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  • 1995-1999  (11)
  • 1998  (6)
  • 1996  (5)
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  • 1995-1999  (11)
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  • 1
    Electronic Resource
    Electronic Resource
    Transport properties of Tl2Ba2CaCu2O8 weak links on LaAlO3 bicrystal substrates (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 9221-9223 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Josephson junctions and dc superconducting quantum interference devices (SQUIDs) have been fabricated in ex situ epitaxial Tl2Ba2CaCu2O8 films on bicrystal LaAlO3 substrates with symmetric 32° [001] tilt grain boundaries. The critical temperature Tc, of the junctions was in the range 105–107 K and the critical current densities at 77 K varied between 3×102 and 3×104 A/cm2, two or three orders of magnitude less than those of the film. The I–V curves are described by a resistively shunted junction model. Close to Tc, the temperature dependence of the critical current was described by (1−T/Tc)2. The flux noise spectra SΦ(f) of dc SQUIDs were measured in the locked-loop regime with constant current bias at temperatures up to 94 K. The white noise level was 50μΦ0/(square root of)Hz at 77 K. The crossover frequency to 1/f noise was low, about 5 Hz, and the flux noise level at 1 Hz was 440μΦ0/(square root of)Hz. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362595
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  • 2
    Electronic Resource
    Electronic Resource
    Electromagnetic and microstructural characterization of YBa2Cu3O7 step edge junctions on (001) LaAlO3 substrates (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 9213-9220 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sharp and straight step edges on (001) LaAlO3 (LAO) substrates were ion milled by using an electron beam defined amorphous carbon thin film mask. YBa2Cu3O7 (YBCO) thin films patterned to narrow strips across the step edges gave high quality Josephson junctions. Their current–voltage (I–V) curves could be well described by the resistively shunted junction model with or without excess current. By varying the YBCO film thickness over a fixed step height, the critical current density (jc) of the junction could be changed by several orders of magnitude. For junctions with high jc, typical IcRn (product of critical current and normal resistance) values of around 100 μV at 77 K and more than 1 mV at 4.2 K were obtained. Some excess current was observed. For junctions with low jc, the dependence of Ic on an applied magnetic field was strong even at low temperatures. The Ic showed a main peak in the center and well-defined periods as a function of applied magnetic field. The minimum Ic value suppressed by the magnetic field was about 20% of its maximum value at 4.2 K. Junctions with low jc usually showed hysteretic I–V curves at low temperatures. The McCumber constant βc fell in the range of 0.8–2. Fiske and flux-flow resonances were observed for some junctions. The shunting capacitances of the junctions were estimated from the McCumber constant βc, Fiske resonances, and flux-flow resonances. A shunting capacitance value per unit area of 12–35 fF/μm2 was obtained. High resolution cross-sectional transmission electron microscopy was used to study YBCO films grown across straight and wavy step edges. Two 90° tilt boundaries were formed at the edge of a step. The top and bottom YBCO films had their c axis oriented normal to the (001) plane of LAO. In the edge region, the c axis of the YBCO film was tilted by 90°, the a axis was normal to the (001) plane of LAO, and the b axis was lying along the step edge. For wavy step edges, second phase particles usually appeared in the YBCO film along the step edge region. Defects were found on the surface of the LAO substrate along the wavy step edge region. These defects might act as nucleation centers for the second phase particles in the YBCO film. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362594
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  • 3
    Electronic Resource
    Electronic Resource
    Coulomb blockade effects at room temperature in thin-film nanoconstrictions fabricated by a novel technique (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3604-3606 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A technique was developed to fabricate and probe nanosize tunneling structures in thin metallic films. Using oblique evaporation through conventional undercut electron-beam lithographic masks, as the sample resistance was measured in situ, we defined constrictions with widths and lengths of about 10 nm in thin granular palladium films. The tunneling conductivity through a network of metallic grains was studied. Single electron tunneling transistor effects were registered. An electrostatic gate voltage at room temperature could clearly modulate Coulomb blockade offsets of the order of 0.1 V in the current–voltage curves. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122838
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  • 4
    Electronic Resource
    Electronic Resource
    Tunneling through grain boundaries of YBa2Cu3O7 step-edge junctions (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2562-2564 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tunneling experiments were done on YBa2Cu3O7 step-edge junctions. The temperature dependence of the superconducting gap parameter, Δ(T), was measured. From the peak-to-peak distance in the conductance curve, Δ was estimated to vary from 24 to 32 meV at 4.2 K. The conductance at high-voltage bias does not increase with increasing voltage. The tunneling results, together with the well-behaved magnetic field dependence of the critical Josephson current, hysteresis, and Fiske-type resonances in current-voltage curves, indicate a dielectric behavior of the grain boundary junction, i.e., a tunnel junction. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116184
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  • 5
    Electronic Resource
    Electronic Resource
    Transport and structural properties of the top and bottom grain boundaries in YBa2Cu3O7−δ step-edge Josephson junctions (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 249-251 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a method to study separately the electrical transport properties of the grain boundaries (GBs) formed at the top and at the bottom edges of YBa2Cu3O7−δ(YBCO) step-edge Josephson junctions. The step-edge junctions were fabricated on (100) LaAlO3 steps using tilted Ar ion milling to define the electrodes and the microbridges. Due to the shadowing effect of the step, a continuous YBCO stripe remains along and at the bottom of the step on both sides of a microbridge. We found that the top GB is responsible for the weak link behavior of our step-edge junctions. The transport properties were correlated with the different microstructural properties of the two GBs formed at the edges of the step. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120700
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  • 6
    Electronic Resource
    Electronic Resource
    Screw-like structures in ex situ Tl2Ba2CuO6 films (1998)
    Springer
    Applied physics 66 (1998), S. 1223-1226 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 74.70; 68.55; 61.16.Ch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 2 Ba2CuO6 films on single-crystal LaAlO3 was investigated using atomic force microscopy and X-ray diffraction. Most of the film surface consisted of flat areas separated by single or several unit-cell steps. This morphology suggests that the films grow predominantly by a step-flow mechanism. A Tl-2201 film grown using a precursor film deposited at 700 °C exhibited stacks of planes arranged in a screw-like manner on a flat background. Islands of 1–3 μm size and a height of 2–20 unit cells were dominant structures on the surface. Possible causes for the formation of the screw-like structures are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/
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  • 7
    Electronic Resource
    Electronic Resource
    Coulomb blockade electrometer with a high-T c island (1996)
    Springer
    JETP letters 63 (1996), S. 126-132 
    Details
    ISSN: 1090-6487
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on a successful attempt to fabricate a Coulomb blockade electrometer consisting of an ultrasmall YBa2Cu3O7−δ (YBCO) island coupled to two gold electrodes through a high-resistance native surface tunnel barrier. A third electrode placed near the island was used as an electrostatic gate. Spectra typical for tunneling into the YBCO superconductor were reproducibly measured. At temperatures below 0.5 K the low-bias conductance was suppressed by the Coulomb blockade. The blockade could be periodically varied by the gate potential. An external magnetic field of up to 5 T strongly influenced the transport via the island but without any change in the period of the Coulomb oscillations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.566990
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  • 8
    Electronic Resource
    Electronic Resource
    Subharmonic Shapiro steps and noise in high-T c superconductor Josephson junctions (1998)
    Springer
    JETP letters 68 (1998), S. 454-459 
    Details
    ISSN: 1090-6487
    Keywords: 74.50.+r ; 74.25.Fy ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An experimental investigation is made of the subharmonic Shapiro steps observed on the I-V curves of high-T c superconductor Josephson junctions and on the bias-voltage dependences of the rf noise and detector response when the junctions are subjected to external submillimeter radiation. Structures of this type are ordinarily described by a nonsinusoidal current-phase relation, which is why subharmonic steps appear. Numerical modeling of the processes occurring in a Josephson junction by means of a simple current-phase relation, as in the case of an SNS junction, gives good agreement with experiment. The width of the characteristic Josephson generation line of the junction was estimated on the basis of the noise dependences and the selective detector response. The width can be explained by taking into account the shot noise of the tunneling component of the conductivity. A model of the conductivity of a high-T c superconductor Josephson junction, consisting of a tunnel junction with microshorts possessing metallic conductivity, is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567889
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  • 9
    Electronic Resource
    Electronic Resource
    Phase-sensitive reentrance into the normal state of mesoscopic SNS structures (1998)
    Springer
    JETP letters 67 (1998), S. 513-520 
    Details
    ISSN: 1090-6487
    Keywords: 74.80.Fp ; 74.50.+r
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Normal (N) metallic (Ag) mesoscopic conductors with two superconducting (S) faces (Al), arranged mirror-symmetrically relative to the streamlines of the current, periodically switch into the normal state as the superconducting phase difference Δϕ between the NS boundaries approaches the values Δϕ =(2n+1)π, n=0,1,2,..., irrespective of temperature and applied voltage. For Δϕ =2nπ and low applied voltages the conductance passes through a maximum and approaches the normal value as temperature decreases (reentrance). As the voltage subsequently increases, the conductance increases and passes through a maximum. As the phase difference moves away from the values Δϕ=2nπ, the maxima shift in the direction of low temperatures and voltages. The latter result shows unequivocally that in our metal structures it is necessary to take into account the next-order corrections to the “weak” proximity effect approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567691
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  • 10
    Electronic Resource
    Electronic Resource
    YBa2Cu3O7−δ /CeO2 heterostructures on sapphire R-plane (1998)
    Springer
    Physics of the solid state 40 (1998), S. 183-186 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract (001)YBa2Cu3O7−δ epitaxial films were prepared by laser ablation on $$(1\bar 102)Al_2 O_3 $$ surface. A thin (001)CeO2 or (111)CeO2 buffer layer was deposited between the substrate and the superconductor film to reduce their chemical interaction. In the initial stages of CeO2 buffer formation, its orientation depended strongly on the intensity of cerium ion interaction with oxygen. Epitaxial growth of (001)YBa2Cu3O7−δ films was achieved both on $$(001)CeO_2 //(1\bar 102)Al_2 O_3 $$ and $$(111)CeO_2 //(1\bar 102)Al_2 O_3 $$ . The T c temperature of epitaxial (001)YBa2Cu3O7−δ films was within 88–90 K, and the current J c at 77 K was in excess of 106 A/cm−2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130267
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