Search Results - (Author, Cooperation:R. Houlton)

2015-02-06

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Animals ; Excitatory Postsynaptic Potentials/*physiology ; Female ; Male ; Mice ; Mice, Inbred C57BL ; Models, Neurological ; Neural Pathways ; Photic Stimulation ; Pyramidal Cells/cytology/physiology ; Synapses/*physiology ; Visual Cortex/*cytology/*physiology

1089-7550

AIP Digital Archive

Physics

High-temperature-superconductor Josephson junctions with an edge geometry of superconductor/normal-metal/superconductor have been fabricated on yttria-stabilized zirconia substrates by engineering the electrode and N-layer material to reduce the lattice mismatches (a, b, and c). With GdBa2Cu3O7−δ as electrodes and Pr-doped Y0.6Pr0.4Ba2Cu3O7−δ as a barrier, the lattice mismatches from electrode and barrier layer are reduced to a very low level. The junctions fabricated with such a design demonstrate resistively shunted junction current-voltage characteristics under dc bias at temperatures in the range of 77–88 K. The quite low specific interface resistivity on the order of 10−10 Ω cm2 indicates that the junction performance is controlled by the normal-metal (N) layer material instead of the interfaces. The use of lattice-matched electrode and N-layer material is one of the key design rules to obtain controllable high-temperature superconductor Josephson junctions. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Surface resistance measurements on Tl-Ba-Ca-Cu-O thick films (∼15 μm) magnetron sputtered onto BaF2-buffered, silver-based (Consil 995) substrates have been made at a microwave frequency of 22 GHz. The relatively large-area films (∼5 cm2) are characterized by surface resistance values of 6.9±2 mΩ at 11.3 K and 30.2±1 mΩ at 77 K; the corresponding values for Cu are 10 and 22 mΩ, respectively. These results demonstrate that Tl-Ba-Ca-Cu-O can be deposited onto large-area, metallic substrates with characteristic surface resistance values lower than Cu at 4 K. Orientation of the film should improve the surface resistance at 77 K, thereby making the fabrication of microwave cavities that are superior to Cu possible.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Surface resistance measurements of films of YBa2Cu3O7 deposited onto single-crystal substrates of LaGaO3 and SrTiO3 have been made at a frequency of 22 GHz. The measurements were made in either a copper or niobium cavity by replacing the end wall with the superconducting film. Typical surface resistance at 20 K are 1–2 mΩ for films on LaGaO3 and 6–8 mΩ for films on SrTiO3, as measured in the copper cavity. The LaGaO3 values lie within the sensitivity range of the Cu cavity (∼2 mΩ) and can only be considered upper limits. Similar measurements in a Nb superconducting cavity resulted in a surface resistance value of 0.2±0.1 mΩ at 4 K for the best LaGaO3-based film. This value is more than an order of magnitude lower than Cu, and suggests that LaGaO3-based films may offer immediate advantages in a number of applications.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We recently demonstrated that insulating surface impurity phases in high-temperature superconductors can be detected by thermally stimulated luminescence. Moreover, we suggested that the intensity of luminescence is related to the magnitude of the rf surface resistance. In this work we show that a quantitative correlation exists between these two quantities, and that luminescence can be a very useful technique for estimating rf surface resistance.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

High-temperature superconductor YBa2Cu3O7−δ based superconducting-normal-superconducting (SNS) Josephson junctions were fabricated using a unique device design. The normal material included a gradient Pr-doped Y1−xPrxBa2Cu3O7−δ layer which was composed of a light doping (x=0.1) next to both YBa2Cu3O7−δ electrodes, a slightly higher doping (x=0.3) towards the center, and a doping concentration of x=0.5 in the middle of the N layer. This design graded the lattice mismatch between YBa2Cu3O7−δ and the N layer, thus avoiding the accumulation of all the lattice strain at one interface. It also results in good chemical, thermal, and structural compatibility between adjacent layers for the desired multilayer structures. The SNS junctions fabricated in this way showed resistively shunted junction current-voltage characteristics under dc bias and Shapiro steps under microwave irradiation at a temperature in the range of 75–87 K. Direct current superconducting quantum interference devices showed a voltage modulation about 5 μV by a magnetic field at liquid nitrogen temperature. © 1994 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have developed Josephson junctions and superconducting quantum interference devices (SQUIDs) in a superconductor-normal-superconductor edge-junction design. These devices are unusual in that we use YBa2Cu3O7−x for both the superconducting and normal layers. The only difference between the layers is the temperature of the substrate during deposition, 695 °C for the superconductor and 670 °C for the N layer. The lower deposition temperature results in material with a significantly reduced Tc and a higher resistivity. The Josephson junctions produced in this fashion have IcRn products typically greater than 100 μV at 77 K. The SQUIDs are not fully optimized but have produced modulation depths of approximately 10 μV at 76 K. These SQUID results are similar to the best results in the literature. © 1995 American Institute of Physics.

Electronic Resource