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  • 1
    Electronic Resource
    Electronic Resource
    Ferroelectricity and structure of BaTiO grown on YBa Cu O thin films (2000)
    Springer
    The European physical journal 14 (2000), S. 477-481 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 74.76.-w Superconducting films - 77.55.+f Dielectric thin films - 77.80.-e Ferroelectricity and antiferroelectricity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We have investigated the crystal structure and the ferroelectric properties of BaTiO3 thin films with YBa2Cu3O as the bottom and Au as the top electrode. Epitaxial heterostructures of YBa2Cu3O and BaTiO3 were prepared by dc and rf sputtering, respectively. The crystal structure of the films was characterised by X-ray diffraction. The ferroelectric behaviour of the BaTiO3 films was confirmed by hysteresis loop measurements using a Sawyer Tower circuit. We obtain a coercive field of 30 kV/cm and a remanent polarisation of 1.25 μC/cm2. At sub-switching fields the capacitance of the films obeys a relation analogous to the Rayleigh law. This behaviour indicates an interaction of domain walls with randomly distributed pinning centres. At a field of 5 MV/m we calculate a 3% contribution of the irreversible domain wall motion to the total dielectric constant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510051056
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  • 2
    Electronic Resource
    Electronic Resource
    Charge-carrier density collapse in and epitaxial thin films (2000)
    Springer
    The European physical journal 14 (2000), S. 509-513 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 71.38.+i Polarons and electron-phonon interactions - 73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects) - 75.30.Vn Colossal magnetoresistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We measured the temperature dependence of the linear high field Hall resistivity of ( K) and ( K) thin films in the temperature range from 4 K up to 360 K in magnetic fields up to 20 T. At low temperatures we find a charge-carrier density of 1.3 and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In this temperature range electron-magnon scattering contributes to the longitudinal resistivity. At the ferromagnetic transition temperature a dramatic drop in the number of charge-carriers n down to 0.6 holes per unit cell, accompanied by an increase in unit cell volume, is observed. Corrections of the Hall data due to a non saturated magnetic state will lead a more pronounced charge-carrier density collapse.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510051059
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  • 3
    Electronic Resource
    Electronic Resource
    Inelastische Elektronenstreuung an endlichen Kernen (1971)
    Springer
    The European physical journal 248 (1971), S. 333-344 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The response function of a finite nucleus is calculated with the help of perturbation theory. Realistic hard core nucleon-nucleon potentials are used. For theT-matrix elements a Bethe-Goldstone like equation is solved using the method of Kallio and Day. Numerical calculations of the response function are carried out for oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01400547
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  • 4
    Electronic Resource
    Electronic Resource
    Critical current density and upper critical field of YBa2Cu3O7 thin films (1991)
    Springer
    The European physical journal 83 (1991), S. 221-226 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Epitaxial YBa2Cu4O7-thin films with thec-axis oriented perpendicular to the film plane were prepared bydc-sputtering from a single stoichiometric target on (100) SrTiO3-substrates. Typical values of the inductively measured superconducting transitions were about 90 K with a width less than 0.5 K. Critical current densities were measured on 5 to 10 μm wide strips as function of magnetic field and temperature. The temperature dependences ofj c follow a universal functionj c(B,T)=j c * (T=0,B)·(1−T/T c (B))α with α=1.5±0.1. ForB=0 andT=77 K we obtainedj c =4·106 A/cm2. The field dependence of the resistive transitions was measured with the magnetic field parallel to thec-axis. The slope of the upper critical fieldB c2 (T) was determined for different criteria. The carrier concentration evaluated from Hall-effect measurements was found to decrease linearly from one per unit cell at 240 K with decreasing temperature extrapolating nearly through zero forT=0. Highly resolved angular dependent measurements of the critical current density withB perpendicular to the current but tilted from thec-axis show a very strong and sharp enhancement ofj c for the magnetic field parallel to the (CuO2)-layers (B⊥c). Additionally to this phenomenon, which is caused by an intrinsic pinning mechanism due to the layered structure of high-T c -superconductors the influence of the anisotropy of the upper critical field onj c (B, T, φ) is evident nearT c .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01309422
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  • 5
    Electronic Resource
    Electronic Resource
    Hyperfine interaction studies on swift O-ions emerging with polarized electrons from ferromagnetic layers into vacuum (1994)
    Springer
    The European physical journal 348 (1994), S. 49-56 
    Details
    ISSN: 1434-601X
    Keywords: 21.10.Ky ; 25.55.−e ; 34.00
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A precision plunger set-up was used to determine in time-differential measurements of hyperfine interactions the degree of polarization of 1s- and 2s-electrons in H- and Li-like oxygen ions on their emergence from magnetized Ni- and Gd-layers into vacuum. In addition a time-integral measurement with Fe-layers served to obtain the polarization of 2s-electrons only. For all three ferromagnetic materials the degree of polarization of 2s-electrons is found to be twice as large as for 1s-electrons. The data are discussed in the context of transient magnetic fields and their underlying polarization mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01291652
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of YBa2Cu3O7/PrBa2Cu3O7 superlattices (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 197-200 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting superlattices ; structural characterization ; flux motion ; critical currents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We investigated the structural and superconducting properties ofc-axis oriented (YBa2Cu3O7) nY /(PrBa2Cu3O7) npr superlattices with thicknesses of the individual layers down to one unit cell (10≥nY≥1; 18〉nPr≥ 1). By transmission electron microscopy and X-ray diffraction we find an excellent structural quality of the samples, though the quantitative analysis shows the existence of defects. In superlattices with decoupled YBa2Cu3O7 layers of two unit cell thickness we find a highT c value of 75 K. We probed the flux line structure in the superlattices by measurements of the critical current density in magnetic fields. The experiments show that the flux-line dynamics is dominated by the movement of pancake vortices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730393
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  • 7
    Electronic Resource
    Electronic Resource
    Raman scattering studies of ultrathin-layer YBa2Cu3O7/PrBa2Cu3O7 superlattices (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 213-216 
    Details
    ISSN: 1572-9605
    Keywords: Raman scattering ; superlattice ; YBa2Cu3O7 ; PrBa2Cu3O7 ; phonon renormalization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We present Raman scattering studies ofc-oriented ultrathin-layer superconducting (YBa2Cu3O7) m /(PrBa2Cu3O7) n superlattices. For the superlattice with (m=2,n=1) sequence, Raman spectra reveal a new line in the spectral region around 320 cm−1. It is interpreted as a mode representing a combination of IR optical phonons of the Y-sublayers with an admixture of aB 1g type Raman active vibration in the Pr sublayers. This new line, which is similar to those from the interior of the Brillouin zone of the original lattice, does not exhibit superconductivity-induced self-energy effects, although its counterpart in the pure substance does. No additional line is found in the (m=1,n=2) superlattice in the same region, supporting our interpretation for the (m=2,n=1) sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730397
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of epitaxial Bi2Sr2CaCu2O8+δ thin films (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 217-219 
    Details
    ISSN: 1572-9605
    Keywords: Bi-2212 thin films ; dc sputtering ; structural characterization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We report a dc sputtering method for the fullin situ preparation of Bi2Sr2CaCu2O8+δ thin films on SrTiO3 and LaAlO3.T c values of more than 90 K can be achieved by oxidizing annealing below the melting point, followed by a reducing anneal at 500°C. The structural properties of the films are revealed by X-ray diffraction in Bragg-Brentano geometry (strongc-axis orientation with FWHM (0 0 10)=0.3) and also byΦ scans (epitaxy within the substrate plane). Rutherford backscattering and channeling confirmed the correct composition of the cations while the minimum yield,χ min, is 23%. Depth profiles by SNMS show a very homogeneous distribution of the cations with no detectable loss of bismuth near the surface. The surface morphology of the films was studied by SEM and by STM. Patterning of the films in lateral geometry can be performed by photolithographic techniques without degradation ofT c .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730398
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  • 9
    Electronic Resource
    Electronic Resource
    Scattering phase shifts in Ni and Zn doped Y-123 (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1415-1420 
    Details
    ISSN: 1573-7357
    Keywords: 74.62Dh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Cu-site substituted thin films of YBa2(Cu1-zMz)3O7-δ (M=Zn,Ni) are reinvestigated. The Tc-suppression and residual resistivities ϱo are measured as a function of the concentration z. We found that for low concentrations z 〈 4% the substituents occupy preferrably the in-plane Cu sites whereas for higher concentrations the chain sites are also occupied. Although the residual resistivities of Ni and Zn differ only slightly, the Tc-suppression of Zn is 2.3 times larger than that of Ni. To reconcile the measured resistivities with predictions of a two dimensional scattering model, it is necessary to assume a scattering potential of finite range and to take scattering phase shifts] δl of higher angular momentum (l 〉 0) into account. The different Tc-suppression rates for Zn and Ni are also discussed within this picture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00753898
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  • 10
    Electronic Resource
    Electronic Resource
    Low-Frequency Relaxation Rate in the Superconducting YBa2Cu3O6.7 (1999)
    Springer
    Journal of low temperature physics 117 (1999), S. 1043-1047 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The submillimeter-wave 3 cm −1 〈 ν 〈 40 cm −1 complex conductivity of the reduced YBa 2 Cu 3 O 6.7 film, (T C =56.5 K) was investigated for temperatures 4 K 〈 T 〈 300 K. The frequency dependence of the effective quasiparticle scattering rate 1/τ*(ν) was extracted from the spectra. 1/τ* is shown to be frequency independent at low frequencies and high temperatures. On decreasing temperature the scattering rate increases with increasing frequencies. Finally, at 6 K it follows a power-law, 1/τ* ∝ ν1.75±0.3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022518122120
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