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ABSTRACT: We examine the solutions of the non-linear equations governing the behavior of a current biased Josephson junction. Both inline and overlap current bias geometries are considered. The solution space is investigated analytically and using numerical techniques. We characterize the types of solutions expected analytically and find good approximations for large magnetic fields. For small magnetic fields the solution space is large and its stability is entangled. We study this space and its stability as a function of magnetic field and applied bias current. Selective results are presented that characterize the general behavior of the solution space.
Journal of Low Temperature Physics 01/1999; 115(1):45-60. · 1.19 Impact Factor
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ABSTRACT: We examine the solutions of the nonlinear equations governing the behavior of a current-biased, double-vertically-stacked, Josephson junction. Both inline and overlap biasing current geometries are considered. The solution space is investigated analytically and using numerical techniques. We characterize the types of solutions expected analytically for zero current and find good approximations for large magnetic fields. We study this space and its stability as a function of magnetic field and applied bias current. Selective results are presented that characterize the general behavior of the solution space.
Phys. Rev. B. 12/1998; 59(1).
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ABSTRACT: We utilized a miniature sputtering cell with mylar windows and multitarget sputtering guns in order to study the growth of YBCO/LaAlO 3 superlattices on SrTiO 3 substrates. Computer modeling of the diffraction spectra enabled us to determine the interface width between the layers. After deposition of the superlattices, the substrate temperature was increased to study any interdiffusion. © 1996 American Institute of Physics.
Applied Physics Letters 04/1996; · 3.84 Impact Factor
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ABSTRACT: We describe the properties of flux quantum circuitry employing the relatively young technology of multilayer Josephson junctions with n superconductor-insulator (SI) layers. Multilayer junctions can be employed as both passive and active devices to increase circuit integration density, allow for new logic/voltage thresholds and higher impedances, and improve thermal noise stability. We present the results from numerical simulations of a conventional RSFQ circuit and two novel circuits with multilayer junction designs. Neural circuitry is a focus of our novel multilayer designs. We also discuss layout and fabrication issues, considering the recent progress in the fabrication of Nb multilayer junctions with AlN tunnel barriers, which exhibit intrinsic overdamping at the level of each SI layer. Included in this discussion is a long term assessment of a multilayer approach in view of deep sub-micron and high T<sub>c</sub> technologies.
IEEE Transactions on Appiled Superconductivity 07/1995; · 1.04 Impact Factor
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ABSTRACT: Polarized second harmonic generation measurements were performed on AlN films deposited on (100) sapphire substrates by the reactive rf sputtering technique. The bulk effective second order nonlinearity observed in these films is typically about 6×10<sup>-9</sup> esu at 1.06 μm, several times larger than that of quartz or KTP. The tensorial properties of the nonlinearity are consistent with the crystal symmetry of AlN and the microcrystallinity of these films.
Applied Physics Letters 12/1993; · 3.84 Impact Factor
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ABSTRACT: A superconducting Josephson transmission line (JTL) fabricated with multilayered tunnel junctions with thin (100 ) superconducting layers may be used as an ionizing radiation detector. The suppression of the superconducting energy gap in the layers of such a JTL, due to the local deposition of energy by incident radiation, will initiate the propagation of one or more fluxons in the device. These fluxons represent digital information in the form processable by single flux quantum (SFQ) superconducting digital circuitry. Designs for JTL based detectors with temporal resolutions on the order of picoseconds and spatial resolution on the order of microns, along with numerical simulation results, are presented.
Journal of Low Temperature Physics 10/1993; 93(3):665-670. · 1.19 Impact Factor
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ABSTRACT: We have measured the temperature and magnetic field dependence of the Hall mobility and transverse magnetoresistance in n‐type InSb films epitaxially grown on GaAs substrates by metalorganic chemical vapor deposition. The films show a giant magnetoresistance: e.g., at 240 K the resistivity increases over 20 times at a magnetic field of 5 T; the low field coefficient of resistivity at 77 K is as high as 47.5 μΩ cm/G. The Hall mobility decreases with magnetic field and saturates at higher fields. By taking the interface carrier transport into account, the observed field dependence of the Hall mobility and magnetoresistance may be understood based on a two‐layer model.
Applied Physics Letters 09/1993; · 3.84 Impact Factor
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ABSTRACT: 'First generation' superconducting tunnel junction X-ray detectors (characterized by a single tunnel junction in direct contact with its substrate, with totally external amplification) remain more than an order of magnitude away from their theoretical energy resolutions which are in the order of eV's. The difficulties that first generation devices are encountering are being attacked by a 'second generation' of superconducting X-ray detector designs including quasiparticle trapping configurations and Josephson junction arrays. A second generation design concept, the multilayered superconducting tunnel junction X-ray detector, consisting of tens to hundreds of tunnel junctions stacked on top of one another (a superlattice), is presented. Some of the possibilities of this engineered materials approach include the tuning of phonon transmission characteristics of the material, suppression of parasitic quasiparticle trapping and intrinsic amplification.
01/1993;
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ABSTRACT: We have studied the Hall effect and the magnetoresistance in [110] textured Fe/Cr multilayers grown by electron beam evaporation. We have observed a strong magnetic field dependence of the Hall coefficient as well as a large magnetoresistance. In all cases the Hall voltage is positive. The ordinary Hall coefficient is positive at room temperature and changes sign at low temperatures; this is similar to the behavior of an antiferromagnet but differs from that observed in Fe‐Cr alloys. The extraordinary Hall coefficient R s is positive and varies with the resistivity ρ as R s ∝ρ<sup>2.6</sup>, suggesting the importance of interface scattering.
Applied Physics Letters 08/1991; · 3.84 Impact Factor
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ABSTRACT: Amorphous Si/Nb superlattices with modulation wavelengths ranging from 20–200 Å have been grown on sapphire substrates at 100–150 °C by dual e‐beam evaporation in an ultra‐high‐vacuum (UHV) system. The low‐angle x‐ray diffraction data can be accounted for by a symmetric trapezoidal composition profile model. The intermixing at the layer interfaces is estimated to be 6–12 Å, depending on the substrate temperatures. In the film growth direction, the coherent domain size of the polycrystalline Nb layers scales with the Nb layer thickness. High‐resolution transmission electron microscopy reveals the existence of microcrystallites in the 20‐Å‐thick amorphous Nb layers; also resolved are the microstructure of the substrate/superlattice and superlattice/thick‐Nb layer interfaces. In addition, Auger depth profiling results are also consistent with the expected composition modulation.
Journal of Applied Physics 01/1990; · 2.17 Impact Factor
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ABSTRACT: We generalize the de Gennes-Takahashi-Tachiki theory of coupled dirty superconductors to include the effects of orbital diamagnetism, spin (Pauli) paramagnetism, spin-orbit scattering, and magnetic impurity scattering. Some new expressions for thin film sandwiches and superlattices are obtained.
Journal of Low Temperature Physics 12/1988; 74(1):103-117. · 1.19 Impact Factor
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ABSTRACT: Y‐Ba‐Cu‐O thin films have been deposited on MgO substrates by dc magnetron sputtering from a stoichiometric YBa 2 Cu 3 O 7-δ target, after which they are subjected to a short heat treatment. Zero resistance is routinely achieved near 60 K, and one film shows zero resistance at 68.0 K.
Applied Physics Letters 11/1987; · 3.84 Impact Factor
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ABSTRACT: Cavity modes in Josephson coupled superconductor/insulator superlattices have been studied based on a theoretical model recently proposed by Sakai et al. In such systems the Swihart velocities form a band bounded by two limiting velocities and corresponding to the in-phase and out-of-phase (in the two neighboring junctions) states, respectively. Cavity modes in stacked double Josephson junctions have also been discussed as a special case.
Physics Letters A. 208:150-156.
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ABSTRACT: Single and stacked Nb/Al-AlNx/Nb superconducting tunnel junctions with both hysteretic (underdamped) and non-hysteretic (overdamped) current-voltage relationships have been produced utilizing reactively sputtered aluminum nitride tunnel barriers. Standard multilayer deposition and lithographic processing techniques, compatible with existing Nb/Al-AlOx/Nb fabrication techniques, are used in fabrication. The degree of damping in the junctions is controlled through the deposition parameters. Critical current dependence on applied magnetic field indicates that the overdamped junctions have a distributed Josephson coupling and are not simple microshorts. The shorter deposition time to grow reactively sputtered AlNx barriers makes this system a promising alternative to fabricate stacked Josephson junctions.
Applied Superconductivity 3:567-572.
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ABSTRACT: When subjected to microwave radiation, the I-V characteristics of stacked Josephson junctions should exhibit interesting new features which are absent in a single junction. Evidence for collectively phase-locked Shapiro steps and coherent phase-locking of fluxon motion to the external microwave field has been found in observations on stacked Nb/AlAlOx/Nb Josephson junctions.
Physics Letters A.
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ABSTRACT: Superconducting tunnel junctions can be configured as high resolution X-ray spectrometers however, because they are thin, STJs suffer from inherent photoabsorption inefficiency. A common approach to enhance quantum efficiency is to couple the junctions to superconducting absorbers and employ quasiparticle traps. An alternative approach is to use vertical stacks of tunnel junctions as detectors. These multilayered superconducting tunnel junctions (MSTJs) need not be thin and may have additional advantages including increased signal to noise ratio. We report on the fabrication of multilayered tunnel junctions and successful X-ray detection by an MSTJ.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 370(1):38-40. · 1.21 Impact Factor
