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  • 1
    Electronic Resource
    Electronic Resource
    Effect of inductance in externally shunted Josephson tunnel junctions (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 382-389 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report measurements on current-voltage (I-V) characteristics of externally shunted Josephson tunnel junctions where the external shunts have nonzero inductance. At low temperatures (T〈6.6 K), we observe standard I-V curves, but as temperature is increased above 6.6 K we observe an anomaly in the I-V curves. We attribute this anomaly to the nonzero inductance in the shunt loop. Numerical simulations which properly take into account the effect of inductance show that the dynamics in the anomalous region of the I-V curve are dominated by subharmonic relaxation oscillations. We use a load-line analysis model to study the transition between the relaxation oscillations and the Josephson oscillations. The analysis is in good agreement with our data. Our analysis further predicts, and our data confirms, that in order for the relaxation oscillations to occur it is necessary to have βC=2πIcR2sC/Φ0〈(4/π)2, regardless of the value of the inductance. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359334
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  • 2
    Electronic Resource
    Electronic Resource
    Temperature dependence of low-frequency noise in Al–Al2O3–Al single-electron transistors (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6536-6540 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the temperature dependence of the charge noise power spectral density Sq in two-junction Al–Al2O3–Al single-electron transistors at temperatures from 85 mK to 4 K. Although individual Lorentzians are often visible, the noise spectra are dominated by excess low-frequency noise with a power-law dependence on frequency f where Sq∝1/fβ and β(similar, equals)1. Below about 0.5 K, Sq is weakly dependent on the temperature T. Above 1 K, the charge noise Sq increases with T, and at 4 K Sq(approximate)10−4 e2/Hz at 1 Hz, about a factor of 100 greater than at 85 mK. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1312846
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  • 3
    Electronic Resource
    Electronic Resource
    Observation of Josephson effect in YBa2Cu3O7−x/Nd1.85Ce0.15CuO4−y bilayer junctions (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2872-2874 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Josephson junctions were fabricated at the interface of YBa2Cu3O7−x (YBCO) and Nd1.85Ce0.15CuO4−y (NCCO) in heteroepitaxially grown superconducting bilayers. Devices of various configurations and sizes were fabricated, and they display a resistively shunted junction like I–V characteristics with hysteresis at low temperatures. A clear ac Josephson effect was observed under microwave irradiation, and critical currents were completely suppressible by external magnetic fields. Oxygen diffusion or charge diffusion at the interface are possible origins for the barrier formation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114813
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  • 4
    Electronic Resource
    Electronic Resource
    Complex dynamics of resistively and inductively shunted Josephson junctions (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 1126-1132 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured Nb–AlOx–Nb Josephson tunnel junctions which have resistive shunts with different parasitic inductances. Numerical simulations reveal that specific features in the experimental current–voltage (I–V) characteristics of these devices are dc signatures of complex ac behavior. Depending on the inductance of the shunt loop and the capacitance of the junction, these features may either appear or disappear as the temperature of the device is increased. Examination of the simulated voltage waveforms allows us to map regions of the parameter space which exhibit complicated behavior. These regions should be avoided when a nearly sinusoidal voltage waveform is desired, as is the case for Josephson junction-based oscillators. The agreement of the experimental and simulated I–V curves also enables us to accurately determine the inductance of the shunts and the capacitance of the junctions. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368113
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  • 5
    Electronic Resource
    Electronic Resource
    Josephson-junction arrays as high-efficiency sources of coherent millimeter-wave radiation (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1137-1139 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent experiments have indicated that Josephson-junction arrays can radiate coherently in a laser-like fashion, as predicted by theoretical work in the 1970s. We present results from measurements of high-efficiency Josephson-junction arrays coupled to resonant cavities. In one of our samples with four columns and 36 rows, the dc to ac (180 GHz) conversion efficiency reaches an asymptotic value of about 32%. Using a simple circuit model we show that we have achieved optimal dc to ac conversion in this sample. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1350431
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  • 6
    Electronic Resource
    Electronic Resource
    Behavior of Al–Al2O3–Al single-electron transistors from 85 mK to 5 K (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2268-2270 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using e-beam lithography and conventional double-angle evaporation, we have fabricated Al–Al2O3–Al single-electron transistors and studied their behavior from 85 mK to about 5 K. The total island capacitance CΣ of the devices ranges from 120 to 200 aF, with typical estimated junction overlaps of about 30 nm×30 nm. At 4.2 K, our devices display well-behaved periodic I–Vg characteristics with the maximum charge-transfer function ∂I/∂Q0 ranging from 4 to 130 pA/e. The electrical characteristics of these devices agree well with the predictions of the Orthodox Theory, with current modulation being observed up to a temperature T(similar, equals)e2/(2CΣkB). Below 1 K small deviations occur, which are partly due to island self-heating effects. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121334
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic homogeneity of colossal-magnetoresistance thin films determined by alternating current magnetic susceptibility (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3456-3458 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report measurements of the alternating current (ac) magnetic susceptibility, χac=χ′+iχ″, performed on colossal-magnetoresistance (CMR) materials. We have studied thin film samples of La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3. For homogeneous samples, the temperature of the peak observed in χ″(T) is in agreement with the temperature of peak resistivity (TP) obtained from transport measurements. This agreement is not found for inhomogeneous samples, where χ″(T) shows multiple peaks. The analysis of χ″(T) enables one to determine the quality of the CMR materials. The results obtained in thin films of La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3, are consistent with those obtained from an homogeneous single crystal of La0.80Sr0.20MnO3. We show that the contactless ac magnetic susceptibility technique is a quick method to reveal inhomogeneities which are not directly evident in direct current transport measurements. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122795
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  • 8
    Electronic Resource
    Electronic Resource
    Ion milling damage and regrowth of oxide substrates studied by ion channeling and atomic force microscopy (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 3098-3100 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the effect of ion milling on the surface crystallinity of the metal oxide substrates LaAlO3, SrTiO3, and NdGaO3 which are used for fabrication of high-Tc Josephson junctions and circuits. Ion channeling of the milled substrates reveals a damage-induced peak corresponding to a disordered layer of (approximate)60 Å at the surface. Annealing the substrates in oxygen ambient at various temperatures ranging from 600 to 1100 °C resulted in the regrowth of the damaged layer at the surface of the substrates as was indicated by the reduction in size of the surface peak observed in the channeled spectrum, as well as by formation of lattice steps as seen by atomic force microscopy. A significant reduction in the damage peak size and the formation of smooth completed lattice steps are seen only after annealing at temperatures ≥950 °C. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119103
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  • 9
    Electronic Resource
    Electronic Resource
    Fabrication of high-temperature superconducting Josephson junctions on substrates patterned by focused ion beam (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1730-1732 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High aspect ratio trenches were patterned on (100) LaAlO3 substrates by focused ion-beam milling prior to film deposition. Subsequent YBCO films deposited by pulsed laser deposition were found to break naturally across these trenches. In situ Au was then deposited to connect the separated YBCO electrodes. Junctions were then patterned across the trenches to form a superconductor/normal/superconductor configuration. The resistively shunted junctions exhibited supercurrents up to 86 K. Under microwave irradiation, the junctions exhibited a number of clear Shapiro steps in the I–V characteristics. The transverse magnetic-field diffraction pattern indicted uniform current distribution across the junction. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122259
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  • 10
    Electronic Resource
    Electronic Resource
    Fabrication of in-plane aligned a-axis oriented YBa2Cu3O7−x trilayer Josephson junctions (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 112-114 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated vertical YBa 2Cu3O7−x/PrBa 2Cu3O7−x/YBa 2Cu3O7−x (YBCO/PBCO/YBCO) Josephson junctions using in-plane aligned a-axis oriented YBCO multilayers on (100) LaSrGaO4(LSGO). The Tc's of the device electrodes are typically greater than 80 K. Josephson coupling is observed for barrier thickness up to 800 A(ring). Strong nonlinear I–V characteristics arising from the properties of PBCO are observed for thicker barrier devices. Chip to chip spread in the device characteristics may be intrinsically due to the PBCO barrier. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118092
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