretation of the differences in the character of CVC branching in a model of capacitively coupled JJs (CCJJ model) and a model of capacitive coupling with diffusion current (CCJJ+DC model) is proposed. It is shown that a decrease in the diffusion current in a JJ leads to the switching of this junction to an oscillating state. The results of model calculations are qualitatively consistent with the experimental data.
Diffusion current in a system of coupled Josephson junctions
NASA Astrophysics Data System (ADS)
Shukrinov, Yu. M.; Rahmonov, I. R.
2012-08-01
The role of a diffusion current in the phase dynamics of a system of coupled Josephson junctions (JJs) has been analyzed. It is shown that, by studying the temporal dependences of the superconducting, quasi-particle, diffusion, and displacement currents and the dependences of average values of these currents on the total current, it is possible to explain the main features of the current-voltage characteristic (CVC) of the system. The effect of a diffusion current on the character of CVC branching in the vicinity of a critical current and in the region of hysteresis, as well as on the part of CVC branch corresponding to a parametric resonance in the system is demonstrated. A clear interpretation of the differences in the character of CVC branching in a model of capacitively coupled JJs (CCJJ model) and a model of capacitive coupling with diffusion current (CCJJ+DC model) is proposed. It is shown that a decrease in the diffusion current in a JJ leads to the switching of this junction to an oscillating state. The results of model calculations are qualitatively consistent with the experimental data.
Cedergren, K; Kirtley, J R; Bauch, T; Rotoli, G; Troeman, A; Hilgenkamp, H; Tafuri, F; Lombardi, F
2010-04-30
We have investigated the static and dynamic properties of long YBa2Cu3O(7-delta) 0-pi Josephson junctions and compared them with those of conventional 0 junctions. Scanning SQUID microscope imaging has revealed the presence of a semifluxon at the phase discontinuity point in 0-pi Josephson junctions. Zero field steps have been detected in the current-voltage characteristics of all junctions. Comparison with simulation allows us to attribute these steps to fluxons traveling in the junction for conventional 0 junctions and to fluxon-semifluxon interactions in the case of 0-pi Josephson junctions.
Simulation and measurement of a Ka-band HTS MMIC Josephson junction mixer
NASA Astrophysics Data System (ADS)
Zhang, Ting; Pegrum, Colin; Du, Jia; Guo, Yingjie Jay
2017-01-01
We report modeling and simulation results for a Ka band high-temperature superconducting (HTS) monolithic microwave integrated circuit (MMIC) Josephson junction mixer. A Verilog-A model of a Josephson junction is established and imported into the system simulator to realize a full HTS MMIC circuit simulation containing the HTS passive circuit models. Impedance matching optimization between the junction and passive devices is investigated. Junction DC I-V characteristics, current and local oscillator bias conditions and mixing performance are simulated and compared with the experimental results. Good agreement is obtained between the simulation and measurement results.
Microwave response and photon emission of a voltage baised Josephson junction
NASA Astrophysics Data System (ADS)
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.
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.
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.
Nonergodic metallic and insulating phases of Josephson junction chains
Pino, Manuel; Ioffe, Lev B.; Altshuler, Boris L.
2016-01-01
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
Magnetically-driven colossal supercurrent enhancement in InAs nanowire Josephson junctions.
Tiira, J; Strambini, E; Amado, M; Roddaro, S; San-Jose, P; Aguado, R; Bergeret, F S; Ercolani, D; Sorba, L; Giazotto, F
2017-04-12
The Josephson effect is a fundamental quantum phenomenon where a dissipationless supercurrent is introduced in a weak link between two superconducting electrodes by Andreev reflections. The physical details and topology of the junction drastically modify the properties of the supercurrent and a strong enhancement of the critical supercurrent is expected to occur when the topology of the junction allows an emergence of Majorana bound states. Here we report charge transport measurements in mesoscopic Josephson junctions formed by InAs nanowires and Ti/Al superconducting leads. Our main observation is a colossal enhancement of the critical supercurrent induced by an external magnetic field applied perpendicular to the substrate. This striking and anomalous supercurrent enhancement cannot be described by any known conventional phenomenon of Josephson junctions. We consider these results in the context of topological superconductivity, and show that the observed critical supercurrent enhancement is compatible with a magnetic field-induced topological transition.
Wendt, J.R.; Tigges, C.P.; Hietala, V.M.; Plut, T.A.; Martens, J.S.; Char, K.; Johansson, M.E.
1994-03-01
A well-controlled, high-yield Josephson junction process in high temperature superconductors (HTS) is necessary for the demonstration of ultra-high-speed devices and circuits which exceed the capabilities of conventional electronics. The authors developed nanobridge Josephson junctions in high quality thin-film YBaCuO with dimensions below 100 nm fabricated using electron-beam nanolithography. They characterized this Josephson junction technology for process yield, junction parameter uniformity, and overall applicability for use in high-performance circuits. To facilitate the determination of junction parameters, they developed a measurement technique based on spectral analysis in the range of 90--160 GHz of phase-locked, oscillating arrays of up to 2,450 Josephson junctions. Because of the excellent yield and uniformity of the nanobridge junctions, they successfully applied the junction technology to a wide variety of circuits. These circuits included transmission-line pulse formers and 32 and 64-bit shift registers. The 32-bit shift register was shown to operate at clock speeds near 100 GHz and is believed to be one of the faster and more complex digital circuit demonstrated to date using high temperature superconductor technology.
Fluxons in a triangular set of coupled long Josephson junctions
NASA Astrophysics Data System (ADS)
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.
Fluxons in a triangular set of coupled long Josephson junctions
Yukon, Stanford P.; Malomed, Boris A.
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.
Dicke-Josephson effect in a cross-typed triple-quantum-dot junction
NASA Astrophysics Data System (ADS)
Wang, Xiao-Qi; Yi, Guang-Yu; Gong, Wei-Jiang
2016-12-01
We investigate the Dicke-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 Dicke effect can modulate the Josephson effect in a nontrivial way. In the noninteracting case, the Dicke effect induces a subpeak in the supercurrent spectrum around the energy zero point. When intradot interactions are taken into account, the role of the Dicke effect changes completely. Namely, it tends to suppress the π-phase current near the position of electron-hole symmetry. With the increase of the Coulomb strength, it has an opportunity to reverse the current direction. We thus conclude that the Dicke-Josephson effect is also an important part in describing the Josephson effect in coupled-dot junctions.
Merkle, K.L.; Huang, Y.
1998-01-01
The electric transport of high-temperature superconductors, such as YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO), can be strongly restricted by the presence of high-angle grain boundaries (GB). This weak-link behavior is governed by the macroscopic GB geometry and the microscopic grain boundary structure and composition at the atomic level. Whereas grain boundaries present a considerable impediment to high current applications of high T{sub c} materials, there is considerable commercial interest in exploiting the weak-link-nature of grain boundaries for the design of microelectronic devices, such as superconducting quantum interference devices (SQUIDs). The Josephson junctions which form the basis of this technology can also be formed by introducing artificial barriers into the superconductor. The authors have examined both types of Josephson junctions by EM techniques in an effort to understand the connection between microstructure/chemistry and electrical transport properties. This knowledge is a valuable resource for the design and production of improved devices.
0-π Transition Driven by Magnetic Proximity Effect in a Josephson Junction
NASA Astrophysics Data System (ADS)
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.
Two-channel Kondo physics in a Majorana island coupled to a Josephson junction
NASA Astrophysics Data System (ADS)
Landau, L. A.; Sela, E.
2017-01-01
We study a Majorana island coupled to a bulk superconductor via a Josephson junction and to multiple external normal leads. In the absence of the Josephson coupling, the system displays a topological Kondo state, which had been largely studied recently. However, we find that this state is unstable even to small Josephson coupling, which instead leads at low temperature T to a new fixed point. Most interesting is the case of three external leads, forming a minimal electronic realization of the long sought two-channel Kondo effect. While the T =0 conductance corresponds to simple resonant Andreev reflection, the leading T dependence forms an experimental fingerprint for non-Fermi-liquid properties.
Feynman's and Ohta's Models of a Josephson Junction
ERIC Educational Resources Information Center
De Luca, R.
2012-01-01
The Josephson equations are derived by means of the weakly coupled two-level quantum system model given by Feynman. Adopting a simplified version of Ohta's model, starting from Feynman's model, the strict voltage-frequency Josephson relation is derived. The contribution of Ohta's approach to the comprehension of the additional term given by the…
Light-modulated 0-π transition in a silicene-based Josephson junction
NASA Astrophysics Data System (ADS)
Zhou, Xingfei; Jin, Guojun
2016-10-01
We investigate the Andreev bound states (ABSs) and Josephson current in a silicene-based superconductor-normal-superconductor junction modulated by a perpendicular electric field and an off-resonant circularly polarized light. Based on the Dirac-Bogoliubov-de Gennes equation, we analytically derive the ABS levels and show they have different phase-difference dependences, which will remarkably influence the velocity of Cooper pairs and then the Josephson current. In the pristine or gated silicene, the ABS levels always show negative slope, which means that the Josephson current is irreversible because of the time-reversal symmetry. When an off-resonant circularly polarized light is applied, whether or not there is a perpendicular electric field, the ABS levels will have positive slope, leading to the emergence of reversed Josephson current due to the nonzero center-of-mass wave vector of Cooper pairs. In this light-modulated silicene-based Josephson junction, valley polarization provides an alternative mechanism for 0-π transition, very different from that for the conventional ferromagnetic Josephson junctions where the spin polarization is essential.
NASA Astrophysics Data System (ADS)
Berdiyorov, G. R.; Savel'ev, S. E.; Milošević, M. V.; Kusmartsev, F. V.; Peeters, F. M.
2013-05-01
Nonlinear dynamics of Josephson vortices (fluxons) in artificial stacks of superconducting-normal-superconducting Josephson junctions under simultaneously applied time-periodic ac and constant biasing dc currents is studied using the time dependent Ginzburg-Landau formalism with a Lawrence-Doniach extension. At zero external magnetic field and dc biasing current the resistive state of the system is characterized by periodic nucleation and annihilation of fluxon-antifluxon pairs, relative positions of which are determined by the state of neighboring junctions. Due to the mutual repulsive interaction, fluxons in different junctions move out of phase. Their collective motion can be synchronized by adding a small ac component to the biasing dc current. Coherent motion of fluxons is observed for a broad frequency range of the applied drive. In the coherent state the maximal output voltage, which is proportional to the number of junctions in the stack, is observed near the characteristic frequency of the system determined by the crossing of the fluxons across the sample. However, in this frequency range the dynamically synchronized state has an alternative—a less ordered state with smaller amplitude of the output voltage. Collective behavior of the junctions is strongly affected by the sloped sidewalls of the stack. Synchronization is observed only for weakly trapezoidal cross sections, whereas irregular motion of fluxons is observed for larger slopes of the sample edge.
Spatially resolved gap closing in single Josephson junctions constructed on Bi2Te3 surface
NASA Astrophysics Data System (ADS)
Pang, Yuan; Wang, Junhua; Lyu, Zhaozheng; Yang, Guang; Fan, Jie; Liu, Guangtong; Ji, Zhongqing; Jing, Xiunian; Yang, Changli; Lu, Li
2016-11-01
Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators. Previously, we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi2Te3 surface. In this paper we report further investigations on the position dependence of gap closing as a function of magnetic flux in single Josephson junctions constructed on Bi2Te3 surface. Project supported by the National Basic Research Program of China (Grant Nos. 2009CB929101 and 2011CB921702), the National Natural Science Foundation of China (Grant Nos. 91221203, 11174340, 11174357, 91421303, and 11527806), and the Strategic Priority Research Program B of the Chinese Academy of Sciences (Grant No. XDB07010100).
Magnetic Field Dependence of the Critical Current of Planar Geometry Josephson Junctions
NASA Astrophysics Data System (ADS)
Ma, Meng; Cho, Ethan; Huynh, Chuong; Cybart, Shane; Dynes, Robert
2015-03-01
We report a study on the magnetic field dependence of the critical current of planar geometry Josephson junctions. We have fabricated Josephson junctions by using a focused helium ion beam to irradiate a narrow barrier in the plane of a 25 nm thick Y-Ba-Cu-O film. The London penetration depth λL is large (~1 μm) because of the ultra-thin thickness of the film. As a result, calculations of the Josephson penetration depth λJ are not realistic nor physical. Therefore in this work, we measure λJ experimentally. We tested devices with bridge widths ranging from 4 to 50 μm, and present measurements of the Fraunhofer quantum diffraction pattern (IC (B)). We observe a crossover from short to long junction behavior, which gives an experimentally measured λJ that ranges between 3 μm to 5 μm. The shape of the IC (B) pattern is strongly affected by the width of the bridge because of self-field effects. As the bridge width increases, Josephson vortices enter the junction and skew the patterns. This work shows that the electronic properties of the planar junctions are very different than those classical ``sandwich'' junctions due to the differences in geometry.
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.
High temperature superconductor step-edge Josephson junctions using Ti-Ca-Ba-Cu-O
Ginley, D.S.; Hietala, V.M.; Hohenwarter, G.K.G.; Martens, J.S.; Plut, T.A.; Tigges, C.P.; Vawter, G.A.; Zipperian, T.E.
1994-10-25
A process is disclosed 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. 8 figs.
Measurement of Aharonov-Casher effect in a Josephson junction chain
NASA Astrophysics Data System (ADS)
Pop, Ioan Mihai; Lecocq, Florent; Pannetier, Bernard; Buisson, Olivier; Guichard, Wiebke
2011-03-01
We have recently measured the effect of superconducting phase-slips on the ground state of a Josephson junction chain and a rhombi chain. Here we report clear evidence of Aharonov-Casher effect in a chain of Josephson junctions. This phenomenon is the dual of the well known Aharonov-Bohm interference. Using a capacitively coupled gate to the islands of the chain, we induce oscillations of the supercurrent by tuning the polarization charges on the islands. We observe complex interference patterns for different quantum phase slip amplitudes, that we understand quantitatively as Aharonov-Casher vortex interferences. European STREP MIDAS.
Pure second harmonic current-phase relation in spin-filter Josephson junctions.
Pal, Avradeep; Barber, Z H; Robinson, J W A; Blamire, M G
2014-01-01
Higher harmonics in current-phase relations of Josephson Junctions are predicted to be observed when the first harmonic is suppressed. Conventional theoretical models predict higher harmonics to be extremely sensitive to changes in barrier thickness, temperature, and so on. Here we report experiments with Josephson junctions incorporating a spin-dependent tunnelling barrier, revealing a current-phase relation for highly spin polarized barriers that is purely second harmonic in nature and is insensitive to changes in barrier thickness. This observation implies that the standard theory of Cooper pair transport through tunnelling barriers is not applicable for spin-dependent tunnelling barriers.
Thin-film metal coated insulation barrier in a Josephson tunnel junction. [Patent application
Hawkins, G.A.; Clarke, J.
1975-10-31
A highly stable, durable, and reproducible Josephson tunnel junction consists of a thin-film electrode of a hard superconductor, a thin oxide insulation layer over the electrode constituting a Josephson tunnel junction barrier, a thin-film layer of stabilizing metal over the barrier, and a second thin-film hard superconductive electrode over the stabilizing film. The thin stabilizing metal film is made only thick enough to limit penetration of the electrode material through the insulation layer so as to prevent a superconductive short.
Modulated microwave absorption spectra from Josephson junctions on a scratched niobium wire
Rubins, R.S. |; Hutton, S.L.; Ravindran, K.; Subbaraman, K.; Drumheller, J.E.
1997-05-01
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, {delta}H of the Josephson lines was found to vary linearly with P{sup 1/2}, 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} {ital 1997} {ital The American Physical Society}
Free and Induced Vortices Motion in the Josephson Junction Coupled with Waveguide
NASA Astrophysics Data System (ADS)
Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
A model for the analytic description of vortices in a system consisting of a long Josephson junction and a waveguide is formulated. For this system all types of elementary vortices and its chains are listed. The allowed range of velocities of an elementary vortex is found. It is established that a free vortex can be a fast one which moves with velocity much greater than the Swihart velocity of Josephson junction. The effect of the waveguide on the induced vortices motion is studied. It is shown that fast vortex can be generated by relatively small values of bias current density. The effect of vortex Cherenkov losses on the bias current is described.
Free and Induced Vortices Motion in the Josephson Junction Coupled with Waveguide
NASA Astrophysics Data System (ADS)
Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
2010-12-01
A model for the analytic description of vortices in a system consisting of a long Josephson junction and a waveguide is formulated. For this system all types of elementary vortices and its chains are listed. The allowed range of velocities of an elementary vortex is found. It is established that a free vortex can be a fast one which moves with velocity much greater than the Swihart velocity of Josephson junction. The effect of the waveguide on the induced vortices motion is studied. It is shown that fast vortex can be generated by relatively small values of bias current density. The effect of vortex Cherenkov losses on the bias current is described.
Defect motion and lattice pinning barriers in Josephson-junction ladders
Kang, H.; Lim, Jong Soo; Fortin, J.-Y.; Choi, J.; Choi, M. Y.
2006-01-01
We study the motion of domain wall defects in a fully frustrated Josephson-junction ladder system, driven by small applied currents. For small system sizes, the energy barrier E{sub B} to the defect motion is computed analytically via symmetry and topological considerations. More generally, we perform numerical simulations directly on the equations of motion, based on the resistively-shunted junction model, to study the dynamics of defects, varying the system size. Coherent motion of domain walls is observed for large system sizes. In the thermodynamical limit, we find E{sub B}=0.1827 in units of the Josephson coupling energy.
Josephson Junction spectrum analyzer for millimeter and submillimeter wavelengths
NASA Technical Reports Server (NTRS)
Larkin, S. Y.; Anischenko, S. E.; Khabayev, P. V.
1995-01-01
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.
Josephson junction spectrum analyzer for millimeter and submillimeter wavelengths
Larkin, S.Y.; Anischenko, S.E.; Khabayev, P.V.
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.
Shape Waves in 2D Josephson Junctions: Exact Solutions and Time Dilation
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Kusmartsev, F. V.; Savel'Ev, Sergey; Yampol'Skii, V. A.; Nori, Franco
2008-09-01
We predict a new class of excitations propagating along a Josephson vortex in two-dimensional Josephson junctions. These excitations are associated with the distortion of a Josephson vortex line and have an analogy with shear waves in solid mechanics. Their shapes can have an arbitrary profile, which is retained when propagating. We derive a universal analytical expression for the energy of arbitrary shape excitations, investigate their influence on the dynamics of a vortex line, and discuss conditions where such excitations can be created. Finally, we show that such excitations play the role of a clock for a relativistically moving Josephson vortex and suggest an experiment to measure a time dilation effect analogous to that in special relativity.
Shape waves in 2D Josephson junctions: exact solutions and time dilation.
Gulevich, D R; Kusmartsev, F V; Savel'ev, Sergey; Yampol'skii, V A; Nori, Franco
2008-09-19
We predict a new class of excitations propagating along a Josephson vortex in two-dimensional Josephson junctions. These excitations are associated with the distortion of a Josephson vortex line and have an analogy with shear waves in solid mechanics. Their shapes can have an arbitrary profile, which is retained when propagating. We derive a universal analytical expression for the energy of arbitrary shape excitations, investigate their influence on the dynamics of a vortex line, and discuss conditions where such excitations can be created. Finally, we show that such excitations play the role of a clock for a relativistically moving Josephson vortex and suggest an experiment to measure a time dilation effect analogous to that in special relativity.
High-quality planar high-T{sub c} Josephson junctions
Bergeal, N.; Grison, X.; Lesueur, J.; Faini, G.; Aprili, M.; Contour, J.P.
2005-09-05
Reproducible high-T{sub c} Josephson junctions have been made in a rather simple two-step process using ion irradiation. A microbridge (1 to 5 {mu}m wide) is firstly designed by ion irradiating a c-axis-oriented YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} film through a gold mask such as the nonprotected part becomes insulating. A lower T{sub c} part is then defined within the bridge by irradiating with a much lower fluence through a narrow slit (20 nm) opened in a standard electronic photoresist. These planar junctions, whose settings can be finely tuned, exhibit reproducible and nearly ideal Josephson characteristics. This process can be used to produce complex Josephson circuits.
Synchronization dynamics on the picosecond time scale in coupled Josephson junction neurons
NASA Astrophysics Data System (ADS)
Segall, K.; LeGro, M.; Kaplan, S.; Svitelskiy, O.; Khadka, S.; Crotty, P.; Schult, D.
2017-03-01
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. The circuit models two mutually coupled excitatory neurons. In some regions of parameter space the neurons are desynchronized. In others, the Josephson neurons synchronize in one of two states, in-phase or antiphase. An experimental alteration of the delay and strength of the connecting synapses can toggle the system back and forth in a phase-flip bifurcation. Firing synchronization states are calculated >70 000 times faster than conventional digital approaches. With their speed and low energy dissipation (10-17J /spike ), this set of proof-of-concept experiments establishes Josephson junction neurons as a viable approach for improvements in neuronal computation as well as applications in neuromorphic computing.
Interaction of Josephson Junction and Distant Vortex in Narrow Thin-Film Superconducting Strips
Kogan, V. G.; Mints, R. G.
2014-01-31
The phase difference between the banks of an edge-type planar Josephson junction crossing the narrow thin-film strip depends on wether or not vortices are present in the junction banks. For a vortex close to the junction this effect has been seen by Golod, Rydh, and Krasnov [Phys. Rev. Lett. 104, 227003 (2010)], who showed that the vortex may turn the junction into π type. It is shown here that even if the vortex is far away from the junction, it still changes the 0 junction to a π junction when situated close to the strip edges. Within the approximation used, the effect is independent of the vortex-junction separation, a manifestation of the topology of the vortex phase which extends to macroscopic distances of superconducting coherence.
NASA Astrophysics Data System (ADS)
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.
A closed cycle cascade Joule Thomson refrigerator for cooling Josephson junction magnetometers
NASA Technical Reports Server (NTRS)
Tward, E.; Sarwinski, R.
1985-01-01
A closed cycle cascade Joule Thomson refrigerator designed to cool Josephson Junction magnetometers to liquid helium temperature is being developed. The refrigerator incorporates 4 stages of cooling using the working fluids CF4 and He. The high pressure gases are provided by a small compressor designed for this purpose. The upper stages have been operated and performance will be described.
Aharonov-Casher effect for plasmons in a ring of Josephson junctions
NASA Astrophysics Data System (ADS)
Süsstrunk, Roman; Garate, Ion; Glazman, Leonid I.
2013-08-01
Phase slips in a one-dimensional closed array of Josephson junctions hybridize the persistent current states and plasmon branches of excitations. The interference between phase slips passing through different junctions of the array makes the hybridization sensitive to the charges of the superconducting islands comprising the array. This in turn results in the Aharonov-Casher effect for plasmons, which in the absence of phase slips are insensitive to island charges.
Spontaneous symmetry breaking and collapse in bosonic Josephson junctions
Mazzarella, Giovanni; Salasnich, Luca
2010-09-15
We investigate an attractive atomic Bose-Einstein condensate (BEC) trapped by a double-well potential in the axial direction and by a harmonic potential in the transverse directions. We obtain numerically a quantum phase diagram which includes all the three relevant phases of the system: Josephson, spontaneous symmetry breaking (SSB), and collapse. We consider also the coherent dynamics of the BEC and calculate the frequency of population-imbalance mode in the Josephson phase and in the SSB phase up to the collapse. We show that these phases can be observed by using ultracold vapors of {sup 7}Li atoms in a magneto-optical trap.
NASA Astrophysics Data System (ADS)
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?
Edge-type Josephson junctions in narrow thin-film strips
NASA Astrophysics Data System (ADS)
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.
Fischer, G M; Mayer, B; Gross, R; Nissel, T; Husemann, K D; Huebener, R P; Freltoft, T; Shen, Y; Vase, P
1994-02-25
With low-temperature scanning electron microscopy, the magnetic flux states in high critical temperature Josephson junctions have been imaged. The experiments were performed with YBa(2)Cu(3)O(7-delta) thin-film grain boundary Josephson junctions fabricated on [001] tilt SrTiO(3) bicrystals. For applied magnetic fields parallel to the grain boundary plane, which correspond to local maxima of the magnetic field dependence of the critical current, the images clearly show the corresponding magnetic flux states in the grain boundary junction. The spatial modulation of the Josephson current density by the external magnetic field is imaged directly with a spatial resolution of about 1 micrometer.
Shunted Josephson tunnel junctions: High-frequency, self-pumped low noise amplifiers
NASA Astrophysics Data System (ADS)
Calander, N.; Claeson, T.; Rudner, S.
1982-07-01
The high-frequency amplification properties of transformer coupled, resistively shunted Josephson tunnel junctions have been investigated. The importance of the shunt loop inductance is stressed. It allows a high cutoff frequency, of significance for good high-frequency performance. The self-pumped parametric amplifier showed none of the excessive noise rise, which has hitherto plagued the development of externally pumped Josephson junction amplifiers. Around 10 GHz, we estimated a noise temperature less than 30 K for an amplifier pumped by a Josephson oscillation with a frequency well above twice the signal frequency. The corresponding gain of 5 dB may be increased in a better impedance matched circuit. The gain was very stable against variations in the bias conditions. A gain-bandwidth product as high as 0.3 was registered. The experimental results agreed well with the established theory for self-pumped parametric Josephson amplifiers. It should be possible to extend the low noise amplification by this device to mm wave frequencies. A relaxation oscillation occurred at a subharmonic of the Josephson frequency when the shunt loop inductance became large. The amplification in this mode followed closely the predictions of a simple model, where the signal modulated the switching of the sawtooth-like (relatively low frequency) relaxation current. Gains of about 15 dB were measured around 10 GHz, but the amplification was sensitive to bias conditions and noisy in this case where the relaxation frequency fell well below the signal frequency. Much improved properties were registered when the inductance was decreased so that the relaxation frequency approached the Josephson frequency and exceeded twice the signal frequency. The behavior then resembled that of a Josephson mode parametric amplifier, but the high content of harmonics of a relaxation oscillation meant that the amplifier became noisier due to converted noise from the many idler frequencies.
Parity Anomaly and Spin Transmutation in Quantum Spin Hall Josephson Junctions
NASA Astrophysics Data System (ADS)
Peng, Yang; Vinkler-Aviv, Yuval; Brouwer, Piet W.; Glazman, Leonid I.; von Oppen, Felix
2016-12-01
We study the Josephson effect in a quantum spin Hall system coupled to a localized magnetic impurity. As a consequence of the fermion parity anomaly, the spin of the combined system of impurity and spin-Hall edge alternates between half-integer and integer values when the superconducting phase difference across the junction advances by 2 π . This leads to characteristic differences in the splittings of the spin multiplets by exchange coupling and single-ion anisotropy at phase differences, for which time-reversal symmetry is preserved. We discuss the resulting 8 π -periodic (or Z4) fractional Josephson effect in the context of recent experiments.
NASA Astrophysics Data System (ADS)
Kim, Jihoon
MgB2 is an unusual binary metallic superconductor in that it has a transition temperature of almost twice that of other metallic compounds and possesses two superconductor gaps. It has proven to be difficult to fabricate in thin film form, predominantly as a result of the high volatility of Mg. In this thesis, critical factors involved in MgB2 thin film growth and the synthesis of multilayer MgB2 Josephson junctions have been studied. The thermochemistry of MgB2 thin film growth has been investigated. The low Mg sticking coefficient at temperatures over 300°C prevents high temperature synthesis with traditional vacuum growth methods. However, as a result of the large kinetic barrier to MgB2 decomposition, metastable growth and subsequent thermal processing is possible. The Mg sticking coefficient is found to be strongly dependent upon B flux. High Mg and B fluxes make it possible to extend the processing window to elevated temperatures by enhancing the Mg sticking coefficient. A transition temperature of 37˜38K was achieved using molecular beam epitaxy (MBE). For the fabrication of Josephson junctions, various barrier layers including native oxide, boron, AIN, and thermal oxide were explored. Cross-bridge junction structures were fabricated using shadow masks. Repeatable tunneling characteristics were observed from metal/native oxide/MgB2 junctions. MgB 2 energy gaps and density of states, as well as the barrier's height and thickness, have been inferred from tunneling conductance measurements. MgB2/native oxide or boron/MgB2 junctions with 1mm 2 areas were fabricated and also exhibited tunneling characteristics. The junctions produced with the cross geometry process have a Josephson coupling energy that is too small compared to the thermal energy to exhibit supercurrent as a result of the junction's large size and high resistance. To overcome this limitation, planar type junctions were prepared using conventional microfabrication techniques. MgB2,/AlN/MgB2 and
Experimental demonstration of Aharonov-Casher interference in a Josephson junction circuit
NASA Astrophysics Data System (ADS)
Pop, I. M.; Douçot, B.; Ioffe, L.; Protopopov, I.; Lecocq, F.; Matei, I.; Buisson, O.; Guichard, W.
2012-03-01
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 in a six Josephson junction chain. In this multijunction circuit, the fluxon can encircle any combination of charges on five superconducting islands, resulting in a complex pattern. We compare the experimental results with predictions of a simplified model that treats fluxons as independent excitations and with the results of the full diagonalization of the quantum problem. Our results demonstrate the accuracy of the fluxon interference description and the quantum coherence of these arrays.
Fabrication of Small Edge Josephson Junctions Between Sr2RuO4 and Al
NASA Astrophysics Data System (ADS)
Zakrzewski, Brian; Cai, Xinxin; Ying, Yiqun; Fobes, David; Liu, Tijiang; Mao, Zhiqiang; Liu, Ying
2015-03-01
Sr2RuO4 is predicted to have a chiral p-wave orbital pairing. However, attempts to measure the chiral edge currents have yielded results inconsistent with theoretical predictions. Josephson junctions between Sr2RuO4 and an s-wave superconductor such as Al may provide an avenue for directly measuring the edge currents. We report progress on fabricating these junctions, using Al electrodes with no oxide barrier. The Josephson junctions are placed on the naturally formed edges of cleaved Sr2RuO4 thin crystal, which is expected to feature a surface less disordered than ramped junctions prepared by focused ion beam and ion mills. Transmission electron microscope studies provide a powerful tool to characterize the interface. We have systematically investigated the effects of nanofabrication processes on the quality of the junction interface. In particular, several post-lithography processes appear to cause irreversible damage to the surface layer of Sr2RuO4, which highlights potential issues for general small scale device fabrication. We also report preliminary measurements of Josephson tunneling from these devices.
Noise properties of nanoscale YBa2Cu3O7-δ Josephson junctions
NASA Astrophysics Data System (ADS)
Gustafsson, D.; Lombardi, F.; Bauch, T.
2011-11-01
We present electric noise measurements of nanoscale biepitaxial YBa2Cu3O7-δ (YBCO) Josephson junctions fabricated by two different lithographic methods. The first (conventional) technique defines the junctions directly by ion milling etching through an amorphous carbon mask. The second (soft patterning) method makes use of the phase competition between the superconducting YBCO (Y123) and the insulating Y2BaCuO5 (Y211) phase at the grain boundary interface on MgO (110) substrates. The voltage noise properties of the two methods are compared in this study. For all junctions (having a thickness of 100 nm and widths of 250-500 nm), we see a significant amount of individual charge traps. We have extracted an approximate value for the effective area of the charge traps from the noise data. From the noise measurements, we infer that the soft-patterned junctions with a grain-boundary (GB) interface manifesting a large c-axis tunneling component have a uniform barrier and a superconductor-insulator-superconductor (SIS) -like behavior. The noise properties of soft-patterned junctions having a GB interface dominated by transport parallel to the ab planes are in accordance with a resonant tunneling barrier model. The conventionally patterned junctions, instead, have suppressed superconducting transport channels with an area much less than the nominal junction area. These findings are important for the implementation of nanosized Josephson junctions in quantum circuits.
Experiments on non-equilibrium superconductor-normal metal-superconductor Josephson junctions
NASA Astrophysics Data System (ADS)
Crosser, Michael S.
By controlling the distribution function within the normal metal of a superconductor/normal metal/superconductor (SNS) Josephson junction, one can reverse the supercurrent-phase relation in the normal wire, creating a pi-junction. This manipulation is done by injecting normal quasiparticle current into the wire, via one or more leads attached at the middle of the junction. Two experiments evolve from this concept. First, in a sample of four reservoirs, two normal and two superconducting, all connected by a wire cross of normal metal, one may inject current either antisymmetrically (AS) or symmetrically (S). In the AS case, current is injected into one normal lead and extracted from the other, creating normal current flow that does not interact with the supercurrent except at the junction. In the S case, current is injected into both normal leads and extracted from the superconductors. Theory predicts that, in the absence of electron energy relaxation in the normal part of the junction, these two situations should result in identical behavior of the Josephson junction. However, due to Joule heating, the S case shows a slightly larger maximum pi-current than the AS case. The second experiment considers a more subtle effect resulting from normal current being injected symmetrically into a SNS Josephson junction. One side of the SNS junction has both normal current and supercurrent flowing in the same direction while the other side has opposing current flows. This situation creates an effective energy gradient across the SNS junction that can appear in the distribution function of the normal wire. Using superconductor/insulator/normal metal tunnelling spectroscopy, it is possible to extract these changes to the distribution function.
Synchronization of a Josephson junction array in terms of global variables.
Vlasov, Vladimir; Pikovsky, Arkady
2013-08-01
We consider an array of Josephson junctions with a common LCR load. Application of the Watanabe-Strogatz approach [Physica D 74, 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-differential equation for the global variables; here stability of the asynchronous states and the properties of the transition synchrony-asynchrony are established numerically.
ac Josephson Effect in Finite-Length Nanowire Junctions with Majorana Modes
NASA Astrophysics Data System (ADS)
San-Jose, Pablo; Prada, Elsa; Aguado, Ramón
2012-06-01
It has been predicted that superconducting junctions made with topological nanowires hosting Majorana bound states (MBS) exhibit an anomalous 4π-periodic Josephson effect. Finding an experimental setup with these unconventional properties poses, however, a serious challenge: for finite-length wires, the equilibrium supercurrents are always 2π periodic as anticrossings of states with the same fermionic parity are possible. We show, however, that the anomaly survives in the transient regime of the ac Josephson effect. Transients are, moreover, protected against decay by quasiparticle poisoning as a consequence of the quantum Zeno effect, which fixes the parity of Majorana qubits. The resulting long-lived ac Josephson transients may be effectively used to detect MBS.
NASA Astrophysics Data System (ADS)
Cedergren, K.; Kafanov, S.; Smirr, J.-L.; Cole, J. H.; Duty, T.
2015-09-01
We have made a systematic investigation of charge transport in one-dimensional chains of Josephson junctions where the characteristic Josephson energy is much less than the single-junction Cooper-pair charging energy, EJ≪EC P . Such chains are deep in the insulating state, where superconducting phase coherence across the chain is absent, and a voltage threshold for conduction is observed at the lowest temperatures. We find that Cooper-pair tunneling in such chains is completely suppressed. Instead, charge transport is dominated by tunneling of single electrons, which is very sensitive to the presence of BCS quasiparticles on the superconducting islands of the chain. Consequently, we observe a strong parity effect, where the threshold voltage vanishes sharply at a characteristic parity temperature T*, which is significantly lower than the critical temperature Tc. A measurable and thermally activated zero-bias conductance appears above T*, with an activation energy equal to the superconducting gap, confirming the role of thermally excited quasiparticles. Conduction below T* and above the voltage threshold occurs via injection of single electrons/holes into the Cooper-pair insulator, forming a nonequilibrium steady state with a significantly enhanced effective temperature. Our results explicitly show that single-electron transport dominates deep in the insulating state of Josephson junction arrays. This conduction process has mostly been ignored in previous studies of both superconducting junction arrays and granular superconducting films below the superconductor-insulator quantum phase transition.
NASA Astrophysics Data System (ADS)
Costa, Andreas; Högl, Petra; Fabian, Jaroslav
2017-01-01
We study theoretically the effects of interfacial Rashba and Dresselhaus spin-orbit coupling in superconductor/ferromagnet/superconductor (S/F/S) Josephson junctions—with allowing for tunneling barriers between the ferromagnetic and superconducting layers—by solving the Bogoljubov-de Gennes equation for realistic heterostructures and applying the Furusaki-Tsukada technique to calculate the electric current at a finite temperature. The presence of spin-orbit couplings leads to out-of-plane and in-plane magnetoanisotropies of the Josephson current, which are giant in comparison to current magnetoanisotropies in similar normal-state ferromagnet/normal metal (F/N) junctions. Especially huge anisotropies appear in the vicinity of 0 -π transitions, caused by the exchange-split bands in the ferromagnetic metal layer. We also show that the direction of the Josephson critical current can be controlled (inducing 0 -π transitions) by the strength of the spin-orbit coupling and, more crucial, by the orientation of the magnetization. Such a control can bring new functionalities into Josephson junction devices.
Nonlinear Phase Dynamics in a Driven Bosonic Josephson Junction
Boukobza, Erez; Moore, Michael G.; Cohen, Doron; Vardi, Amichay
2010-06-18
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 {phi} 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 {phi}={pi} 'inverted pendulum' coherent state, and protects the fringe visibility.
Thickness dependent interlayer transport in vertical MoS2 Josephson junctions
NASA Astrophysics Data System (ADS)
Island, Joshua O.; Steele, Gary A.; van der Zant, Herre S. J.; Castellanos-Gomez, Andres
2016-09-01
We report on observations of thickness dependent Josephson coupling and multiple Andreev reflections (MAR) in vertically stacked molybdenum disulfide (MoS2)—molybdenum rhenium (MoRe) Josephson junctions. MoRe, a chemically inert superconductor, allows for oxide free fabrication of high transparency vertical MoS2 devices. Single and bilayer MoS2 junctions display relatively large critical currents (up to 2.5 μA) and the appearance of sub-gap structure given by MAR. In three and four layer thick devices we observe orders of magnitude lower critical currents (sub-nA) and reduced quasiparticle gaps due to proximitized MoS2 layers in contact with MoRe. We anticipate that this device architecture could be easily extended to other 2D materials.
Phase retrapping in a φ Josephson junction: Onset of the butterfly effect
NASA Astrophysics Data System (ADS)
Menditto, R.; Sickinger, H.; Weides, M.; Kohlstedt, H.; Žonda, M.; Novotný, T.; Koelle, D.; Kleiner, R.; Goldobin, E.
2016-05-01
We investigate experimentally the retrapping of the phase in a φ Josephson junction upon return of the junction to the zero-voltage state. Since the Josephson energy profile U0(ψ ) in φ JJ is a 2 π periodic double-well potential with minima at ψ =±φ mod2 π , the question is at which of the two minima -φ or +φ the phase will be trapped upon return from a finite voltage state during quasistatic decrease of the bias current (tilt of the potential). By measuring the relative population of two peaks in escape histograms, we determine the probability of phase trapping in the ±φ wells for different temperatures. Our experimental results agree qualitatively with theoretical predictions. In particular, we observe an onset of the butterfly effect with an oscillating probability of trapping. Unexpectedly, this probability saturates at a value different from 50% at low temperatures.
Band-gaps in long Josephson junctions with periodic phase-shifts
NASA Astrophysics Data System (ADS)
Ahmad, Saeed; Susanto, Hadi; Wattis, Jonathan A. D.
2017-04-01
We investigate analytically and numerically a long Josephson junction on an infinite domain, having arbitrary periodic phase shift of κ, that is, the so-called 0-κ long Josephson junction. The system is described by a one-dimensional sine-Gordon equation and has relatively recently been proposed as artificial atom lattices. We discuss the existence of periodic solutions of the system and investigate their stability both in the absence and presence of an applied bias current. We find critical values of the phase-discontinuity and the applied bias current beyond which static periodic solutions cease to exist. Due to the periodic discontinuity in the phase, the system admits regions of allowed and forbidden bands. We perturbatively investigate the Arnold tongues that separate the region of allowed and forbidden bands, and discuss the effect of an applied bias current on the band-gap structure. We present numerical simulations to support our analytical results.
Macroscopic quantum effects in the zero voltage state of the current biased Josephson junction
Clarke, J.; Devoret, M.H.; Martinis, J.; Esteve, D.
1985-05-01
When a weak microwave current is applied to a current-biased Josephson tunnel junction in the thermal limit the escape rate from the zero voltage state is enhanced when the microwave frequency is near the plasma frequency of the junction. The resonance curve is markedly asymmetric because of the anharmonic properties of the potential well: this behavior is well explained by a computer simulation using a resistively shunted junction model. This phenomenon of resonant activation enables one to make in situ measurements of the capacitance and resistance shunting the junction, including contributions from the complex impedance presented by the current leads. For the relatively large area junctions studied in these experiments, the external capacitive loading was relatively unimportant, but the damping was entirely dominated by the external resistance.
All magnesium diboride Josephson junctions with MgO and native oxide barriers
NASA Astrophysics Data System (ADS)
Costache, M. V.; Moodera, J. S.
2010-02-01
We present results on all-MgB2 tunnel junctions, where the tunnel barrier is deposited MgO or native-oxide of base electrode. For the junctions with MgO, the hysteretic I-V curve resembles a conventional underdamped Josephson junction characteristic with critical current-resistance product nearly independent of the junction area. The dependence of the critical current with temperature up to 20 K agrees with the [Ambegaokar and Baratoff, Phys. Rev. Lett. 10, 486 (1963)] expression. For the junctions with native-oxide, conductance at low bias exhibits subgap features while at high bias reveals thick barriers. As a result no supercurrent was observed in the latter, despite the presence of superconducting-gaps to over 30 K.
Area-dependence of spin-triplet supercurrent in ferromagnetic Josephson junctions
NASA Astrophysics Data System (ADS)
Wang, Yixing; Pratt, W. P., Jr.; Birge, Norman O.
2012-06-01
Josephson junctions containing multiple ferromagnetic layers can carry spin-triplet supercurrent under certain conditions. Large-area junctions containing multiple domains are expected to have a random distribution of 0 or π coupling across the junction surface, whereas magnetized samples should have uniquely π coupling everywhere. We have measured the area-dependence of the critical current in such junctions, and confirm that the critical current scales linearly with area in magnetized junctions. For as-grown (multidomain) samples, the results are mixed. Samples grown on a thick Nb base exhibit critical currents that scale sublinearly with area, while samples grown on a smoother Nb/Al multilayer base exhibit critical currents that scale linearly with area. The latter results are consistent with a theoretical picture due to Zyuzin and Spivak that predicts that the as-grown samples should have global π/2 coupling.
A Nanoscale-Localized Ion Damage Josephson Junction Using Focused Ion Beam and Ion Implanter.
Wu, C H; Ku, W S; Jhan, F J; Chen, J H; Jeng, J T
2015-05-01
High-T(c) Josephson junctions were fabricated by nanolithography using focused ion beam (FIB) milling and ion implantation. The junctions were formed in a YBa2Cu3O7-x, thin film in regions defined using a gold-film mask with 50-nm-wide (top) slits, engraved by FIB. The focused ion beam system parameters for dwell time and passes were set to remove gold up to a precise depth. 150 keV oxygen ions were implanted at a nominal dose of up to 5 x 10(13) ions/cm2 into YBa2Cu3O7-x microbridges through the nanoscale slits. The current-voltage curves of the ion implantation junctions exhibit resistive-shunted-junction-like behavior at 77 K. The junction had an approximately linear temperature dependence of critical current. Shapiro steps were observed under microwave irradiation. A 50-nm-wide slit and 0-20-nm-thick buffer layers were chosen in order to make Josephson junctions due to the V-shape of the FIB-milled trench.
An ion-beam-assisted process for high-T{sub c} Josephson junctions
Huang, M.Q.; Chen, L.; Zhao, Z.X.; Yang, T.; Nie, J.C.; Wu, P.J.; Xiong, X.M.
1997-10-01
We have developed a non-ion-etching ion-beam-assisted-deposition (IBAD) process for fabricating high critical-temperature (T{sub c}) grain boundary Josephson junctions through a photoresist liftoff mask. The YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) junctions fabricated through this process exhibited the resistively-shunted-junction (RSJ)-like I{endash}V characteristics. The well-defined Shapiro steps have been seen on the I{endash}V curves under microwave radiation. The magnetic modulation of critical current of a 4 {mu}m width YBCO junction tallied with the prior simulated Fraunhofer diffraction pattern of a Josephson junction with a spatially homogeneous critical current density. The maximum peak-to-peak modulation voltage across the dc superconducting quantum interference device (SQUID) fabricated by using these junctions reached up to 32 {mu}V at 77 K. The magnetic modulation of the SQUID exhibited periodic behavior with the observed modulation period of 5.0{times}10{sup {minus}4}G. {copyright} {ital 1997 American Institute of Physics.}
The Bose-Hubbard model: from Josephson junction arrays to optical lattices
NASA Astrophysics Data System (ADS)
Bruder, C.; Fazio, R.; Schön, G.
2005-09-01
[Dedicated to Bernhard Mühlschlegel on the occasion ofhis 80th birthday]The Bose-Hubbard model is a paradigm for the study of strongly correlated bosonic systems. We review some of its properties with emphasis on the implications on quantum phase transitions of Josephson junction arrays and quantum dynamics of topological excitations as well as the properties of ultra-cold atoms in optical lattices.
Vortex motion rectification in Josephson junction arrays with a ratchet potential.
Shalóm, D E; Pastoriza, H
2005-05-06
By means of electrical transport measurements we have studied the rectified motion of vortices in ratchet potentials engineered on overdamped Josephson junction arrays. The rectified voltage as a function of the vortex density shows a maximum efficiency close a matching condition to the period of the ratchet potential indicating a collective vortex motion. Vortex current reversals were detected varying the driving force and vortex density revealing the influence of vortex-vortex interaction in the ratchet effect.
Monaco, R; Mygind, J; Rivers, R J
2002-08-19
Phase transitions create a domain structure with defects, which has been argued by Zurek and Kibble (ZK) to depend in a characteristic way on the quench rate. We present an experiment to measure the ZK scaling exponent sigma. Using long symmetric Josephson tunnel junctions, for which the predicted index is sigma=0.25, we find sigma=0.27+/-0.05. Further, we agree with the ZK prediction for the overall normalization.
Universal quantum fluctuations of a cavity mode driven by a Josephson junction.
Armour, A D; Blencowe, M P; Brahimi, E; Rimberg, A J
2013-12-13
We analyze the quantum dynamics of a superconducting cavity coupled to a voltage-biased Josephson junction. The cavity is strongly excited at resonances where the voltage energy lost by a Cooper pair traversing the circuit is a multiple of the cavity photon energy. We find that the resonances are accompanied by substantial squeezing of the quantum fluctuations of the cavity over a broad range of parameters and are able to identify regimes where the fluctuations in the system take on universal values.
Incipient Berezinskii-Kosterlitz-Thouless transition in two-dimensional coplanar Josephson junctions
NASA Astrophysics Data System (ADS)
Massarotti, D.; Jouault, B.; Rouco, V.; Charpentier, S.; Bauch, T.; Michon, A.; De Candia, A.; Lucignano, P.; Lombardi, F.; Tafuri, F.; Tagliacozzo, A.
2016-08-01
Superconducting hybrid junctions are revealing a variety of effects. Some of them are due to the special layout of these devices, which often use a coplanar configuration with relatively large barrier channels and the possibility of hosting Pearl vortices. A Josephson junction with a quasi-ideal two-dimensional barrier has been realized by growing graphene on SiC with Al electrodes. Chemical vapor deposition offers centimeter size monolayer areas where it is possible to realize a comparative analysis of different devices with nominally the same barrier. In samples with a graphene gap below 400 nm, we have found evidence of Josephson coherence in the presence of an incipient Berezinskii-Kosterlitz-Thouless transition. When the magnetic field is cycled, a remarkable hysteretic collapse and revival of the Josephson supercurrent occurs. Similar hysteresis are found in granular systems and are usually justified within the Bean critical state model (CSM). We show that the CSM, with appropriate account for the low-dimensional geometry, can partly explain the odd features measured in these junctions.
Josephson current in finite-lenght nanowire SNS junctions with Majorana fermions
NASA Astrophysics Data System (ADS)
Aguado, Ramon; Prada, Elsa; San Jose, Pablo
2012-02-01
The dc Josephson effect (JE) through infinite-lenght junctions of one-dimensional topological superconductors exhibits an anomalous 4π periodic phase (φ) dependence which originates from a parity-protected level crossing of zero-energy Majorana bound states (MBS) at φ=π. This ``fractional'' JE provides an important experimental detection tool for MBS. In this talk, I will discuss the JE in more realistic SNS junctions of arbitrary transparency and when both the normal and the nanowire regions are of finite length, namely beyond the short-junction and infinite topological superconductor limits. In general, the spectrum of Andreev bound states can become rather intricate and dense as opposed to the infinite-lenght case. Moreover, the low-energy spectrum around φ=π shows always anticrossings, originated from hybridization of four MBS, which may preclude the experimental observation of the fractional JE. At finite bias voltages, Landau-Zener dynamics involving the MBS and quasi-continuum Andreev levels gives rise to a nontrivial ac Josephson current. Interestingly, the ac current phase diagram as a function of the Josephson frequency/normal transmission shows fractional JE regions which are tunable through bias/gate voltages.
Heteroclinic chaos in a Josephson-junction system perturbed by dichotomous noise excitation
NASA Astrophysics Data System (ADS)
Lei, Youming; Fu, Rui
2015-12-01
The chaotic behavior in a Josephson-junction system perturbed by dichotomous noise excitation is discussed in detail. Conditions for the onsets of chaos are derived by virtue of the random Melnikov method together with the mean-square criterion. It is shown that with the increase of the noise transition rate, the threshold of the dichotomous noise amplitude for the onset of chaos in the system increases. The effects of dichotomous noise on the Josephson-junction system are also determined by numerical simulations via the mean largest Lyapunov exponents, which verifies that the injection of the dichotomous noise can cause the change of the sign of the largest Lyapunov exponent and lead to noise-induced chaos. Phase portraits and time histories are further used to verify these results. It can be concluded that by changing the internal parameters of the dichotomous noise, we can adjust the threshold for the onset of the chaos and then control dynamical behaviors in the Josephson-junction system subjected to dichotomous noise excitation.
Nonideal quantum measurement effects on the switching-current distribution of Josephson junctions
NASA Astrophysics Data System (ADS)
Pierro, Vincenzo; Filatrella, Giovanni
2016-10-01
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-junction switching current taking into account the effect of the bias sweeping rate and introducing a simple nonideal quantum measurement scheme. The measurements are modeled 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 to the quantum Zeno effect, and it is close to, but distinguishable from, the Wentzel-Kramers-Brillouin approximation. For energy barriers comparable to the quantum fundamental energy state and in the fast bias current ramp rate the difference is neat, and remains sizable in the asymptotic slow rate limit. This behavior is a consequence of the quantum character of the system that confirms the presence of a backreaction of quantum measurements on the outcome of mesoscopic Josephson junctions.
Samokhvalov, A. V.
2007-03-15
Commensurability effects have been theoretically studied in a hybrid system consisting of a Josephson junction located in a nonuniform field induced by an array of magnetic particles. A periodic phase-difference distribution in the junction that is caused by the formation of a regular lattice of Abrikosov vortices generated by the magnetic field of the particles in superconducting electrodes is calculated. The dependence of the critical current through the junction I{sub c} on the applied magnetic field H is shown to differ strongly from the conventional Fraunhofer diffraction pattern because of the periodic modulation of the Josephson phase difference created by the vortices. More specifically, the I{sub c}(H) pattern contains additional resonance peaks, whose positions and heights depend on the parameters and magnetic state of the particles in the array. These specific features of the I{sub c}(H) dependence are observed when the period of the Josephson current modulation by the field of the magnetic particles and the characteristic scale of the change in the phase difference by the applied magnetic field are commensurable. The conditions that determine the positions of the commensurability peaks are obtained, and they are found to agree well with experimental results.
Fluxon dynamics in two-gap superconductor-based long Josephson junction
NASA Astrophysics Data System (ADS)
Ghimire, Bal Ram
A superconducting tunnel junction with two-gap superconductors, such as MgB2 and iron-based superconductors, can lead to more interesting phase dynamics than those with one-gap superconductors. The phase dynamics in a long Josephson junction (LJJ) may be described by using the sine-Gordon equation. The difference in the phase dynamics between the LJJ with two-gap superconductors and that with the one-gap superconductors arises due to the presence of multiple tunneling channels between the superconductor (S) layers and the inter-band Josephson effect within the same S layer. The inter-band Josephson effect leads to both spatial and temporal modulation of the critical current between the two adjacent S layers. In this work, the effects of critical current modulation on the trajectories of the single Josephson vortex (i.e., fluxon) and the current-voltage characteristics of the two-gap superconductor-based LJJ are estimated. Also, the possibility of a broken time-reversal symmetry state ground state of a single LJJ due to the presence of additional tunneling channels is investigated by using a microscopic model for two-gap superconductors. The consequence of this broken time reversal ground state is discussed. Finally, the equation of motion for fluxon for coupled LJJs interacting via both the magnetic induction effect and charging effect is investigated. As the inter-band Josephson effect is found to affect the dynamics of a single fluxon in a single LJJ, this effect is explicitly taken into account for a two-coupled LJJ stack. This equation of motion is expected to be an excellent starting point for exploring interesting LJJ properties such as collective dynamics of fluxons as well as fractional fluxons.
External noise-induced transitions in a current-biased Josephson junction
Huang, Qiongwei; Xue, Changfeng; Tang, Jiashi
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.
Using ion irradiation to make high-T{sub c} Josephson junctions
Bergeal, N.; Lesueur, J.; Sirena, M.; Faini, G.; Aprili, M.; Contour, J. P.; Leridon, B.
2007-10-15
In this article we describe the effect of ion irradiation on high-T{sub c} 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-T{sub c} film and a mesa one defined in a trilayer structure.
Strongly-coupled Josephson junction array for simulation of frustrated one-dimensional spin models
NASA Astrophysics Data System (ADS)
Zhou, Zhengwei; Du, Lianghui; Zhou, Xingxiang; Han, Yongjian; Guo, Guangcan
2013-03-01
We study the capacitance-coupled Josephson-junction array beyond the small-coupling limit. We find that, when the scale of the system is large, its Hamiltonian can be obtained without the small-coupling approximation and the system can be used to simulate strongly frustrated one-dimensional Ising spin problems. To engineer the system Hamiltonian for an ideal theoretical model, we apply a dynamical-decoupling technique to eliminate undesirable couplings in the system. Using a six-site junction array as an example, we numerically evaluate the system to show that it exhibits important characteristics of the frustrated spin model.
Niobium nitride Josephson Junction studies and devices. Final report, 1 Jul-31 Dec 90
Sinclair, W.R.
1991-02-26
We suggest here a novel class of molecules for use in making monolayer thick insulating barriers for Josephson junctions employing all NbN conductors. For the experiments discussed here the smallest member of that class has been chosen. From sessile drop experiments we determine that this compound indeed reacts with NbN as postulated. Measurements of the electrical properties are less definitive. In no couple is shorting noted but the superconductivity of the bottom layer is eliminated near the junction presumably due to diffusion of the reactant molecule into the film.
Temporal stability of Y Ba Cu O nano Josephson junctions from ion irradiation
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.
2D SQIF arrays using 20 000 YBCO high R n Josephson junctions
NASA Astrophysics Data System (ADS)
Mitchell, E. E.; Hannam, K. E.; Lazar, J.; Leslie, K. E.; Lewis, C. J.; Grancea, A.; Keenan, S. T.; Lam, S. K. H.; Foley, C. P.
2016-06-01
Superconducting quantum interference filters (SQIFs) have been created using two dimensional arrays of YBCO step-edge Josephson junctions connected together in series and parallel configurations via superconducting loops with a range of loop areas and loop inductances. A SQIF response, as evidenced by a single large anti-peak at zero applied flux, is reported at 77 K for step-edge junction arrays with the junction number N = 1 000 up to 20 000. The SQIF sensitivity (slope of peak) increased linearly with N up to a maximum of 1530 V T-1. Array parameters related to geometry and average junction characteristics are investigated in order to understand and improve the SQIF performance in high temperature superconducting arrays. Initial investigations also focus on the effect of the SQUID inductance factor on the SQIF sensitivity by varying both the mean critical current and the mean inductance of the loops in the array. The RF response to a 30 MHz signal is demonstrated.
Zero-field steps and coherent emission of externally heated long Josephson junctions
NASA Astrophysics Data System (ADS)
Grib, Alexander; Seidel, Paul; Tonouchi, Masayoshi
2017-01-01
IV-characteristics of stacks of two inductively interacting long Josephson junctions with the homogeneous and inhomogeneous distributions of critical currents were investigated numerically. It was assumed that the inhomogeneous linear distribution of critical currents along the junction was created by heating of one end of the stack. Even zero-field steps were found in the IV-curve of the stack with the homogeneous distribution of critical currents, whereas odd zero-field steps appeared in the IV-curve of the stack with the heated end. Due to the inductive interaction between junctions in a stack of two junctions, each of the zero-field steps splits into two steps which correspond to frequencies of collective excitations in the system. Strong coherent emission was found at the step which corresponds to the frequency of in-phase oscillations.
Vortex qubit based on an annular Josephson junction containing a microshort
NASA Astrophysics Data System (ADS)
Price, A. N.; Kemp, A.; Gulevich, D. R.; Kusmartsev, F. V.; Ustinov, A. V.
2010-01-01
We report theoretical and experimental work on the development of a vortex qubit based on a microshort in an annular Josephson junction. The microshort creates a potential barrier for the vortex, which produces a double-well potential under the application of an in-plane magnetic field; the field strength tunes the barrier height. A one-dimensional model for this system is presented, from which we calculate the vortex-depinning current and attempt frequency as well as the interwell coupling. Implementation of an effective microshort is achieved via a section of insulating barrier that is locally wider in the junction plane. Using a junction with this geometry we demonstrate classical state preparation and readout. The vortex is prepared in a given potential well by sending a series of “shaker” bias-current pulses through the junction. Readout is accomplished by measuring the vortex-depinning current.
Self-Consistent Dynamics of a Josephson Junction in the Presence of an Arbitrary Environment
NASA Astrophysics Data System (ADS)
Joyez, Philippe
2013-05-01
We derive microscopically the dynamics associated with the dc Josephson effect in a superconducting tunnel junction interacting with an arbitrary electromagnetic environment. To do so, we extend to superconducting junctions the so-called P(E) theory (see, e.g., Ingold and Nazarov, arXiv:cond-mat/0508728) that accurately describes the interaction of a nonsuperconducting tunnel junction with its environment. We show the dynamics of this system is described by a small set of coupled correlation functions that take into account both Cooper pair and quasiparticle tunneling. When the phase fluctuations are small the problem is fully solved self-consistently, using and providing the exact linear admittance Y(ω) of the interacting junction.
Critical Current Scaling in Long Diffusive Graphene-Based Josephson Junctions
NASA Astrophysics Data System (ADS)
Ke, Chung Ting; Borzenets, Ivan V.; Draelos, Anne W.; Amet, Francois; Bomze, Yuriy; Jones, Gareth; Craciun, Monica; Russo, Saverio; Yamamoto, Michihisa; Tarucha, Seigo; Finkelstein, Gleb
2016-08-01
We present transport measurements on long diffusive graphene-based Josephson junctions. Several junctions are made on a single-domain crystal of CVD graphene and feature the same contact width of ~9$\\mu$m but vary in length from 400 to 1000 nm. As the carrier density is tuned with the gate voltage, the critical current in the these junctions spans a range from a few nA up to more than $5\\mu$A, while the Thouless energy, ETh, covers almost two orders of magnitude. Over much of this range, the product of the critical current and the normal resistance IcRn is found to scale linearly with ETh, as expected from theory. However, the ratio IcRn /ETh is found to be 0.1-0.2: much smaller than the predicted ~10 for long diffusive SNS junctions.
Josephson-junction single plaquette as a model for the high-Tc grain-boundary junctions
NASA Astrophysics Data System (ADS)
Kim, Jinhee; Shin, Hyun Joon; Lee, Hu Jong
1994-03-01
We have calculated the widths of the integer and half-integer voltage steps in a square Josephson-junction single plaquette as a function of ac level for various filling factors f. The characteristic features of the step widths, corresponding to n=0, 1/2, and 1, show clear differences between small and large values of f, and are in reasonable agreement with the results observed experimentally in high-Tc single grain-boundary junctions. When the inhomogeneity in the critical current of the junctions parallel and perpendicular to the external current is introduced to the model the equations of motion for a single plaquette become equivalent to those of a dc superconducting quantum interference device in the limit of small loop inductance.
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Kusmartsev, F. V.; Savel'Ev, Sergey; Yampol'Skii, V. A.; Nori, Franco
2009-09-01
We predict a class of excitations propagating along a Josephson vortex in two-dimensional Josephson junctions. These excitations are associated with the distortion of a Josephson vortex line of an arbitrary profile. We derive a universal analytical expression for the energy of arbitrary-shape excitations, investigate their influence on the dynamics of a vortex line, and discuss conditions where such excitations can be created. Finally, we show that such excitations play the role of a clock for a relativistically-moving Josephson vortex and suggest an experiment to measure a time-dilation effect analogous to that in special relativity. The position of the shape excitation on a Josephson vortex acts like a “minute hand” showing the time in the rest frame associated with the vortex. Remarkably, at some conditions, the shape wave can carry negative energy: a vortex with the shape excitation can have less energy than the same vortex without it.
Fabrication of Josephson Tunnel Junctions by Reactive Ion Milling.
1980-07-21
NR 319-096 00 |" PRFORMIG 6OGANIZATION NAM ANOOORS / E. AGAM ML gu. RJECT. AC I .- A. Buhzuian, :Applied &ngeeig Physics 0l47C52 Cornell Univeruity...JUNCTIONS BY REACTIVE ION MILLING Alan W. Kleinsasser and Robert A. Buhman School of Applied ’an ’d Engineering Physics and National F Research and...interface between Nb and Vb2 0 5 in therally grown oxide films consists of RHO and RHO 2 , and poor Junction quality has been attrib- uted to such
ac Josephson effects in Nb/InAs/Nb junctions with integrated resonators
NASA Astrophysics Data System (ADS)
Biedermann, K.; Chrestin, A.; Matsuyama, T.; Merkt, U.
2001-04-01
Investigations of the ac Josephson effect in Nb/p-type InAs/Nb junctions are presented. Two distinguished features of these devices are an integrated resonator formed by the overlap of two Nb electrodes with an intermediate anodic oxide and their high characteristic voltages IcRN of about 1 mV. Under radio-frequency irradiation, we observe Shapiro steps whose widths follow Bessel functions for high irradiated power. Because of the integrated resonator, self-resonances of the ac Josephson effect can be studied in the current-voltage characteristics. Using a modified resistively shunted junction model which accounts for the presence of the resonator and a nonuniform lateral current distribution, we can describe the magnetic-field dependence of the resonance amplitude. A resonance is also observed when the Josephson frequency is exactly half the lowest resonance frequency, which is beyond the simple model. A possible explanation is provided by a nonsinusoidal current-phase relation established under nonequilibrium conditions.
Amplitude control of the spin-triplet supercurrent in S/F/S Josephson junctions
Martinez, William M.; Pratt, Jr., W. P.; Birge, Norman O.
2016-02-17
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 supercurrentmore » in the three samples that have been studied so far. In conclusion, 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”.« less
Josephson critical current of long SNS junctions in the presence of a magnetic field
NASA Astrophysics Data System (ADS)
Meier, Hendrik; Fal'Ko, Vladimir I.; Glazman, Leonid I.
We evaluate the Josephson critical current of a long and wide two-dimensional superconductor-normal metal-superconductor (SNS) junction, taking into account the effect of electron reflection off the side edges of the junction. Considering clean junctions, we find that the effect of edges alters the usual Fraunhofer-like dependence of the Josephson critical current Ic on the magnetic flux Φ. At relatively weak fields, B <~Φ0 /W2 , the edge effect lifts zeros of the Ic (Φ) dependence and gradually shifts the maxima of that function by Φ0 / 2 . (Here W is the width of the junction and Φ0 the magnetic flux quantum.) At higher fields, B >~Φ0 /W2 , the edge effect leads to an accelerated decay of the critical current Ic (Φ) with increasing Φ. Our results are robust with respect to the roughness of realistic boundaries. Finally, we discuss the role of mesoscopic fluctuations of Ic (Φ) originating from the scattering off the edges, and compare our findings to recent experiments.
Traveling wave parametric amplifier with Josephson junctions using minimal resonator phase matching
White, T. C.; Mutus, J. Y.; Hoi, I.-C.; Barends, R.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Jeffrey, E.; Kelly, J.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; Martinis, John M.; Megrant, A.; Chaudhuri, S.; and others
2015-06-15
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.
Nb/InAs nanowire proximity junctions from Josephson to quantum dot regimes
NASA Astrophysics Data System (ADS)
Gharavi, Kaveh; Holloway, Gregory W.; LaPierre, Ray R.; Baugh, Jonathan
2017-02-01
The superconducting proximity effect is probed experimentally in Josephson junctions fabricated with InAs nanowires contacted by Nb leads. Contact transparencies t∼ 0.7 are observed. The electronic phase coherence length at low temperatures exceeds the channel length. However, the elastic scattering length is a few times shorter than the channel length. Electrical measurements reveal two regimes of quantum transport: (i) the Josephson regime, characterised by a dissipationless current up to ∼100 nA, and (ii) the quantum dot (QD) regime, characterised by the formation of Andreev bound states (ABS) associated with spontaneous QDs inside the nanowire channel. In regime (i), the behaviour of the critical current I c versus an axial magnetic field {B}| | shows an unexpected modulation and persistence to fields > 2 T. In the QD regime, the ABS are modelled as the current-biased solutions of an Anderson-type model. The applicability of devices in both transport regimes to Majorana fermion experiments is discussed.
Yokoyama, Tomohiro; Eto, Mikio; Nazarov, Yuli V.
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.
Traveling wave parametric amplifier with Josephson junctions using minimal resonator phase matching
NASA Astrophysics Data System (ADS)
White, T. C.; Mutus, J. Y.; Hoi, I.-C.; Barends, R.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Jeffrey, E.; Kelly, J.; Megrant, A.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; Chaudhuri, S.; Gao, J.; Martinis, John M.
2015-06-01
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.
Spin supercurrent, magnetization dynamics, and φ-state in spin-textured Josephson junctions
NASA Astrophysics Data System (ADS)
Kulagina, Iryna; Linder, Jacob
2014-08-01
The prospect of combining the dissipationless nature of superconducting currents with the spin polarization of magnetic materials is interesting with respect to exploring superconducting analogs of topics in spintronics. In order to accomplish this aim, it is pivotal to understand not only how such spin supercurrents can be created, but also how they interact dynamically with magnetization textures. In this paper, we investigate the appearance of a spin supercurrent and the resulting magnetization dynamics in a textured magnetic Josephson current by using three experimentally relevant models: (i) a superconductor∣ferromagnet∣superconductor (S∣F∣S) junction with spin-active interfaces, (ii) a S∣F1∣F2∣F3∣S Josephson junction with a ferromagnetic trilayer, and (iii) a Josephson junction containing a domain wall. In all of these cases, the supercurrent is spin polarized and exerts a spin-transfer torque on the ferromagnetic interlayers which causes magnetization dynamics. Using a scattering matrix formalism in the clean limit, we compute the Andreev bound states and resulting free energy of the system which in turn is used to solve the Landau-Lifshiftz-Gilbert equation. We compute both how the inhomogeneous magnetism influences the phase dependence of the charge supercurrent and the magnetization dynamics caused by the spin polarization of the supercurrent. Using a realistic experimental parameter set, we find that the spin supercurrent can induce magnetization switching that is controlled by the superconducting phase difference. Moreover, we demonstrate that the combined effect of chiral spin symmetry breaking of the system as a whole with interface scattering causes the systems above to act as phase batteries that may supply any superconducting phase difference φ in the ground state. Such a φ-junction is accompanied by an anomalous supercurrent appearing even at zero phase difference, and we demonstrate that the flow direction of this current is
High Density Planar High Temperature Superconducting Josephson Junctions Arrays
2006-09-01
material. We have found that a circuit fabrication technique pioneered in our lab during previous AFOSR funding periods can be used to fabricate arrays of...junctions fab- ricated from high temperature superconducting material. We have found that a circuit fabrication technique pioneered in our lab during...YBCO thin films. Initially films used were grown in the lab at UCSD using pulsed laser ab- lation. However since this technique is limited to producing
A 100 GHz Josephson mixer using resistively-shunted Nb tunnel junctions
NASA Technical Reports Server (NTRS)
Schoelkopf, R. J.; Phillips, T. G.; Zmuidzinas, J.
1993-01-01
The authors describe preliminary mixer results using resistively shunted Nb/AlO(x)/Nb tunnel junctions in a 100-GHz waveguide mixer mount. The mixer utilizes robust, lithographically defined devices which have nonhysteretic I-V curves. A receiver temperature of 390 K (DSB) has been obtained with a conversion loss of -6.5 dB. The receiver's behavior agrees qualitatively with the behavior predicted by the resistively shunted junction model. Substantial improvements in performance are expected with the use of better-optimized shunted junctions, and numerical simulations suggest that, if devices with higher ICRN (critical current-normal state resistance) products can be obtained, Josephson effect mixers could be competitive with SIS mixers at high frequencies.
Controlling the Phase of Ferromagnetic Josephson Junctions for Cryogenic Memory Applications
NASA Astrophysics Data System (ADS)
Niedzielski, Bethany; Gingrich, Eric; Glick, Joseph; Wang, Yixing; Miller, Don; Loloee, Reza; Pratt, William, Jr.; Birge, Norman
Josephson junctions containing ferromagnetic layers are currently of interest for use in cryogenic memory where either the phase or critical current can be switched between two distinct states. We present the first direct phase measurements of such a junction demonstrating control of the phase. If a junction contains one ferromagnetic layer, the thickness of that layer dictates the ground state phase between the superconducting electrodes, which can be either 0 or π. If the junction contains two ferromagnetic layers and the layer thicknesses are carefully chosen, then the phase of a single junction can be switched between 0 and π by changing the relative magnetization directions of the two layers from antiparallel to parallel. We have successfully fabricated and directly measured the relative phase of two such spin valve junctions in a SQUID loop to confirm the phase change from π to 0 and back again of each junction. We report our continued progress in optimizing the control of such systems. This work was supported by IARPA via ARO Contract W911NF-14-C-0115.
NASA Astrophysics Data System (ADS)
Chien, Wei-Chen; Lin, Kuan-Yu; Liou, Saxon; Ho, I.-Lin; Kuo, Watson
2017-04-01
We conduct microwave impedance measurements on a one-dimensional (1D) array of Josephson junctions to experimentally determine the Josephson inductance and shunt resistance of the constituent junctions. The effective Josephson energy provides an estimate of the environmental impedance, which is greatly increased due to phase fluctuations in the neighboring junctions. This enhancement is attributed to the charge solitons in the 1D system. In general, the environmental impedance is dominated by the junction’s normal resistance in the superconducting phase coherent regime, but overwhelmed by zero-bias resistance and differential resistance, respectively, in the Coulomb blockaded regime and in the phase fluctuating regime. The change in phase fluctuations owing to a dc bias agrees with the finite temperature phase diffusion model.
Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions
NASA Astrophysics Data System (ADS)
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.
Observation of 0–π transition in SIsFS Josephson junctions
Ruppelt, N. Vavra, O.; Kohlstedt, H.; Sickinger, H.; Menditto, R.; Goldobin, E.; Koelle, D.; Kleiner, R.
2015-01-12
The 0–π transition in Superconductor-Insulator-superconductor-Ferromagnet-Superconductor (SIsFS) Josephson junctions (JJs) was investigated experimentally. As predicted by theory, an s-layer inserted into a ferromagnetic SIFS junction can enhance the critical current density up to the value of an SIS tunnel junction. We fabricated Nb′ | AlO{sub x} | Nb | Ni{sub 60}Cu{sub 40} | Nb JJs with wedge-like s (Nb) and F (Ni{sub 60}Cu{sub 40}) layers and studied the Josephson effect as a function of the s- and F-layer thickness, d{sub s} and d{sub F}, respectively. For d{sub s} = 11 nm, π-JJs with SIFS-type j{sub c}(d{sub F}) and critical current densities up to j{sub c}{sup π}=60 A/cm{sup 2} were obtained at 4.2 K. Thicker d{sub s} led to a drastic increase of the critical current decay length, accompanied by the unexpected disappearance of the 0–π transition dip in the j{sub c}(d{sub F}) dependence. Our results are relevant for superconducting memories, rapid single flux quantum logic circuits, and solid state qubits.
Anomalous Fraunhofer interference in epitaxial superconductor-semiconductor Josephson junctions
NASA Astrophysics Data System (ADS)
Suominen, H. J.; Danon, J.; Kjaergaard, M.; Flensberg, K.; Shabani, J.; Palmstrøm, C. J.; Nichele, F.; Marcus, C. M.
2017-01-01
We investigate patterns of critical current as a function of perpendicular and in-plane magnetic fields in superconductor-semiconductor-superconductor (SNS) junctions based on InAs/InGaAs heterostructures with an epitaxial Al layer. This material system is of interest due to its exceptionally good superconductor-semiconductor coupling, as well as large spin-orbit interaction and g factor in the semiconductor. Thin epitaxial Al allows the application of large in-plane field without destroying superconductivity. For fields perpendicular to the junction, flux focusing results in aperiodic node spacings in the pattern of critical currents known as Fraunhofer patterns by analogy to the related interference effect in optics. Adding an in-plane field yields two further anomalies in the pattern. First, higher-order nodes are systematically strengthened, indicating current flow along the edges of the device, as a result of confinement of Andreev states driven by an induced flux dipole; second, asymmetries in the interference appear that depend on the field direction and magnitude. A model is presented, showing good agreement with experiment, elucidating the roles of flux focusing, Zeeman and spin-orbit coupling, and disorder in producing these effects.
Two-Point Phase Correlations of a One-Dimensional Bosonic Josephson Junction
Betz, T.; Manz, S.; Buecker, R.; Berrada, T.; Koller, Ch.; Schmiedmayer, J.; Kazakov, G.; Mazets, I. E.; Stimming, H.-P.; Perrin, A.; Schumm, T.
2011-01-14
We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable double well potential on an atom chip. Matter wave interferometry gives direct access to the relative phase field, which reflects the interplay of thermally driven fluctuations and phase locking due to tunneling. The thermal equilibrium state is characterized by probing the full statistical distribution function of the two-point phase correlation. Comparison to a stochastic model allows us to measure the coupling strength and temperature and hence a full characterization of the system.
NASA Astrophysics Data System (ADS)
Zemlyanaya, E. V.; Bashashin, M. V.; Rahmonov, I. R.; Shukrinov, Yu. M.; Atanasova, P. Kh.; Volokhova, A. V.
2016-10-01
We consider a model of system of long Josephson junctions (LJJ) with inductive and capacitive coupling. Corresponding system of nonlinear partial differential equations is solved by means of the standard three-point finite-difference approximation in the spatial coordinate and utilizing the Runge-Kutta method for solution of the resulting Cauchy problem. A parallel algorithm is developed and implemented on a basis of the MPI (Message Passing Interface) technology. Effect of the coupling between the JJs on the properties of LJJ system is demonstrated. Numerical results are discussed from the viewpoint of effectiveness of parallel implementation.
Granato, Enzo
2008-07-11
Phase coherence and vortex order in a Josephson-junction array at irrational frustration are studied by extensive Monte Carlo simulations using the parallel-tempering method. A scaling analysis of the correlation length of phase variables in the full equilibrated system shows that the critical temperature vanishes with a power-law divergent correlation length and critical exponent nuph, in agreement with recent results from resistivity scaling analysis. A similar scaling analysis for vortex variables reveals a different critical exponent nuv, suggesting that there are two distinct correlation lengths associated with a decoupled zero-temperature phase transition.
Unpaired Majorana modes in Josephson-Junction Arrays with gapless bulk excitations
Pino, M.; Tsvelik, A.; Ioffe, L. B.
2015-11-06
In this study, the search for Majorana bound states in solid-state physics has been limited to materials that display a gap in their bulk spectrum. We show that such unpaired states appear in certain quasi-one-dimensional Josephson-junction 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 a realistic set of parameters this energy splitting remains much smaller than the energy of the bulk eigenstates even for short chains of length L~10.
NASA Astrophysics Data System (ADS)
Mishra, Arindam; Saha, Suman; Hens, Chittaranjan; Roy, Prodyot K.; Bose, Mridul; Louodop, Patrick; Cerdeira, Hilda A.; Dana, Syamal K.
2017-01-01
An array of excitable Josephson junctions under a global mean-field interaction and a common periodic forcing shows the emergence of two important classes of coherent dynamics, librational and rotational motion, in the weaker and stronger coupling limits, respectively, with transitions to chimeralike states and clustered states in the intermediate coupling range. In this numerical study, we use the Kuramoto complex order parameter and introduce two measures, a libration index and a clustering index, to characterize the dynamical regimes and their transitions and locate them in a parameter plane.
Polaron effects on the dc- and ac-tunneling characteristics of molecular Josephson junctions
NASA Astrophysics Data System (ADS)
Wu, B. H.; Cao, J. C.; Timm, C.
2012-07-01
We study the interplay of polaronic effect and superconductivity in transport through molecular Josephson junctions. The tunneling rates of electrons are dominated by vibronic replicas of the superconducting gap, which show up as prominent features in the differential conductance for the dc and ac current. For relatively large molecule-lead coupling, a features that appears when the Josephson frequency matches the vibron frequency can be identified with an over-the-gap structure observed by Marchenkov [Nat. Nanotech. 1748-338710.1038/nnano.2007.2182, 481 (2007)]. However, we are more concerned with the weak-coupling limit, where resonant tunneling through the molecular level dominates. We find that certain features involving both Andreev reflection and vibron emission show an unusual shift of the bias voltage V at their maximum with the gate voltage Vg as V˜(2/3)Vg. Moreover, due to the polaronic effect, the ac Josephson current shows a phase shift of π when the bias eV is increased by one vibronic energy quantum ℏωv. This distinctive even-odd effect is explained in terms of the different sign of the coupling to vibrons of electrons and of Andreev-reflected holes.
Parametric amplification of vortex-antivortex pair generation in a Josephson junction
NASA Astrophysics Data System (ADS)
Berdiyorov, G. R.; Milošević, M. V.; Savel'ev, S.; Kusmartsev, F.; Peeters, F. M.
2014-10-01
Using advanced three-dimensional simulations, we show that an Abrikosov vortex, trapped inside a cavity perpendicular to an artificial Josephson junction, can serve as a very efficient source for generation of Josephson vortex-antivortex pairs in the presence of the applied electric current. In such a case, the nucleation rate of the pairs can be tuned in a broad range by an out-of-plane ac magnetic field in a broad range of frequencies. This parametrically amplified vortex-antivortex nucleation can be considered as a macroscopic analog of the dynamic Casimir effect, where fluxon pairs mimic the photons and the ac magnetic field plays the role of the oscillating mirrors. The emerging vortex pairs in our system can be detected by the pronounced features in the measured voltage characteristics, or through the emitted electromagnetic radiation, and exhibit resonant dynamics with respect to the frequency of the applied magnetic field. Reported tunability of the Josephson oscillations can be useful for developing high-frequency emission devices.
Local dissipation effects in two-dimensional quantum Josephson junction arrays with a magnetic field
Polak, T.P.; Kopec, T.K.
2005-07-01
We study the quantum phase transitions in two-dimensional arrays of Josephson-couples junctions with short range Josephson couplings (given by the Josephson energy E{sub J}) and the charging energy E{sub C}. We map the problem onto the solvable quantum generalization of the spherical model that improves over the mean-field theory method. The arrays are placed on the top of a two-dimensional electron gas separated by an insulator. We include effects of the local dissipation in the presence of an external magnetic flux f={phi}/{phi}{sub 0} in square lattice for several rational fluxes f=0,(1/2),(1/3),(1/4), and (1/6). We also have examined the T=0 superconducting-insulator phase boundary as a function of a dissipation {alpha}{sub 0} for two different geometry of the lattice: square and triangular. We have found a critical value of the dissipation parameter independent on geometry of the lattice and presence magnetic field.
NASA Astrophysics Data System (ADS)
Kawabata, Shiro; Kato, Takeo; Bauch, Thilo
2009-03-01
We investigate classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a Josephson junction coupled with an LC circuit theoretically. The TA and MQT escape rate are calculated analytically by taking into account the two-dimensional nature of the classical and quantum phase dynamics. We find that the MQT escape rate is largely suppressed by the coupling to the LC circuit. On the other hand, this coupling gives rise to slight reduction of the TA escape rate. These results are relevant for the interpretation of a recent experiment on the MQT and TA phenomena in grain boundary YBCO Josephson junctions.
Phase control of the spin-triplet state in S/F/S Josephson junctions
NASA Astrophysics Data System (ADS)
Gingrich, Eric C.
For decades, the proximity effect in superconductor/ferromagnetic (S/F) hybrid systems was thought to be very short-ranged, with coherence lengths on the order of a nanometer. That changed in 2003 when Bergeret et al. suggested systems involving s-wave superconductors and ferromagnets with non-collinear magnetizations could generate spin-triplet supercurrent. This was a significant prediction that radically changed the outlook for these systems, with the possibility of bringing the ferromagnetic coherence length up to ranges similar to the normal metal coherence length. With the experimental confirmation of the spin-triplet state in S/F/S Josephson junctions in 2010, the flood-gates opened into a range of interesting studies. We have performed measurements on the magnetic and superconducting properties of the multilayer Ni/[Co/Ni]n. This arrangement of ferromagnetic materials, when grown with thicknesses of 0.4 nm Ni and 0.2 nm Co, demonstrate a magnetization that lies perpendicular to the plane of the films. Because it will, in the virgin state, possess a non-collinear magnetization with ferromagnets which have magnetizations that lie within the plane, it is a convenient multilayer for the generation of spin-triplet supercurrent. Our measurements of S/F'/F/F'/S Josephson junctions, where F' is a hard ferromagnet and F is the Co/Ni multilayer, confirmed the presence of the spin-triplet state, and demonstrated the viability of the Co/Ni multilayer as a triplet generating ferromagnet. We have also performed studies on the characteristics of a number of soft ferromagnetic alloys. These alloys are important for their potential as a soft ferromagnetic switching layer for application in our triplet control devices. To that end, we have created sputtering targets for four different ferromagnetic alloys: Molybdenum-doped Permalloy, Niobium-doped Permalloy, Copper-doped Permalloy, and Palladium Iron. These studies have included: atomic concentration measurements using EDS
NASA Astrophysics Data System (ADS)
Otten, Daniel; Rubbert, Sebastian; Ulrich, Jascha; Hassler, Fabian
2016-09-01
Josephson junctions are the most prominent nondissipative and at the same time nonlinear elements in superconducting circuits allowing Cooper pairs to tunnel coherently between two superconductors separated by a tunneling barrier. Due to this, physical systems involving Josephson junctions show highly complex behavior and interesting novel phenomena. Here, we consider an infinite one-dimensional chain of superconducting islands where neighboring islands are coupled by capacitances. We study the effect of Josephson junctions shunting each island to a common ground superconductor. We treat the system in the regime where the Josephson energy exceeds the capacitive coupling between the islands. For the case of two offset charges on two distinct islands, we calculate the interaction energy of these charges mediated by quantum phase slips due to the Josephson nonlinearities. We treat the phase slips in an instanton approximation and map the problem onto a classical partition function of interacting particles. Using the Mayer cluster expansion, we find that the interaction potential of the offset charges decays with a universal inverse-square power-law behavior.
Phase slippage and self-trapping in a self-induced bosonic Josephson junction
Abad, M.; Guilleumas, M.; Mayol, R.; Pi, M.; Jezek, D. M.
2011-09-15
A dipolar condensate confined in a toroidal trap constitutes a self-induced Josephson junction when the dipoles are oriented perpendicularly to the trap symmetry axis and the s-wave scattering length is small enough. The ring-shaped double-well potential coming from the anisotropic character of the mean-field dipolar interaction is robust enough to sustain self-trapping dynamics, which takes place when the initial population imbalance between the two wells is large. We show that, in this system, the self-trapping regime is directly related to a vortex-induced phase-slip dynamics. A vortex and antivortex are spontaneously nucleated in the low-density regions before a minimum of the population imbalance is reached and then cross the toroidal section in opposite directions through the junctions. This vortex dynamics yields a phase slip between the two weakly linked condensates causing an inversion of the particle flux.
NASA Astrophysics Data System (ADS)
Park, Sunghun; Recher, Patrik
2015-12-01
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 e V =±(α -2 π l )ℏ/TJ, where α =π /2 is the exchange phase of the two circulating MBS, TJ is the half rotation time of MBS, and l an integer. This result constitutes a clear experimental signature of Majorana fermion exchange.
Numerical Study of a System of Long Josephson Junctions with Inductive and Capacitive Couplings
NASA Astrophysics Data System (ADS)
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.
Low frequency critical current noise and two level system defects in Josephson junctions
NASA Astrophysics Data System (ADS)
Nugroho, Christopher Daniel
The critical current in a Josephson junction is known to exhibit a 1/falpha low frequency noise. Implemented as a superconducting qubit, this low frequency noise can lead to decoherence. While the 1/f noise has been known to arise from an ensemble of two level systems connected to the tunnel barrier, the precise microscopic nature of these TLSs remain a mystery. In this thesis we will present measurements of the 1/f alpha low frequency noise in the critical current and tunneling resistance of Al-AlOx-Al Josephson junctions. Measurements in a wide range of resistively shunted and unshunted junctions confirm the equality of critical current and tunneling resistance noise. That is the critical current fluctuation corresponds to fluctuations of the tunneling resistance. In not too small Al-AlOx-Al junctions we have found that the fractional power spectral density scales linearly with temperature. We confirmed that the 1/falpha power spectrum is the result of a large number of two level systems modulating the tunneling resistance. At small junction areas and low temperatures, the number of thermally active TLSs is insufficient to integrate out a featureless 1/ f spectral shape. By analyzing the spectral variance in small junction areas, we have been able to deduce the TLS defect density, n ≈ 2.53 per micrometer squared per Kelvin spread in the TLS energy per factor e in the TLS lifetimes. This density is consistent with the density of tunneling TLSs found in glassy insulators, as well as the density deduced from coherent TLSs interacting at qubit frequencies. The deduced TLS density combined with the magnitude of the 1/f power spectral density in large area junctions, gives an average TLS effective area, A ˜ 0.3 nanometer squared. In ultra small tunnel junctions, we have studied the time-domain dynamics of isolated TLSs. We have found a TLS whose dynamics is described by the quantum tunneling between the two localized wells, and a one-phonon absorption
NASA Astrophysics Data System (ADS)
Guarcello, Claudio; Valenti, Davide; Spagnolo, Bernardo
2015-11-01
We study by numerical methods the phase dynamics in ballistic graphene-based short Josephson junctions. A superconductor-graphene-superconductor system exhibits superconductive quantum metastable states similar to those present in normal current-biased Josephson junctions. We investigate the effects of thermal and correlated fluctuations on the escape time from these metastable states, when the system is driven by an oscillating bias current in the presence of Gaussian white and colored noise sources. Varying the intensity and the correlation time of the noise source, it is possible to analyze the behavior of the escape time, or switching time, from a superconductive metastable state in different temperature regimes. Moreover, we are able to clearly distinguish dynamical regimes characterized by the dynamic resonant activation effect, in the absence of noise source, and the stochastic resonant activation phenomenon induced by the noise. For low initial values of the bias current, the dynamic resonant activation shows double-minimum structures, strongly dependent on the value of the damping parameter. Noise-enhanced stability is also observed in the system investigated. We analyze the probability density function (PDF) of the switching times. The PDFs for frequencies within the dynamic resonant activation minima are characterized by single peaks with exponential tails. The PDFs for noise intensities around the maxima of the switching time, peculiarity of the noise-enhanced stability phenomenon, are composed of regular sequences of two peaks for each period of the driving current, with exponentially decaying envelopes.
Quantum decay of the persistent current in a Josephson junction ring
NASA Astrophysics Data System (ADS)
Garanin, D. A.; Chudnovsky, E. M.
2016-03-01
We study the persistent current in a ring consisting of N ≫1 Josephson junctions threaded by the magnetic flux. When the dynamics of the ring is dominated by the capacitances of the superconducting islands the system is equivalent to the x y spin system in 1 +1 dimensions at the effective temperature T*=√{2 J U } , with J being the Josephson energy of the junction and U being the charging energy of the superconducting island. The numerical problem is challenging due to the absence of thermodynamic limit and slow dynamics of the Kosterlitz-Thouless transition. It is investigated on lattices containing up to ×106 sites. At T*≪J the quantum phase slips are frozen. The low-T* dependence of the persistent current computed numerically agrees quantitatively with the analytical formula provided by the spin-wave approximation. The high-T* behavior depends strongly on the magnetic flux and on the number of superconducting islands N . We present a detailed numerical study of the unbinding of vortex-antivortex pairs responsible for the phase slips, the superconductor-insulator transition, and evolution of the persistent current in a finite-size system.
Hydrogen-inclusion-induced variation of critical current in Nb-AlOx-Nb Josephson junctions
NASA Astrophysics Data System (ADS)
Hinode, Kenji; Satoh, Tetsuro; Nagasawa, Shuichi; Hidaka, Mutsuo
2008-07-01
The critical current density (Jc) of Nb-AlOx-Nb Josephson-junction (JJ) arrays was found to depend on their wiring structure. The Jc values of all JJs wired with a niobium electrode covered with a palladium layer increased by about 20%, while the Jc values of those with electrodes without palladium coverage stayed unchanged (except for that of the two junctions directly connected to the pads of an electrical probe covered with palladium.) To explain this Jc increase, we propose a "hydrogen mechanism," that is, the hydrogen inclusion into niobium electrodes occurs during fabrication, and its desorption occurs after fabrication. Hydrogen atoms incorporated in the electrodes are thought to influence the mechanical and the electronical properties of niobium, resulting in the deviation of critical current density. Hydrogen desorption analysis and measurements on niobium-film properties verified the occurrence of hydrogen incorporation into the niobium films during the fabrication process for superconducting JJ circuits. The incorporation and desorption processes were confirmed to proceed, even in air, if the niobium film is covered with palladium. As hydrogen diffuses quickly in niobium but stops in aluminum or aluminum oxide, differences in hydrogen concentration can happen within a circuit consisting of electrically connected multiple junctions. This hydrogen concentration difference can explain the observation that two junctions with increased Jc exist in the serial junction array without palladium coverage.
Backbending current-voltage characteristic for an annular Josephson junction in a magnetic field
NASA Astrophysics Data System (ADS)
Ustinov, Alexey V.; Malomed, Boris A.; Goldobin, Edward
1999-07-01
Excitation of the Josephson plasma radiation by a fluxon moving in an annular Josephson junction is studied experimentally, numerically, and using an analytical approach. An externally applied magnetic field H forms a cosinelike potential relief for the fluxon in a ring-shaped junction. The motion of the fluxon in the junction leads to an emission of plasma waves, which give rise to a resonance at a certain fluxon velocity. The experimental data agree well with numerical simulations which indicate a locking of the fluxon to the radiation frequency. The peculiar feature indicated by both experiment and numerical simulations is the shape of the resonance in the current-voltage (I-V) characteristic which shows a clear backbending, with a negative differential resistance. The analytical approach developed in this work is based on the perturbation theory for radiation emission generated by a kink in the perturbed sine-Gordon equation. To explain the observed effect, we introduce an addition to the perturbation theory, which proves to be crucial for explanation of the backbending I-V curves: We take into account the fact that the background radiation field, supported by a balance between emission from the moving kink and dissipative absorption, narrows the junction's plasma frequency gap. In the case when the emission has a resonant character, even a small change of the gap produces a strong reciprocal effect on the emission power. Following this idea, we develop a fully analytical self-consistent approximation that readily allows us to obtain the backbending I-V curves.
Fano-Josephson effect in the junction with DIII-class topological and s-wave superconductors
NASA Astrophysics Data System (ADS)
Jiang, Cui; Yi, Guang-Yu; Meng, Guang-Yi; Gong, Wei-Jiang
2017-04-01
We investigate the Josephson effects in the junction formed by the direct and indirect couplings between DIII-class topological and s-wave superconductors. As a result, the Josephson current is found to oscillate in period 2 π . The presence of Majorana doublet in the DIII-class superconductor renders the current finite at the case of zero phase difference, with its sign determined by the fermion parity of such a junction. In addition to the dot level and intradot Coulomb interaction, the Fano interference is an important factor to adjust the Josephson current. It is believed that these results will be helpful in understanding the transport properties of the DIII-class superconductor.
Current-voltage characteristics of tunnel Josephson junctions with a ferromagnetic interlayer
NASA Astrophysics Data System (ADS)
Vasenko, A. S.; Kawabata, S.; Golubov, A. A.; Kupriyanov, M. Yu.; Lacroix, C.; Bergeret, F. S.; Hekking, F. W. J.
2011-07-01
We present a quantitative study of the current-voltage characteristics (CVC) of diffusive superconductor/insulator/ferromagnet/superconductor (SIFS) tunnel Josephson junctions. In order to obtain the CVC we calculate the density of states (DOS) in the F/S bilayer for arbitrary length of the ferromagnetic layer, using quasiclassical theory. For a ferromagnetic layer thickness larger than the characteristic penetration depth of the superconducting condensate into the F layer, we find an analytical expression which agrees with the DOS obtained from a self-consistent numerical method. We discuss general properties of the DOS and its dependence on the parameters of the ferromagnetic layer. In particular we focus our analysis on the DOS oscillations at the Fermi energy. Using the numerically obtained DOS we calculate the corresponding CVC and discuss their properties. Finally, we use CVC to calculate the macroscopic quantum tunneling (MQT) escape rate for the current biased SIFS junctions by taking into account the dissipative correction due to the quasiparticle tunneling. We show that the influence of the quasiparticle dissipation on the macroscopic quantum dynamics of SIFS junctions is small, which is an advantage of SIFS junctions for superconducting qubits applications.
Josephson current in a graphene SG/ferromagnetic barrier/SG junction
NASA Astrophysics Data System (ADS)
Soodchomshom, Bumned; Tang, I.-Ming; Hoonsawat, Rassmidara
2008-12-01
The Josephson current passing through a SG1/FB/SG2 graphene junction, where SG and FB are those parts of a graphene layer which are induced into the superconducting state and into the ferromagnetic state, respectively, and where the small thickness of the FB layer L is studied. The ferromagnetic barrier strength is taken to be given by χH ∼ HL/ℏvF, where H is the strength of the exchange energy and vF ∼ 106m/s is the Fermi velocity of quasiparticles. The eigenstates of the relativistic quasiparticles in the graphene are taken to be the solutions of the Dirac Bogoliubov-de Gennes equations. It is found that the energy levels of the Andreev bound states for the Weyl-Dirac particles in the SG1/FB/SG2 junction are independent of the direction of the spins and that they depend on the strength of ferromagnetic barrier potential. The critical supercurrent is seen to vary in an oscillatory (periodic) manner as χH is varied. The oscillatory behavior of the critical supercurrent carried by the Cooper pairs formed by massless the Weyl-Dirac particles is different from the behavior of the supercurrent carried by the Cooper pairs formed by non-relativistic particles in a conventional SC/FI/SC (FI being a ferromagnetic insulator) junction. In those types of junctions, the supercurrent does not exhibit a similar oscillatory dependence.
Preparation of overdamped NbTiN Josephson junctions with bilayered Ti-TiN barriers
NASA Astrophysics Data System (ADS)
Yamamori, Hirotake; Sasaki, Hitoshi; Kohjiro, Satoshi
2010-12-01
Overdamped NbTiN Josephson junctions with Ti-TiN bilayered normal-metal barrier are proposed for metrological applications. Binary arrays consisting of 32 768 NbTiN/Ti-TiN/NbTiN junctions were fabricated for quantum voltage standards, and a Shapiro step at 1 V with the step height of about 0.5 mA was generated at around 8 K. The Ti layer was added to protect the base NbTiN electrode from nitrogen plasma during the deposition of the TiN layer. While the critical current Ic and the junction resistance Rn are mainly dominated by the thickness of the TiN barrier, Ic can be also adjusted by changing the thickness of the Ti barrier to maximize the operating margin for voltage standard circuits. An optimization of the NbTiN film in terms of film stress is also described for fabrication of circuits containing such a large number of junctions.
Sub-terahertz sound excitation and detection by a long Josephson junction
NASA Astrophysics Data System (ADS)
Koshelets, V. P.
2014-06-01
The paper reports on experimental observations of sub-terahertz sound wave generation and detection by a long Josephson junction. This effect was discovered in spectral measurements of sub-terahertz electromagnetic emission from a flux-flow oscillator (FFO) deposited on an optically polished Si substrate. The ‘back action’ of the acoustic waves generated by the FFO and reflected by the bottom surface of the Si substrate results in the appearance of resonant steps in the FFO IVCs with spacings as small as 29 nV for a 0.3 mm substrate thickness; these steps manifest themselves in a pronounced resonant structure in the emission spectra, with spacings of about 14 MHz, precisely according to the Josephson relation. The mechanism of acoustic wave generation and detection by the FFO is discussed; a possibility for employing the discovered effect for FFO frequency stabilization has been demonstrated. A simple and reliable way to suppress the superfine resonant structure has been developed and proved; this invention allows continuous frequency tuning and FFO phase locking at any desired frequency, all of which are vitally important for most applications.
Nb/InAs nanowire proximity junctions from Josephson to quantum dot regimes.
Gharavi, Kaveh; Holloway, Gregory W; LaPierre, Ray R; Baugh, Jonathan
2017-02-24
The superconducting proximity effect is probed experimentally in Josephson junctions fabricated with InAs nanowires contacted by Nb leads. Contact transparencies [Formula: see text] are observed. The electronic phase coherence length at low temperatures exceeds the channel length. However, the elastic scattering length is a few times shorter than the channel length. Electrical measurements reveal two regimes of quantum transport: (i) the Josephson regime, characterised by a dissipationless current up to ∼100 nA, and (ii) the quantum dot (QD) regime, characterised by the formation of Andreev bound states (ABS) associated with spontaneous QDs inside the nanowire channel. In regime (i), the behaviour of the critical current I c versus an axial magnetic field [Formula: see text] shows an unexpected modulation and persistence to fields [Formula: see text] T. In the QD regime, the ABS are modelled as the current-biased solutions of an Anderson-type model. The applicability of devices in both transport regimes to Majorana fermion experiments is discussed.
Effect of light irradiation on Fiske resonances and the Josephson effect in high-T{sub c} junctions
Elly, J.; Medici, M.G.; Gilabert, A.; Schmidl, F.; Seidel, P.; Hoffmann, A.; Schuller, I.K.
1997-10-01
We have performed photoexcitation experiments in high T{sub c} YBa{sub 2}Cu{sub 3}O{sub x} grain-boundary Josephson junctions. While the Josephson critical current is substantially enhanced, the normal state resistance decreases, and the positions of the extreme in the Fraunhofer diffraction pattern remain unchanged. These measurements show that the magnetic field penetration depth is not affected by light irradiation. On the other hand, the position and intensity of Fiske steps due to electromagnetic resonances increase substantially, which implies that the ratio of the thickness barrier to the dielectric constant changes by a factor of 2. {copyright} {ital 1997} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Rahmonov, I. R.; Shukrinov, Yu. M.; Atanasova, P. Kh.; Zemlyanaya, E. V.; Bashashin, M. V.
2017-01-01
We have studied the current-voltage characteristic of a system of long Josephson junctions taking into account the inductive and capacitive coupling. The dependence of the average time derivative of the phase difference on the bias current and spatiotemporal dependences of the phase difference and magnetic field in each junction are considered. The possibility of branching of the current-voltage characteristic in the region of zero field step, which is associated with different numbers of fluxons in individual Josephson junctions, is demonstrated. The current-voltage characteristic of the system of Josephson junctions is compared with the case of a single junction, and it is shown that the observed branching is due to coupling between the junctions. The intensity of electromagnetic radiation associated with motion of fluxons is calculated, and the effect of coupling between junctions on the radiation power is analyzed.
NASA Astrophysics Data System (ADS)
Barash, Yu. S.
2017-01-01
Superconductivity is shown to be completely destroyed in thin mesoscopic or nanoscopic rings closed by the junction with a noticeable interfacial pair breaking and/or a Josephson coupling, if a ring's radius r is less than the minimum radius rmin. The quantity rmin depends on the phase difference χ across the junction, or on the magnetic flux that controls χ in the flux-biased ring. It also depends on the Josephson and interfacial effective coupling constants, and in particular, on whether the ring is closed by the 0 or the π junction. The current-phase relation is substantially modified when the ring's radius exceeds rmin for some of the phase difference values, or slightly goes beyond its maximum. The modified critical temperature Tc and the temperature-dependent supercurrent near Tc are identified here as functions of the ring's radius and the magnetic flux.
NASA Astrophysics Data System (ADS)
Mélin, Régis; Caputo, Jean-Guy; Yang, Kang; Douçot, Benoît
2017-02-01
A three-terminal Josephson junction consists of three superconductors coupled coherently to a small nonsuperconducting island, such as a diffusive metal, a single or double quantum dot. A specific resonant single quantum dot three-terminal Josephson junction (Sa,Sb,Sc) biased with voltages (V ,-V ,0 ) is considered, but the conclusions hold more generally for resonant semiconducting quantum wire setups. A simple physical picture of the steady state is developed, using Floquet theory. It is shown that the equilibrium Andreev bound states (for V =0 ) evolve into nonequilibrium Floquet-Wannier-Stark-Andreev (FWS-Andreev) ladders of resonances (for V ≠0 ). These resonances acquire a finite width due to multiple Andreev reflection (MAR) processes. We also consider the effect of an extrinsic linewidth broadening on the quantum dot, introduced through a Dynes phenomenological parameter. The dc-quartet current manifests a crossover between the extrinsic relaxation dominated regime at low voltage to an intrinsic relaxation due to MAR processes at higher voltage. Finally, we study the coupling between the two FWS-Andreev ladders due to Landau-Zener-Stückelberg transitions, and its effect on the crossover in the relaxation mechanism. Three important low-energy scales are identified, and a perspective is to relate those low-energy scales to a recent noise cross-correlation experiment (Y. Cohen et al., arXiv:1606.08436).
Quantum vortices near the superconductor-insulator transition in Josephson junction arrays
NASA Astrophysics Data System (ADS)
van Otterlo, Anne; Fazio, Rosario; Scho¨n, Gerd
1994-02-01
We investigate the properties of vortices in Josephson junction arrays in the regime close to the superconductor-insulator transition. We derive general expressions for the vortex mass and the vortex-spinwave coupling in terms of the charge-charge correlation function, which we evaluate in a self consistent harmonic approximation, as well as by means of Monte Carlo simulations. Our main conclusions are that close to the transition to the insulating phase the vortex mass vanishes and the threshold velocity above which vortices couple to spinwaves diverges. Thus, in the quantum regime close to the phase transition there is a velocity window in which vortices may move ballistically without damping, this in contrast to the flux flow behaviour in classical arrays.
Autonomous quantum refrigerator in a circuit QED architecture based on a Josephson junction
NASA Astrophysics Data System (ADS)
Hofer, Patrick P.; Perarnau-Llobet, Martí; Brask, Jonatan Bohr; Silva, Ralph; Huber, Marcus; Brunner, Nicolas
2016-12-01
An implementation of a small quantum absorption refrigerator in a circuit QED architecture is proposed. The setup consists of three harmonic oscillators coupled to a Josephson junction. The refrigerator is autonomous in the sense that it does not require any external control for cooling, but only thermal contact between the oscillators and heat baths at different temperatures. In addition, the setup features a built-in switch, which allows the cooling to be turned on and off. If timing control is available, this enables the possibility for coherence-enhanced cooling. Finally, we show that significant cooling can be achieved with experimentally realistic parameters and that our setup should be within reach of current technology.
Effects of a rotating magnetization on pair correlations in a ballistic regime Josephson Junction
NASA Astrophysics Data System (ADS)
Bill, Andreas; Leal, Luis
Pair correlations in clean superconducting-magnetic proximity systems are studied with a focus on the singlet-triplet mixing resulting from magnetic inhomogeneities. The system is modeled in the clean limit using a tight-binding Hamiltonian and the Bogoliubov -de Gennes equations are solved to determine the Gor'kov functions of the system. Three different magnetic configurations are considered: an exchange spring, a helical magnet, and misaligned homogeneous ferromagnetic layers; each is sandwiched between two superconductors to form a Josephson junction. The goal of the study is to revisit how pair correlations are affected by different magnetization configurations and magnitudes in the clean limit. We discuss our results in the light of those obtained in the diffusive regime. We gratefully acknowledge support from the National Science Foundation under Grant DMR- 1309341 and the ORSP Student Research Assistantship at CSU Long Beach.
Role of aperiodic order for fluxon dynamics in Josephson junction arrays
NASA Astrophysics Data System (ADS)
Lennholm, Erik; Hörnquist, Michael
1999-01-01
We perform numerical simulations of a kink-shaped soliton, a fluxon, propagating in arrays of Josephson junctions ordered according to the period-doubling sequence, the Fibonacci sequence, the paper-folding sequence, the Rudin-Shapiro sequence, and the Thue-Morse sequence. The equation of motion is the discrete sine-Gordon equation with additional terms describing dissipation and an injected bias current. With the use of an effective potential we explain the behavior of the fluxon when it gets pinned in different arrays. The potential also gives a qualitative understanding of the deviation of the velocity of a propagating fluxon compared with an earlier obtained formula. It turns out that the self-similarity of the underlying sequences is important for the detailed dynamics, but not for the speed of a propagating fluxon. Finally, we show how this effective potential can be used to arrange an array to have some desired properties.
NASA Astrophysics Data System (ADS)
Mutus, J.; White, T.; Hoi, I.-C.; Barends, R.; Campbell, B.; Chen, Y.; Chen, Z.; Chiaro, B.; Fowler, A.; Dunsworth, A.; Jeffrey, E.; Kelly, J.; Megrant, A.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Quintana, C.; Sank, D.; Vainsencher, A.; Wenner, J.; Gao, J.; Chaudhuri, S.; Cleland, A. N.; Martinis, J. M.
2015-03-01
Travelling wave parametric amplifiers (TWPAs) promise wide-band performance with high saturation power for amplifying microwave frequency signals. Designing a TWPA requires a careful balance of many parameters in order to approach quantum-limited noise performance with sufficient gain and saturation power. We present a design 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 maintain the phase matching condition between pump, signal and idler in order to increase gain. The design and performance of the device will be presented, demonstrating high-gain, wide bandwidth and high dynamic range.
Large Tunable Thermophase in Superconductor – Quantum Dot – Superconductor Josephson Junctions
Kleeorin, Yaakov; Meir, Yigal; Giazotto, Francesco; Dubi, Yonatan
2016-01-01
In spite of extended efforts, detecting thermoelectric effects in superconductors has proven to be a challenging task, due to the inherent superconducting particle-hole symmetry. Here we present a theoretical study of an experimentally attainable Superconductor – Quantum Dot – Superconductor (SC-QD-SC) Josephson Junction. Using Keldysh Green’s functions we derive the exact thermo-phase and thermal response of the junction, and demonstrate that such a junction has highly tunable thermoelectric properties and a significant thermal response. The origin of these effects is the QD energy level placed between the SCs, which breaks particle-hole symmetry in a gradual manner, allowing, in the presence of a temperature gradient, for gate controlled appearance of a superconducting thermo-phase. This thermo-phase increases up to a maximal value of ±π/2 after which thermovoltage is expected to develop. Our calculations are performed in realistic parameter regimes, and we suggest an experimental setup which could be used to verify our predictions. PMID:27734919
Flux flow and vortex tunneling in two-dimensional arrays of small Josephson junctions
Chen, C.D.; Delsing, P.; Haviland, D.B.; Harada, Y.; Claeson, T.
1996-10-01
We have measured the temperature dependence and magnetic field dependence of the zero-bias resistance ({ital R}{sub 0}) as well as the current-voltage ({ital I}-{ital V}) characteristics for several two-dimensional arrays of small aluminum Josephson junctions. {ital R}{sub 0}({ital T}) decreases with decreasing temperature, which can be described in terms of two types of vortex motion: flux, flow, and vortex tunneling. At temperatures higher than the Kosterlitz-Thouless transition temperature ({ital T}{gt}{ital T}{sub {ital c}}) or at a bias current greater than the current corresponding to the onset of the nonlinear {ital I}-{ital V} characteristics ({ital I}{gt}{ital I}{sub {ital d}}), the effective damping resistance which characterizes flux-flow motion is found to be approximately equal to the junction normal-state resistance {ital R}{sub {ital N}}. At low temperatures and at small bias current, {ital R}{sub 0} is temperature independent and remains finite down to our minimum attainable temperature. This finite resistance is found to be dependent on the array size as well as the junction parameters. {copyright} {ital 1996 The American Physical Society.}
Low temperature properties of spin filter NbN/GdN/NbN Josephson junctions
NASA Astrophysics Data System (ADS)
Massarotti, D.; Caruso, R.; Pal, A.; Rotoli, G.; Longobardi, L.; Pepe, G. P.; Blamire, M. G.; Tafuri, F.
2017-02-01
A ferromagnetic Josephson junction (JJ) represents a special class of hybrid system where different ordered phases meet and generate novel physics. In this work we report on the transport measurements of underdamped ferromagnetic NbN/GdN/NbN JJs at low temperatures. In these junctions the ferromagnetic insulator gadolinium nitride barrier generates spin-filtering properties and a dominant second harmonic component in the current-phase relation. These features make spin filter junctions quite interesting also in terms of fundamental studies on phase dynamics and dissipation. We discuss the fingerprints of spin filter JJs, through complementary transport measurements, and their implications on the phase dynamics, through standard measurements of switching current distributions. NbN/GdN/NbN JJs, where spin filter properties can be controllably tuned along with the critical current density (Jc), turn to be a very relevant term of reference to understand phase dynamics and dissipation in an enlarged class of JJs, not necessarily falling in the standard tunnel limit characterized by low Jc values.
NASA Astrophysics Data System (ADS)
Choudhari, Tarun; Deo, Nivedita
2017-01-01
A superconductor-topological insulator-superconductor (S/TI/S) junction having normal region at angle θ is studied theoretically to investigate the junction angle dependency of the Andreev reflection and the formation of the Andreev bound states in the step and planar S/TI/S structures. It is found that the Andreev reflection becomes θ dependent only in the presence of the potential barrier at the TI/S interface. In particular, the step and planar TI/S junction have totally different conductive behavior with bias voltage and potential barrier in the regime of retro and specular Andreev reflection. Interestingly, we find that the elliptical cross section of Dirac cone, an important feature of topological insulator with step surface defect, affects the Fabry-Perot resonance of the Andreev reflection induced Andreev bound states (which become Majorana zero energy states at low chemical potential) in the step S/TI/S structure. Unlike the usual planar S/TI/S structures, we find these ellipticity affected Andreev bound states lead to non-monotonic Josephson super-current in the step S/TI/S structure whose non-monotonicity can be controlled with the use of the potential barrier, which may find applications in nanoelectronics.
Coherent Charge Transport in Ballistic InSb Nanowire Josephson Junctions
Li, S.; Kang, N.; Fan, D. X.; Wang, L. B.; 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 evidence for phase-coherent, ballistic charge transport through the nanowires in the junctions. We demonstrate that our devices show gate-tunable proximity-induced supercurrent and clear signatures of multiple Andreev reflections in the differential conductance, indicating phase-coherent transport within the junctions. We also observe periodic modulations of the critical current that can be associated with the Fabry-Pérot interference in the nanowires in the ballistic transport regime. Our work shows that the InSb nanowires grown by molecular-beam epitaxy are of excellent material quality and hybrid superconducting devices made from these nanowires are highly desirable for investigation of the novel physics in topological states of matter and for applications in topological quantum electronics. PMID:27102689
NASA Astrophysics Data System (ADS)
Rangel, Rafael; Negruz, Marcos
2016-04-01
In this work, we derive an analytical procedure that allows us to write the multidimensional washboard ratchet potential (MDWBP) U f for a two-dimensional Josephson junction array. The array has an applied perpendicular magnetic field. The magnetic field is given in units of the quantum flux per plaquette or frustration of the form {f}=\\frac{{M}}{{N}}[{{{Φ }}}0], where Φ0 is the flux quantum. The derivation is done under the assumption that the checkerboard pattern ground state or unit cell of a two-dimensional Josephson junction array is preserved under current biasing. The resistively and capacitively shunted Josephson junction model with a white noise term describes the dynamics for each junction in the array. The multidimensional potential is the unique expression of the collective effects that emerge from the array in contrast to the single junction. The first step in the procedure is to write the equation for the phases for the unit cell. In doing this, one takes into account the constraints imposed for the gauge invariant phases due to frustration. Second, and the key idea of the procedure, is to perform a variable transformation from the original systems of stochastic equations to a system of variables where the condition for the equality of mixed second partial happens. This is achieved via Poincaré's theorem for differential forms. In this way, we find to a nonlinear matrix equation (equation (9) in the text), that permits us to find the new coordinate variables x f where the potential exists. The transformation matrix also permits the correct transformation of the original white noise terms of each junction to the intensities in the x f variables. The commensurate symmetries of the ground state pinned vortex lattice leads to discrete symmetries to the part of the washboard potential that does not contain a tilt due to the external bias current (equation (11) in the text). In this work we apply the procedure for the important cases f=\\frac{1
NASA Astrophysics Data System (ADS)
Bellver, Fernando Gimeno; Garratón, Manuel Caravaca; Soto Meca, Antonio; López, Juan Antonio Vera; Guirao, Juan L. G.; Fernández-Martínez, Manuel
In this paper, we explore the chaotic behavior of resistively and capacitively shunted Josephson junctions via the so-called Network Simulation Method. Such a numerical approach establishes a formal equivalence among physical transport processes and electrical networks, and hence, it can be applied to efficiently deal with a wide range of differential systems. The generality underlying that electrical equivalence allows to apply the circuit theory to several scientific and technological problems. In this work, the Fast Fourier Transform has been applied for chaos detection purposes and the calculations have been carried out in PSpice, an electrical circuit software. Overall, it holds that such a numerical approach leads to quickly computationally solve Josephson differential models. An empirical application regarding the study of the Josephson model completes the paper.
NASA Astrophysics Data System (ADS)
Gong, Wei-Jiang; Gao, Zhen; Shan, Wan-Fei; Yi, Guang-Yu
2016-03-01
One Majorana doublet can be realized at each end of the time-reversal-invariant Majorana nanowires. We investigate the Josephson effect in the Majorana-doublet-presented junction modified by different inter-doublet coupling manners. It is found that when the Majorana doublets couple indirectly via a non-magnetic quantum dot, only the normal Josephson effect occurs, and the fermion parity in the system just affects the current direction and amplitude. However, one magnetic field applied on the dot can induce the fractional Josephson effect in the odd-parity case. Next if the direct and indirect couplings between the Majorana doublets coexist, no fractional Josephson effect takes place, regardless of the presence of magnetic field. Instead, there almost appears the π-period-like current in some special cases. All the results are clarified by analyzing the influence of the fermion occupation in the quantum dot on the parity conservation in the whole system. We ascertain that this work will be helpful for describing the dot-assisted Josephson effect between the Majorana doublets.
NASA Astrophysics Data System (ADS)
Ngabonziza, Prosper; Stehno, Martin, P.; Myoren, Hiroaki; Brinkman, Alexander
In recent years, extensive efforts have been made to improve the coupling between topological insulators and s-wave superconductors in topological insulator Josephson devices (TIJDs). Despite significant progress, essential questions remain open such as the bulk contribution to the Josephson critical current or the existence (and number) of 4 π -periodic bound states (Majoranas) in TIJDs. To address these issues, we fabricated Nb/Bi2Te3/Nb Josephson junctions alongside Hall bar devices on MBE-grown Bi2Te3 topological insulator thin films. Using the SrTiO3 [111] substrate as a gate dielectric, we tuned the carrier density electrostatically and measured the Josephson supercurrent and the normal state transport properties of our thin film devices. We identify three gate voltage ranges with distinct behavior: A region of intermediate gate bias where the measured quantities change rapidly with the applied electric field, and two saturation regions for large bias of either polarity. We discuss carrier distribution and band alignment in the material as well as implications for the effective Josephson coupling in TIJDs. This work is financially supported by the Dutch Foundation for Fundamental Research on Matter (FOM), the Netherlands Organization for Scientific Research (NWO), and by the European Research Council (ERC).
YBa2Cu3O7 Nanowire Josephson Junctions Directly Written with a Focused Helium Ion Beam
NASA Astrophysics Data System (ADS)
Cybart, Shane A.; Cho, Ethan Y.; Zhou, Yuchao W.; Dynes, Robert C.
We will present electrical transport measurements for superconducting nanowire Josephson junctions with widths ranging between 500 to 25 nm. The junctions were fabricated by using a 500-pm diameter helium ion beam to pattern superconducting nanowires, into 25-nm thick YBa2Cu3O7 (YBCO) thin films. The key to this direct-write method is that irradiated regions of the YBCO turn insulating for moderate ion doses which allows for very fine features to be defined (~2 nm). Nanowire junctions were fabricated with the length of the nanowire oriented along different crystallographic directions in the a - b plane. They exhibit a large increase in the anisotropy of the Josephson critical current and voltage state conductance as the nanowire width is decreased. In the narrowest of wires, the conductance changes by an order of magnitude. We interpret these observations to be due to the Josephson junctions being smaller than the granularity of the films. Measuring these single grains reveals characteristics of the a - b plane d-wave symmetry of superconductivity in YBCO. This work is funded by AFOSR.
Structural and intrinsic Josephson properties of Bi2Sr2Ca1-yYyCu2O8+δ single crystal
NASA Astrophysics Data System (ADS)
Yamaki, K.; Murata, K.; Irie, A.
2016-10-01
In this study, Bi2Sr2Ca1-yYyCu2O8+δ (BSCYCO) single crystals with yttrium doping content of y = 0-0.30 were synthesized by a self-flux method. The critical temperature and c-axis lattice constant of BSCYCO were controlled by the substitution of yttrium at the calcium site. A 290 × 90 × 0.4 μm3 mesa structure was fabricated using photolithography and argon-ion milling. A multibranch structure in current-voltage characteristics was successfully observed for mesas of BSCYCO (y = 0-0.10). The critical current of intrinsic Josephson junctions (IJJs) in BSCYCO mesas was systematically investigated.
Intrinsic Josephson properties in Pb1-ySr2Y1-xCaxCu2+yO7+δ epitaxial films
NASA Astrophysics Data System (ADS)
Komori, Sachio; Kakeya, Itsuhiro
2014-12-01
We report the first observation of intrinsic Josephson junction (IJJ) characteristics in the Pb1-ySr2Y1-xCaxCu2+yO7+δ (Pb1212) epitaxial film. Pb1212 epitaxial film has been grown on SrTiO3 (100) substrates by a two-step growth technique. A small mesa structure (S = 4μm2) has been fabricated on a film surface using a standard photolithography and an Ar ion milling technique. The superconducting transition temperature of the IJJ is 43 K. At 4.2 K, the value of Jc (the critical current density) is 2.2 kA/cm2. The depth of the hysteresis defined as α = (Jc+Jr)/ Jc is 0.89, where Jr is the return current density. The temperature dependence of Jc shows good agreement with Ambegaokar-Baratoff theory.
Side Gate Tunable Josephson Junctions at the LaAlO3/SrTiO3 Interface
2017-01-01
Novel physical phenomena arising at the interface of complex oxide heterostructures offer exciting opportunities for the development of future electronic devices. Using the prototypical LaAlO3/SrTiO3 interface as a model system, we employ a single-step lithographic process to realize gate-tunable Josephson junctions through a combination of lateral confinement and local side gating. The action of the side gates is found to be comparable to that of a local back gate, constituting a robust and efficient way to control the properties of the interface at the nanoscale. We demonstrate that the side gates enable reliable tuning of both the normal-state resistance and the critical (Josephson) current of the constrictions. The conductance and Josephson current show mesoscopic fluctuations as a function of the applied side gate voltage, and the analysis of their amplitude enables the extraction of the phase coherence and thermal lengths. Finally, we realize a superconducting quantum interference device in which the critical currents of each of the constriction-type Josephson junctions can be controlled independently via the side gates. PMID:28071920
Oelze, B.; Ruck, B.; Sodtke, E.; Kirichenko, A.F.; Kupriyanov, M.Y.; Prusseit, W.
1997-02-01
A 3 bit single flux quantum (SFQ) shift register based on high-T{sub c} bicrystal Josephson junctions has been designed, fabricated, and experimentally tested. The circuit consists of 26 bicrystal Josephson junctions and includes the shift register itself, two dc-SFQ converters, one readout superconducting quantum interference device, serving as a SFQ-dc converter, and three Josephson transmission lines. The correct operation of all circuit components has been demonstrated by low frequency testing at a temperature of 50 K. {copyright} {ital 1997 American Institute of Physics.}
Anodization-based process for the fabrication of all niobium nitride Josephson junction structures
Ottaviani, Ivano; Cirillo, Matteo; De Matteis, Fabio; Francini, Roberto; Merlo, Vittorio; Davoli, Ivan
2017-01-01
We studied the growth and oxidation of niobium nitride (NbN) films that we used to fabricate superconductive tunnel junctions. The thin films were deposited by dc reactive magnetron sputtering using a mixture of argon and nitrogen. The process parameters were optimized by monitoring the plasma with an optical spectroscopy technique. This technique allowed us to obtain NbN as well as good quality AlN films and both were used to obtain NbN/AlN/NbN trilayers. Lift-off lithography and selective anodization of the NbN films were used, respectively, to define the main trilayer geometry and/or to separate electrically, different areas of the trilayers. The anodized films were characterized by using Auger spectroscopy to analyze compounds formed on the surface and by means of a nano-indenter in order to investigate its mechanical and adhesion properties. The transport properties of NbN/AlN/NbN Josephson junctions obtained as a result of the above described fabrication process were measured in liquid helium at 4.2 K. PMID:28382243
NASA Astrophysics Data System (ADS)
Ebisu, Hiromi; Lu, Bo; Taguchi, Katsuhisa; Golubov, Alexander A.; Tanaka, Yukio
2016-01-01
We consider a superconducting nanowire proximity coupled to a superconductor/ferromagnet/superconductor (S/F/S) junction, where the magnetization penetrates into a superconducting segment in a nanowire decaying as ˜exp[-∣n/∣ ξ ] , where n is the site index and the ξ is the decay length. We tune chemical potential and spin-orbit coupling so that the topological superconducting regime hosting the Majorana fermion is realized for long ξ . We find that when ξ becomes shorter, zero energy state at the interface between a superconductor and a ferromagnet splits into two states at nonzero energy. Accordingly, the behavior of the Josephson current is drastically changed due to this "zero mode-nonzero mode crossover." By tuning the model parameters, we find an almost second-harmonic current-phase relation sin2 φ , where φ is the phase difference of the junction. Based on the analysis of Andreev bound state (ABS), we clarify that the current-phase relation is determined by coupling of the states within the energy gap. We find that the emergence of crossing points of ABS is a key ingredient to generate sin2 φ dependence in the current-phase relation. We further study both the energy and φ dependence of pair amplitudes in the ferromagnetic region. For large ξ , an odd-frequency spin-triplet s -wave component is dominant. The magnitude of the odd-frequency pair amplitude is enhanced at the energy level of ABS.
NASA Astrophysics Data System (ADS)
Ito, Hiroshi; Taniguchi, Soya; Ishikawa, Kouta; Akaike, Hiroyuki; Fujimaki, Akira
2017-03-01
Nb Josephson junctions (JJs) were fabricated with a Pd89Ni11 ferromagnetic interlayer and an AlO x tunnel barrier layer for use in large-scale superconducting integrated circuits. The junctions had a small critical current (I c) spread, where the standard deviation 1σ was less than 2% at 4.2 K for junctions with the same designed size. It was observed that the electrical behavior of the junctions could be controlled by manipulating the film thickness of the PdNi interlayer. The junctions behaved as a π-JJ for thicknesses of 9 and 11 nm, showing 1σ in the I c spread of 1.2% for 9 nm.
Baba, Shoji Sailer, Juergen; Deacon, Russell S.; Oiwa, Akira; Shibata, Kenji; Hirakawa, Kazuhiko; Tarucha, Seigo
2015-11-30
We report conductance and supercurrent measurements for InAs single and parallel double quantum dot Josephson junctions contacted with Nb or NbTiN superconducting electrodes. Large superconducting gap energy, high critical field, and large switching current are observed, all reflecting the features of Nb-based electrodes. For the parallel double dots, we observe an enhanced supercurrent when both dots are on resonance, which may reflect split Cooper pair tunneling.
NASA Astrophysics Data System (ADS)
Sergeenkov, S.; Rivera, V. A. G.; Marega, E.; Araujo-Moreira, F. M.
2011-06-01
We present recent results on the magnetic field dependence of current-voltage characteristics (CVC) for an artificially prepared two-dimensional array of unshunted Nb-AlO x-Nb Josephson junctions. The results obtained from the measured CVC and critical current IC(T,H) differential magnetoresistance (DMR) R(T,H)=[ of the array are found to exhibit behavior compatible with field induced Kosterlitz-Thouless transition describing unbinding of vortex-antivortex pairs under applied magnetic field.
Transport in arrays of submicron Josephson junctions over a ground plane
Ho, Teressa Rae
1997-12-01
One-dimensional (1D) and two-dimensional (2D) arrays of Al islands linked by submicron Al/Al_{x}O_{y}/Al tunnel junctions were fabricated on an insulating layer grown on a ground plane. The arrays were cooled to temperatures as low as 20 mK where the Josephson coupling energy E_{J} of each junction and the charging energy E_{C} of each island were much greater than the thermal energy k_{B}T. The capacitance C_{g} between each island and the ground plane was much greater than the junction capacitance C. Two classes of arrays were studied. In the first class, the normal state tunneling resistance of the junctions was much larger than the resistance quantum for single electrons, R_{N}>> R_{Qe}≡ h/e^{2} ~ 25.8 kΩ, and the islands were driven normal by an applied magnetic field such that E_{J} = 0 and the array was in the Coulomb blockade regime. The arrays were made on degenerately-doped Si, thermally oxidized to a thickness of approximately 100 nm. The current-voltage (I - V) characteristics of a 1D and a 2D array were measured and found to display a threshold voltage V_{T} below which little current flows. In the second class of arrays, the normal state tunneling resistance of the junctions was close to the resistance quantum for Cooper pairs, R_{N}≈R_{Q}≡h/4e^{2}≈6.45kΩ, such that E_{J}/E_{C}≈1. The arrays were made on GaAs/Al_{0.3}Ga_{0.7}As heterostructures with a two-dimensional electron gas approximately 100 nm below the surface. One array displayed superconducting behavior at low temperature. Two arrays displayed insulating behavior at low temperature, and the size of the Coulomb gap increased with increasing R_{g}.
An investigation of the SNS Josephson junction as a three-terminal device. Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Meissner, H.; Prans, G. P.
1973-01-01
A particular phenomenon of the SNS Josephson junction was investigated; i.e., control by a current entering the normal region and leaving through one of the superconducting regions. The effect of the control current on the junction was found to be dependent upon the ration of the resistances of the two halves of the N layer. A low frequency, lumped, nonlinear model was proposed to describe the electrical characteristics of the device, and a method was developed to plot the dynamic junction resistance as a function of junction current. The effective thermal noise temperature of the sample was determined. Small signal linearized analysis of the device suggests its use as an impedance transformer, although geometric limitations must be overcome. Linear approximation indicates that it is reciprocal and no power gain is possible. It is felt that, with suitable metallurgical and geometrical improvements, the device has promise to become a superconducting transistor.
NASA Astrophysics Data System (ADS)
Alidoust, Mohammad; Halterman, Klaus
2015-03-01
Using a spin-parameterized quasiclassical Keldysh-Usadel technique, we theoretically study supercurrent transport in several types of diffusive ferromagnetic (F)/superconducting (S) configurations with differing magnetization textures. We separate out the even- and odd-frequency components of the supercurrent within the low proximity limit and identify the relative contributions from the singlet and triplet channels. We first consider inhomogeneous one-dimensional Josephson structures consisting of a uniform bilayer magnetic S/F/F/S structure and a trilayer S/F/F/F/S configuration, in which case the outer F layers can have either a uniform or conical texture relative to the central uniform F layer. Our results demonstrate that for supercurrents flowing perpendicular to the F/F interfaces, incorporating a conical texture yields the most effective way to observe the signatures of long-ranged spin-triplet supercurrents. We also consider three different types of finite-sized two-dimensional magnetic structures subjected to an applied magnetic field normal to the junction plane: a S/F/S junction with uniform magnetization texture and two S/F/F/S configurations with differing F/F bilayer arrangements. In one case, the F/F interface is parallel with the S/F junction interfaces while in the other case, the F/F junction is oriented perpendicular to the S/F interfaces. We then discuss the proximity vortices and corresponding spatial maps of currents inside the junctions. For the uniform S/F/S junction, we analytically calculate the magnetic field induced supercurrent and pair potential in both the narrow and wide junction regimes, thus providing insight into the variations in the Fraunhofer diffraction patterns and proximity vortices when transitioning from a wide junction to a narrow one. Our extensive computations demonstrate that the induced long-range spin-triplet supercurrents can deeply penetrate uniform F/F bilayers when spin-singlet supercurrents flow parallel to the
Alidoust, Mohammad; Halterman, Klaus
2015-03-28
Using a spin-parameterized quasiclassical Keldysh-Usadel technique, we theoretically study supercurrent transport in several types of diffusive ferromagnetic (F)/superconducting (S) configurations with differing magnetization textures. We separate out the even- and odd-frequency components of the supercurrent within the low proximity limit and identify the relative contributions from the singlet and triplet channels. We first consider inhomogeneous one-dimensional Josephson structures consisting of a uniform bilayer magnetic S/F/F/S structure and a trilayer S/F/F/F/S configuration, in which case the outer F layers can have either a uniform or conical texture relative to the central uniform F layer. Our results demonstrate that for supercurrents flowing perpendicular to the F/F interfaces, incorporating a conical texture yields the most effective way to observe the signatures of long-ranged spin-triplet supercurrents. We also consider three different types of finite-sized two-dimensional magnetic structures subjected to an applied magnetic field normal to the junction plane: a S/F/S junction with uniform magnetization texture and two S/F/F/S configurations with differing F/F bilayer arrangements. In one case, the F/F interface is parallel with the S/F junction interfaces while in the other case, the F/F junction is oriented perpendicular to the S/F interfaces. We then discuss the proximity vortices and corresponding spatial maps of currents inside the junctions. For the uniform S/F/S junction, we analytically calculate the magnetic field induced supercurrent and pair potential in both the narrow and wide junction regimes, thus providing insight into the variations in the Fraunhofer diffraction patterns and proximity vortices when transitioning from a wide junction to a narrow one. Our extensive computations demonstrate that the induced long-range spin-triplet supercurrents can deeply penetrate uniform F/F bilayers when spin-singlet supercurrents flow parallel to the
Evidence for coherent quantum phase slips across a Josephson junction array
NASA Astrophysics Data System (ADS)
Manucharyan, Vladimir E.; Masluk, Nicholas A.; Kamal, Archana; Koch, Jens; Glazman, Leonid I.; Devoret, Michel H.
2012-01-01
Superconducting order in a sufficiently narrow and infinitely long wire is destroyed at zero temperature by quantum fluctuations, which induce 2π slips of the phase of the order parameter. However, in a finite-length wire, coherent quantum phase slips would manifest themselves simply as shifts of energy levels in the excitation spectrum of an electrical circuit incorporating this wire. The higher the phase slips' probability amplitude, the larger are the shifts. Phase slips occurring at different locations along the wire interfere with each other. Due to the Aharonov-Casher effect, the resulting full amplitude of a phase slip depends on the offset charges surrounding the wire. Slow temporal fluctuations of the offset charges make the phase-slip amplitudes random functions of time, and therefore turn energy level shifts into linewidths. We experimentally observed this effect on a long Josephson junction array acting as a “slippery” wire. The slip-induced linewidths, despite being only of order 100kHz, were resolved from the flux-dependent dephasing of the fluxonium qubit.
Cryogenic Memories based on Spin-Singlet and Spin-Triplet Ferromagnetic Josephson Junctions
NASA Astrophysics Data System (ADS)
Gingrich, Eric
The last several decades have seen an explosion in the use and size of computers for scientific applications. The US Department of Energy has set an ExaScale computing goal for high performance computing that is projected to be unattainable by current CMOS computing designs. This has led to a renewed interest in superconducting computing as a means of beating these projections. One of the primary requirements of this thrust is the development of an efficient cryogenic memory. Estimates of power consumption of early Rapid Single Flux Quantum (RSFQ) memory designs are on the order of MW, far too steep for any real application. Therefore, other memory concepts are required. S/F/S Josephson Junctions, a class of device in which two superconductors (S) are separated by one or more ferromagnetic layers (F) has shown promise as a memory element. Several different systems have been proposed utilizing either the spin-singlet or spin-triplet superconducting states. This talk will discuss the concepts underpinning these devices, and the recent work done to demonstrate their feasibility. This research is supported in part by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), via U.S. Army Research Office Contract W911NF-14-C-0115.
Anomalous transport effects on switching currents of graphene-based Josephson junctions
NASA Astrophysics Data System (ADS)
Guarcello, Claudio; Valenti, Davide; Spagnolo, Bernardo; Pierro, Vincenzo; Filatrella, Giovanni
2017-03-01
We explore the effect of noise on the ballistic graphene-based small Josephson junctions in the framework of the resistively and capacitively shunted model. We use the non-sinusoidal current–phase relation specific for graphene layers partially covered by superconducting electrodes. The noise induced escapes from the metastable states, when the external bias current is ramped, given the switching current distribution, i.e. the probability distribution of the passages to finite voltage from the superconducting state as a function of the bias current, that is the information more promptly available in the experiments. We consider a noise source that is a mixture of two different types of processes: a Gaussian contribution to simulate an uncorrelated ordinary thermal bath, and non-Gaussian, α-stable (or Lévy) term, generally associated to non-equilibrium transport phenomena. We find that the analysis of the switching current distribution makes it possible to efficiently detect a non-Gaussian noise component in a Gaussian background.
Anomalous transport effects on switching currents of graphene-based Josephson junctions.
Guarcello, Claudio; Valenti, Davide; Spagnolo, Bernardo; Pierro, Vincenzo; Filatrella, Giovanni
2017-03-01
We explore the effect of noise on the ballistic graphene-based small Josephson junctions in the framework of the resistively and capacitively shunted model. We use the non-sinusoidal current-phase relation specific for graphene layers partially covered by superconducting electrodes. The noise induced escapes from the metastable states, when the external bias current is ramped, given the switching current distribution, i.e. the probability distribution of the passages to finite voltage from the superconducting state as a function of the bias current, that is the information more promptly available in the experiments. We consider a noise source that is a mixture of two different types of processes: a Gaussian contribution to simulate an uncorrelated ordinary thermal bath, and non-Gaussian, α-stable (or Lévy) term, generally associated to non-equilibrium transport phenomena. We find that the analysis of the switching current distribution makes it possible to efficiently detect a non-Gaussian noise component in a Gaussian background.
NASA Astrophysics Data System (ADS)
Mélin, Régis; Feinberg, Denis; Douçot, Benoît
2016-03-01
In a transparent three-terminal Josephson junction, modeling nonequilibrium transport is numerically challenging, owing to the interplay between multiple Andreev reflection (MAR) thresholds and multipair resonances in the pair current. An approximate method, coined as "partially resummed perturbation theory in the number of nonlocal Green's functions", is presented that can be operational on a standard computer and demonstrates compatibility with results existing in the literature. In a linear structure made of two neighboring interfaces (with intermediate transparency) connected by a central superconductor, tunneling through each of the interfaces separately is taken into account to all orders. On the contrary, nonlocal processes connecting the two interfaces are accounted for at the lowest relevant order. This yields logarithmically divergent contributions at the gap edges, which are sufficient as a semi-quantitative description. The method is able to describe the current in the full two-dimensional voltage range, including commensurate as well as incommensurate values. The results found for the multipair (for instance quartet) current-phase characteristics as well as the MAR thresholds are compatible with previous results. At intermediate transparency, the multipair critical current is much larger than the background MAR current, which supports an experimental observation of the quartet and multipair resonances. The paper provides a proof of principle for addressing in the future the interplay between quasiparticles and multipairs in four-terminal structures.
Annealing of ion irradiated high T{sub C} Josephson junctions studied by numerical simulations
Sirena, M.; Matzen, S.; Bergeal, N.; Lesueur, J.; Faini, G.; Bernard, R.; Briatico, J.; Crete, D. G.
2009-01-15
Recently, annealing of ion irradiated high T{sub c} Josephson iunctions (JJs) has been studied experimentally in the perspective of improving their reproducibility. Here we present numerical simulations based on random walk and Monte Carlo calculations of the evolution of JJ characteristics such as the transition temperature T{sub c}{sup '} and its spread {delta}T{sub c}{sup '}, and compare them with experimental results on junctions irradiated with 100 and 150 keV oxygen ions, and annealed at low temperatures (below 80 deg. C). We have successfully used a vacancy-interstitial annihilation mechanism to describe the evolution of the T{sub c}{sup '} and the homogeneity of a JJ array, analyzing the evolution of the defects density mean value and its distribution width. The annealing first increases the spread in T{sub c}{sup '} for short annealing times due to the stochastic nature of the process, but then tends to reduce it for longer times, which is interesting for technological applications.
Döring, S. Monecke, M.; Schmidt, S.; Schmidl, F.; Tympel, V.; Seidel, P.; Engelmann, J.; Kurth, F.; Iida, K.; Holzapfel, B.; Haindl, S.; Mönch, I.
2014-02-28
We tested oxidized titanium layers as barriers for hybrid Josephson junctions with high I{sub c}R{sub n}-products and for the preparation of junctions for tunneling spectroscopy. For that we firstly prepared junctions with conventional superconductor electrodes, such as lead and niobium, respectively. By tuning the barrier thickness, we were able to change the junction's behavior from a Josephson junction to tunnel-like behavior applicable for quasi-particle spectroscopy. Subsequently, we transferred the technology to junctions using Co-doped BaFe{sub 2}As{sub 2} thin films prepared by pulsed laser deposition as base electrode and evaporated Pb as counter electrode. For barriers with a thickness of 1.5 nm, we observe clear Josephson effects with I{sub c}R{sub n}≈90 μV at 4.2 K. These junctions behave SNS'-like (SNS: superconductor-normal conductor-superconductor) and are dominated by Andreev reflection transport mechanism. For junctions with barrier thickness of 2.0 nm and higher, no Josephson but SIS'- (SIS: superconductor-insulator-superconductor) or SINS'-like (SINS: superconductor-normal conductor-insulator-superconductor) behavior with a tunnel-like conductance spectrum was observed.
NASA Astrophysics Data System (ADS)
Ruck, B.; Chong, Y.; Dittmann, R.; Engelhardt, A.; Sodtke, E.; Siegel, M.
1999-11-01
We have designed, fabricated and successfully tested a first-order delta-sigma modulator using a high-temperature superconducting multilayer technology with bicrystal Josephson junctions. The circuit has been fabricated on a SrTiO3 bicrystal substrate. The YBa2Cu3O7/SrTiO3/YBa2Cu3O7 trilayer was fabricated by laser deposition. The bottom layer served as a superconducting groundplane. The Josephson junctions were formed at the bicrystal line in the upper layer. The integrator resistance has been made from a Pd/Au thin film. The circuit consists of a dc-SFQ converter, a Josephson transmission line, a comparator, an L/R integrator and an output stage. The correct operation of the modulator has been tested using dc measurements. The linearity of the modulator was studied by measuring the harmonic distortions of a 19.5 kHz sine wave input signal. From the recorded spectrum, a minimum resolution of at least 5 bits can be estimated. This accuracy was limited by the noise of the preamplifier. The correct operation of the current feedback loop was demonstrated by cutting the feedback inductance.
NASA Astrophysics Data System (ADS)
Knipper, Richard; Anders, Solveig; Schubert, Marco; Peiselt, Katja; Scheller, Thomas; Franke, Dirk; Dellith, Jan; Meyer, Hans-Georg
2016-09-01
Josephson junctions generate, when subjected to microwave irradiation, voltages with a very high precision and are used in metrology applications. So-called PJVS (programmable Josephson voltage-standards) are capable of generating both AC and DC voltages of up to 10 V. Our work addresses a full fabrication scenario for 10 V PJVS arrays driven at 70 GHz to be used in low microwave-power conditions as in, but not limited to GUNN diodes or cryocooler applications. Nb x Si1-x in its function as a barrier material was characterised with AFM, RBS and reflectometry in order to establish a reliable technological foundation. A 10 V PJVS array driven with microwave power below 50 mW is further presented, which was achieved by optimising the fabrication technology regarding the degree of homogeneity of the Josephson junctions composition and thickness. Control over these parameters is crucial in choosing a stable and well-suited characteristic voltage (I c R n product) and critical current density j c. With this, a low-power operation of a PJVS array is possible without the need for liquid helium cooling, which is currently limiting the availability of PJVS based metrology.
NASA Astrophysics Data System (ADS)
Berdiyorov, Golibjon R.; Savel'ev, Sergey; Kusmartsev, Feodor V.; Peeters, François M.
2015-11-01
We use the anisotropic time-dependent Ginzburg-Landau theory to investigate the effect of a square array of out-of-plane magnetic dots on the dynamics of Josephson vortices (fluxons) in artificial stacks of superconducting-normal-superconducting (SNS) Josephson junctions in the presence of external DC and AC currents. Periodic pinning due to the magnetic dots distorts the triangular lattice of fluxons and results in the appearance of commensurability features in the current-voltage characteristics of the system. For the larger values of the magnetization, additional peaks appear in the voltage-time characteristics of the system due to the creation and annihilation of vortex-antivortex pairs. Peculiar changes in the response of the system to the applied current is found resulting in a "superradiant" vortex-flow state at large current values, where a rectangular lattice of moving vortices is formed. Synchronizing the motion of fluxons by adding a small ac component to the biasing dc current is realized. However, we found that synchronization becomes difficult for large magnetization of the dots due to the formation of vortex-antivortex pairs.
Preparation of multilayer films for integrated high- Tc SQUIDs with ramp-edge Josephson junctions
NASA Astrophysics Data System (ADS)
Adachi, S.; Hata, K.; Sugano, T.; Wakana, H.; Hato, T.; Tarutani, Y.; Tanabe, K.
2008-09-01
We proposed a novel multilayer structure having a new combination of oxides for integrated high- Tc SQUID with ramp-edge Josephson junctions. La 0.1Er 0.95Ba 1.95Cu 3O y (L1ErBCO) and SmBa 2Cu 3O y (SmBCO) were used as counter- and base-electrodes, respectively. An SrSnO 3 (SSO) layer was deposited as an insulating layer. Prior to deposition of SmBCO, Pr 1.4Ba 1.6Cu 2.6Ga 0.4O y (P4G4) and SSO were deposited on MgO (100) substrate in order to improve film quality of L1ErBCO/SSO/SmBCO layers. The black-colored P4G4 layer was expected to work as a temperature homogenizer over a whole substrate area during deposition of the upper layers. All the layers except L1ErBCO were deposited by an off-axis magnetron sputtering. An L1ErBCO layer was deposited by a pulsed laser deposition method. A thin Cu-poor L1ErBCO layer was initially deposited to form an adequate barrier on the ramp-edge of SmBCO. Gradiometer arrays having multilayered feedback coils and pickup loops were made in a chip and their proper operation at 77 K was confirmed. The present multilayer structure is promising for application to SQUIDs with more complicated designs.
Chen, C.D.; Delsing, P.; Haviland, D.B.; Harada, Y.; Claeson, T.
1995-06-01
We have studied the superconductor-insulator (SI) phase transition for two-dimensional (2D) arrays of small Josephson junctions in a weak magnetic field. The data were analyzed within the context of the theory of the magnetic-field-tuned SI transition in 2D superconductors. We show resistance scaling curves over several orders of magnitude for the 2D arrays. The critical exponent {ital z}{sub {ital B}} is determined to be 1.05, in good agreement with the theory. Moreover, the transverse (Hall) resistance at the critical field is found to be very small in comparison to the longitudinal resistance.
NASA Astrophysics Data System (ADS)
Kuo, Watson; Chen, C. D.
2003-03-01
We have studied experimentally the magnetic field induced superconductor-insulator quantum phase transition in one-dimensional arrays of small Josephson junctions. It is found that the critical magnetic field that separates the two phases corresponds to the onset of Coulomb blockade of Cooper pairs tunneling in the current-voltage characteristics. The resistance data are analyzed in the context of the superfluid-insulator transition in one dimension. Combining results from Haviland et. al.,2 we construct an experimental phase diagram using Josepshon coupling-to-charging energy ratio(EJ/ECP) and dissipation strength.
Chacón, Ricardo
2008-12-01
Optimal energy amplification via autoresonance in dissipative systems subjected to separatrix crossings is discussed through the universal model of a damped driven pendulum. Analytical expressions of the autoresonance responses and forces as well as the associated adiabatic invariants for the phase space regions separated by the underlying separatrix are derived from the energy-based theory of autoresonance. Additionally, applications to a single Josephson junction, topological solitons in Frenkel-Kontorova chains, as well as to the three-wave problem in dissipative media are discussed in detail from the autoresonance analysis.
NASA Astrophysics Data System (ADS)
Hikino, S.; Yunoki, S.
2015-07-01
We theoretically study the magnetization inside a normal metal induced in an s -wave superconductor/ferromagnetic metal/normal metal/ferromagnetic metal/s -wave superconductor (S /F 1 /N /F 2 /S ) Josephson junction. Using the quasiclassical Green's function method, we show that the magnetization becomes finite inside the N . The origin of this magnetization is due to odd-frequency spin-triplet Cooper pairs formed by electrons of equal and opposite spins, which are induced by the proximity effect in the S /F 1 /N /F 2 /S junction. We find that the magnetization M (d ,θ ) in the N can be decomposed into two parts, M (d ,θ ) =MI(d ) +MII(d ,θ ) , where θ is the superconducting phase difference between the two S s and d is the thickness of N . The θ -independent magnetization MI(d ) exists generally in S /F junctions, while MII(d ,θ ) carries all θ dependence and represents the fingerprint of the phase coherence between the two S s in Josephson junctions. The θ dependence thus allows us to control the magnetization in the N by tuning θ for a fixed d . We show that the θ -independent magnetization MI(d ) weakly decreases with increasing d , while the θ -dependent magnetization MII(d ,θ ) rapidly decays with d . Moreover, we find that the time-averaged magnetization
NASA Astrophysics Data System (ADS)
Jiang, Lei; Xu, Yong; Zhang, Chuanwei
2016-10-01
Atomtronics has the potential for engineering new types of functional devices, such as Josephson junctions (JJs). Previous studies have mainly focused on JJs whose ground states have zero or π superconducting phase difference across the junctions, while arbitrary phase-tunable JJs may have important applications in superconducting electronics and quantum computation. Here we show that a phase-tunable JJ can be implemented in a spin-orbit-coupled cold atomic gas with the magnetic tunneling barrier generated by a spin-dependent focused laser beam. We consider the JJ confined in either a linear harmonic trap or a circular ring trap. In the ring trap, the magnetic barrier induces a spontaneous mass current for the ground state of the JJ, demonstrating the magnetoelectric effects of cold atoms.
NASA Astrophysics Data System (ADS)
Zeng, Lunjie; Tran, Dung Trung; Tai, Cheuk-Wai; Svensson, Gunnar; Olsson, Eva
2016-07-01
Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.
NASA Astrophysics Data System (ADS)
Kurter, C.; Finck, A. D. K.; English, C. D.; Hor, Y. S.; van Harlingen, D. J.
2013-03-01
It is predicted that the presence of Majorana fermions manifests itself with a 4 π periodic current-phase relation (CPR) in planar Josephson junctions formed with topological weak links. To test this proposal, we have fabricated planar junctions by depositing Nb leads on exfoliated Bi2Se3 single crystals. The temperature and magnetic field dependence of the proximity-induced supercurrent have been examined in various doping regimes accessed via top gating. The critical current modulation with magnetic field deviates from the usual Fraunhofer diffraction pattern, suggesting modifications to a sinusoidal CPR consistent with a sin (2 ϕ) component. We are corroborating those results with direct measurements of the CPR using a phase-sensitive SQUID interferometry technique.
Zeng, Lunjie; Tran, Dung Trung; Tai, Cheuk-Wai; Svensson, Gunnar; Olsson, Eva
2016-07-12
Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.
Zeng, Lunjie; Tran, Dung Trung; Tai, Cheuk-Wai; Svensson, Gunnar; Olsson, Eva
2016-01-01
Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits. PMID:27403611
Amundsen, Morten; Ouassou, Jabir Ali; Linder, Jacob
2017-01-01
Multiterminal Josephson junctions have recently been proposed as a route to artificially mimic topological matter with the distinct advantage that its properties can be controlled via the superconducting phase difference, giving rise to Weyl points in 4-terminal geometries. A key goal is to accurately determine when the system makes a transition from a gapped to non-gapped state as a function of the phase differences in the system, the latter effectively playing the role of quasiparticle momenta in conventional topological matter. We here determine the proximity gap phase diagram of diffusive n-terminal Josephson junctions (), both numerically and analytically, by identifying a class of solutions to the Usadel equation at zero energy in the full proximity effect regime. We present an analytical equation which provides the phase diagram for an arbitrary number of terminals n. After briefly demonstrating the validity of the analytical approach in the previously studied 2- and 3-terminal cases, we focus on the 4-terminal case and map out the regimes where the electronic excitations in the system are gapped and non-gapped, respectively, demonstrating also in this case full agreement between the analytical and numerical approach. PMID:28094289
NASA Astrophysics Data System (ADS)
Amundsen, Morten; Ouassou, Jabir Ali; Linder, Jacob
2017-01-01
Multiterminal Josephson junctions have recently been proposed as a route to artificially mimic topological matter with the distinct advantage that its properties can be controlled via the superconducting phase difference, giving rise to Weyl points in 4-terminal geometries. A key goal is to accurately determine when the system makes a transition from a gapped to non-gapped state as a function of the phase differences in the system, the latter effectively playing the role of quasiparticle momenta in conventional topological matter. We here determine the proximity gap phase diagram of diffusive n-terminal Josephson junctions (), both numerically and analytically, by identifying a class of solutions to the Usadel equation at zero energy in the full proximity effect regime. We present an analytical equation which provides the phase diagram for an arbitrary number of terminals n. After briefly demonstrating the validity of the analytical approach in the previously studied 2- and 3-terminal cases, we focus on the 4-terminal case and map out the regimes where the electronic excitations in the system are gapped and non-gapped, respectively, demonstrating also in this case full agreement between the analytical and numerical approach.
NASA Astrophysics Data System (ADS)
Cho, Ethan; Ma, Meng; Huynh, Chuong; Pratt, Kevin; Paulson, Doug; Glyantsev, Victor; Dynes, Robert; Cybart, Shane
We will present electrical transport data for Y-Ba-Cu-O superconducting quantum interference devices (SQUIDs) with focused helium ion damage Josephson junctions. The junctions were directly written with a 30 keV focused helium ion beam, which locally creates disorder in Y-Ba-Cu-O that induces a superconducting-insulator transition. SQUIDs with Josephson junctions written with a dose of 4 ×1016 He+/cm2 have metallic barriers and show a current-voltage characteristic (I-V) well-described by the resistively shunted junction model. The spectral density of the flux noise is 10 μΦ0 / √ Hz at 10 Hz and the white noise at higher frequencies is 2 μΦ0 / √ Hz. SQUIDs with junctions written with higher ion doses (~ 9 ×1016 He+/cm2) have insulating Josephson barriers with a critical current of 22 μA and a resistance of 12 Ω at 4 K. The I-V for all of these devices is not hysteretic due to the small capacitance and the resistance. At higher voltage the junction I-V curve shows tunnel-junction behavior and a superconducting energy gap edge at 20 mV. We will discuss how these results are a promising step forward for sensitive magnetic sensors made from high temperature superconductors at various temperatures.
NASA Astrophysics Data System (ADS)
Masterov, D. V.; Parafin, A. E.; Revin, L. S.; Chiginev, A. V.; Skorokhodov, E. V.; Yunin, P. A.; Pankratov, A. L.
2017-02-01
YBa2Cu3O{}7-δ (YBCO) films were fabricated by magnetron sputtering with modification of the substrate surface by preliminary topology masks. Formation features of Josephson junctions on bicrystal Zr1-xYxO2 (YSZ) substrates have been considered. The structural and electrical properties of such junctions were investigated. As a result, the presented technology allows us to fabricate YBCO structures on YSZ substrates with a buffer cerium dioxide (CeO2) layer where YBCO film sputtering is the final stage of structure formation. In particular, long Josephson junctions with good characteristics have been fabricated by this technology and measured, allowing us to achieve critical currents of 80 mA for 150 um junctions.
2016-09-01
to the characteristics and extract the non-ideality. These capabilities and calibration results will assist in the characterization of advanced...superconductor-ionic quantum memory and computation devices. iv CONTENTS EXECUTIVE SUMMARY...Josephson effect makes these measurements useful for characterization and calibration of superconducting quantum memory and computational devices
Resonance tunneling of cooper pairs in a superconductor-polymer-superconductor josephson junction
Ionov, A. I.
2013-05-15
It is shown that the superconducting current flowing though a polymer in a superconductor-polymer-superconductor Josephson structure is due to resonant tunneling of Cooper pairs. The critical current and the thickness of the polymer in which the superconducting current is observed depend on the coherence length of a Cooper pair in the superconductor contacting the polymer.
NbN Josephson and Tunnel Junctions for Space THz Observation and Signal Processing
2005-07-13
jonctions Josephson en nitrures supraconducteurs (TiN et NbN) ; application à la logique RSFQ, Ph.D. thesis, SPSMS/LCP CEA - Grenoble and DEMIRM...Accepted for Publication in June 2005. [14] V. Larrey, Etude et réalisation de jonctions SIS à base de nitrure de niobium et d’une barrière tunnel
Cybart, Shane A; Anton, Steven; Wu, Stephen; Clarke, John; Dynes, Robert
2009-09-01
Very large scale integration of Josephson junctions in a two-dimensional series-parallel array has been achieved by ion irradiating a YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} film through slits in a nano-fabricated mask created with electron beam lithography and reactive ion etching. The mask consisted of 15,820 high-aspect ratio (20:1), 35-nm wide slits that restricted the irradiation in the film below to form Josephson junctions. Characterizing each parallel segment k, containing 28 junctions, with a single critical current I{sub ck} we found a standard deviation in I{sub ck} of about 16%.
Self-consistent study of the Josephson effect for SNS junction with mixed s + d-wave superconductors
NASA Astrophysics Data System (ADS)
Zheng, Zhiming; Zhang, Weiyi; Xing, D. Y.
1998-06-01
The quasiclassical theory has been applied to study the Josephson junction consisting of mixed s + d-wave superconductors. The order parameter and critical current are calculated selfconsistently for various d-wave ratio vd2 and relative crystal orientation angle θ of the two superconductors. It is found that both the magnitude and the form of critical current depend sensitively on vd2 and θ. For vd2 > 0.63, there always exists an angle θ where the current-phase relation I( fgf) has a period of π instead of 2π in conventional s-wave superconductors. Our result can be used to determine whether the high Tc superconductor is a pure d-wave or mixed s + d-wave superconductor.
NASA Astrophysics Data System (ADS)
Xiang, Shao-Hua; Zhao, Yu-Jing; Zhu, Xi-Xiang; Song, Ke-Hui
2015-08-01
We investigate the time evolutions of the continuous-variable entanglement and Gaussian quantum discord in a system consisting of a mesoscopic Josephson junction coupled to a single-mode optical cavity field. We can obtain the time-dependent covariance matrix using known symplectic operation and local canonical transformations. We compare the dynamics of Gaussian quantum discord with that of entanglement. It is shown that the entanglement dynamics of two-mode squeezed thermal state is richer and undergoes three different features: periodical oscillation, sudden death and revival, and no-creation of entanglement, conditioned on the average number of thermal photons in each mode, whereas the Gaussian quantum discord can only exhibit a periodical oscillation behavior during the evolution.
Holographic s-wave and p-wave Josephson junction with backreaction
NASA Astrophysics Data System (ADS)
Wang, Yong-Qiang; Liu, Shuai
2016-11-01
In this paper, we study the holographic models of s-wave and p-wave Josephoson junction away from probe limit in (3+1)-dimensional spacetime, respectively. With the backreaction of the matter, we obtained the anisotropic black hole solution with the condensation of matter fields. We observe that the critical temperature of Josephoson junction decreases with increasing backreaction. In addition to this, the tunneling current and condenstion of Josephoson junction become smaller as backreaction grows larger, but the relationship between current and phase difference still holds for sine function. Moreover, condenstion of Josephoson junction deceases with increasing width of junction exponentially.
Josephson-vortex Cherenkov radiation
Mints, R.G.; Snapiro, I.B.
1995-10-01
We predict the Josephson-vortex Cherenkov radiation of an electromagnetic wave. We treat a long one-dimensional Josephson junction. We consider the wavelength of the radiated electromagnetic wave to be much less than the Josephson penetration depth. We use for calculations the nonlocal Josephson electrodynamics. We find the expression for the radiated power and for the radiation friction force acting on a Josephson vortex and arising due to the Cherenkov radiation. We calculate the relation between the density of the bias current and the Josephson vortex velocity.
NASA Astrophysics Data System (ADS)
Kawabata, Shiro; Bauch, Thilo; Kato, Takeo
2009-11-01
We investigate classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a YBa2Cu3O7-δ (YBCO) Josephson junction coupled to an LC circuit theoretically. Due to the coupling between the junction and the LC circuit, the macroscopic phase dynamics can be described as the escape process of a fictitious particle with an anisotropic mass moving in a two-dimensional potential. We analytically calculate the escape rate including both the TA and MQT regime by taking into account the peculiar dynamical nature of the system. In addtion to large suppression of the MQT rate at zero temperature, we study details of the temperature dependence of the escape rate across a crossover region. These results are in an excellent agreement with recent experimental data for the MQT and TA rate in a YBCO biepitaxial Josephson junction. Therefore the coupling to the LC circuit is essential in understanding the macroscopic quantum dynamics and the qubit operation based on the YBCO biepitaxial Josephson junctions.
Josephson broadband spectroscopy to 1 THz
NASA Astrophysics Data System (ADS)
Edstam, J.; Olsson, H. K.
1994-05-01
We demonstrate the operation of a ``Josephson Broadband Spectrometer'' (JOBS) with a frequency range and bandwidth of 1 THz. The JOBS uses the inherent frequency tuning of the Josephson oscillations (f=2 eV/h) as a probe of the complex impedance environment, ZL(f), of the Josephson junction. Spectra taken of microstrip resonators (YBa2Cu3O7/SiO/Au) display up to nine harmonic resonances corresponding to a bandwidth of 1000 GHz. We find the surface resistance of YBa2Cu3O7 to scale as f2 over this frequency range, whereas the London penetration depth is frequency independent. The upper frequency limit of the measurement is set by the resonator loss whereas the JOBS presumably has an even larger intrinsic bandwidth.
Meng, Hao; Wu, Jiansheng; Wu, Xiuqiang; Ren, Mengyuan; Ren, Yajie
2016-01-01
The long-range spin-triplet supercurrent transport is an interesting phenomenon in the superconductor/ferromagnet () heterostructure containing noncollinear magnetic domains. Here we study the long-range superharmonic Josephson current in asymmetric junctions. It is demonstrated that this current is induced by spin-triplet pairs − or + in the thick layer. The magnetic rotation of the particularly thin layer will not only modulate the amplitude of the superharmonic current but also realise the conversion between − and + . Moreover, the critical current shows an oscillatory dependence on thickness and exchange field in the layer. These effect can be used for engineering cryoelectronic devices manipulating the superharmonic current. In contrast, the critical current declines monotonically with increasing exchange field of the layer, and if the layer is converted into half-metal, the long-range supercurrent is prohibited but still exists within the entire region. This phenomenon contradicts the conventional wisdom and indicates the occurrence of spin and charge separation in present junction, which could lead to useful spintronics devices. PMID:26892755
Josephson effects in a Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ break junction at 77 K
Zhao, S.P.; Tao, H.J.; Chen, Y.F.; Che, G.C.; Yang, Q.S.
1989-03-10
Josephson effects in a Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ break junction at 77 K are reported. The I-V characteristics show clear Shapiro steps under microwave radiation and magnetic dependence of the critical current is of the typical Fraunhofer diffraction pattern. Estimate of the magnetic penetration depth is given. Discussions of the I-V curve concerning nonstationary processes are presented.
Ginzburg, S. L.; Nakin, A. V.; Savitskaya, N. E.
2012-02-15
The theory of the bulk-SQUID effect in discrete superconductors is constructed for the first time. It is shown that the bulk-SQUID effect emerges in the system of 2D intrinsically stochastic multijunction SQUID (i.e., with random values of critical currents of the junctions, injection currents, and the coupling coefficients between the junction) due to generation frequency locking in all junctions. It is demonstrated that the bulk-SQUID effect occurs in a wide range of random parameters of the system. This domain of variation of the system parameters can be divided into three subdomains. The first one is the subdomain of coherent dynamics of phases at the junctions, the second is the subdomain of incoherent dynamics, in which the phases of the junctions are not locked, but the bulk-SQUID effect persists, and the third is the subdomain of transient dynamics, in which coherent dynamics and the bulk-SQUID effect are observed in parts. A simple mathematical model of noninteracting junctions, which correctly describes basic features of the dynamics of the initial system and makes it possible to calculate some of its statistical characteristics, is proposed and analyzed.
Closing the proximity gap in a metallic Josephson junction between three superconductors
NASA Astrophysics Data System (ADS)
Padurariu, C.; Jonckheere, T.; Rech, J.; Mélin, R.; Feinberg, D.; Martin, T.; Nazarov, Yu. V.
2015-11-01
We describe the proximity effect in a short disordered metallic junction between three superconducting leads. Andreev bound states in the multiterminal junction may cross the Fermi level. We reveal that for a quasicontinuous metallic density of states, crossings at the Fermi level manifest as a closing of the proximity-induced gap. We calculate the local density of states for a wide range of transport parameters using quantum circuit theory. The gap closes inside an area of the space spanned by the superconducting phase differences. We derive an approximate analytic expression for the boundary of the area and compare it to the full numerical solution. The size of the area increases with the transparency of the junction and is sensitive to asymmetry. The finite density of states at zero energy is unaffected by the electron-hole decoherence present in the junction, although decoherence is important at higher energies. Our predictions can be tested using tunneling transport spectroscopy. To encourage experiments, we calculate the current-voltage characteristic in a typical measurement setup. We show how the structure of the local density of states can be mapped out from the measurement.
Cybart, Shane A; Cho, E Y; Wong, T J; Wehlin, Björn H; Ma, Meng K; Huynh, Chuong; Dynes, R C
2015-07-01
Since the discovery of the high-transition-temperature superconductors (HTSs), researchers have explored many methods to fabricate superconducting tunnel junctions from these materials for basic science purposes and applications. HTS circuits operating at liquid-nitrogen temperatures (∼77 K) would significantly reduce power requirements in comparison with those fabricated from conventional superconductors. The difficulty is that the superconducting coherence length is very short and anisotropic in these materials, typically ∼2 nm in the a-b plane and ∼0.2 nm along the c axis. The electrical properties of Josephson junctions are therefore sensitive to chemical variations and structural defects on atomic length scales. To make multiple uniform HTS junctions, control at the atomic level is required. In this Letter we demonstrate all-HTS Josephson superconducting tunnel junctions created by using a 500-pm-diameter focused beam of helium ions to directly write tunnel barriers into YBa2Cu3O(7-δ) (YBCO) thin films. We demonstrate the ability to control the barrier properties continuously from conducting to insulating by varying the irradiation dose. This technique could provide a reliable and reproducible pathway for scaling up quantum-mechanical circuits operating at liquid-nitrogen temperatures, as well as an avenue to conduct novel planar superconducting tunnelling studies for basic science.
NASA Astrophysics Data System (ADS)
Cybart, Shane A.; Cho, E. Y.; Wong, T. J.; Wehlin, Björn H.; Ma, Meng K.; Huynh, Chuong; Dynes, R. C.
2015-07-01
Since the discovery of the high-transition-temperature superconductors (HTSs), researchers have explored many methods to fabricate superconducting tunnel junctions from these materials for basic science purposes and applications. HTS circuits operating at liquid-nitrogen temperatures (˜77 K) would significantly reduce power requirements in comparison with those fabricated from conventional superconductors. The difficulty is that the superconducting coherence length is very short and anisotropic in these materials, typically ˜2 nm in the a-b plane and ˜0.2 nm along the c axis. The electrical properties of Josephson junctions are therefore sensitive to chemical variations and structural defects on atomic length scales1. To make multiple uniform HTS junctions, control at the atomic level is required. In this Letter we demonstrate all-HTS Josephson superconducting tunnel junctions created by using a 500-pm-diameter focused beam of helium ions to directly write tunnel barriers into YBa2Cu3O7-δ (YBCO) thin films. We demonstrate the ability to control the barrier properties continuously from conducting to insulating by varying the irradiation dose. This technique could provide a reliable and reproducible pathway for scaling up quantum-mechanical circuits operating at liquid-nitrogen temperatures, as well as an avenue to conduct novel planar superconducting tunnelling studies for basic science.
Intrinsic Josephson Junctions in the Superconducting Compound Fe (Se_{1-x }Tex )y
NASA Astrophysics Data System (ADS)
Ionov, Aleksander N.; Melekh, Bernard A.-T.
2016-12-01
Transport of Cooper pairs in the direction perpendicular to the layers of an Fe (Se_{0.3 }Te_{0.7})_{0.9} superconductor proceeds through the weak link via the proximity effect. We observed radiation from the chalcogen Fe (Se_{0.3 }Te_{0.7})_{0.9} superconductor in its resistive state.
2009-08-26
Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 15. SUBJECT TERMS superconducting qubits, quasiparticles, coherence John ...ARO 8. PERFORMING ORGANIZATION REPORT NUMBER 19a. NAME OF RESPONSIBLE PERSON 19b. TELEPHONE NUMBER John Martinis 805-893-3910 3. DATES...Junction Qubits from Nonequilibrium Quasiparticle Excitations John M. Martinis,1 M. Ansmann,1 and J. Aumentado2 1Department of Physics, University of
Spectral density of Cooper pairs in two level quantum dot-superconductors Josephson junction
NASA Astrophysics Data System (ADS)
Dhyani, A.; Rawat, P. S.; Tewari, B. S.
2016-09-01
In the present paper, we report the role of quantum dot energy levels on the electronic spectral density for a two level quantum dot coupled to s-wave superconducting leads. The theoretical arguments in this work are based on the Anderson model so that it necessarily includes dot energies, single particle tunneling and superconducting order parameter for BCS superconductors. The expression for single particle spectral function is obtained by using the Green's function equation of motion technique. On the basis of numerical computation of spectral function of superconducting leads, it has been found that the charge transfer across such junctions can be controlled by the positions and availability of the dot levels.
NASA Astrophysics Data System (ADS)
Huang, Guang-Yao; Leijnse, Martin; Flensberg, Karsten; Xu, H. Q.
2014-12-01
We theoretically investigate electronic transport through a junction where a quantum dot (QD) is tunnel coupled on both sides to semiconductor nanowires with strong spin-orbit interaction and proximity-induced superconductivity. The results are presented as stability diagrams, i.e., the differential conductance as a function of the bias voltage applied across the junction and the gate voltage used to control the electrostatic potential on the QD. A small applied magnetic field splits and modifies the resonances due to the Zeeman splitting of the QD level. Above a critical field strength, Majorana bound states (MBS) appear at the interfaces between the two superconducting nanowires and the QD, resulting in a qualitative change of the entire stability diagram, suggesting this setup as a promising platform to identify MBS. Our calculations are based on a nonequilibrium Green's function description and is exact when Coulomb interactions on the QD can be neglected. In addition, we develop a simple pictorial view of the involved transport processes, which is equivalent to a description in terms of multiple Andreev reflections, but provides an alternative way to understand the role of the QD level in enhancing transport for certain gate and bias voltages. We believe that this description will be useful in future studies of interacting QDs coupled to superconducting leads (with or without MBS), where it can be used to develop a perturbation expansion in the tunnel coupling.
Sirena, M.; Fabreges, X.; Bergeal, N.; Lesueur, J.; Faini, G.; Bernard, R.; Briatico, J.
2007-12-24
A simple model has been proposed to explain the spread in the characteristics of high T{sub c} Josephson junctions made by ion irradiation, assuming that the source of dispersion is the slit's size variation. Accordingly, increasing ion energy should lead to a significant reduction of inhomogeneities. Test samples have been fabricated using two different beam energies. As predicted, the spread in critical current decreases upon increasing energy. Moreover, since the actual width of the barrier is reduced in this case, the I{sub c}R{sub n} product increases significantly. These results seem promising for future technological applications.
ERIC Educational Resources Information Center
Clarke, John
1970-01-01
Discusses the theory of the Josephson Effect, the derivation of the Josephson voltage-frequency relation, and methods of measuring the fundamental constatn ratio e/h. Various types of Josephson junctions are described. The impact of the measurement of e/h upin the fundamental constants and quantum electro-dynamics is briefly discussed.…
Dynamics of Josephson pancakes in layered superconductors
Mints, R.G.; Snapiro, I.B.
1994-03-01
We consider a pointlike vortex in a layered superconductor with linear defects in the superconducting layers. We treat these defects as Josephson junctions with high critical current density. We consider the electrodynamics of these junctions within the framework of nonlocal Josephson electrodynamics. We show that Josephson current through a linear defect in a superconducting layer results in a pointlike vortex with a superconducting core residing in this layer (Josephson pancake). We find the mobility of a Josephson pancake. We consider a small amplitude wave in a Josephson junction with nonlocal electrodynamics. We treat a bending wave for an infinite stack of Josephson pancakes. We find the dispersion relation for these waves. We show that their velocities tend to a certain finite limit when the wavelength tends to infinity.
Barrier structure of ramp-edge-type Josephson junction made of La-doped ErBCO and SmBCO electrodes
NASA Astrophysics Data System (ADS)
Adachi, S.; Tsukamoto, A.; Oshikubo, Y.; Tanabe, K.
2016-11-01
We fabricated SQUIDs containing ramp-edge-type Josephson junctions using La-doped ErBCO and SmBCO. The structure of the barrier was investigated by means of transmission electron microscope (TEM). The sample piece for the observation was picked up from a chip exhibiting moderate junction characteristics as DC SQUID at 77 K. The image of high-angle annular dark-field scanning TEM (HAADF-STEM) for the barrier indicated that about 1.5-nm-thick barrier homogeneously formed and the ordered structure of the triple perovskite was lost. Using an energy dispersive X-ray analyzer, the composition at the barrier region was estimated to be Ba:La:Sm:Er:Cu = 23:1:25:10:41. It was found that significant concentration of Sm occurred at the barrier region. The formation mechanism of the barrier is discussed on the basis of the fabrication process and the obtained results.
NASA Astrophysics Data System (ADS)
Ostroukh, V. P.; Baxevanis, B.; Akhmerov, A. R.; Beenakker, C. W. J.
2016-09-01
The critical current of a Josephson junction is an oscillatory function of the enclosed magnetic flux Φ , because of quantum interference modulated with periodicity h /2 e . We calculate these Fraunhofer oscillations in a two-dimensional (2D) ballistic superconductor-normal-metal-superconductor (SNS) junction. For a Fermi circle the amplitude of the oscillations decays as 1 /Φ or faster. If the Fermi circle is strongly warped, as it is on a square lattice near the band center, we find that the amplitude decays slower, ∝1 /√{Φ } , when the magnetic length lm=√{ℏ /e B } drops below the separation L of the NS interfaces. The crossover to the slow decay of the critical current is accompanied by the appearance of a 2D array of current vortices and antivortices in the normal region, which form a bipartite rectangular lattice with lattice constant ≃lm2/L . The 2D lattice vanishes for a circular Fermi surface, when only the usual single row of Josephson vortices remains.
Amplitude control of the spin-triplet supercurrent in $S/F/S$ Josephson junctions
Martinez, William M.; Pratt, Jr., W. P.; Birge, Norman O.
2016-02-17
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. In conclusion, 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”.
Klemm, R. A.; Arnold, G.; Bille, A.; Rieck, C. T.; Scharnberg, K.
1999-09-20
Li et al. found that the critical current density J{sub c}{sup J} across atomically clean c-axis twist junctions of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} is the same as that of the constituent single crystal, J{sub c}{sup S}, independent of the twist angle {phi}{sub 0}, even at and below T{sub c}. They investigated theoretically if a d{sub x{sup 2}{minus}y{sup 2}} wave order parameter might twist by mixing in d{sub xy}-wave components, but found that such mixing cannot possibly explain the data near to T{sub c}. Combined with group theoretical arguments, they then conclude that the order parameter contains at least a substantial s-wave component, but does not contain any purported d{sub x{sup 2}{minus}y{sup 2}}-wave component, except possibly below a second, unobserved phase transition. By studying tunneling models, they further conclude that the intrinsic c-axis Josephson tunneling in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} is likely to be mostly incoherent.
Spin-asymmetric Josephson plasma oscillations
NASA Astrophysics Data System (ADS)
Kreula, J. M.; Valtolina, G.; Törmä, P.
2017-01-01
The spin-asymmetric Josephson effect is a proposed quantum-coherent tunneling phenomenon where Cooper-paired fermionic spin-1/2 particles, which are subjected to spin-dependent potentials across a Josephson junction, undergo frequency-synchronized alternating-current Josephson oscillations with spin-dependent amplitudes. Here, in line with present-day techniques in ultracold Fermi gas setups, we consider the regime of small Josephson oscillations and show that the Josephson plasma oscillation amplitude becomes spin dependent in the presence of spin-dependent potentials, while the Josephson plasma frequency is the same for both spin components. Detecting these spin-dependent Josephson plasma oscillations provides a possible means to establish the yet-unobserved spin-asymmetric Josephson effect with ultracold Fermi gases using existing experimental tools.
Monaco, R; Mygind, J; Aaroe, M; Rivers, R J; Koshelets, V P
2006-05-12
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 phase transition clearly follows an allometric dependence on tau(Q) with a scaling exponent sigma = 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 sigma = 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.
Fabricating Nanogaps in YBa2 Cu3 O7 -δ for Hybrid Proximity-Based Josephson Junctions
NASA Astrophysics Data System (ADS)
Baghdadi, Reza; Arpaia, Riccardo; Charpentier, Sophie; Golubev, Dmitri; Bauch, Thilo; Lombardi, Floriana
2015-07-01
The advances of nanotechnologies applied to high-critical-temperature superconductors (HTSs) have recently given a huge boost to the field, opening new prospectives for their integration in hybrid devices. The feasibility of this research goes through the realization of HTS nanogaps with superconductive properties close to the as-grown bulk material at the nanoscale. Here we present a fabrication approach allowing the realization of YBa2 Cu3 O7 -δ (YBCO) nanogaps with dimensions as small as 35 nm. To assess the quality of the nanogaps, we measure, before and after an ozone treatment, the current-voltage characteristics and the resistance versus temperature of YBCO nanowires with various widths and lengths, fabricated by using different lithographic processes. The analysis of the superconducting transition with a thermally activated vortex-entry model allows us to determine the maximum damage the nanowires undergo during the patterning which relates to the upper bound for the dimension of the nanogap. We find that the effective width of the nanogap is of the order of 100 nm at the superconducting transition temperature while retaining the geometrical value of about 35 nm at lower temperatures. The feasibility of the nanogaps for hybrid Josephson devices is demonstrated by bridging them with thin Au films. We detect a Josephson coupling up to 85 K with an almost ideal magnetic-field response of the Josephson current. These results pave the way for the realization of complex hybrid devices, where tiny HTS nanogaps can be instrumental to study the Josephson effect through barriers such as topological insulators or graphene.
Intrinsic Islet Heterogeneity and Gap Junction Coupling Determine Spatiotemporal Ca2+ Wave Dynamics
Benninger, Richard K.P.; Hutchens, Troy; Head, W. Steven; McCaughey, Michael J.; Zhang, Min; Le Marchand, Sylvain J.; Satin, Leslie S.; Piston, David W.
2014-01-01
Insulin is released from the islets of Langerhans in discrete pulses that are linked to synchronized oscillations of intracellular free calcium ([Ca2+]i). Associated with each synchronized oscillation is a propagating calcium wave mediated by Connexin36 (Cx36) gap junctions. A computational islet model predicted that waves emerge due to heterogeneity in β-cell function throughout the islet. To test this, we applied defined patterns of glucose stimulation across the islet using a microfluidic device and measured how these perturbations affect calcium wave propagation. We further investigated how gap junction coupling regulates spatiotemporal [Ca2+]i dynamics in the face of heterogeneous glucose stimulation. Calcium waves were found to originate in regions of the islet having elevated excitability, and this heterogeneity is an intrinsic property of islet β-cells. The extent of [Ca2+]i elevation across the islet in the presence of heterogeneity is gap-junction dependent, which reveals a glucose dependence of gap junction coupling. To better describe these observations, we had to modify the computational islet model to consider the electrochemical gradient between neighboring β-cells. These results reveal how the spatiotemporal [Ca2+]i dynamics of the islet depend on β-cell heterogeneity and cell-cell coupling, and are important for understanding the regulation of coordinated insulin release across the islet. PMID:25468351
NASA Astrophysics Data System (ADS)
Iskin, M.
2016-07-01
We first show that the many-body Hamiltonian governing the physical properties of an alkaline-earth 173Yb Fermi gas across the recently realized orbital Feshbach resonance is exactly analogous to that of two-band s -wave superconductors with contact interactions; i.e., even though the free-particle bands have a tunable energy offset in between and are coupled by a Josephson-type attractive interband pair scattering, the intraband interactions have exactly the same strength. We then introduce two intraband order parameters within the BCS mean-field approximation and investigate the competition between their in-phase and out-of-phase (i.e., the so-called π -phase) solutions in the entire BCS-BEC evolution at zero temperature.
Josephson magnetic rotary valve
Soloviev, I. I.; Klenov, N. V.; Bakurskiy, S. V.; Bol'ginov, V. V.; Ryazanov, V. V.; Kupriyanov, M. Yu.; Golubov, A. A.
2014-12-15
We propose a control element for a Josephson spin valve. It is a complex Josephson device containing ferromagnetic (F) layer in the weak-link area consisting of two regions, representing 0 and π Josephson junctions, respectively. The valve's state is defined by mutual orientations of the F-layer magnetization vector and boundary line between 0 and π sections of the device. We consider possible implementation of the control element by introduction of a thin normal metal layer in a part of the device area. By means of theoretical simulations, we study properties of the valve's structure as well as its operation, revealing such advantages as simplicity of control, high characteristic frequency, and good legibility of the basic states.
Microwave integrated circuit for Josephson voltage standards
NASA Technical Reports Server (NTRS)
Holdeman, L. B.; Toots, J.; Chang, C. C. (Inventor)
1980-01-01
A microwave integrated circuit comprised of one or more Josephson junctions and short sections of microstrip or stripline transmission line is fabricated from thin layers of superconducting metal on a dielectric substrate. The short sections of transmission are combined to form the elements of the circuit and particularly, two microwave resonators. The Josephson junctions are located between the resonators and the impedance of the Josephson junctions forms part of the circuitry that couples the two resonators. The microwave integrated circuit has an application in Josephson voltage standards. In this application, the device is asymmetrically driven at a selected frequency (approximately equal to the resonance frequency of the resonators), and a d.c. bias is applied to the junction. By observing the current voltage characteristic of the junction, a precise voltage, proportional to the frequency of the microwave drive signal, is obtained.
Laser-induced modification of the critical current in Y-Ba-Cu-O step-edge Josephson junctions
NASA Astrophysics Data System (ADS)
Adam, Roman; Kula, Witold; Murduck, J. M.; Pettiette-Hall, C.; Sobolewski, Roman
1996-03-01
Transport properties of YBa2Cu3O7- x (YBCO) step-edge weak links were measured in the absence and presence of the magnetic field B, both before and after the cw-laser annealing. Depending on the laser power density, either an increase (up to 75%) or decrease (up to 100%) of the junction critical current I c was observed. The I c (B) characteristics of the laser-treated junctions exhibited about 10% variations of the I c (B) periodicity, indicating permanent changes in the junction barrier and/or adjacent YBCO electrodes.
Sonne, Gustav; Gorelik, Leonid Y
2011-04-22
We demonstrate that a suspended nanowire forming a weak link between two superconductors can be cooled to its motional ground state by a supercurrent flow. The predicted cooling mechanism has its origins in magnetic field induced inelastic tunneling of the macroscopic superconducting phase associated with the junction. Furthermore, we show that the voltage drop over the junction is proportional to the average population of the vibrational modes in the stationary regime, a phenomenon which can be used to probe the level of cooling.
Gardner, Jasmine M; Deserno, Markus; Abrams, Cameron F
2016-08-21
We use a combination of coarse-grained molecular dynamics simulations and theoretical modeling to examine three-junctions in mixed lipid bilayer membranes. These junctions are localized defect lines in which three bilayers merge in such a way that each bilayer shares one monolayer with one of the other two bilayers. The resulting local morphology is non-lamellar, resembling the threefold symmetric defect lines in inverse hexagonal phases, but it regularly occurs during membrane fission and fusion events. We realize a system of junctions by setting up a honeycomb lattice, which in its primitive cell contains two hexagons and four three-line junctions, permitting us to study their stability as well as their line tension. We specifically consider the effects of lipid composition and intrinsic curvature in binary mixtures, which contain a fraction of negatively curved lipids in a curvature-neutral background phase. Three-junction stability results from a competition between the junction and an open edge, which arises if one of the three bilayers detaches from the other two. We show that the stable phase is the one with the lower defect line tension. The strong and opposite monolayer curvatures present in junctions and edges enhance the mole fraction of negatively curved lipids in junctions and deplete it in edges. This lipid sorting affects the two line tensions and in turn the relative stability of the two phases. It also leads to a subtle entropic barrier for the transition between junction and edge that is absent in uniform membranes.
NASA Astrophysics Data System (ADS)
Gardner, Jasmine M.; Deserno, Markus; Abrams, Cameron F.
2016-08-01
We use a combination of coarse-grained molecular dynamics simulations and theoretical modeling to examine three-junctions in mixed lipid bilayer membranes. These junctions are localized defect lines in which three bilayers merge in such a way that each bilayer shares one monolayer with one of the other two bilayers. The resulting local morphology is non-lamellar, resembling the threefold symmetric defect lines in inverse hexagonal phases, but it regularly occurs during membrane fission and fusion events. We realize a system of junctions by setting up a honeycomb lattice, which in its primitive cell contains two hexagons and four three-line junctions, permitting us to study their stability as well as their line tension. We specifically consider the effects of lipid composition and intrinsic curvature in binary mixtures, which contain a fraction of negatively curved lipids in a curvature-neutral background phase. Three-junction stability results from a competition between the junction and an open edge, which arises if one of the three bilayers detaches from the other two. We show that the stable phase is the one with the lower defect line tension. The strong and opposite monolayer curvatures present in junctions and edges enhance the mole fraction of negatively curved lipids in junctions and deplete it in edges. This lipid sorting affects the two line tensions and in turn the relative stability of the two phases. It also leads to a subtle entropic barrier for the transition between junction and edge that is absent in uniform membranes.
Zhang, Z H; Gui, Y S; Fu, L; Fan, X L; Cao, J W; Xue, D S; Freitas, P P; Houssameddine, D; Hemour, S; Wu, K; Hu, C-M
2012-07-20
An intrinsic thermoelectric coupling effect in the linear response regime of magnetic tunneling junctions (MTJ) is reported. In the dc response, it leads to a nonlinear correction to Ohm's law. Dynamically, it enables a novel Seebeck rectification and second harmonic generation, which apply for a broad frequency range and can be magnetically controlled. A phenomenological model on the footing of the Onsager reciprocal relation and the principle of energy conservation explains very well the experimental results obtained from both dc and frequency-dependent transport measurements performed up to GHz frequencies. Our work refines previous understanding of magnetotransport and microwave rectification in MTJs. It forms a new foundation for utilizing spin caloritronics in high-frequency applications.
Mazzarella, G.; Toigo, F.; Salasnich, L.; Parola, A.
2011-05-15
We consider a bosonic Josephson junction made of N ultracold and dilute atoms confined by a quasi-one-dimensional double-well potential within the two-site Bose-Hubbard model framework. The behavior of the system is investigated at zero temperature by varying the interatomic interaction from the strongly attractive regime to the repulsive one. We show that the ground state exhibits a crossover from a macroscopic Schroedinger-cat state to a separable Fock state through an atomic coherent regime. By diagonalizing the Bose-Hubbard Hamiltonian we characterize the emergence of the macroscopic cat states by calculating the Fisher information F, the coherence by means of the visibility {alpha} of the interference fringes in the momentum distribution, and the quantum correlations by using the entanglement entropy S. Both Fisher information and visibility are shown to be related to the ground-state energy by employing the Hellmann-Feynman theorem. This result, together with a perturbative calculation of the ground-state energy, allows simple analytical formulas for F and {alpha} to be obtained over a range of interactions, in excellent agreement with the exact diagonalization of the Bose-Hubbard Hamiltonian. In the attractive regime the entanglement entropy attains values very close to its upper limit for a specific interaction strength lying in the region where coherence is lost and self-trapping sets in.
Excess low-frequency flux noise in dc SQUIDS incorporating Nb/AIOXIDE/Nb Josephson junctions
NASA Astrophysics Data System (ADS)
Huber, Martin E.; Cromar, Michael W.
1990-08-01
We have fabricated thin-film do SQUIDs (Superconducting QUantum Interference Devices) incorporating Nb/AlOxide/Nb tunnel junctions. The spectral density of the voltage noise, Sv, of stripline SQUIDs is characterized between 1 Hz and 2000 Hz. In this frequency range, S v is proportional to the square of the responsivity (ϖV/ϖΦ) over a significant range of bias conditions with an unusual frequency dependence. In a 7 pH SQZIK the spectral density of the flux noise, S Φ, at 1 Hz is less than 10 -11Φ02/Hz, where Φ0 ≡ h/2 e. The observed noise does not appear to be environmental; also, it is independent of the value of the junction shunt resistance and whether the stripline material is a Pbln alloy or Nb. Subject to the constraint of a constant product of the junction area, critical current density, and SQUID self-inductance in the SQUIDs studied, S Φ is inversely proportional to the junction area.
Ishimaru, Y.; Wen, J.; Koshizuka, N.; Enomoto, Y.
1997-05-01
We have investigated gap symmetry of high-T{sub c} superconductors using Josephson junctions formed along a boundary of an a-axis-oriented YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) grain surrounded by c-axis-oriented YBCO grains (a/c boundary). There are two types of a/c boundary junctions; one is the boundary between (001) of a-axis-oriented grains and (100) of c-axis-oriented grains, and the other is the boundary between (001) of a-axis-oriented grains and (110) of c-axis-oriented grains. TEM observation shows clean, sharp, and nearly single-facet interface along the grain boundaries in both types. In the case of the (100)-(001) type a/c boundary junction, typical resistively shunted junction (RSJ)-type I-V curves, Shapiro steps under microwave irradiation, and Fraunhofer-like diffraction pattern of I{sub c} under magnetic field are observed, indicating that the boundary works as a Josephson junction. In the case of the (110)-(001)-type a/c boundary junction, typical RSJ type I-V curves and Shapiro steps under microwave irradiation are also observed. However, the diffraction pattern of I{sub c} under magnetic field has the minimum value at zero magnetic field. This property is analogous to one observed for a corner junction which is formed between Pb and YBCO. These results show that the (110) of YBCO has a phase difference of {pi} and d{sub x{sup 2}{minus}y{sup 2}} superconducting-gap symmetry is in CuO{sub 2} planes of YBCO. But, the (001) of YBCO has no phase difference of {pi} in spite of the existence of d-wave symmetry in YBCO. {copyright} {ital 1997} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Arjoranta, Juho; Heikkilä, Tero T.
2016-01-01
We study the effect of the intrinsic (Rashba or Dresselhaus) spin-orbit interaction in superconductor-nanowire-superconductor (SNS) weak links in the presence of a spin-splitting field that can result either from an intrinsic exchange field or the Zeeman effect of an applied field. We solve the full nonlinear Usadel equations numerically [The code used for calculating the results in this paper is available in https://github.com/wompo/Usadel-for-nanowires] and analyze the resulting supercurrent through the weak link and the behavior of the density of states in the center of the wire. We point out how the presence of the spin-orbit interaction gives rise to a long-range spin triplet supercurrent, which remains finite even in the limit of very large exchange fields. In particular, we show how rotating the field leads to a sequence of transitions between the 0 and π states as a function of the angle between the exchange field and the spin-orbit field. Simultaneously, the triplet pairing leads to a zero-energy peak in the density of states. We proceed by solving the linearized Usadel equations, showing the correspondence to the solutions of the full equations and detail the emergence of the long-range supercurrent components. Our studies are relevant for ongoing investigations of supercurrent in semiconductor nanowires in the limit of several channels and in the presence of disorder.
Low-frequency noise in high-T_{c} superconductor Josephson junctions, SQUIDs, and magnetometers
Miklich, Andrew Hostetler
1994-05-01
Design and performance of high-T_{c} dc superconducting quantum interference devices (SQUEDs), junctions that comprise them, and magnetometers made from them are described, with attention to sources of 1/f noise. Biepitaxial junctions are found to have large levels of critical current fluctuations which make them unsuitable for low-noise SQUIDS; this suggests a poorly connected interface at the grain boundary junction. SQUIDs from bicrystal junctions have levels of critical current noise controllable using bias current reversal techniques which leave the noise white down to frequencies of a few Hz. A SQUID with an energy resolution of 1.5 x 10^{-30} J Hz^{-1} at 1 Hz is reported. Magnetometers in which a (9 mm)^{2} pickup loop is directly coupled to a SQUID body have achieved field resolutions of 93 fT Hz^{-1/2} down to frequencies below I Hz, improving to 39 fT Hz^{-1/2} at 1 Hz with the addition of a 50mm-diameter single-turn flux transformer. Poor coupling to pickup loop makes it difficult to satisfy competing goals of high field resolution and small detector size necessary for multichannel biomagnetic imaging. Improved coupling is demonstrated by the use of multiturn-input-coil flux transformers, and a resolution of 35 fT Hz^{-1/2} in the white noise region is reported with a (10 mm)^{2} pickup loop. However, additional 1/f noise from processed multilayer structures in the transformer limits the resolution at 1 Hz to 114 fT Hz^{-1/2}. High-T_{c} SQUIDs exhibit additional 1/f noise when cooled in a nonzero static magnetic field because of additional flux vortices trapped in the film, with the noise power at 1 Hz typically increasing by a factor of 10--20 in a field of 0.05mT (0.5 G). Finally, a SQUID-based voltmeter with a resolution of 9.2 pV.Hz^{-1/2} at 10 Hz (24 pV Hz^{-1/2} at 1 Hz) is described.
Narla, A.; Sliwa, K. M.; Hatridge, M.; Shankar, S.; Frunzio, L.; Schoelkopf, R. J.; Devoret, M. H.
2014-06-09
Josephson junction parametric amplifiers are playing a crucial role in the readout chain in superconducting quantum information experiments. However, their integration with current 3D cavity implementations poses the problem of transitioning between waveguide, coax cables, and planar circuits. Moreover, Josephson amplifiers require auxiliary microwave components, like directional couplers and/or hybrids, that are sources of spurious losses and impedance mismatches that limit measurement efficiency and amplifier tunability. We have developed a wireless architecture for these parametric amplifiers that eliminates superfluous microwave components and interconnects. This greatly simplifies their assembly and integration into experiments. We present an experimental realization of such a device operating in the 9–11 GHz band with about 100 MHz of amplitude gain-bandwidth product, on par with devices mounted in conventional sample holders. The simpler impedance environment presented to the amplifier also results in increased amplifier tunability.
NASA Astrophysics Data System (ADS)
Schmelz, M.; Stolz, R.; Zakosarenko, V.; Schönau, T.; Anders, S.; Fritzsch, L.; Mück, M.; Meyer, M.; Meyer, H.-G.
2012-11-01
We review the development of low parasitic capacitance sub-micrometer cross-type Josephson tunnel junctions for their use in highly sensitive and field-stable SQUID magnetometers. The potential of such junctions is shown on I-V characteristics as well as on Fraunhofer diffraction patterns. The evaluation of Fiske steps lead to a specific junction capacitance of about 62 fF/μm2 for a critical current density of about 1.7 kA/cm2. The avoidance of any idle-region - the undesired overlap between superconducting electrodes around the junction - due to a self-aligned junction definition process lead to highly sensitive SQUIDs; multiloop SQUID magnetometers exhibiting exceptionally low magnetic field noise levels as low as 0.3 fT/Hz1/2, as well as large usable voltage swings of more than 150 μVpp. Furthermore, junction dimensions in the sub-micrometer range allowed for very high tolerable background fields during cool-down of up to 6.5 mT. In operation mode, the SQUID magnetometers recovered completely from magnetization pulses of up to 76 mT. With respect to their easy and reliable usage as well as their high sensitivity, the presented SQUID sensors are adequate for many applications, like in geophysics, biomagnetism or low-field magnetic resonance imaging.
An 8-b Josephson digital signal processor
NASA Astrophysics Data System (ADS)
Kotani, Seigo; Inoue, Atsuki; Imamura, Takeshi; Hasuo, Shinya
1990-12-01
A 6.3 K-gate Josephson digital signal processor (DSP) that performs 240-psec 8-b multiplication and 410-psec 13-b addition is described. The structure of the DSP, which is based on a three-stage pipeline, and the design of the components used in the DSP are reviewed. The DSP contains 23,000 Josephson junctions on a 5 x 5-mm die and was fabricated using 1.5-micron all-niobium Josephson techniques. Measurements indicate that the DSP can attain a nonparallel processing speed of 1 gigaoperation per second with 12-mW power dissipation.
NASA Astrophysics Data System (ADS)
Barone, Antonio; Pagano, Sergio
In this chapter we briefly review the main applications of Josephson effect together with the most successful devices realized. We will give an overview of the various devices, providing also some basic concepts of the underlying physical mechanisms involved, and the associated limit performances. Some considerations on the concrete possibilities of successful "market ready" implementation will also be given.
Flux cloning in Josephson transmission lines.
Gulevich, D R; Kusmartsev, F V
2006-07-07
We describe a novel effect related to the controlled birth of a single Josephson vortex. In this phenomenon, the vortex is created in a Josephson transmission line at a T-shaped junction. The "baby" vortex arises at the moment when a "mother" vortex propagating in the adjacent transmission line passes the T-shaped junction. In order to give birth to a new vortex, the mother vortex must have enough kinetic energy. Its motion can also be supported by an externally applied driving current. We determine the critical velocity and the critical driving current for the creation of the baby vortices and briefly discuss the potential applications of the found effect.
Flux Cloning in Josephson Transmission Lines
Gulevich, D.R.; Kusmartsev, F.V.
2006-07-07
We describe a novel effect related to the controlled birth of a single Josephson vortex. In this phenomenon, the vortex is created in a Josephson transmission line at a T-shaped junction. The 'baby' vortex arises at the moment when a 'mother' vortex propagating in the adjacent transmission line passes the T-shaped junction. In order to give birth to a new vortex, the mother vortex must have enough kinetic energy. Its motion can also be supported by an externally applied driving current. We determine the critical velocity and the critical driving current for the creation of the baby vortices and briefly discuss the potential applications of the found effect.
1D Josephson quantum interference grids: diffraction patterns and dynamics
NASA Astrophysics Data System (ADS)
Lucci, M.; Badoni, D.; Corato, V.; Merlo, V.; Ottaviani, I.; Salina, G.; Cirillo, M.; Ustinov, A. V.; Winkler, D.
2016-02-01
We investigate the magnetic response of transmission lines with embedded Josephson junctions and thus generating a 1D underdamped array. The measured multi-junction interference patterns are compared with the theoretical predictions for Josephson supercurrent modulations when an external magnetic field couples both to the inter-junction loops and to the junctions themselves. The results provide a striking example of the analogy between Josephson phase modulation and 1D optical diffraction grid. The Fiske resonances in the current-voltage characteristics with voltage spacing {Φ0}≤ft(\\frac{{\\bar{c}}}{2L}\\right) , where L is the total physical length of the array, {Φ0} the magnetic flux quantum and \\bar{c} the speed of light in the transmission line, demonstrate that the discrete line supports stable dynamic patterns generated by the ac Josephson effect interacting with the cavity modes of the line.
Anomalous spin Josephson effect
NASA Astrophysics Data System (ADS)
Wang, Mei-Juan; Wang, Jun; Hao, Lei; Liu, Jun-Feng
2016-10-01
We report a theoretical study on the spin Josephson effect arising from the exchange coupling of the two ferromagnets (Fs), which are deposited on a two-dimensional (2D) time-reversal-invariant topological insulator. An anomalous spin supercurrent Js z˜sin(α +α0) is found to flow in between the two Fs and the ground state of the system is not limited to the magnetically collinear configuration (α =n π ,n is an integer) but determined by a controllable angle α0, where α is the crossed angle between the two F magnetizations. The angle α0 is the dynamic phase of the electrons traveling in between the two Fs and can be controlled electrically by a gate voltage. This anomalous spin Josephson effect, similar to the conventional φ0 superconductor junction, originates from the definite electron chirality of the helical edge states in the 2D topological insulator. These results indicate that the magnetic coupling in a topological system is different from the usual one in conventional materials.
Effect of environment fluctuations on a Josephson current
NASA Astrophysics Data System (ADS)
Galaktionov, A. V.
2017-01-01
An influence of an electromagnetic environment on a Josephson current through a tunnel junction is studied with the aid of Ambegaokar-Eckern-Schön effective action. Two types of environment are investigated: one, characterized by a resonant mode, and an ohmic one. The crossover to a Josephson π-junction is possible for both of them. In addition the resonant-mode environment results in an increase of a Josephson current when the ratio of the doubled superconducting gap to the frequency of the mode is close to an integer number.
Anomalous Josephson current in superconducting topological insulator
NASA Astrophysics Data System (ADS)
Yamakage, Ai; Sato, Masatoshi; Yada, Keiji; Kashiwaya, Satoshi; Tanaka, Yukio
2013-03-01
We investigate the effect of helical Majorana fermions at the surface of superconducting topological insulators (STIs) on the Josephson current by referring to possible pairing states of Cu-doped Bi2Se3. The surface state in the present STI has a spin helicity because the directions of spin and momentum are locked to each other. The Josephson current-phase relation in an STI/s-wave superconductor junction shows robust sin(2φ) owing to mirror symmetry, where φ denotes the macroscopic phase difference between the two superconductors. In contrast, the maximum Josephson current in an STI/STI junction exhibits a nonmonotonic temperature dependence depending on the relative spin helicity of the two surface states. Detecting these features qualifies as distinct experimental evidence for the identification of the helical Majorana fermion in STIs.
2011-01-01
Using an atomic force microscope (AFM) at a controlled contact force, we report the electrical signal response of multi-walled carbon nanotubes (MWCNTs) disposed on a golden thin film. In this investigation, we highlight first the theoretical calculation of the contact resistance between two types of conductive tips (metal-coated and doped diamond-coated), individual MWCNTs and golden substrate. We also propose a circuit analysis model to schematize the «tip-CNT-substrate» junction by means of a series-parallel resistance network. We estimate the contact resistance R of each contribution of the junction such as Rtip-CNT, RCNT-substrate and Rtip-substrate by using the Sharvin resistance model. Our final objective is thus to deduce the CNT intrinsic radial resistance taking into account the calculated electrical resistance values with the global resistance measured experimentally. An unwished electrochemical phenomenon at the tip apex has also been evidenced by performing measurements at different bias voltages with diamond tips. For negative tip-substrate bias, a systematic degradation in color and contrast of the electrical cartography occurs, consisting of an important and non-reversible increase of the measured resistance. This effect is attributed to the oxidation of some amorphous carbon areas scattered over the diamond layer covering the tip. For a direct polarization, the CNT and substrate surface can in turn be modified by an oxidation mechanism. PMID:21711904
A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy
Jäck, Berthold Eltschka, Matthias; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R.; Hardock, Andreas; Kern, Klaus
2015-01-05
Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a λ/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25 GHz to 200 GHz and that large photon flux in excess of 10{sup 20 }cm{sup −2} s{sup −1} is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale.
NASA Astrophysics Data System (ADS)
Jaris, M.; Yahagi, Y.; Mahato, B. K.; Dhuey, S.; Cabrini, S.; Nikitin, V.; Stout, J.; Hawkins, A. R.; Schmidt, H.
2016-11-01
We report the all-optical observation of intrinsic spin dynamics and extraction of magnetic material parameters from arrays of sub-100 nm spin-transfer torque magnetic random access memory (STT-MRAM) devices with a CoFeB/MgO interface. To this end, the interference of surface acoustic waves with time-resolved magneto-optic signals via magneto-elastic coupling was suppressed using a dielectric coating. The efficacy of this method is demonstrated experimentally and via modeling on a nickel nanomagnet array. The magnetization dynamics for both coated nickel and STT-MRAM arrays shows a restored field-dependent Kittel mode from which the effective damping can be extracted. We observe an increased low-field damping due to extrinsic contributions from magnetic inhomogeneities and variations in the nanomagnet shape, while the intrinsic Gilbert damping remains unaffected by patterning. The data are in excellent agreement with a local resonance model and have direct implications for the design of STT-MRAM devices as well as other nanoscale spintronic technologies.
Signatures of time-reversal-invariant topological superconductivity in the Josephson effect
NASA Astrophysics Data System (ADS)
Mellars, Ehren; Béri, Benjamin
2016-11-01
For Josephson junctions based on s -wave superconductors, time-reversal symmetry is known to allow for powerful relations between the normal-state junction properties, the excitation spectrum, and the Josephson current. Here we provide analogous relations for Josephson junctions involving one-dimensional time-reversal-invariant topological superconductors supporting Majorana-Kramers pairs, considering both topological-topological and s -wave-topological junctions. Working in the regime where the junction is much shorter than the superconducting coherence length, we obtain a number of analytical and numerical results that hold for arbitrary normal-state conductance and the most general forms of spin-orbit coupling. The signatures of topological superconductivity we find include the fractional ac Josephson effect, which arises in topological-topological junctions provided that the energy relaxation is sufficiently slow. We also show, for both junction types, that robust signatures of topological superconductivity arise in the dc Josephson effect in the form of switches in the Josephson current due to zero-energy crossings of Andreev levels. The junction spin-orbit coupling enters the Josephson current only in the topological-topological case and in a manner determined by the switch locations, thereby allowing quantitative predictions for experiments with the normal-state conductance, the induced gaps, and the switch locations as inputs.
NASA Astrophysics Data System (ADS)
Probst, B.; Domínguez, F.; Schroer, A.; Yeyati, A. Levy; Recher, P.
2016-10-01
We study the critical Josephson current flowing through a double quantum dot weakly coupled to two superconducting leads. We use analytical as well as numerical methods to investigate this setup in the limit of small and large bandwidth leads in all possible charging states, where we account for on-site interactions exactly. Our results provide clear signatures of nonlocal spin-entangled pairs, which support interpretations of recent experiments [R. S. Deacon, A. Oiwa, J. Sailer, S. Baba, Y. Kanai, K. Shibata, K. Hirakawa, and S. Tarucha, Nat. Commun. 6, 7446 (2015), 10.1038/ncomms8446]. In addition, we find that the ground state with one electron on each quantum dot can undergo a tunable singlet-triplet phase transition in the regime where the superconducting gap in the leads is not too large, which gives rise to an additional new signature of nonlocal Cooper-pair transport.
High Power Josephson Effect Sources
1994-09-01
large spacing was nsed ,along with cooling water, os Iao a d$ to ensure the substrate temperature did not rise durn theCox flow Osiltr.adsaljnto ry~ h m...Here two arra’s. a 400 s.m Josephson effect detector and an SIS mixer are "I integrated on a single silicon substrate . One array func- tions as the...junction’s shunt resistor, on array’s output power and detector’s current- voltage characteristics are also discussed. I. INTRODUCTION - U Phb &z locked
Sensitivity of Josephson-effect millimeter-wave radiometer
NASA Technical Reports Server (NTRS)
Ohta, H.; Feldman, M. J.; Parrish, P. T.; Chiao, R. Y.
1974-01-01
The noise temperature and the minimum detectable temperature of a Josephson junction in video detection of microwave and millimeter-wave radiation has been calculated. We use the well-known method based on a Fokker-Planck equation. The noise temperature can be very close to ambient temperature. Because its predetection bandwidth is very wide, a Josephson-effect radio telescope receiver can have a minimum detectable temperature better than that of a traveling-wave maser.
Koren, G.; Aharoni, E.; Polturak, E.; Cohen, D. )
1991-02-11
Thin-film YBa{sub 2}Cu{sub 3}O{sub 7}-YBa{sub 2}Cu{sub 3}O{sub 7} edge junctions of 0.4{times}10 {mu}m{sup 2} cross section were prepared {ital in} {ital situ} by a multistep laser ablation deposition process. The fabrication time was about 3 h and the yield of good devices was 50%. Typical junctions reached zero resistance at 72 K and had a critical current density {ital J}{sub {ital c}} of 300 A/cm{sup 2} at 70 K. Their {ital J}{sub {ital c}} as a function of temperature increased slowly with decreasing temperature down to 65 K and much faster below it. In the region of low {ital J}{sub {ital c}} we observed suppression of the critical current by a magnetic field. Under microwave radiation clear Shapiro steps were observed whose magnitude versus the microwave field agreed qualitatively with the resistively shunted junction model of a current biased junction.
Yang, Yan; Zhu, Jian; Zhang, Na; Zhao, Yu; Li, Wan-Yun; Zhao, Fu-You; Ou, Yu-Rong; Qin, Shu-Kui; Wu, Qiong
2016-02-01
Hepatocellular carcinoma (HCC) is generally believed to have low sensitivity to chemotherapeutic agents including oxaliplatin (OXA). Studies have demonstrated that gap junctions (GJs) composed of connexin (Cx) proteins have the potential to modulate drug chemosensitivity in multiple tumor cells. In the present study, we investigated the characteristics of Cx and GJs in HCC at both histologic and cytologic levels, and the effects of GJ and its effective components on OXA cytotoxicity in HCC cells in vitro. Immunohistochemistry was performed in 76 HCCs and 20 normal liver tissues to detect and locate the expression of Cx26, Cx32 and Cx43. At cytologic levels, the expression and localization of Cxs were evaluated by RT-PCR, western blot and immunofluorescence assay, respectively. The GJ function between adjacent cells was detected using dye transfer assay. The role of GJs in the modulation of OXA toxicity in HCC cells was explored using pharmacologic and molecular biologic methods. We found that Cx expression in HCC tissues was significantly lower than in normal liver tissues, and the 'internalization' from cell membrane to cytoplasm was remarkable. In vitro experiments revealed the presence of functional GJs in the SMMC-7721 HCC cells due to a small amount of Cx protein along the plasma membrane at cell-cell contacts. Regulation of this part of GJs positively influenced OXA cytotoxicity. Using RNA interference, only specific inhibition of Cx26 but not Cx32 or Cx43 reduced OXA cytotoxicity. Conversely, Cx26 overexpression by transfection of Cx26 plasmid DNA enhanced OXA cytotoxicity. This study demonstrated that during hepatocarcinogenesis, the reduced expression and internalization of Cx proteins impaired the GJ function, which further attenuated OXA cytotoxicity. Impaired GJ function may contribute to low intrinsic chemosensitivity of HCC cells to OXA, mediated by Cx26.
Josephson effects in condensates of excitons and exciton polaritons
Shelykh, I. A.; Solnyshkov, D. D.; Pavlovic, G.; Malpuech, G.
2008-07-15
We analyze theoretically the phenomena related to the Josephson effect for exciton and polariton condensates, taking into account their specific spin degrees of freedom. We distinguish between two types of Josephson effects: the extrinsic effect, related to the coherent tunneling of particles with the same spin between two spatially separated potential traps, and the intrinsic effect, related to the 'tunneling' between different spinor components of the condensate within the same trap. We show that the Josephson effect in the nonlinear regime can lead to nontrivial polarization dynamics and produce spontaneous separation of the condensates with opposite polarization in real space.
NASA Astrophysics Data System (ADS)
Malishevskiĭ, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskiĭ, S. G.
2007-06-01
It is demonstrated that when the velocity of vortices in a Josephson junction magnetically coupled to a waveguide approaches the limits of the allowed ranges, the relative contribution of the Cherenkov losses to the transport current density increases drastically.
Inverse ac Josephson effect at terahertz frequencies
NASA Astrophysics Data System (ADS)
Danchi, W. C.; Golightly, W. J.; Sutton, E. C.
1989-04-01
Using the Werthamer (1966) theory of superconducting tunnel junctions, it is shown that zero-crossing ac Josephson steps can occur at frequencies much higher than those expected previously, as long as the voltage waveform is nearly sinusoidal. Limits on the amount of permitted rounding of the Riedel (1964) peak were derived from analytical calculations, and numerical frequency-domain and time-domain computations for realistic junctions were carried out, yielding support for these limits. It is shown that previous arguments that zero-crossing steps could never be observed above the value of half the gap voltage are incorrect, due to the neglect of the Riedel peak.
Josephson effects in a Bose–Einstein condensate of magnons
Troncoso, Roberto E.; Núñez, Álvaro S.
2014-07-15
A phenomenological theory is developed, that accounts for the collective dynamics of a Bose–Einstein condensate of magnons. In terms of such description we discuss the nature of spontaneous macroscopic interference between magnon clouds, highlighting the close relation between such effects and the well known Josephson effects. Using those ideas, we present a detailed calculation of the Josephson oscillations between two magnon clouds, spatially separated in a magnonic Josephson junction. -- Highlights: •We presented a theory that accounts for the collective dynamics of a magnon-BEC. •We discuss the nature of macroscopic interference between magnon-BEC clouds. •We remarked the close relation between the above phenomena and Josephson’s effect. •We remark the distinctive oscillations that characterize the Josephson oscillations.
Mesoscopic lateral S/N/S weak links: Josephson effects and Josephson-like vortex flow
NASA Astrophysics Data System (ADS)
Carapella, G.; Sabatino, P.; Gombos, M.
2017-02-01
We report an experimental and numerical study of magneto-transport properties of mesoscopic lateral S/N/S superconducting weak links where the N region is made of the same material as the S banks, though with strongly reduced critical temperature. Magnetoresistance oscillations and clear dc and ac Josephson effects are observed. Experimental results are analyzed in the framework of the time-dependent Ginzburg-Landau model for mesoscopic type II superconductors with an inhomogeneous critical temperature. The analysis suggests that dissipative branches of the current-voltage curve of the weak link in the presence of a magnetic field are accounted for by moving ‘Josephson-like’ vortices. These relatively fast excitations are anisotropic as per the ordinary Josephson vortex in tunnel junctions, but have a normal core like the ordinary Abrikosov vortex in plain superconducting strips. Moreover, unlike the vortex in tunneling junctions, in the lateral S/N/S weak link, the extension of the moving vortex is larger than the extension of the static one. Further, we report in some detail on the lateral proximity effect, and the deviations from the ideality of the current-phase relation of this kind of lateral weak link in the Josephson regime.
Josephson device for voltage measurement
NASA Astrophysics Data System (ADS)
Régent, A.; Villegier, J. C.; Angénieux, G.; Monllor, C.; Delahaye, F.
This paper describes a new Josephson device with microwave integrated circuit for voltage standard. The circuit is essentially made of a resonator (Nb), the Josephson junction (Nb, NbOx, Pb-In) and a capacitive microstrip section (Pb-In) which ends the rf part; the dc connections are through Cauer Filters (Nb or Pb-In). A niobium film is deposited on the opposite side of the fused quartz substrate as a ground plane. The circuit is enclosed in a special package with outside dc and rf connections. The technology ensures very good cyclability and lifetime with storage at room temperature. In liquid helium (4.2 K) with a very weak rf power less than 0.5 milliwatts at the frequency resonance (11.5 GHz), 100 μ A high current steps were obtained near a polarization of 4.5 mV. These devices allows a precision of 1 × 10 -7 on the volt standard when used with a series-parallel divider of fixed value (ratio 225). The precise adjustment of the voltages is made by a slight drift of the rf frequency of the source, allowed by the high rf coupling factor of the device and the band width of its resonance.
Four-junction superconducting circuit
NASA Astrophysics Data System (ADS)
Qiu, Yueyin; Xiong, Wei; He, Xiao-Ling; Li, Tie-Fu; You, J. Q.
2016-06-01
We develop a theory for the quantum circuit consisting of a superconducting loop interrupted by four Josephson junctions and pierced by a magnetic flux (either static or time-dependent). In addition to the similarity with the typical three-junction flux qubit in the double-well regime, we demonstrate the difference of the four-junction circuit from its three-junction analogue, including its advantages over the latter. Moreover, the four-junction circuit in the single-well regime is also investigated. Our theory provides a tool to explore the physical properties of this four-junction superconducting circuit.
Strong-coupling BCS models of Josephson qubits.
Alicki, R; Miklaszewski, W
2013-01-23
The strong-coupling version of the BCS theory for superconductors is used to derive microscopic models for all types of small Josephson junctions--charge qubit, flux qubit and phase qubit. Applied to Josephson qubits it yields a more complicated structure of the lowest-lying energy levels than that obtained from phenomenological models based on quantization of the Kirchhoff equations. In particular, highly degenerate levels emerge, which act as probability sinks for the qubit. The alternative formulae concerning spectra of superconducting qubits are presented and compared with the experimental data. In contrast to the existing theories those formulae contain microscopic parameters of the model. In particular, for the first time, the density of Cooper pairs at zero temperature is estimated for an Al-based flux qubit. Finally, the question whether small Josephson junctions can be treated as macroscopic quantum systems is briefly discussed.
Dissipation in microwave quantum circuits with hybrid nanowire Josephson elements
NASA Astrophysics Data System (ADS)
Mugnai, D.; Ranfagni, A.; Agresti, A.
2017-04-01
Recent experiments on hybrid Josephson junctions have made the argument a topical subject. However, a quantity which remains still unknown is the tunneling (or response) time, which is strictly connected to the role that dissipation plays in the dynamics of the complete system. A simple way for evaluating dissipation in microwave circuits, previously developed for describing the dynamics of conventional Josephson junctions, is now presented as suitable for application even to non-conventional junctions. The method is based on a stochastic model, as derived from the telegrapher's equation, and is particularly devoted to the case of junctions loaded by real transmission lines. When the load is constituted by lumped-constant circuits, a connection with the stochastic model is also maintained. The theoretical model demonstrated its ability to analyze both classically-allowed and forbidden processes, and has found a wide field of applicability, namely in all cases in which dissipative effects cannot be ignored.
Hybrid-free Josephson Parametric Converter
NASA Astrophysics Data System (ADS)
Frattini, N. E.; Narla, A.; Sliwa, K. M.; Shankar, S.; Hatridge, M.; Devoret, M. H.
A necessary component for any quantum computation architecture is the ability to perform efficient quantum operations. In the microwave regime of superconducting qubits, these quantum-limited operations can be realized with a non-degenerate Josephson junction based three-wave mixer, the Josephson Parametric Converter (JPC). Currently, the quantum signal of interest must pass through a lossy 180 degree hybrid to be presented as a differential drive to the JPC. This hybrid therefore places a limit on the quantum efficiency of the system and also increases the device footprint. We present a new design for the JPC eliminating the need for any external hybrid. We also show that this design has nominally identical performance to the conventional JPC. Work supported by ARO, AFOSR and YINQE.
NASA Astrophysics Data System (ADS)
Hui, Hoi-Yin; Sau, Jay D.
2017-01-01
Time-reversal invariance places strong constraints on the properties of the quantum spin Hall edge. One such restriction is the inevitability of dissipation in a Josephson junction between two superconductors formed on such an edge without the presence of interaction. Interactions and spin-conservation breaking are key ingredients for the realization of the dissipationless ac Josephson effect on such quantum spin Hall edges. We present a simple quantum impurity model that allows us to create a dissipationless fractional Josephson effect on a quantum spin Hall edge. We then use this model to substantiate a general argument that shows that any such nondissipative Josephson effect must necessarily be 8 π periodic.
Noise and Chaos in Driven Josephson Junctions
1987-03-01
dimension and (e) experimental noise power measurements at 10 kHz as a function of dc bias. Fig. 5.14 Effect of added noise on the Poincare sections...kHz 0.008 0.011 0.0008 IMHz 0.003 0.003 0.0003 10 MHz 0.0008 0.001 0.00008 Table 3.1. Skin Depth of Various Materials. ( Henry W. Ott "Noise... Henry & Prober design^^ and the Magerlein design.^^ 1) Henry & Prober design It uses a VCO (Voltage-Controlled-Oscillator) to generate a pulse sequence
Josephson Phase Qubit Circuit for the Evaluation of Advanced Tunnel Barrier Materials
2008-11-21
gradiometer loop. An overlapped gradiometer three- junction direct current superconducting quantum interference device (SQUID) with 64 pH mutual...qubit circuit. (a) Micrograph of an individual qubit circuit consisting of a Josephson junction in a gradiometer loop, state readout measurement
Internal Josephson effects in spinor dipolar Bose-Einstein condensates
Yasunaga, Masashi; Tsubota, Makoto
2010-02-15
We theoretically study the internal Josephson effect, which is driven by spin-exchange interactions and magnetic dipole-dipole interactions, in a three-level system for spin-1 Bose-Einstein condensates, obtaining novel spin dynamics. We introduce single spatial mode approximations into the Gross-Pitaevskii equations and derive the Josephson-type equations, which are analogous to tunneling currents through three junctions between three superconductors. From an analogy with two interacting nonrigid pendulums, we identify unique varied oscillational modes, called the 0-{pi}, 0-running, running-running, 2n{pi} and running-2{pi}, single nonrigid pendulum, and two rigid pendulums phase modes. These Josephson modes in the three states are expected to be found in real atomic Bose gas systems.
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Gaifullin, M.; Kusmartseva, O. E.; Kusmartsev, F. V.; Hirata, K.
2008-09-01
We propose a device able to generate trains of Josephson fluxons without application of external magnetic field - fluxon pump. The pulses of individual fluxons are generated by cloning single fluxons trapped inside a reservoir. When an electric current is applied, a flow of fluxons is generated in the long attachment connected to the reservoir of fluxons. The role of a reservoir is played by Josephson junctions in the form of a loop where one or several fluxons are permanently trapped.
High-frequency dynamics of hybrid oxide Josephson heterostructures
NASA Astrophysics Data System (ADS)
Komissinskiy, P.; Ovsyannikov, G. A.; Constantinian, K. Y.; Kislinski, Y. V.; Borisenko, I. V.; Soloviev, I. I.; Kornev, V. K.; Goldobin, E.; Winkler, D.
2008-07-01
We summarize our results on Josephson heterostructures Nb/Au/YBa2Cu3Ox that combine conventional (S) and oxide high- Tc superconductors with a dominant d -wave symmetry of the superconducting order parameter (D). The heterostructures were fabricated on (001) and (1 1 20) YBa2Cu3Ox films grown by pulsed laser deposition. The structural and surface studies of the (1 1 20) YBa2Cu3Ox thin films reveal nanofaceted surface structure with two facet domain orientations, which are attributed as (001) and (110)-oriented surfaces of YBa2Cu3Ox and result in S/D(001) and S/D(110) nanojunctions formed on the facets. Electrophysical properties of the Nb/Au/YBa2Cu3Ox heterostructures are investigated by the electrical and magnetic measurements at low temperatures and analyzed within the faceting scenario. The superconducting current-phase relation (CPR) of the heterostructures with finite first and second harmonics is derived from the Shapiro steps, which appear in the I-V curves of the heterostructures irradiated at frequencies up to 100 GHz. The experimental positions and amplitudes of the Shapiro steps are explained within the modified resistive Josephson junction model, where the second harmonic of the CPR and capacitance of the Josephson junctions are taken into account. We experimentally observe a crossover from a lumped to a distributed Josephson junction limit for the size of the heterostructures smaller than Josephson penetration depth. The effect is attributed to the variations of the harmonics of the superconducting CPR across the heterojunction, which may give rise to splintered vortices of magnetic flux quantum. Our investigations of parameters and phenomena that are specific for superconductors having d -wave symmetry of the superconducting order parameter may be of importance for applications such as high-frequency detectors and novel elements of a possible quantum computer.
Josephson-CMOS Hybrid Memories
2007-04-25
Liu, X . Meng, S. R. Whiteley, and T. Van Duzer, “Characterization of 4 K CMOS devices and circuits for hybrid Josephson- CMOS systems,” IEEE Trans. on...Josephson- CMOS hybrid memories Qingguo Liu Electrical Engineering and Computer Sciences University of California at Berkeley Technical Report No. UCB...to 00-00-2007 4. TITLE AND SUBTITLE Josephson- CMOS hybrid memories 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S
Josephson effect and nonequilibrium superconductivity in superconducting tunnel structures
NASA Astrophysics Data System (ADS)
Rudenko, E. M.
2012-04-01
Nonequilibrium superconductivity induced by tunnel current injection of quasiparticles is studied. It is found that an instability in the form of a negative voltage jump in the oscillator current-voltage characteristic (CVC), which leads to an inhomogeneous state, as well as the spatial structure of the inhomogeneous state are very sensitive to low magnetic fields. The shape of the CVC of low-resistance tunnel junctions for bias voltages V ≈ 2Δ/e depends strongly on the junction dimensions and barrier transparency. These results are interpreted in terms of Josephson vortices (fluxons) in a tunnel oscillator. Studies of the nonequilibrium phenomena, with the Josephson properties of low-resistance tunnel structures taken into account, reveal a number of new effects, such as nonequilibrium suppression of the energy gap at bias voltages V < 2Δ/e, the possible existence of an entire series of instabilities of the nonequilibrium superconducting state during tunnel injection, and inhomogeneity in the tunnel injector effect.
Josephson photonics with a two-mode superconducting circuit
NASA Astrophysics Data System (ADS)
Armour, A. D.; Kubala, B.; Ankerhold, J.
2015-05-01
We analyze the quantum dynamics of two electromagnetic oscillators coupled in series to a voltage-biased Josephson junction. When the applied voltage leads to a Josephson frequency across the junction which matches the sum of the two mode frequencies, tunneling Cooper pairs excite photons in both modes simultaneously leading to far-from-equilibrium states. These states display highly nonclassical features including strong antibunching, violation of Cauchy-Schwartz inequalities, and number squeezing. We obtain approximate analytic results for both the regimes of low and high photon occupancies which are supported by a full numerical treatment. The impact of asymmetries between the two modes is explored, revealing a pronounced enhancement of number squeezing when the modes are damped at different rates.
Protected Josephson Rhombus Chains
NASA Astrophysics Data System (ADS)
Bell, Matthew T.; Paramanandam, Joshua; Ioffe, Lev B.; Gershenson, Michael E.
2014-04-01
We have studied the low-energy excitations in a minimalistic protected Josephson circuit which contains two basic elements (rhombi) characterized by the π periodicity of the Josephson energy. Novel design of these elements, which reduces their sensitivity to the offset charge fluctuations, has been employed. We have observed that the lifetime T1 of the first excited state of this quantum circuit in the protected regime is increased up to 70 μs, a factor of ˜100 longer than that in the unprotected state. The quality factor ω01T1 of this qubit exceeds 106. Our results are in agreement with theoretical expectations; they demonstrate the feasibility of symmetry protection in the rhombus-based qubits fabricated with existing technology.
Josephson effect without superconductivity: realization in quantum Hall bilayers.
Fogler, M M; Wilczek, F
2001-02-26
We show that a quantum Hall bilayer with the total filling nu = 1 should exhibit a dynamical regime similar to the flux flow in large Josephson junctions. This analogy may explain a conspicuous peak in the interlayer tunneling conductance [Phys. Rev. Lett. 84, 5808 (2000)]. The flux flow is likely to be spatiotemporally chaotic at low-bias voltage, which will manifest itself through broadband noise. The peak position can be controlled by an in-plane magnetic field.
NASA Astrophysics Data System (ADS)
Huebner, Torsten; Boehnke, Alexander; Martens, Ulrike; Thomas, Andy; Schmalhorst, Jan-Michael; Reiss, Günter; Münzenberg, Markus; Kuschel, Timo
2016-06-01
We present a comparison of the tunnel magneto-Seebeck effect for laser-induced and intrinsic heating. Therefore, Co40Fe40B20 /MgAl2O4 and Co25Fe55B20 /MgO magnetic tunnel junctions have been prepared. The TMS ratio of 3% in case of the MAO MTJ agrees well with ratios found for other barrier materials, while the TMS ratio of 23% of the MgO MTJ emphasizes the influence of the CoFe composition. We find results using the intrinsic method that differ in sign and magnitude in comparison to the results of the laser heating. The intrinsic contributions can alternatively be explained by the Brinkman model and the given junction properties. Especially, we are able to demonstrate that the symmetric contribution is solely influenced by the barrier asymmetry. Thus, we conclude that the symmetry analysis used for the intrinsic method is not suitable to unambiguously identify an intrinsic tunnel magneto-Seebeck effect.
Terahertz Josephson spectral analysis and its applications
NASA Astrophysics Data System (ADS)
Snezhko, A. V.; Gundareva, I. I.; Lyatti, M. V.; Volkov, O. Y.; Pavlovskiy, V. V.; Poppe, U.; Divin, Y. Y.
2017-04-01
Principles of Hilbert-transform spectral analysis (HTSA) are presented and advantages of the technique in the terahertz (THz) frequency range are discussed. THz HTSA requires Josephson junctions with high values of characteristic voltages I c R n and dynamics described by a simple resistively shunted junction (RSJ) model. To meet these requirements, [001]- and [100]-tilt YBa2Cu3O7‑x bicrystal junctions with deviations from the RSJ model less than 1% have been developed. Demonstrators of Hilbert-transform spectrum analyzers with various cryogenic environments, including integration into Stirling coolers, are described. Spectrum analyzers have been characterized in the spectral range from 50 GHz to 3 THz. Inside a power dynamic range of five orders, an instrumental function of the analyzers has been found to have a Lorentz form around a single frequency of 1.48 THz with a spectral resolution as low as 0.9 GHz. Spectra of THz radiation from optically pumped gas lasers and semiconductor frequency multipliers have been studied with these spectrum analyzers and the regimes of these radiation sources were optimized for a single-frequency operation. Future applications of HTSA will be related with quick and precise spectral characterization of new radiation sources and identification of substances in the THz frequency range.
High-T{sub c} superconducting Josephson mixers for terahertz heterodyne detection
Malnou, M.; Feuillet-Palma, C.; Olanier, L.; Lesueur, J.; Bergeal, N.; Ulysse, C.; Faini, G.; Febvre, P.; Sirena, M.
2014-08-21
We report on an experimental and theoretical study of the high-frequency mixing properties of ion-irradiated YBa{sub 2}Cu{sub 3}O{sub 7} Josephson junctions embedded in THz antennas. We investigated the influence of the local oscillator power and frequency on the device performances. The experimental data are compared with theoretical predictions of the general three-port model for mixers in which the junction is described by the resistively shunted junction model. A good agreement is obtained for the conversion efficiency in different frequency ranges, spanning above and below the characteristic frequencies f{sub c} of the junctions.
Two Superconducting Charge Qubits Coupled by a Josephson Inductance
NASA Astrophysics Data System (ADS)
Watanabe, Michio; Yamamoto, Tsuyoshi; Pashkin, Yuri A.; Astafiev, Oleg; Nakamura, Yasunobu; Tsai, Jaw-Shen
2007-03-01
When the quantum oscillations [Pashkin et al., Nature 421, 823 (2003)] and the conditional gate operation [Yamamoto et al., Nature 425, 941 (2003)] were demonstrated using superconducting charge qubits, the charge qubits were coupled capacitively, where the coupling was always on and the coupling strength was not tunable. This fixed coupling, however, is not ideal because for example, it makes unconditional gate operations difficult. In this work, we aimed to tunably couple two charge qubits. We fabricated circuits based on the theoretical proposal by You, Tsai, and Nori [PRB 68, 024510 (2003)], where the inductance of a Josephson junction, which has a much larger junction area than the qubit junctions, couples the qubits and the coupling strength is controlled by the external magnetic flux. We confirmed by spectroscopy that the large Josephson junction was indeed coupled to the qubits and that the coupling was turned on and off by the external magnetic flux. In the talk, we will also discuss the quantum oscillations in the circuits.
Motion of a Josephson vortex in the field of a random potential
Mineev, M.B.; Feigel'man, M.V.; Shmidt, V.V.
1981-07-01
We consider the motion and pinning of a Josephson vortex in a field produced by random inhomogeneities in a long junction. We find the distribution function of the force of vortex pinning on the inhomogeneities. We construct the current-voltage characteristic (CVC) of the junction. For inhomogeneities which are weak compared to the ohmic losses the CVC has a single hysteresis, in the opposite case it has two.
AC Josephson effect applications in microwave systems
NASA Astrophysics Data System (ADS)
Larkin, Serguey Y.
1996-12-01
analysis allow to get the picture of temperature distribution along the plasma cord diameter in accordance with dynamics of thermonuclear process development. Modem raclioastronomic research gives scientists the unique information on the world tructure. It is also necessary to analyze Space microwave radiation providing exclusive sensitivity of the equipment. In both cases equipment is required to be superwide band, to have high sensitivity and ability to operate at more than 300 GHz frequencies. Today all these requirements are met by the devices using the ac Josephson effect. The Josephson junctions are used as an active transforming element in such devices. At the end of 20 century the sphere of their utilization embraces medicine, communications, radiophysics, space exploration, ecology, military use, etc. The State Research Center "Fonon" ( SRC "Fonon") of the State Committee on Science and Technology of Ukraine was founded in 1991. The main aim of its creation was to concentrate the scientific and financial efforts for development and production of unique devices based on the results of fundamental study in physics of high T superconductivity. First of all we were interested in technological research on the obtaining of low impedance Josephson junctions out of the High T thin films. Using such junctions in combination with our original techniques developed in our Center we have succeed in creating the following new generation equipment: industrial set-up of the frequency meter in the range of 60 ... 600 GHz; experimental set-up of the spectrum analyzer operating in the range of 50 250 GHz; experimental model of radiometric receiver in 180...260 GHz range. All the above devices are based on the using ac Josephson effect for the receiving and processing mm- and submm- microwave signals.
2016-01-01
The four-way (Holliday) DNA junction of homologous recombination is processed by the symmetrical cleavage of two strands by a nuclease. These junction-resolving enzymes bind to four-way junctions in dimeric form, distorting the structure of the junction in the process. Crystal structures of T7 endonuclease I have been determined as free protein, and the complex with a DNA junction. In neither crystal structure was the N-terminal 16-amino acid peptide visible, yet deletion of this peptide has a marked effect on the resolution process. Here we have investigated the N-terminal peptide by inclusion of spin-label probes at unique sites within this region, studied by electron paramagnetic resonance. Continuous wave experiments show that these labels are mobile in the free protein but become constrained on binding a DNA junction, with the main interaction occurring for residues 7–10 and 12. Distance measurements between equivalent positions within the two peptides of a dimer using PELDOR showed that the intermonomeric distances for residues 2–12 are long and broadly distributed in the free protein but are significantly shortened and become more defined on binding to DNA. These results suggest that the N-terminal peptides become more organized on binding to the DNA junction and nestle into the minor grooves at the branchpoint, consistent with the biochemical data indicating an important role in the resolution process. This study demonstrates the presence of structure within a protein region that cannot be viewed by crystallography. PMID:27387136
Majorana dc Josephson current mediated by a quantum dot.
Xu, Luting; Li, Xin-Qi; Sun, Qing-Feng
2017-05-17
The Josephson supercurrent through a hybrid Majorana-quantum dot-Majorana junction is investigated. We particularly analyze the effect of spin-selective coupling between the Majorana and quantum dot states, which only emerges in the topological phase and will influence the current through bent junctions and/or in the presence of magnetic fields in the quantum dot. We find that the characteristic behavior of the supercurrent through this system is quite counterintuitive, differing remarkably from the resonant tunneling, e.g. through the similar (normal phase) superconductor-quantum dot-superconductor junction. Our analysis is carried out under the influence of the full set-up parameters and for both the [Formula: see text] and [Formula: see text] periodic currents. The present study is expected to be relevant to the future exploration of applications of Majorana-nanowire circuits.
Thermal depinning of fluxons in discrete Josephson rings
Mazo, J. J.; Naranjo, F.; Segall, K.
2008-11-01
We study the thermal depinning of single fluxons in rings made of Josephson junctions. Due to thermal fluctuations a fluxon can be excited from its energy minima and move through the array, causing a voltage across each junction. We find that for the initial depinning, the fluxon behaves as a single particle and follows a Kramers-type escape law. However, under some conditions this single-particle description breaks down. At low values of the discreteness parameter and low values of the damping, the depinning rate is larger than what the single-particle result would suggest. In addition, for some values of the parameters the fluxon can undergo low-voltage diffusion before switching to the high-voltage whirling mode. This type of diffusion is similar to phase diffusion in a single junction but occurs without frequency-dependent damping. We study the switching to the whirling state as well.
Thermal transport through ac-driven transparent Josephson weak links
NASA Astrophysics Data System (ADS)
Virtanen, P.; Giazotto, F.
2014-07-01
We discuss how phase coherence manifests in the heat transport through superconducting single and multichannel Josephson junctions in time-dependent situations. We consider the heat current driven through the junction by a temperature difference in dc voltage and ac phase biased situations. At low bias, the electromagnetic driving mainly modifies the form of the coherent resonance that transports a large part of the heat current, rather than simply dissipating energy in the junction. We find a description for the heat current in terms of quasiparticle n-photon absorption and emission rates, and discuss analytical and numerical results concerning them. In addition to the ensemble average heat transport, we describe also its fluctuations.
Self-Oscillating Josephson Quantum Heat Engine
NASA Astrophysics Data System (ADS)
Marchegiani, G.; Virtanen, P.; Giazotto, F.; Campisi, M.
2016-11-01
The design of a mesoscopic self-oscillating heat engine that works thanks to purely quantum effects is presented. The proposed scheme is amenable to experimental implementation with current state-of-the-art nanotechnology and materials. One of the main features of the structure is its versatility: The engine can deliver work to a generic load without galvanic contact. This versatility makes it a promising building block for low-temperature on-chip energy-management applications. The heat engine consists of a circuit featuring a thermoelectric element based on a ferromagnetic insulator-superconductor tunnel junction and a Josephson weak link that realizes a purely quantum dc-ac converter. This makeup enables the contactless transfer of work to the load (a generic RL circuit). The performance of the heat engine is investigated as a function of the thermal gradient applied to the thermoelectric junction. Power up to 1 pW can be delivered to a load RL=10 Ω .
Jonction Josephson en couche épaisse d'oxydes supraconducteurs
NASA Astrophysics Data System (ADS)
Gunther, C.; Monfort, Y.; Sing, M. Lam Chok; Bloyet, D.; Brousse, T.; Provost, J.; Raveau, B.
1992-02-01
Constrictions engraved in YBaCuO thick films fabricated by screen printing on YSZ substrate (J_c>3 000 A/cm^2 at 77 K) have been studied. Microwave irradiation of the devices at LN2 showed distinct Shapiro steps demonstrating the presence intrinsic Josephson junctions. The latter have an I_c(T) dependence fitting (1-T/T_c)^2 characteristic of SNS junctions. Furthermore, dc SQUID effects have also been observed with a peak-to-peak response simeq 0.2 μV and with a magnetic field periodicity extending through several hundred of φ_0. An energy resolution close to 3× 10^{-29} J/Hz is estimated for our constriction operating in the white noise frequency range (f>50 Hz) at 77 K. This sensitivity is adequate to use this flux sensor in many applications : geomagnetism, magnetocardiology, ... Nous avons étudié des constrictions gravées dans des couches épaisses d'YBaCuO déposées sur substrat de YSZ (J_c>3 000 A/cm^2 à 77 K). L'observation de marches de Shapiro lors d'irradiations des échantillons à 77 K par un champ HF met clairement en évidence la présence de jonctions Josephson intrinsèques de type SNS, leur dépendance en température du courant critique étant en (1-T/T_c)^2. De plus, nous avons obtenu des réponses en champ magnétique, caractéristiques des SQUIDs dc, d'amplitude 0,2 μVcc et dont la périodicité s'étend sur plusieurs centaines de φ_0. La résolution en énergie est de l'ordre de 3× 10^{-29} J/Hz en zone de bruit blanc (f>50 Hz) à 77 K. Cette sensibilité est suffisante pour envisager son utilisation dans des applications telles que : géomagnétisme, magnétocardiologie, ...
Observation of Soliton Fusion in a Josephson Array
Pfeiffer, J.; Schuster, M.; Abdumalikov, A.A. Jr.; Ustinov, A.V.
2006-01-27
The behavior of topological solitons in a parallel array of a Josephson junction is studied experimentally. We observe the fusion of two relativistic 2{pi} solitons of the same polarity into a single 4{pi} soliton. The 4{pi} soliton carries two quanta of magnetic flux and, most strikingly, travels 18% faster than an ordinary 2{pi} soliton under the same driving force. We also find a variety of bunched states composed of 2{pi} solitons of the same polarity, moving with fixed separation.
New fluxon resonant mechanism in annular Josephson tunnel structures.
Nappi, C; Lisitskiy, M P; Rotoli, G; Cristiano, R; Barone, A
2004-10-29
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 effects in an alternating current biased transition edge sensor
NASA Astrophysics Data System (ADS)
Gottardi, L.; Kozorezov, A.; Akamatsu, H.; van der Kuur, J.; Bruijn, M. P.; den Hartog, R. H.; Hijmering, R.; Khosropanah, P.; Lambert, C.; van der Linden, A. J.; Ridder, M. L.; Suzuki, T.; Gao, J. R.
2014-10-01
We report the experimental evidence of the ac Josephson effect in a transition edge sensor (TES) operating in a frequency domain multiplexer and biased by ac voltage at MHz frequencies. The effect is observed by measuring the non-linear impedance of the sensor. The TES is treated as a weakly linked superconducting system and within the resistively shunted junction model framework. We provide a full theoretical explanation of the results by finding the analytic solution of the non-inertial Langevian equation of the system and calculating the non-linear response of the detector to a large ac bias current in the presence of noise.
Resonant subgap current transport in Josephson field effect transistor
NASA Astrophysics Data System (ADS)
Bezuglyi, E. V.; Bratus', E. N.; Shumeiko, V. S.
2017-01-01
We study theoretically the current-voltage characteristics (IVCs) of the Josephson field effect transistor—a ballistic SNINS junction with superconducting (S) electrodes confining a planar normal-metal region (N), which is controlled by the gate-induced potential barrier (I). Using the computation technique developed earlier for long single-channel junctions in the coherent multiple Andreev reflection (MAR) regime, we find a significant difference of the subgap current structure compared to the subharmonic gap structure in tunnel junctions and atomic-size point contacts. For long junctions, whose lengths significantly exceed the coherence length, the IVC exhibits current peaks at multiples (harmonics) of the distance δm between the static Andreev levels e Vn=n δm . Moreover, the averaged IVC follows the powerlike behavior rather than the exponential one and has a universal scaling with the junction transparency. This result is qualitatively understood using an analytical approach based on the concept of resonant MAR trajectories. In shorter junctions having lengths comparable to the coherence length, the IVC has an exponential form common for point contacts, however the current structures appear at the subharmonics of the interlevel distance e Vn=δm/n rather than the gap subharmonics 2 Δ /n .
NASA Astrophysics Data System (ADS)
Gouchi, Jun; Sumiyama, Akihiko; Motoyama, Gaku; Yamaguchi, Akira; Kimura, Noriaki; Yamamoto, Etsuji; Haga, Yoshinori; Ōnuki, Yoshichika
2012-11-01
The Josephson critical current Ic between a single-crystal UPt3 and Al has been measured for the junctions on the UPt3 surface perpendicular to the hexagonal a[11\\bar{2}0], b[10\\bar{1}0], and c[0001] axes. The magnetic field dependence of Ic shows a Fraunhofer diffraction pattern for a current flow parallel to the c-axis, suggesting that the Josephson coupling is uniform throughout the junction. Small modifications applied to the Fraunhofer pattern have been observed for a current flow parallel to the a- and b-axes. These results contradict the E2u scenario for the odd-parity order parameter in UPt3, in which the Josephson effect is forbidden in the three directions, whereas the recently proposed E1u scenario permits, at least, the a- and c-axis Josephson couplings.
Josephson effect in CeCoIn{sub 5} microbridges as seen via quantum interferometry
Foyevtsov, Oleksandr; Porrati, Fabrizio; Huth, Michael
2011-07-15
A superconducting quantum interference device (SQUID) was prepared on a micron-sized single crystal using a selected growth domain of a thin film of CeCoIn{sub 5} grown by molecular beam epitaxy. SQUID voltage oscillations of good quality were obtained as well as interference effects stemming from the individual Josephson microbridges. The transport characteristics in the superconducting state exhibited several peculiarities which we ascribe to the periodic motion of vortices in the microbridges. The temperature dependence of the Josephson critical current shows good correspondence to the Ambegaokar-Baratoff relation, expected for the ideal Josephson junction. The results indicate a promising pathway to identify the type of order parameter in CeCoIn{sub 5} by means of phase-sensitive measurements on microbridges.
Identifying the chiral d-wave superconductivity by Josephson φ0-states
NASA Astrophysics Data System (ADS)
Liu, Jun-Feng; Xu, Yong; Wang, Jun
2017-03-01
We propose the Josephson junctions linked by a normal metal between a d + id superconductor and another d + id superconductor, a d-wave superconductor, or a s-wave superconductor for identifying the chiral d + id superconductivity. The time-reversal breaking in the chiral d-wave superconducting state is shown to result in a Josephson φ0-junction state where the current-phase relation is shifted by a phase φ0 from the sinusoidal relation, other than 0 and π. The ground-state phase difference φ0 and the critical current can be used to definitely confirm and read the information about the d + id superconductivity. A smooth evolution from conventional 0-π transitions to tunable φ0-states can be observed by changing the relative magnitude of two types of d-wave components in the d + id pairing. On the other hand, the Josephson junction involving the d + id superconductor is also the simplest model to realize a φ0- junction, which is useful in superconducting electronics and superconducting quantum computation.
Identifying the chiral d-wave superconductivity by Josephson φ0-states
Liu, Jun-Feng; Xu, Yong; Wang, Jun
2017-01-01
We propose the Josephson junctions linked by a normal metal between a d + id superconductor and another d + id superconductor, a d-wave superconductor, or a s-wave superconductor for identifying the chiral d + id superconductivity. The time-reversal breaking in the chiral d-wave superconducting state is shown to result in a Josephson φ0-junction state where the current-phase relation is shifted by a phase φ0 from the sinusoidal relation, other than 0 and π. The ground-state phase difference φ0 and the critical current can be used to definitely confirm and read the information about the d + id superconductivity. A smooth evolution from conventional 0-π transitions to tunable φ0-states can be observed by changing the relative magnitude of two types of d-wave components in the d + id pairing. On the other hand, the Josephson junction involving the d + id superconductor is also the simplest model to realize a φ0- junction, which is useful in superconducting electronics and superconducting quantum computation. PMID:28266582
Low-noise THz MgB2 Josephson mixer
NASA Astrophysics Data System (ADS)
Cunnane, Daniel; Kawamura, Jonathan H.; Acharya, Narendra; Wolak, Matthäus A.; Xi, X. X.; Karasik, Boris S.
2016-09-01
The potential applications for high frequency operation of the Josephson effect in MgB2 include THz mixers, direct detectors, and digital circuits. Here we report on MgB2 weak links which exhibit the Josephson behavior up to almost 2 THz and using them for low-noise heterodyne detection of THz radiation. The devices are made from epitaxial film grown in the c-axis direction by the hybrid physical-chemical vapor deposition method. The current in the junctions travels parallel to the surface of the film, thus making possible a large contribution of the quasi-two-dimensional σ-gap in transport across the weak link. These devices are connected to a planar spiral antenna with a dielectric substrate lens to facilitate coupling to free-space radiation for use as a detector. The IcRn product of the junction is 5.25 mV, giving confirmation of a large gap parameter. The sensitivity of the mixer was measured from 0.6 THz to 1.9 THz. At a bath temperature of over 20 K, a mixer noise temperature less than 2000 K (DSB) was measured near 0.6 THz.
Microwave quantum refrigeration based on the Josephson effect
NASA Astrophysics Data System (ADS)
Solinas, Paolo; Bosisio, Riccardo; Giazotto, Francesco
2016-06-01
We present a microwave quantum refrigeration principle based on the Josephson effect. When a superconducting quantum interference device (SQUID) is pierced by a time-dependent magnetic flux, it induces changes in the macroscopic quantum phase and an effective finite bias voltage appears across the SQUID. This voltage can be used to actively cool, well below the lattice temperature, one of the superconducting electrodes forming the interferometer. The achievable cooling performance combined with the simplicity and scalability intrinsic to the structure pave the way to a number of applications in quantum technology.
Critical-current diffraction patterns of grain-boundary Josephson weak links
Peterson, R.L.; Ekin, J.W. )
1990-11-01
We discuss the diffraction patterns and other characteristics of the critical current as a function of magnetic field in grain-boundary Josephson barriers. Diffraction patterns occur not just for {ital SIS} junctions but for all types of Josephson links, including {ital SNS} junctions, which may be present at grain boundaries in high-{Tc} superconductors. We discuss the generality of the Airy diffraction pattern, which is expected to characterize grain-boundary barriers in bulk material more accurately than the Fraunhofer pattern. The transport critical-current density in many bulk, granular high-{ital T}{sub {ital c}} superconductors has a power-law dependence on very low magnetic fields, characteristic of averaged diffraction patterns, and cannot be fitted by an exponential magnetic-field dependence, which may result from the material properties of the barriers.
Terahertz and Millimetre Wave Imaging with a Broadband Josephson Detector Working above 77 K
NASA Astrophysics Data System (ADS)
Du, Jia; Hellicar, A. D.; Hanham, S. M.; Li, L.; Macfarlane, J. C.; Leslie, K. E.; Foley, C. P.
2011-05-01
A high-Tc superconducting (HTS) broadband Josephson detector has been developed and applied to millimetre wave (mm-wave) and terahertz (THz) imaging. The detector is based on a YBa2Cu3O7-x (YBCO) step-edge Josephson junction, which is coupled to a thin-film log-periodic antenna, designed for operation at 200-600 GHz, and a hemispheric silicon lens. The junction parameters have been optimised to achieve a high IcRn value so that the detector responds well to the specified frequencies at liquid nitrogen temperature (77 K). Images at ˜200 GHz and ˜600 GHz were acquired with the same detector; each demonstrated their unique properties. The results demonstrate the potential of achieving a cheaper, compact and portable multi-spectral imager based on a HTS detector.
Dynamical simulations of fractional giant Shapiro steps in two-dimensional Josephson arrays
Free, J.U.; Benz, S.P.; Rzchowski, M.S.; Tinkham, M.; Lobb, C.J. Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 ); Octavio, M. )
1990-04-01
We have performed computer simulations of arrays of resistively shunted Josephson junctions in the presence of commensurate magnetic fields and alternating and direct currents. We have found {ital fractional} giant Shapiro steps in the simulated current-voltage characteristics in agreement with recent experimental measurements. The detailed motion of the magnetic-field-induced vortices is shown to be in agreement with a previously proposed phenomenological model of Benz {ital et} {ital al}. (Phys. Rev. Lett. 64, 693 (1990)).
Terahertz radiation from Josephson sandwiches
NASA Astrophysics Data System (ADS)
Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
2010-08-01
Basic results are presented from a study of the Cerenkov emission of electromagnetic waves by solitary vortices and Swihart waves moving in a long Josephson sandwich embedded in a dielectric. The energy fluxes of the electromagnetic field along a long sandwich are examined. The magnitudes of the fluxes are compared over a wide range of frequencies and wave numbers of surface waves in the sandwich.
Josephson current through a quantum dot coupled to a molecular magnet
NASA Astrophysics Data System (ADS)
Stadler, P.; Holmqvist, C.; Belzig, W.
2013-09-01
Josephson currents are carried by sharp Andreev states within the superconducting energy gap. We theoretically study the electronic transport of a magnetically tunable nanoscale junction consisting of a quantum dot connected to two superconducting leads and coupled to the spin of a molecular magnet. The exchange interaction between the molecular magnet and the quantum dot modifies the Andreev states due to a spin-dependent renormalization of the quantum dot's energy level and the induction of spin flips. A magnetic field applied to the central region of the quantum dot and the molecular magnet further tunes the Josephson current and starts a precession of the molecular magnet's spin. We use a nonequilibrium Green's function approach to evaluate the transport properties of the junction. Our calculations reveal that the energy level of the dot, the magnetic field, and the exchange interaction between the molecular magnet and the electrons occupying the energy level of the quantum dot can trigger transitions from a 0 to a π state of the Josephson junction. The redistribution of the occupied states induced by the magnetic field strongly modifies the current-phase relation. The critical current exhibits a sharp increase as a function of either the energy level of the dot, the magnetic field, or the exchange interaction.
Josephson effect studies of pairing symmetry in Fe-based superconductors
NASA Astrophysics Data System (ADS)
Zhang, Xiaohang
2010-03-01
To investigate the pairing symmetry in the recently discovered Fe-based superconductors, Josephson effect studies have been performed on two types of c-axis junctions incorporating 122-type iron pnictide superconductors: junctions between s-wave superconductors and iron pnictide superconductors [1] and junctions between electron-doped and hole-doped iron pnictide superconductors [2]. The ac Josephson effect was observed in the I-V characteristics for both types of junctions under microwave irradiation. By applying external magnetic fields parallel to the junction interfaces, Fraunhofer-like patterns were obtained. Analysis based on the obtained modulation patterns suggests that the Josephson current is flowing along the c-axis direction within a typical area of 10 x 10 (μm)^2. The presence of Josephson coupling between an s-wave superconductor and a 122-type iron pnictide superconductor along the c-axis strongly supports an s-wave symmetry in the iron pnictide superconductor. Moreover, our observed Josephson effect in the bicrystal junctions indicates that phase coherence can be established between electron-doped and hole-doped iron pnictide superconductors. Such a phase-coherent p-n structure is an important component [3] for performing definitive phase-sensitive tests for the proposed s± symmetry in Fe-based superconductors. Progress in carrying out such tests will be discussed. Recent results on systematic measurements of the energy gap using Andreev reflection spectroscopy with highly transparent contacts will also be presented. This work is supported by the NSF (DMR-0653535) and performed in collaboration with S. R. Saha, N. P. Butch, K. Kirshenbaum, J. Paglione, R. L. Greene, I. Takeuchi at UMD, and Y. S. Oh, Y. Liu, L. Q. Yan, K. H. Kim at SNU. [4pt] [1] X. H. Zhang et al., Phys. Rev. Lett. 102, 147002 (2009).[0pt] [2] X. H. Zhang et al., Appl. Phy. Lett. 95, 062510 (2009).[0pt] [3] D. Parker and I. I. Mazin, Phys. Rev. Lett. 102, 227007 (2009).
Operation of NIST Josephson Array Voltage Standards
Hamilton, Clark A.; Burroughs, Charles; Chieh, Kao
1990-01-01
This paper begins with a brief discussion of the physical principles and history of Josephson effect voltage standards. The main body of the paper deals with the practical details of the array design, cryoprobe construction, bias source requirements, adjustment of the system for optimum performance, calibration algorithms, and an assessment of error sources for the NIST-developed Josephson array standard. PMID:28179776
Nearly quantum limited nanoSQUIDs based on cross-type Nb/AlO x /Nb junctions
NASA Astrophysics Data System (ADS)
Schmelz, M.; Zakosarenko, V.; Schönau, T.; Anders, S.; Linzen, S.; Stolz, R.; Meyer, H.-G.
2017-01-01
We report on the development of nearly quantum limited SQUIDs with miniature pickup loop dimensions. The implemented high quality and low capacitance cross-type Nb/AlO x /Nb Josephson junctions offer large I C R N -products and therefore enable an exceptional low noise level of the SQUIDs. Devices with loop dimensions of 1 μm exhibit white flux noise levels as low as 45 nΦ0 Hz-1/2 corresponding to an energy resolution ɛ of about 1 h at 4.2 K, with h being Planck’s constant. Moreover, the large usable voltage swings of the devices of about 300 μV allow highly sensitive and easy single-stage operation while exploring nearly the intrinsic noise of the SQUIDs, beneficial e.g. for sensor arrays in SQUID microscopy.
Ferromagnetic-Insulator-Based Superconducting Junctions as Sensitive Electron Thermometers
NASA Astrophysics Data System (ADS)
Giazotto, F.; Solinas, P.; Braggio, A.; Bergeret, F. S.
2015-10-01
We present an exhaustive theoretical analysis of charge and thermoelectric transport in a normal-metal-ferromagnetic-insulator-superconductor junction and explore the possibility of its use as a sensitive thermometer. We investigate the transfer functions and the intrinsic noise performance for different measurement configurations. A common feature of all configurations is that the best temperature-noise performance is obtained in the nonlinear temperature regime for a structure based on an Europium chalcogenide ferromagnetic insulator in contact with a superconducting Al film structure. For an open-circuit configuration, although the maximal intrinsic temperature sensitivity can achieve 10 nK Hz-1 /2 , a realistic amplifying chain will reduce the sensitivity up to 10 μ K Hz-1 /2 . To overcome this limitation, we propose a measurement scheme in a closed-circuit configuration based on state-of-the-art superconducting-quantum-interference-device detection technology in an inductive setup. In such a case, we show that temperature-noise can be as low as 35 nK Hz-1 /2 . We also discuss a temperature-to-frequency converter where the obtained thermovoltage developed over a Josephson junction operated in the dissipative regime is converted into a high-frequency signal. We predict that the structure can generate frequencies up to approximately 120 GHz and transfer functions up to 200 GHz /K at around 1 K. If operated as an electron thermometer, the device may provide temperature-noise lower than 35 nK Hz-1 /2 thereby being potentially attractive for radiation-sensing applications.
Control of Josephson current by Aharonov-Casher phase in a Rashba ring
NASA Astrophysics Data System (ADS)
Liu, Xin; Borunda, M. F.; Liu, Xiong-Jun; Sinova, Jairo
2009-11-01
We study the interference effect induced by the Aharonov-Casher phase on the Josephson current through a semiconducting ring attached to superconducting leads. Using a one-dimensional model that incorporates spin-orbit coupling in the semiconducting ring, we calculate the Andreev levels analytically and numerically, and predict oscillations of the Josephson current due to the AC phase. This result is valid from the point-contact limit to the long channel-length case, as defined by the ratio of the junction length and the BCS healing length. We show in the long channel-length limit that the impurity scattering has no effect on the oscillation of the Josephson current, in contrast to the case of conductivity oscillations in a spin-orbit-coupled ring system attached to normal leads where impurity scattering reduces the amplitude of oscillations. Our results suggest a scheme to measure the AC phase with, in principle, higher sensitivity. In addition, this effect allows for control of the Josephson current through the gate-voltage-tuned AC phase.
Josephson and persistent spin currents in Bose-Einstein condensates of magnons
NASA Astrophysics Data System (ADS)
Nakata, Kouki; van Hoogdalem, Kevin A.; Simon, Pascal; Loss, Daniel
2014-10-01
Using the Aharonov-Casher (A-C) phase, we present a microscopic theory of the Josephson and persistent spin currents in quasiequilibrium Bose-Einstein condensates (BECs) of magnons in ferromagnetic insulators. Starting from a microscopic spin model that we map onto a Gross-Pitaevskii Hamiltonian, we derive a two-state model for the Josephson junction between the weakly coupled magnon-BECs. We then show how to obtain the alternating-current (ac) Josephson effect with magnons as well as macroscopic quantum self-trapping in a magnon-BEC. We next propose how to control the direct-current (dc) Josephson effect electrically using the A-C phase, which is the geometric phase acquired by magnons moving in an electric field. Finally, we introduce a magnon-BEC ring and show that persistent magnon-BEC currents flow due to the A-C phase. Focusing on the feature that the persistent magnon-BEC current is a steady flow of magnetic dipoles that produces an electric field, we propose a method to directly measure it experimentally.
Two-Volt Josephson Arbitrary Waveform Synthesizer Using Wilkinson Dividers.
Flowers-Jacobs, Nathan E; Fox, Anna E; Dresselhaus, Paul D; Schwall, Robert E; Benz, Samuel P
2016-09-01
The root-mean-square (rms) output voltage of the NIST Josephson arbitrary waveform synthesizer (JAWS) has been doubled from 1 V to a record 2 V by combining two new 1 V chips on a cryocooler. This higher voltage will improve calibrations of ac thermal voltage converters and precision voltage measurements that require state-of-the-art quantum accuracy, stability, and signal-to-noise ratio. We achieved this increase in output voltage by using four on-chip Wilkinson dividers and eight inner-outer dc blocks, which enable biasing of eight Josephson junction (JJ) arrays with high-speed inputs from only four high-speed pulse generator channels. This approach halves the number of pulse generator channels required in future JAWS systems. We also implemented on-chip superconducting interconnects between JJ arrays, which reduces systematic errors and enables a new modular chip package. Finally, we demonstrate a new technique for measuring and visualizing the operating current range that reduces the measurement time by almost two orders of magnitude and reveals the relationship between distortion in the output spectrum and output pulse sequence errors.
Two-Volt Josephson Arbitrary Waveform Synthesizer Using Wilkinson Dividers
Flowers-Jacobs, Nathan E.; Fox, Anna E.; Dresselhaus, Paul D.; Schwall, Robert E.; Benz, Samuel P.
2016-01-01
The root-mean-square (rms) output voltage of the NIST Josephson arbitrary waveform synthesizer (JAWS) has been doubled from 1 V to a record 2 V by combining two new 1 V chips on a cryocooler. This higher voltage will improve calibrations of ac thermal voltage converters and precision voltage measurements that require state-of-the-art quantum accuracy, stability, and signal-to-noise ratio. We achieved this increase in output voltage by using four on-chip Wilkinson dividers and eight inner-outer dc blocks, which enable biasing of eight Josephson junction (JJ) arrays with high-speed inputs from only four high-speed pulse generator channels. This approach halves the number of pulse generator channels required in future JAWS systems. We also implemented on-chip superconducting interconnects between JJ arrays, which reduces systematic errors and enables a new modular chip package. Finally, we demonstrate a new technique for measuring and visualizing the operating current range that reduces the measurement time by almost two orders of magnitude and reveals the relationship between distortion in the output spectrum and output pulse sequence errors. PMID:27453676
Development of High Temperature Superconducting Josephson Junction Device Technology
2007-11-02
volatilization rate" in this and earlier publications. Feedback from the crystal monitor is used to adjust the thallium source temperature. The...on different substrates will be published 168/SPIE Vol. 2697 20 40 26 (degrees) 60 80 c 3 c3 Ui 15 < " efl T: 180 <|> (degrees) j^p/^ffi
Dynamical Properties of Two-Dimensional Josephson Junction Arrays
1990-05-01
6.2 Experimental Results 94 6.3 The Ginzburg -Landau Equations and Simulation Algorithm 96 6.4 Simulation Results and Discussion 102 vi 6.5 Other Notable...arrays in commensurate magnetic fields will be described in Chapter 5. Chapter 6 describes the results of Ginzburg -Landau calculations of 2 the TC of...in the system. 2 The helicity modulus for zero magnetic field, as determined from Monte Carlo simulations on finite arrays, is plotted in Fig. 1.2
Anomalous Josephson Hall effect in magnet/triplet superconductor junctions
NASA Astrophysics Data System (ADS)
Yokoyama, Takehito
2015-11-01
We investigate anomalous Hall effect in a magnet coupled to a triplet superconductor under phase gradient. It is found that the anomalous Hall supercurrent arises from the nontrivial structure of the magnetization. The magnetic structure manifested in the Hall supercurrent is characterized by even order terms of the exchange coupling, essentially different from that discussed in the context of anomalous Hall effect, reflecting the dissipationless nature of the supercurrent. We also discuss a possible candidate for magnetic structure to verify our prediction.
Tunable plasma edge in Josephson junction loaded wire array metamaterial
NASA Astrophysics Data System (ADS)
Trepanier, Melissa; Zhang, Daimeng; Koshelets, V. P.; Anlage, Steven
It is desirable to have a tunable negative permittivity medium that operates in the microwave domain. The effective plasma frequency of a JJ-loaded wire array can be tuned as a function of dc current and temperature in the low current limit. To demonstrate this effect we observe a change in transmission through a single layer of 8 superconducting Nb wires that spans a rectangular waveguide. A simple model that treats the wires as an artificial dielectric with a tunable effective permittivity shows good agreement with measured results for tuning of the plasma edge. In addition we have observed interesting behavior at higher current and rf input power. The dynamics are very rich, highly hysteretic, and nonlinear. This work is supported by the NSF-GOALI and OISE programs through Grant # ECCS-1158644, and CNAM.
Phase-dependent magnetoconductance fluctuations in a chaotic Josephson junction
NASA Astrophysics Data System (ADS)
Brouwer, P. W.; Beenakker, C. W. J.
1996-11-01
Motivated by recent experiments by Den Hartog et al., we present a random-matrix theory for the magnetoconductance fluctuations of a chaotic quantum dot that is coupled by point contacts to two superconductors and one or two normal metals. There are aperiodic conductance fluctuations as a function of the magnetic field through the quantum dot and 2π-periodic fluctuations as a function of the phase difference φ of the superconductors. If the coupling to the superconductors is weak compared to the coupling to the normal metals, the φ dependence of the conductance is harmonic, as observed in the experiment. In the opposite regime, the conductance becomes a random 2π-periodic function of φ, in agreement with the theory of Altshuler and Spivak. The theoretical method employs an extension of the circular ensemble which can describe the magnetic-field dependence of the scattering matrix.
Sub-Micrometer Epitaxial Josephson Junctions for Quantum Circuits
2011-10-31
that the surface morphology of the Re base-electrode is independent of furnace treatment and miscut angle. At first we used a 165 nm thick rhenium ...substrate. Using this technique, we obtain crystalline rhenium films. We find that these film are characterized by ...... 100 nm diameter hexagonal islands...energy (1.9 J /m2) than rhenium (2.2 J /m2) and acts as a wetting layer, resulting in a significantly smoother surface, as shown in figures 1 (a) and
Theoretical Modeling of Josephson Junctions for Digital Electronics
2005-11-29
the Mott insulator-superfluid transition in the Bose Hubbard model", National Institute of Standards and Technology, Gaithersberg (November, 2002...Phys. Rev. B 69, 165105--1-5 (2004). [20] D. 0. Demchencko, A. V. Joura, and J. K. Freericks, Effect of particle-hole asymmetry on the Mott- Hubbard
Measurements on Two-Dimensional Arrays of Mesoscopic Josephson Junctions
1993-02-01
effect, the magnetic analog of the Aharonov - Bohm effect (with the AC effect, it is theoretically predicted that one can measure the interference... Aharonov and Bohm (1959), and Aharonov and Casher (1984). 148 REFERENCES Aharonov , Y., and D. Bohm , Phys. Rev. B 3, 485 (1959). Aharonoy, Y., and A...are reasonably well- understood, with the possible exceptions of ballistic motion of vortices [van der Zant, et al. (1992b)] and the Aharonov -Casher (AC
Josephson Junction Digital Waveform Generation for Very Wideband Radars
1992-01-31
designs available from TRW’s microcell library. The cell design will be optimized as necessary for operation at 4 GHz and higher clock rates. 1-BIT FULL...sourcesI 41 " , c . (04- I 4’lteon of~ mtor - on Send comments relJardirg (hi’s burden ,%umate or .,)ny ,(her olpect of iha, s rd 1 ’ .,I 3thon H4,-aau4...This operation is accomplished by adding the input word to the accumulated output word each clock cycle. The sine- ROM converts this phase word into
Observing Majorana bound states of Josephson vortices in topological superconductors
Grosfeld, Eytan; Stern, Ady
2011-01-01
In recent years there has been an intensive search for Majorana fermion states in condensed matter systems. Predicted to be localized on cores of vortices in certain nonconventional superconductors, their presence is known to render the exchange statistics of bulk vortices non-Abelian. Here we study the equations governing the dynamics of phase solitons (fluxons) in a Josephson junction in a topological superconductor. We show that the fluxon will bind a localized zero energy Majorana mode and will consequently behave as a non-Abelian anyon. The low mass of the fluxon, as well as its experimentally observed quantum mechanical wave-like nature, will make it a suitable candidate for vortex interferometry experiments demonstrating non-Abelian statistics. We suggest two experiments that may reveal the presence of the zero mode carried by the fluxon. Specific experimental realizations will be discussed as well. PMID:21730165
Interactions between electrons, mesoscopic Josephson effect and asymmetric current fluctuations
NASA Astrophysics Data System (ADS)
Huard, B.
2006-07-01
This article discusses three experiments on the properties of electronic transport at the mesoscopic scale. The first one allowed to measure the energy exchange rate between electrons in a metal contaminated by a very weak concentration of magnetic impurities. The role played by magnetic impurities in the Kondo regime on those energy exchanges is quantitatively investigated, and the global measured exchange rate is larger than expected. The second experiment is a measurement of the current-phase relation in a system made of two superconductors linked through a single atom. We thus provide quantitative support for the recent description of the mesoscopic Josephson effect. The last experiment is a measurement of the asymmetry of the current fluctuations in a mesoscopic conductor, using a Josephson junction as a threshold detector. Cet ouvrage décrit trois expériences portant sur les propriétés du transport électronique à l'échelle mésoscopique. La première a permis de mesurer le taux d'échange d'énergie entre électrons dans un métal contenant une très faible concentration d'impuretés magnétiques. Nous avons validé la description quantitative du rôle des impuretés magnétiques dans le régime Kondo sur ces échanges énergétiques et aussi montré que le taux global d'échange est plus fort que prévu. La seconde expérience est une mesure de la relation courant-phase dans un système constitué de deux supraconducteurs couplés par un seul atome. Elle nous a permis de conforter quantitativement la récente description de l'effet Josephson mésoscopique. La dernière expérience est unemesure de l'asymétrie des fluctuations du courant dans un conducteur mésoscopique en utilisant une Jonction Josephson comme détecteur de seuil.
Polaritonic Rabi and Josephson Oscillations
Rahmani, Amir; Laussy, Fabrice P.
2016-01-01
The dynamics of coupled condensates is a wide-encompassing problem with relevance to superconductors, BECs in traps, superfluids, etc. Here, we provide a unified picture of this fundamental problem that includes i) detuning of the free energies, ii) different self-interaction strengths and iii) finite lifetime of the modes. At such, this is particularly relevant for the dynamics of polaritons, both for their internal dynamics between their light and matter constituents, as well as for the more conventional dynamics of two spatially separated condensates. Polaritons are short-lived, interact only through their material fraction and are easily detuned. At such, they bring several variations to their atomic counterpart. We show that the combination of these parameters results in important twists to the phenomenology of the Josephson effect, such as the behaviour of the relative phase (running or oscillating) or the occurence of self-trapping. We undertake a comprehensive stability analysis of the fixed points on a normalized Bloch sphere, that allows us to provide a generalized criterion to identify the Rabi and Josephson regimes in presence of detuning and decay. PMID:27452872
Correlating quantum decoherence and material defects in a Josephson qubit
NASA Astrophysics Data System (ADS)
Hite, D. A.; McDermott, R.; Simmonds, R. W.; Cooper, K. B.; Steffen, M.; Nam, S.; Pappas, D. P.; Martinis, J. M.
2004-03-01
Superconducting tunnel junction devices are promising candidates for constructing quantum bits (qubits) for quantum computation because of their inherently low dissipation and ease of scalability by microfabrication. Recently, the Josephson phase qubit has been characterized spectroscopically as having spurious microwave resonators that couple to the qubit and act as a dominant source of decoherence. While the origin of these spurious resonances remains unknown, experimental evidence points to the material system of the tunnel barrier. Here, we focus on our materials research aimed at elucidating and eliminating these spurious resonators. In particular, we have studied the use of high quality Al films epitaxially grown on Si(111) as the base electrode of the tunnel junction. During each step in the Al/AlOx/Al trilayer growth, we have investigated the structure in situ by AES, AED and LEED. While tunnel junctions fabricated with these epitaxial base electrodes prove to be of non-uniform oxide thickness and too thin, I-V characteristics have shown a lowering of subgap currents by a factor of two. Transport measurements will be correlated with morphological structure for a number of devices fabricated with various degrees of crystalline quality.
Sheikhzada, Ahmad; Gurevich, Alex
2015-01-01
Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Here we address the breakdown of the topologically-protected stability of such defects driven by strong external forces. We focus on Josephson vortices that appear at planar weak links of suppressed superconductivity which have attracted much attention for electronic applications, new sources of THz radiation, and low-dissipative computing. Our numerical simulations show that a rapidly moving vortex driven by a constant current becomes unstable with respect to generation of vortex-antivortex pairs caused by Cherenkov radiation. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of an expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. Our work gives a new insight into instability of a moving topological defect which destroys global long-range order in a way that is remarkably similar to the crack propagation in solids. PMID:26639165
The ω-SQUIPT as a tool to phase-engineer Josephson topological materials
NASA Astrophysics Data System (ADS)
Strambini, E.; D'Ambrosio, S.; Vischi, F.; Bergeret, F. S.; Nazarov, Yu. V.; Giazotto, F.
2016-12-01
Multi-terminal superconducting Josephson junctions based on the proximity effect offer the opportunity to tailor non-trivial quantum states in nanoscale weak links. These structures can realize exotic topologies in several dimensions, for example, artificial topological superconductors that are able to support Majorana bound states, and pave the way to emerging quantum technologies and future quantum information schemes. Here we report the realization of a three-terminal Josephson interferometer based on a proximized nanosized weak link. Our tunnelling spectroscopy measurements reveal transitions between gapped (that is, insulating) and gapless (conducting) states that are controlled by the phase configuration of the three superconducting leads connected to the junction. We demonstrate the topological nature of these transitions: a gapless state necessarily occurs between two gapped states of different topological indices, in much the same way that the interface between two insulators of different topologies is necessarily conducting. The topological numbers that characterize such gapped states are given by superconducting phase windings over the two loops that form the Josephson interferometer. As these gapped states cannot be transformed to one another continuously without passing through a gapless condition, they are topologically protected. The same behaviour is found for all of the points of the weak link, confirming that this topology is a non-local property. Our observation of the gapless state is pivotal for enabling phase engineering of different and more sophisticated artificial topological materials.
Sheikhzada, Ahmad; Gurevich, Alex
2015-12-07
Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Here we address the breakdown of the topologically-protected stability of such defects driven by strong external forces. We focus on Josephson vortices that appear at planar weak links of suppressed superconductivity which have attracted much attention for electronic applications, new sources of THz radiation, and low-dissipative computing. Our numerical simulations show that a rapidly moving vortex driven by a constant current becomes unstable with respect to generation of vortex-antivortex pairs caused by Cherenkov radiation. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of an expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. Our work gives a new insight into instability of a moving topological defect which destroys global long-range order in a way that is remarkably similar to the crack propagation in solids.
Sheikhzada, Ahmad; Gurevich, Alex
2015-12-07
Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Here we address the breakdown of the topologically-protected stability of such defects driven by strong external forces. We focus on Josephson vortices that appear at planar weak links of suppressed superconductivity which have attracted much attention for electronic applications, new sources of THz radiation, and low-dissipative computing. Our numerical simulations show that a rapidly moving vortex driven by a constant current becomes unstable with respect to generation of vortex-antivortex pairs caused by Cherenkov radiation. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of an expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. In conclusion, our work gives a new insight into instability of a moving topological defect which destroys global long-range order in a way that is remarkably similar to the crack propagation in solids.
Sheikhzada, Ahmad; Gurevich, Alex
2015-12-07
Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Here we address the breakdown of the topologically-protected stability of such defects driven by strong external forces. We focus on Josephson vortices that appear at planar weak links of suppressed superconductivity which have attracted much attention for electronic applications, new sources of THz radiation, and low-dissipative computing. Our numerical simulations show that a rapidly moving vortex driven by a constant current becomes unstable with respect to generation of vortex-antivortex pairs caused by Cherenkov radiation. As a result,more » vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of an expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. In conclusion, our work gives a new insight into instability of a moving topological defect which destroys global long-range order in a way that is remarkably similar to the crack propagation in solids.« less
Basset, J.; Delagrange, R.; Weil, R.; Kasumov, A.; Bouchiat, H.; Deblock, R.
2014-07-14
We propose a scheme to measure both the current-phase relation and differential conductance dI/dV of a superconducting junction, in the normal and the superconducting states. This is done using a dc Superconducting Quantum Interference Device with two Josephson junctions in parallel with the device under investigation and three contacts. As a demonstration, we measure the current-phase relation and dI/dV of a small Josephson junction and a carbon nanotube junction. In this latter case, in a regime where the nanotube is well conducting, we show that the non-sinusoidal current phase relation we find is consistent with the theory for a weak link, using the transmission extracted from the differential conductance in the normal state. This method holds great promise for future investigations of the current-phase relation of more exotic junctions.
YBCO step-edge junctions with high IcRn
NASA Astrophysics Data System (ADS)
Mitchell, E. E.; Foley, C. P.
2010-06-01
Step-edge junctions represent one type of grain boundary Josephson junction employed in high-temperature superconducting junction technology. To date, the majority of results published in the literature focus on [001]-tilt grain boundary junctions (GBJs) produced using bicrystal substrates. We investigate the step morphology and YBCO (yttrium barium copper oxide) film structure of YBCO-based step-edge junctions on MgO [001] substrates which structurally resemble [100]-tilt junctions. High-resolution electron microscopy reveals a clean GBJ interface of width ~ 1 nm and a single junction at the top edge. The dependence of the transport properties on the MgO step-edge and junction morphology is examined at 4.2 K, to enable direct comparison with results for other junction studies such as [001]-tilt and [100]-tilt junctions and building on previously published 77 K data. MgO step-edge junctions show a slower reduction in critical current density with step angle compared with [001]-tilt junctions. For optimized step parameters, transport measurements revealed large critical current and normal resistance (IcRN) products (~3-5 mV), comparable with the best results obtained in other kinds of [100]-tilt GBJs in YBCO at 4.2 K. Junction-based devices such as SQUIDs (superconducting quantum interference devices) and THz imagers show excellent performance when MgO-based step-edge junctions are used.
THz Cherenkov radiation of Josephson vortex
NASA Astrophysics Data System (ADS)
Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
2008-01-01
It is shown that Josephson vortices travelling in sandwich embedded in dielectric media radiate electromagnetic waves with THz frequencies. This phenomenon is caused by the Cherenkov effect and takes place if vortex velocity exceeds the speed of light in dielectric.
Design and Characterization of a millikelvin dual-tip Josephson STM
NASA Astrophysics Data System (ADS)
Roychowdhury, A.; Dreyer, M.; Anderson, J. R.; Lobb, C. J.; Wellstood, F. C.
2014-03-01
We describe the design and characterization of a dual-tip Josephson STM that operates at millikelvin temperatures. We report an effective noise temperature for the STM on the order of 200 mK. In addition to the expected phase diffusive super current in the ultra-small Nb-Nb junction formed by one tip and the sample, our high resolution spectroscopy at mK temperatures reveals resonant coupling between the STM junction and the electromagnetic environment it is embedded in, as predicted by P(E) theory. We have for the first time, observed Shapiro-like steps in this limit by measuring the response of the P(E) supercurrent to microwave radiation as a function of amplitude. Fits to theory indicate that the coupling of an ultra-small Josephson junction to its environment/circuit may be used to a) directly measure dissipation channels associated with circuit resonances and b) calibrate the frequency dependent microwave attenuation in cryogenic circuits as seen by the junction.
Josephson A/D Converter Development.
1981-10-01
by Zappe and A Landman [20]. They conclude that the simple model of the Josephson effect is applicable up to frequencies at least as high (a) as 300...GHz. B. Time-Domain Experiments 4ooF so The early high - frequency experiments with Josephson devices I .O suggested their use as very fast logic switches...exactly as for the phenomenological model . The tunneling pacitive current paths dominate the circuit at high frequencies . current is the sum of two
Symmetry analysis of transport properties in helical superconductor junctions
NASA Astrophysics Data System (ADS)
Cheng, Qiang; Zhang, Yinhan; Zhang, Kunhua; Jin, Biao; Zhang, Changlian
2017-03-01
We study the discrete symmetries satisfied by helical p-wave superconductors with the d-vectors {{k}x}\\hat{x}+/- {{k}y}\\hat{y} or {{k}y}\\hat{x}+/- {{k}x}\\hat{y} and the transformations brought by symmetry operations to ferromagnet and spin-singlet superconductors, which show intimate associations with the transport properties in heterojunctions, including helical superconductors. In particular, the partial symmetries of the Hamiltonian under spin-rotation and gauge-rotation operations are responsible for the novel invariances of the conductance in tunnel junctions and the new selection rules for the lowest current and peculiar phase diagrams in Josephson junctions, which were reported recently. The symmetries of constructed free energies for Josephson junctions are also analyzed, and are consistent with the results from the Hamiltonian.
Symmetry analysis of transport properties in helical superconductor junctions.
Cheng, Qiang; Zhang, Yinhan; Zhang, Kunhua; Jin, Biao; Zhang, Changlian
2017-03-01
We study the discrete symmetries satisfied by helical p-wave superconductors with the d-vectors [Formula: see text] or [Formula: see text] and the transformations brought by symmetry operations to ferromagnet and spin-singlet superconductors, which show intimate associations with the transport properties in heterojunctions, including helical superconductors. In particular, the partial symmetries of the Hamiltonian under spin-rotation and gauge-rotation operations are responsible for the novel invariances of the conductance in tunnel junctions and the new selection rules for the lowest current and peculiar phase diagrams in Josephson junctions, which were reported recently. The symmetries of constructed free energies for Josephson junctions are also analyzed, and are consistent with the results from the Hamiltonian.
Nonlinear dynamics of Josephson vortices in a film screen under dc and ac magnetic fields
NASA Astrophysics Data System (ADS)
Sheikhzada, A.; Gurevich, A.
2014-11-01
We present detailed numerical simulations of Josephson vortices in a long Josephson junction perpendicular to a thin film screen under strong dc and ac magnetic fields. By solving the sine-Gordon equation, we calculated the threshold magnetic field for penetration of fluxons as a function of frequency, and the power dissipated by oscillating fluxons as functions of the ac field amplitude and frequency. We considered the effects of superimposed ac and dc fields, and a bi-harmonic magnetic field resulting in a vortex ratchet dynamics. The results were used to evaluate the contribution of weak-linked grain boundaries to the nonlinear surface resistance of polycrystalline superconductors under strong electromagnetic fields, particularly thin film screens and resonator cavities.
Modeling the switching processes in the Josephson AND and OR logic gates
NASA Astrophysics Data System (ADS)
Tyhanskyi, M. V.; Krysko, R. R.
2013-02-01
We propose a design principle of digital logic gates based on Josephson cryotrons. The operation mode of digital logic gates AND and OR based on tunnel junctions "superconductor-insulator-superconductor" was described. Mathematical models of the switching processes in the logic elements were developed, the transient characteristics during the logic state change were calculated, and the basic parameters of these models were determined. It was shown that digital logic gates "AND" and "OR" can be realized based on individual Josephson cryotrons and their logic state can be controlled by using current pulses as control inputs. Such logic gates satisfy all the requirements for digital logic elements and have switching time of about 2-3 ps.
One-dimensional Josephson arrays as superlattices for single Cooper pairs
NASA Astrophysics Data System (ADS)
Odintsov, A. A.
1996-07-01
We investigate uniform one-dimensional arrays of small Josephson junctions [EJ<
One-dimensional Josephson arrays as superlattices for single Cooper pairs
NASA Astrophysics Data System (ADS)
Odintsov, Arkadi
1996-03-01
We investigate uniform one-dimensional arrays of small Josephson junctions (EJ << E_C, EC = (2e)^2/2C) with a realistic Coulomb interaction U(x) = EC λ exp( - |x|/λ) (here λ >> 1 is the screening length in units of the lattice constant of the array). At low energies this system can be described in terms of interacting Bose particles (extra single Cooper pairs) on the lattice. With increasing concentration ν of extra Cooper pairs, a crossover from the Bose gas phase to the Wigner crystal phase and then to the superlattice regime occurs. The phase diagram in the superlattice regime consists of commensurable insulating phases with ν = 1/l (l is integer) separated by superconducting regions where the current is carried by excitations with fractional electric charge q = ± 2e/l. The Josephson current through a ring-shaped array pierced by magnetic flux is calculated for all of the phases.
Quantum state engineering with flux-biased Josephson phase qubits by rapid adiabatic passages
NASA Astrophysics Data System (ADS)
Nie, W.; Huang, J. S.; Shi, X.; Wei, L. F.
2010-09-01
In this article, the scheme of quantum computing based on the Stark-chirped rapid adiabatic passage (SCRAP) technique [L. F. Wei, J. R. Johansson, L. X. Cen, S. Ashhab, and F. Nori, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.100.113601 100, 113601 (2008)] is extensively applied to implement quantum state manipulations in flux-biased Josephson phase qubits. The broken-parity symmetries of bound states in flux-biased Josephson junctions are utilized to conveniently generate the desirable Stark shifts. Then, assisted by various transition pulses, universal quantum logic gates as well as arbitrary quantum state preparations can be implemented. Compared with the usual π-pulse operations widely used in experiments, the adiabatic population passages proposed here are insensitive to the details of the applied pulses and thus the desirable population transfers can be satisfyingly implemented. The experimental feasibility of the proposal is also discussed.
Balanced double-loop mesoscopic interferometer based on Josephson proximity nanojunctions
Ronzani, Alberto Altimiras, Carles; Giazotto, Francesco
2014-01-20
We report on the fabrication and characterization of a two-terminal mesoscopic interferometer based on three V/Cu/V Josephson junctions having nanoscale cross-section. The junctions have been arranged in a double-ring geometry realized by metallic thin film deposition through a suspended mask defined by electron beam lithography. Although a significant amount of asymmetry between the critical current of each junction is observed, we show that the interferometer is able to suppress the supercurrent to a level lower than 6 parts per thousand, being here limited by measurement resolution. The present nano-device is suitable for low-temperature magnetometric and gradiometric measurements over the micrometric scale.
Generating entangled quantum microwaves in a Josephson-photonics device
NASA Astrophysics Data System (ADS)
Dambach, Simon; Kubala, Björn; Ankerhold, Joachim
2017-02-01
When connecting a voltage-biased Josephson junction in series to several microwave cavities, a Cooper-pair current across the junction gives rise to a continuous emission of strongly correlated photons into the cavity modes. Tuning the bias voltage to the resonance where a single Cooper pair provides the energy to create an additional photon in each of the cavities, we demonstrate the entangling nature of these creation processes by simple witnesses in terms of experimentally accessible observables. To characterize the entanglement properties of the such created quantum states of light to the fullest possible extent, we then proceed to more elaborate entanglement criteria based on the knowledge of the full density matrix and provide a detailed study of bi- and multipartite entanglement. In particular, we illustrate how due to the relatively simple design of these circuits changes of experimental parameters allow one to access a wide variety of entangled states differing, e.g., in the number of entangled parties or the dimension of state space. Such devices, besides their promising potential to act as a highly versatile source of entangled quantum microwaves, may thus represent an excellent natural testbed for classification and quantification schemes developed in quantum information theory.
Fraunhofer pattern arising from an edge-stepped topological surface Josephson current distribution
NASA Astrophysics Data System (ADS)
Lee, Jae Hyeong; Lee, Gil-Ho; Lee, Janghee; Park, Joonbum; Nam, Seung-Geol; Shin, Yun-Sok; Kim, Jun Sung; Lee, Hu-Jong
2015-03-01
We report a surface-dominant Josephson effect in superconductor-topological insulator-superconductor (S-TI-S) devices, where a Bi1.5Sb0.5Te1.7Se1.3 (BSTS) crystal flake was adopted as an intervening TI between Al superconducting electrodes. We observed a Fraunhofer critical current modulation in a perpendicular magnetic field in an Al-TI-Al junction for both local and nonlocal current biasing. For the local biasing, the Fraunhofer signal was highly robust to the magnetic field up to the critical field of the Al electrodes, corresponding to the edge-stepped nonuniform supercurrent distribution arising from the top and rough side surfaces of the BSTS flake. A Fraunhofer-like pattern was also observed in a neighboring Au-TI-Au normal junction when it was nonlocally biased by the Al-TI-Al junction. All these strongly suggest Josephson coupling established via topologically robust conducting channels present on the surface of the 3D topological insulator. Current: Department of Physics, Harvard University, Cambridge, USA.
Metastable states and macroscopic quantum tunneling in a cold atom josephson ring
Solenov, Dmitry; Mozyrsky, Dmitry
2009-01-01
We study macroscopic properties of a system of weakly interacting neutral bosons confined in a ring-shaped potential with a Josephson junction. We derive an effective low energy action for this system and evaluate its properties. In particular we find that the system possesses a set of metastable current-carrying states and evaluate the rates of transitions between these states due to macroscopic quantum tunneling. Finally we discuss signatures of different metastable states in the time-of-flight images and argue that the effect is observable within currently available experimental technique.
Cooling of a suspended nanowire by an ac Josephson current flow.
Sonne, Gustav; Peña-Aza, Milton E; Gorelik, Leonid Y; Shekhter, Robert I; Jonson, Mats
2010-06-04
We consider a nanoelectromechanical Josephson junction, where a suspended nanowire serves as a superconducting weak link, and show that an applied dc bias voltage can result in suppression of the flexural vibrations of the wire. This cooling effect is achieved through the transfer of vibronic energy quanta first to voltage-driven Andreev states and then to extended quasiparticle electronic states. Our analysis, which is performed for a nanowire in the form of a metallic carbon nanotube and in the framework of the density matrix formalism, shows that such self-cooling is possible down to the ground state of the flexural vibration mode of the nanowire.
A Josephson radiation comb generator
Solinas, P.; Gasparinetti, S.; Golubev, D.; Giazotto, F.
2015-01-01
We propose the implementation of a Josephson Radiation Comb Generator (JRCG) based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. When the magnetic flux crosses a diffraction node of the critical current interference pattern, the superconducting phase undergoes a jump of π and a voltage pulse is generated at the extremes of the SQUID. Under periodic drive this allows one to generate a sequence of sharp, evenly spaced voltage pulses. In the frequency domain, this corresponds to a comb-like structure similar to the one exploited in optics and metrology. With this device it is possible to generate up to several hundreds of harmonics of the driving frequency. For example, a chain of 50 identical high-critical-temperature SQUIDs driven at 1 GHz can deliver up to a 0.5 nW at 200 GHz. The availability of a fully solid-state radiation comb generator such as the JRCG, easily integrable on chip, may pave the way to a number of technological applications, from metrology to sub-millimeter wave generation. PMID:26193628
Crespi, Vincent Henry; Cohen, Marvin Lou; Louie, Steven Gwon Sheng; Zettl, Alexander Karlwalter
2003-01-01
The present invention comprises a new nanoscale metal-semiconductor, semiconductor-semiconductor, or metal-metal junction, designed by introducing topological or chemical defects in the atomic structure of the nanotube. Nanotubes comprising adjacent sections having differing electrical properties are described. These nanotubes can be constructed from combinations of carbon, boron, nitrogen and other elements. The nanotube can be designed having different indices on either side of a junction point in a continuous tube so that the electrical properties on either side of the junction vary in a useful fashion. For example, the inventive nanotube may be electrically conducting on one side of a junction and semiconducting on the other side. An example of a semiconductor-metal junction is a Schottky barrier. Alternatively, the nanotube may exhibit different semiconductor properties on either side of the junction. Nanotubes containing heterojunctions, Schottky barriers, and metal-metal junctions are useful for microcircuitry.
Crespi, Vincent Henry; Cohen, Marvin Lou; Louie, Steven Gwon; Zettl, Alexander Karlwalte
2004-12-28
The present invention comprises a new nanoscale metal-semiconductor, semiconductor-semiconductor, or metal-metal junction, designed by introducing topological or chemical defects in the atomic structure of the nanotube. Nanotubes comprising adjacent sections having differing electrical properties are described. These nanotubes can be constructed from combinations of carbon, boron, nitrogen and other elements. The nanotube can be designed having different indices on either side of a junction point in a continuous tube so that the electrical properties on either side of the junction vary in a useful fashion. For example, the inventive nanotube may be electrically conducting on one side of a junction and semiconducting on the other side. An example of a semiconductor-metal junction is a Schottky barrier. Alternatively, the nanotube may exhibit different semiconductor properties on either side of the junction. Nanotubes containing heterojunctions, Schottky barriers, and metal-metal junctions are useful for microcircuitry.
Josephson Supercurrent through the Topological Surface States of Strained Bulk HgTe
NASA Astrophysics Data System (ADS)
Oostinga, Jeroen B.; Maier, Luis; Schüffelgen, Peter; Knott, Daniel; Ames, Christopher; Brüne, Christoph; Tkachov, Grigory; Buhmann, Hartmut; Molenkamp, Laurens W.
2013-04-01
Strained bulk HgTe is a three-dimensional topological insulator, whose surface electrons have a high mobility (˜30000cm2/Vs), while its bulk is effectively free of mobile charge carriers. These properties enable a study of transport through its unconventional surface states without being hindered by a parallel bulk conductance. Here, we show transport experiments on HgTe-based Josephson junctions to investigate the appearance of the predicted Majorana states at the interface between a topological insulator and a superconductor. Interestingly, we observe a dissipationless supercurrent flow through the topological surface states of HgTe. The current-voltage characteristics are hysteretic at temperatures below 1 K, with critical supercurrents of several microamperes. Moreover, we observe a magnetic-field-induced Fraunhofer pattern of the critical supercurrent, indicating a dominant 2π-periodic Josephson effect in the unconventional surface states. Our results show that strained bulk HgTe is a promising material system to get a better understanding of the Josephson effect in topological surface states, and to search for the manifestation of zero-energy Majorana states in transport experiments.
Josephson coupling between superconducting islands on single- and bi-layer graphene
NASA Astrophysics Data System (ADS)
Mancarella, Francesco; Fransson, Jonas; Balatsky, Alexander
2016-05-01
We study the Josephson coupling of superconducting (SC) islands through the surface of single-layer graphene (SLG) and bilayer graphene (BLG) in the long-junction regime, as a function of the distance between the grains, temperature, chemical potential and external (transverse) gate-voltage. For SLG, we provide a comparison with existing literature. The proximity effect is analyzed through a Matsubara Green’s function approach. This represents the first step in a discussion of the conditions for the onset of a granular superconductivity within the film, made possible by Josephson currents flowing between superconductors. To ensure phase coherence over the 2D sample, a random spatial distribution can be assumed for the SC islands on the SLG sheet (or intercalating the BLG sheets). The tunable gate-voltage-induced band gap of BLG affects the asymptotic decay of the Josephson coupling-distance characteristic for each pair of SC islands in the sample, which results in a qualitatively strong field dependence of the relation between Berezinskii-Kosterlitz-Thouless transition critical temperature and gate voltage.
Phonon-Josephson resonances in atomtronic circuits
NASA Astrophysics Data System (ADS)
Bidasyuk, Y. M.; Prikhodko, O. O.; Weyrauch, M.
2016-09-01
We study the resonant excitation of sound modes from Josephson oscillations in Bose-Einstein condensates. From the simulations for various setups using the Gross-Pitaevskii mean-field equations and Josephson equations we observe additional tunneling currents induced by resonant phonons. The proposed experiment may be used for spectroscopy of phonons as well as other low-energy collective excitations in Bose-Einstein condensates. We also argue that the observed effect may mask the observation of Shapiro resonances if not carefully controlled.
Hybrid Josephson-CMOS Random Access Memory with Interfacing to Josephson Digital Circuits
2013-10-16
as reliable high-speed Josephson voltage drivers, Superconductor Science and Technology, (01 2013): 1. doi: TOTAL: 4 (b) Papers published in non...Theodore Van Duzer, ISEC, Washington, DC 2011 "Hybrid Josephson-CMOS Random Access Memory, T. Van Duzer, US Workshop on Superconductor Electronics: Devices...Proceeding publications (other than abstracts): Received Paper 08/22/2013 2.00 Thomas Ortlepp. Vortex transitional superconductor random access memory
Subgap conductivity in SIN-junctions of high barrier transparency
NASA Astrophysics Data System (ADS)
Lotkhov, S. V.; Balashov, D. V.; Khabipov, M. I.; Buchholz, F.-I.; Zorin, A. B.
2006-11-01
We investigate the current-voltage characteristics of high-transparency superconductor-insulator-normal metal (SIN) junctions with the specific tunnel resistance ρ ≲ 30 Ω μm2. The junctions were fabricated from different superconducting and normal conducting materials, including Nb, Al, AuPd and Cu. The subgap leakage currents were found to be appreciably larger than those given by the standard tunnelling model. We explain our results using the model of two-electron tunnelling in the coherent diffusive transport regime. We demonstrate that even in the high-transparency SIN-junctions, a noticeable reduction of the subgap current can be achieved by splitting a junction into several submicron sub-junctions. These structures can be used as nonlinear low-noise shunts in rapid-single-flux-quantum (RSFQ) circuitry for controlling Josephson qubits.
Bi2Sr2CaCu2O8+δ intrinsic SQUIDs as candidates of high-Tc phase qubits
NASA Astrophysics Data System (ADS)
Jin, X. Y.; Lisenfeld, J.; Koval, Y.; Lukashenko, A.; Ustinov, A. V.; Müller, P.
2009-03-01
An intrinsic SQUID is a superconducting ring made of Bi2Sr2CaCu2O8+δ single crystal, intercepted by two intrinsic Josephson junction stacks. The inductance parameter βL can be tuned in a wide range by changing the height and the cross-section area of the stacks. When biased with dc current, the device showed typical properties of hysteretic dc-SQUIDs. When a device was coupled with a coil and a Nb readout dc-SQUID, typical rf-SQUID behavior was observed. By choosing a proper reset field, quantum escape from a single minimum has been measured on a sample of βL˜10. The escape rate can be fine-tuned by applying short pulses down to 1 ns, which allows a fast readout technique. With these prerequisites achieved, our experiments have opened the path to directly using these intrinsic SQUIDs as high-Tc phase qubits. The first attempts to measure Rabi oscillations on these devices will be discussed.
Goodenough, Daniel A; Paul, David L
2009-07-01
Gap junctions are aggregates of intercellular channels that permit direct cell-cell transfer of ions and small molecules. Initially described as low-resistance ion pathways joining excitable cells (nerve and muscle), gap junctions are found joining virtually all cells in solid tissues. Their long evolutionary history has permitted adaptation of gap-junctional intercellular communication to a variety of functions, with multiple regulatory mechanisms. Gap-junctional channels are composed of hexamers of medium-sized families of integral proteins: connexins in chordates and innexins in precordates. The functions of gap junctions have been explored by studying mutations in flies, worms, and humans, and targeted gene disruption in mice. These studies have revealed a wide diversity of function in tissue and organ biology.
Goodenough, Daniel A.; Paul, David L.
2009-01-01
Gap junctions are aggregates of intercellular channels that permit direct cell–cell transfer of ions and small molecules. Initially described as low-resistance ion pathways joining excitable cells (nerve and muscle), gap junctions are found joining virtually all cells in solid tissues. Their long evolutionary history has permitted adaptation of gap-junctional intercellular communication to a variety of functions, with multiple regulatory mechanisms. Gap-junctional channels are composed of hexamers of medium-sized families of integral proteins: connexins in chordates and innexins in precordates. The functions of gap junctions have been explored by studying mutations in flies, worms, and humans, and targeted gene disruption in mice. These studies have revealed a wide diversity of function in tissue and organ biology. PMID:20066080
Nielsen, Morten Schak; Axelsen, Lene Nygaard; Sorgen, Paul L.; Verma, Vandana; Delmar, Mario; Holstein-Rathlou, Niels-Henrik
2013-01-01
Gap junctions are essential to the function of multicellular animals, which require a high degree of coordination between cells. In vertebrates, gap junctions comprise connexins and currently 21 connexins are known in humans. The functions of gap junctions are highly diverse and include exchange of metabolites and electrical signals between cells, as well as functions, which are apparently unrelated to intercellular communication. Given the diversity of gap junction physiology, regulation of gap junction activity is complex. The structure of the various connexins is known to some extent; and structural rearrangements and intramolecular interactions are important for regulation of channel function. Intercellular coupling is further regulated by the number and activity of channels present in gap junctional plaques. The number of connexins in cell-cell channels is regulated by controlling transcription, translation, trafficking, and degradation; and all of these processes are under strict control. Once in the membrane, channel activity is determined by the conductive properties of the connexin involved, which can be regulated by voltage and chemical gating, as well as a large number of posttranslational modifications. The aim of the present article is to review our current knowledge on the structure, regulation, function, and pharmacology of gap junctions. This will be supported by examples of how different connexins and their regulation act in concert to achieve appropriate physiological control, and how disturbances of connexin function can lead to disease. © 2012 American Physiological Society. Compr Physiol 2:1981-2035, 2012. PMID:23723031
The Josephson Effect: 50 Years of Science and Technology
ERIC Educational Resources Information Center
Warburton, Paul A.
2011-01-01
The Josephson effect, the 50th anniversary of which will be celebrated in 2012, remains one of the most spectacular manifestations of quantum mechanics in all of experimental science. It was first predicted in 1962 and then experimentally verified in 1963. At its most fundamental level the Josephson effect is nothing more than the electronic…
NASA Technical Reports Server (NTRS)
Barner, J. B.; Kleinsasser, A. W.; Hunt, B. D.
1996-01-01
The ability to controllably fabricate High-Temperature Superconductor (HTS) S-Normal-S (SNS) Josephson Juntions (JJ's) enhances the possibilities fro many applications, including digital circuits, SQUID's, and mixers. A wide variety of approaches to fabricating SNS-like junctions has been tried and analyzed in terms of proximity effect behavior.
1952-03-01
Variation with the Height of the Principal Radii of Curvature in Somigliana’s Theory"), Bollettino di Geodesia e Scienze Affini, anno VIII, 1950 46...MARUSSI, A., "Principi di Geodesia Intrinseca applicati al campo di Somigliana" ("Principles of Intrinsic Geodesy Applied to Somigliana’s Field...34), Bollettino di Geodesia e Scienze Affini, anno VIII, 1950; and also Atti della XLII Riunione _dela Socie&Ljtsjjganaper il Progresso delle Scienze, Roma
Stable Josephson reference voltages between 0. 1 and 1. 3 V for high-precision voltage standards
Niemeyer, J.; Grimm, L.; Meier, W.; Hinken, J.H.; Vollmer, E.
1985-12-01
A new series array of 1440 Josephson tunnel junctions has been developed and tested as a reference voltage standard. It yields microwave induced quantized voltage steps up to 1.3 V. The steps are usually stable for more than 5 h with a microwave driving frequency of either 70 or 90 GHz. A high-resolution comparison of a constant voltage step at the 1-V level with the electromotive force of a saturated Weston cell is described. The comparison shows that the step voltage is constant to within +- 1 nV over the full step width.
Stable Josephson reference voltages between 0.1 and 1.3 V for high precision voltage standards
NASA Astrophysics Data System (ADS)
Niemeyer, J.; Grimm, L.; Meier, W.; Hinken, J. H.; Vollmer, E.
1985-12-01
A new series array of 1440 Josephson tunnel junctions has been developed and tested as a reference voltage standard. It yields microwave induced quantized voltage steps up to 1.3 V. The steps are usually stable for more than 5 h with a microwave driving frequency of either 70 or 90 GHz. A high-resolution comparison of a constant voltage step at the 1-V level with the electromotive force of a saturated Weston cell is described. The comparison shows that the step voltage is constant to within + or - 1 nV over the full step width.
Topics in the Theory of Josephson Arrays and Disordered Magnetic Systems
NASA Astrophysics Data System (ADS)
Porter, Christopher D.
This thesis consists of two parts. In the first part, we discuss several topics in the theory of Josephson junction arrays. The second part is concerned with two problems in the theory of magnetic systems: charge transfer ferromagnetism, and the clustering of Fe adatoms on graphene. In the field of Josephson arrays we consider three topics. First, the effects of a current bias on arrays of underdamped junctions are considered, for several junction geometries including both 2D and 3D systems. Approximate phase diagrams are constructed for various values of the ratio of charging energy to Josephson coupling. The effects of finite temperature are also discussed. Next, we examine the rich response of Josephson arrays to magnetic fields in the case of Josephson ladders with nonuniform spacing, known as superconducting quantum interference filters (SQIFs). Such ladders are already used for the detection of DC magnetic fields, but here their applicability to detecting AC fields is also discussed. It is shown that, for sufficiently low frequencies, the voltage produced by an AC field is equivalent to a convolution of the DC voltage response with the sinusoidal field oscillation. These SQIFs are studied in an effort to greatly increase the period of their response to external magnetic fields. Finally, we investigate underdamped 2D and 3D arrays with a special inhomogeneity. Specifically, insulating regions of varying width are sandwiched between superconducting regions of the arrays. The phase ordering in the superconducting regions is shown to penetrate into the insulating regions, leading to an unusual type of proximity effect. Our calculations for these arrays are done using mean field and perturbation theory, mean field theory and numerical methods, and our results are quantitatively confirmed by quantum Monte Carlo calculations. The superconducting correlation length is calculated inside the insulating region and it is found that the structure yields multiple layers of
Theory of a weak-link superconductor-ferromagnet Josephson structure
NASA Astrophysics Data System (ADS)
Gelhausen, J.; Eschrig, M.
2016-09-01
We propose a model for the theoretical description of a weak-link Josephson junction, in which the weak link is spin-polarized due to proximity to a ferromagnetic metal [S-(F |S )-S, where S is a superconductor and F is a ferromagnetic metal]. Employing Usadel transport theory appropriate for diffusive systems, we show that the weak link is described within the framework of Andreev circuit theory by an effective self-energy resulting from the implementation of spin-dependent boundary conditions. This leads to a considerable simplification of the model, and allows for an efficient numerical treatment. As an application of our model, we show numerical calculations of important physical observables such as the local density of states, proximity-induced minigaps, spin-magnetization, and the phase and temperature dependence of Josephson currents of the S-(F |S )-S system. We discuss multivalued current-phase relationships at low temperatures as well as their crossover to sinusoidal form at high temperatures. Additionally, we numerically treat (S-F-S) systems that exhibit a magnetic domain wall in the F region and calculate the temperature-dependence of the critical currents.
Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current
Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei
2017-01-01
The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1–2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy. PMID:28262731
Nonreciprocal Microwave Signal Processing with a Field-Programmable Josephson Amplifier
NASA Astrophysics Data System (ADS)
Lecocq, F.; Ranzani, L.; Peterson, G. A.; Cicak, K.; Simmonds, R. W.; Teufel, J. D.; Aumentado, J.
2017-02-01
We report on the design and implementation of a field-programmable Josephson amplifier (FPJA)—a compact and lossless superconducting circuit that can be programmed in situ by a set of microwave drives to perform reciprocal and nonreciprocal frequency conversion and amplification. In this work, we demonstrate four modes of operation: frequency conversion (transmission of -0.5 dB, reflection of -30 dB), circulation (transmission of -0.5 dB, reflection of -30 dB, isolation of 30 dB), phase-preserving amplification (gain >20 dB , one photon of added noise) and directional phase-preserving amplification (reflection of -10 dB, forward gain of 18 dB, reverse isolation of 8 dB, one photon of added noise). The system exhibits quantitative agreement with the theoretical prediction. Based on a gradiometric superconducting quantum-interference device with Nb /Al -Al Ox/Nb Josephson junctions, the FPJA is first-order insensitive to flux noise and can be operated without magnetic shielding at low temperature. Owing to its flexible design and compatibility with existing superconducting fabrication techniques, the FPJA offers a straightforward route toward on-chip integration with superconducting quantum circuits such as qubits and microwave optomechanical systems.
NASA Astrophysics Data System (ADS)
Lee, Yu-Li; Lee, Yu-Wen
2016-05-01
We study the behavior of a topological Josephson junction in which two topological superconductors are coupled through a quantum dot. We focus on the case with the bulk superconducting gap being the largest energy scale. Two parameter regimes are investigated: a weak tunneling between the dot and the superconductors, with the dot near its charge degeneracy point, and a strong-tunneling regime in which the transmission between the dot and the superconductors is nearly perfect. We show that in the former situation, the Andreev spectrum for each sector with fixed fermion parity consists of only two levels, which gives rise to the nontrivial current-phase relation. Moreover, we study the Rabi oscillation between the two levels and indicate that the corresponding frequency is a 4 π -periodic function of the phase difference between the two superconductors, which is immune to the quasiparticle poisoning. In the latter case, we find that the Coulomb charging energy enhances the effect of backscattering at the interfaces between the dot and the superconductors. Both the temperature and the gate-voltage dependence of the critical Josephson current are examined.
Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current
NASA Astrophysics Data System (ADS)
Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei
2017-03-01
The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1–2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.
Enhancement of Shapiro-like steps in multiterminal Josephson structures
NASA Astrophysics Data System (ADS)
Savinov, D. A.
2016-08-01
The distinctive features of current-voltage characteristics are studied for mesoscopic multiterminal structures effected by external irradiation. Considering a simple model of applied dc+ac voltage, we calculate Shapiro-like steps in Josephson systems with several weakly coupled superconducting electrodes. Owing to the action of an external alternating signal, the dc current is found to be rather increased than it appears in the same multiterminal Josephson node without the radiation. The possible applications of our results for the experimental observation of the Shapiro-like steps in such Josephson structures are discussed.
Oscillations in Josephson transmission line stimulated by load in the presence of noise
NASA Astrophysics Data System (ADS)
Pankratov, A. L.; Pankratova, E. V.; Shamporov, V. A.; Shitov, S. V.
2017-03-01
The joint action of the matching to a common RC-load and thermal noise on the spectral properties of parallel Josephson junction array is studied. It is demonstrated that proper matching suppresses the chaotic dynamics of the system. The efficiency of radiation is found to be highest within a limited frequency band, which corresponds to transformation of the shuttle soliton oscillating regime into the linear wave resonance synchronization mode. In this frequency band the spectral linewidth agrees well with a double of the linewidth for a shuttle fluxon oscillator, divided by a number of the oscillators in the array. When the oscillations demonstrate strong amplitude modulation, the linewidth increases roughly by a factor of five compared with theoretical linewidth formula.
Josephson STM at mK temperatures: Coupling to the electronic environment
NASA Astrophysics Data System (ADS)
Dreyer, Michael; Dana, Rami; Liao, Wan-Ting; Lobb, Cris; Wellstood, Fred; Anderson, Bob
Ultra-small Josephson junctions can couple to modes in the electronic environment. This leads to sub-gap peaks in the I(V) curve in addition to the phase diffuse supercurrent. The I(V) curve can - in principle - be explained by P(E) theory which describes the probability of tunneling at energy E. A recent study showed that antenna modes of the STM tips could be responsible for the observed sideband structures. In our case the explanation appears to be less simple. We employ a dual tip STM at a temperature of 30 mK. The I(V) spectra of the two tips show distinct patterns with only one shared mode. While the supercurrent branch for the ''inner'' tip is visible, it is obscured by a resonance for the ``outer'' tip. Possible causes and applications to other systems will be discussed. Support from NSF (DMR- 0605763) and Laboratory for Physical Sciences.
Time-dependent photon heat transport through a mesoscopic Josephson device
NASA Astrophysics Data System (ADS)
Lu, Wen-Ting; Zhao, Hong-Kang
2017-02-01
The time-oscillating photon heat current through a dc voltage biased mesoscopic Josephson Junction (MJJ) has been investigated by employing the nonequilibrium Green's function approach. The Landauer-like formula of photon heat current has been derived in both of the Fourier space and its time-oscillating versions, where Coulomb interaction, self inductance, and magnetic flux take effective roles. Nonlinear behaviors are exhibited in the photon heat current due to the quantum nature of MJJ and applied external dc voltage. The magnitude of heat current decreases with increasing the external bias voltage, and subtle oscillation structures appear as the superposition of different photon heat branches. The overall period of heat current with respect to time is not affected by Coulomb interaction, however, the magnitude and phase of it vary considerably by changing the Coulomb interaction.
Deterministic hopping in a Josephson circuit described by a one-dimensional mapping
Miracky, R.F.; Devoret, M.H.; Clarke, J.
1985-04-01
Analog simulations of the hopping noise of a current-biased Josephson tunnel junction shunted with an inductor in series with a resistor reveal a 1/..omega.. spectral density over two decades of frequency ..omega.. for a narrow range of bias currents. The amplitude of the low-frequency part of the spectrum decreases when white noise, representing Nyquist noise in the resistor at a few degrees Kelvin, is added to the simulation. We explain the shape of the power spectrum and its dependence on bias current and added white noise in terms of a deterministic process, involving a one-dimensional mapping, that is analogous to that found in Pomeau-Manneville intermittency. Moreover, we are able to establish a detailed relationship between the origin of the mapping and the differential equation describing the dynamics of the system.
A Broadband Quantum-Limited Josephson Parametric Amplifier, Part I: Exp.
NASA Astrophysics Data System (ADS)
White, T. C.; Barends, R.; Bochmann, J.; Campbell, B.; Chen, Y.; Chen, Z.; Chiaro, B.; Dunsworth, A.; Jeffrey, E.; Kelly, J.; Megrant, A.; Mutus, J. Y.; Neill, C.; O'Malley, P.; Quintana, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; Cleland, A. N.; Martinis, J. M.
2014-03-01
While Josephson parametric amplifiers (JPA) have achieved noise performance near the quantum limit, their bandwidth and saturation power is constrained by the resonant design. For a 50 ohm environment the relationship between junction critical current, frequency, and coupled Q means that bandwidth and saturation vary inversely. We present a device in which the coupled Q was lowered by engineering the environment impedance, increasing both bandwidth and saturation power without changing the resonator circuit parameters. The 50 ohm environment was transformed to 15 ohms at the resonator using a hybrid co-planar waveguide/micro-strip transmission line to create a broadband impedance matching network. This device exhibits regions with near quantum-limited bandwidth exceeding 700 MHz and saturation powers as high as -105 dBm.
Quantum phase-slip junction under microwave irradiation
NASA Astrophysics Data System (ADS)
Di Marco, A.; Hekking, F. W. J.; Rastelli, G.
2015-05-01
We consider the dynamics of a quantum phase-slip junction (QPSJ), a dual Josephson junction, connected to a microwave source with frequency ωmw. With respect to an ordinary Josephson junction, a QPSJ can sustain dual Shapiro steps, consisting of well-defined current plateaus at multiple integers of e ωmw/π in the current-voltage (I -V ) characteristic. The experimental observation of these plateaus has been elusive up to now. We argue that thermal as well as quantum fluctuations can smear the I -V characteristic considerably. In order to understand these effects, we study a current-biased QPSJ under microwave irradiation and connected to an inductive and resistive environment. We find that the effect of the fluctuations is governed by the resistance of the environment and by the ratio of the phase-slip energy and the inductive energy. Our results are of interest for experiments aiming at the observation of dual Shapiro steps in QPSJ devices for the definition of a new quantum current standard.
On the electrodynamics of Josephson effect in anisotropic superconductors
Mints, R.G.
1989-01-01
Specificities of Josephson effect electrodynamics in anisotropic superconductors are of considerable interest for the study of high temperature superconductors with strongly anisotropic layered structure. In this paper the authors give the calculation for the tunnel Josephson contact of an isolated vortex, the law of dispersion of its low-amplitude oscillations, the critical field H/sub cl/ for the penetration of magnetic flux, and the maximum current across a rectangular contact.
Josephson vortices as flexible waveguides for terahertz waves
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Savel'ev, Sergey; Yampol'skii, V. A.; Kusmartsev, F. V.; Nori, Franco
2008-09-01
We propose using the Josephson vortices (fluxons) as adjustable and malleable waveguides of electromagnetic radiation. Our theoretical and numerical calculations show that electromagnetic waves can propagate along the Josephson vortices and always follow the vortex lines. By changing external parameters, such as electric currents or magnetic fields, the shape and configuration of the guiding vortex lines can be controlled. We describe the design of a multifunctional three-terminal device that controls the transmission (redirecting or splitting) of a beam of electromagnetic waves.
Switching Current Distributions in Superconductor-Topological Insulator-Superconductor Junctions
NASA Astrophysics Data System (ADS)
Murphy, Andrew; Zhang, Can; Huemiller, Erik; Oh, Seongshik; Eckstein, James; van Harlingen, Dale; Bezryadin, Alexey
It has been proposed that localized Majorana fermion (MF) modes can exist in lateral Josephson junctions with a 3D-topological insulator barrier at locations at which the phase difference across the junction is an odd multiple of π. These states enter the junctions bound to the nodes of the Josephson vortices as a perpendicular magnetic field is increased. Each mode contributes a local 4 π-periodic sin(φ/2)-component to the junction's current-phase relation, adding to the usual sin(φ) dependence. The sign of this new term encodes the parity of the Majorana pair. As a way to detect these states and measure their parity, we study the distribution of switching currents in Nb-Bi2Se3-Nb junctions fabricated on thin Bi2Se3 films in which the superconductivity is induced by a pair of closely spaced Nb electrodes. We expect that such measurements will be sensitive to the parity of the MFs, yielding a splitting of the distribution. Preliminary measurements of the critical current distributions show the onset of unusual features when the magnetic field is increased which we are analyzing to determine if they may arise from Majorana fermions in the junctions.
Lossless, coherent Josephson three-wave combiner
NASA Astrophysics Data System (ADS)
Abdo, Baleegh; Sliwa, Katrina; Schackert, Flavius; Bergeal, Nicolas; Hatridge, Michael; Frunzio, Luigi; Stone, Douglas; Devoret, Michel
2013-03-01
We designed and operated a three-wave beam-splitter/combiner, based on Josephson parametric converters, which performs frequency conversion without introducing losses and thus adding no noise to the processed signal. We in particular show that the unitary signal-idler scattering parameters of the device can be fully modulated in-situ by varying the intensity and phase of the pump tone feeding the system. By operating the device as a 50/50 beam-combiner, we interfere coherently two input coherent microwave beams with different frequencies and demonstrate that the resulting interference fringes generated by the relative phase of the pump is in agreement with theoretical predictions. Potential applications of the device include quantum information transduction and realization of an ultra-sensitive interferometer with controllable feedback. Work supported by: IARPA, ARO, and NSF
Simplifying the circuit of Josephson parametric converters
NASA Astrophysics Data System (ADS)
Abdo, Baleegh; Brink, Markus; Chavez-Garcia, Jose; Keefe, George
Josephson parametric converters (JPCs) are quantum-limited three-wave mixing devices that can play various important roles in quantum information processing in the microwave domain, including amplification of quantum signals, transduction of quantum information, remote entanglement of qubits, nonreciprocal amplification, and circulation of signals. However, the input-output and biasing circuit of a state-of-the-art JPC consists of bulky components, i.e. two commercial off-chip broadband 180-degree hybrids, four phase-matched short coax cables, and one superconducting magnetic coil. Such bulky hardware significantly hinders the integration of JPCs in scalable quantum computing architectures. In my talk, I will present ideas on how to simplify the JPC circuit and show preliminary experimental results