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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 41 (1999), S. 355-361 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the growth characteristics, structure, and parameters of the epitaxial heterostructures (001)NdBa2Cu3O7−δ /(100)SrTiO3/(001)NdBa2Cu3O7−δ grown by laser ablation on a (100)LaAlO3 substrate with a thin (∼2 nm) YBa2Cu3O7−δ intermediate layer. The use of an YBa2Cu3O7−δ intermediate layer promotes layered growth of the (200 nm) NdBa2Cu3O7−δ layer, whose free-surface roughness is 4–5 nm. The resistance of the NdBa2Cu3O7−δ layers began to fall off abruptly at T=92 K, and at T≈87 K it vanished completely. The critical current density in the NdBa2Cu3O7−δ layers at T=76 K exceeded 106 cm2 A/cm2. The dielectric constant of the (400 nm) SrTiO3 layer sandwiched between the NdBa2Cu3O7−δ epitaxial layers grew by roughly threefold as the temperature was lowered in the interval 300–4.2 K. When a bias voltage of ±2.5V was applied to the NdBa2Cu3O7−δ electrodes, the relative dielectric constant of the (400 nm) SrTiO3 intermediate layer fell from 1150 to 400 (T=32 K, f=100 kHz). The conductivity of the SrTiO3 intermediate layer in the direction perpendicular to the substrate plane increased with temperature and the electric field strength.
    Type of Medium: Electronic Resource
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  • 2
    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
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  • 3
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper describes the design and experimental testing of a high-sensitivity hot-electron bolometer based a film of normal metal, exploiting the Andreev reflection from superconductor boundaries, and cooled with the help of a superconductor-insulator-normal metal junction. At the measured thermal conductivity, G≈6×10−12 W/K, and a time constant of τ=0.2 μs, and a temperature of 300 mK, the estimated noise-equivalent power NEP=5×10−18 W/Hz1/2, assuming that temperature fluctuations are the major source of noise. At a temperature of 100 mK, the thermal conductivity drops to G≈7×10−14 W/K, which yields NEP=2×10−19 W/Hz1/2 at a time constant of τ=5 μs. The microbolometer has been designed to serve as a detector of millimeter and FIR waves in space-based radio telescopes.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Epitaxial SrBi2Nb2O9 films were grown by laser ablation on (001)YBa2Cu3O7−δ /(100)SrTiO3 and (001)NdGaO3, with c axis normal to the substrate plane. The SrBi2Nb2O9 films were grown in a layer-by-layer regime on NdGaO3 substrates in 25-Å steps at a condensation temperature of 700 °C. Microinclusions of secondary phases and a-oriented grains were observed to exist on the surface of (001)SrBi2Nb2O9 films grown on (001)YBa2Cu3O7−δ /(100)SrTiO3. The dielectric permittivity of the SrBi2Nb2O9 films measured along the c axis is 123 (T=300 K, f=100 kHz), and tan δ≈0.04.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 39 (1997), S. 195-199 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The formation of epitaxial heterostructures including YBa2Cu3O7−δ and SrTiO3 thin films on R-plane sapphire substrates has been studied. The thin CeO2 layer and the CeO2/SrBi2Nb2O9 epitaxial bilayer served as buffers. The temperature dependence of the dielectric permittivity ɛ of the SrTiO3 film behaved in essentially different ways when incorporated in the YBa2Cu3O7−δ /SrTiO3/YBa2Cu3O7−δ and in Ag/SrTiO3/YBa2Cu3O7−δ capacitor structures. An external bias U b=±2.5 V applied to a plane-parallel YBa2Cu3O7−δ /SrTiO3/YBa2Cu3O7−δ capacitor structure (T〈100 K) reduced the ɛ of the SrTiO3 film to one half its original value.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 42 (2000), S. 2103-2108 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Precisely (100)-oriented, 200-nm thick La0.67Ca0.33MnO3 films have been grown by laser ablation on a sapphire (R-plane) substrate covered by a (100)SrTiO3/(001)Bi2SrNb2O9/(001)CeO2 trilayer buffer. The azimuthal misorientation of crystal grains (50–300 nm) in the La0.67Ca0.33MnO3 films decreased by about 40% as the condensation temperature was increased ered from 760 to 810° C. The lattice parameter of the grown manganate films was reduced to 3.81–3.82 Å by enriching them with oxygen. The maximum in the temperature dependence of the electrical resistivity of the La0.67Ca0.33MnO3 films grown was shifted toward lower temperatures by 20–50 K relative to its position for bulk ceramic samples of a stoichiometric composition. The largest magnetoresistance (MR=42% at H=0.4 T) was found in La0.67Ca0.33MnO3 films with a Mn4+ concentration on the order of 50% (T=166 K).
    Type of Medium: Electronic Resource
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  • 7
    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
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  • 8
    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
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 39 (1997), S. 1542-1547 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A bi-epitaxial (001)YBa2Cu3O7−δ /(110)BaZrO3/(001)CeO2 three-layer heterostructure has been grown on (100)SrTiO3 by laser ablation. The epitaxial relations between the layers making up the heterostructure were derived from x-ray diffraction data. The I cRn product for the bi-epitaxial Josephson junctions thus obtained was within 1–1.5 mV for 4.2 K, and 30–60 µV for 77 K. The normal resistance R n=(2–5 Ω) was practically independent of temperature. The magnetic field dependences of I c had typically a clearly pronounced main maximum, followed by distorted subsequent peaks. Interaction of the Josephson ac current with self-induced electromagnetic waves at the 45° grain boundary and with external microwave radiation (f=11 GHz) produced current steps in the I-V characteristics of the bi-epitaxial junctions at the corresponding voltages.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 40 (1998), S. 183-186 
    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
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