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  • Articles  (50)
  • 74.72.Bk  (50)
  • Springer  (50)
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  • Physics  (50)
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  • Articles  (50)
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  • Springer  (50)
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  • Physics  (50)
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  • 1
    Electronic Resource
    Electronic Resource
    Low-temperature (T〈180 K) relaxation processes and possible “electronic phase separation” in RBa2Cu3O6+x (R=Y, Tm, Lu) single crystals (1996)
    Springer
    JETP letters 63 (1996), S. 830-834 
    Details
    ISSN: 1090-6487
    Keywords: 74.72.Bk ; 74.72.Jt ; 64.75.+g ; 77.22.Gm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Low-temperature (120–180 K) relaxational effects are observed in oxygen-deficient RBa2Cu3O6+x (R=Y, Tm, Lu) single crystals. Isothermal holding of the crystals after rapid cooling increases their resistance. The characteristic times and the activation energy of the relaxation process, E a ≈0.46 eV, are determined. The possible relation between the observed effects and the appearance of “electronic phase separation” is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567098
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  • 2
    Electronic Resource
    Electronic Resource
    Shape of the Cu(2) NQR spectra in YBa2Cu3O7, TmBa2Cu3O7 and TmBa2Cu4O8 (1997)
    Springer
    JETP letters 66 (1997), S. 624-629 
    Details
    ISSN: 1090-6487
    Keywords: 76.60.Gv ; 74.72.Bk ; 74.72.Yg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a study of shape of the Cu(2) NQR spectra in YBa2Cu3O7, TmBa2Cum3O7, and TmBa2Cu4O8 compounds at temperatures of 4.2–300 K. The results of the quantitative analysis lead us to conclude that the shape of the Cu(2) NQR spectra in all the samples studied can be described in the framework of the “motional narrowing” model, which implies that the Cu(2) nucleus possesses two different NQR frequencies between which it can rapidly jump. The difference in frequencies seems to be related to the charge-stripe correlations in CuO2 planes resulting in a dynamical modulation of the electric field gradients at the Cu(2) nuclei.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567612
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  • 3
    Electronic Resource
    Electronic Resource
    Linear low-temperature dependence of the surface impedance of a Ba0.6K0.4BiO3 single crystal (1996)
    Springer
    JETP letters 64 (1996), S. 832-838 
    Details
    ISSN: 1090-6487
    Keywords: 84.37.+q ; 74.72.Yg ; 74.72.Bk ; 74.72.Hs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The temperature dependences of the real part R s and the imaginary part X s of the surface impedance Z s =R s +iX s of the superconductor Ba0.6K0.4BiO3 (T c ≃30 K) are measured at a frequency of 9.4 GHz. Its temperature dependence Z s (T) and that of the complex conductivity σ s (T) can be described on the basis of a two-fluid model under two assumptions: The density of superconducting carriers increases linearly, and the relaxation time increases as a power law (∝1/T 5), with decreasing temperature T〈T c . This model also describes well the curves Z s (T) and σs (T) recently measured for YBa2Cu3O6.95 and Bi2Sr2CaCu2O8 single crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567255
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  • 4
    Electronic Resource
    Electronic Resource
    Anisotropy of the superconducting properties of YBa2Cu3O7−x single crystals with reduced oxygen content (1998)
    Springer
    JETP letters 68 (1998), S. 332-337 
    Details
    ISSN: 1090-6487
    Keywords: 74.72.Bk ; 74.25.Fy ; 74.62.Bf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In an investigation of the resistivity anisotropy of YBa2Cu3O7−x single crystals with suboptimal oxygen content it is observed that the superconducting transition for the component ρc of the resistivity tensor is shifted to lower temperatures with respect to the transition for the component ρab. A similar shift is also observed for the transition in the temperature dependence of the dynamic magnetic susceptibility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567869
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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    A new optical method for measuring the electron-phonon interaction parameter λ〈Ω2〉 using the spectral dependence of the relaxation rate (1999)
    Springer
    JETP letters 70 (1999), S. 329-333 
    Details
    ISSN: 1090-6487
    Keywords: 78.47.+p ; 63.20.Kr ; 74.25.Jb ; 74.25.Kc ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The spectral dependence of the electron-phonon relaxation rate γe−ph(ℏω) in metals is studied in pump-supercontinuum-probe (PSCP) experiments with femtosecond time resolution. Investigation of this spectral dependence, which exhibits a substantial slowing of the relaxation rate γe−ph(ℏω) near the Fermi level E F , using the parametrization γe−ph(ℏω)∝λ〈Ω2〉 (ℏω−E F )2 makes it possible to determine directly the electron-phonon interaction parameter λ〈Ω2〉. The parameter λ〈Ω2〉 for YBa2Cu3O7−δ is analyzed using this method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.568175
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  • 7
    Electronic Resource
    Electronic Resource
    Stripe motion in CuO2 planes of Y1−x Pr x Ba2Cu3O7 as observed from the Cu(2) quadrupole resonance (1997)
    Springer
    JETP letters 65 (1997), S. 821-827 
    Details
    ISSN: 1090-6487
    Keywords: 61.72.Hh ; 74.72.Bk ; 74.80.−g ; 76.60.Gv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The NQR spectra of copper in the compounds YBa2Cu3O7, TmBa2Cu3O7, and Y0.9Pr0.1Ba2Cu3O7 at temperatures of 4.2–200 K are investigated by a pulsed NQR technique at frequencies of 28–33 MHz. Quantitative analysis of the spectra shows that the shape of the “plane” Cu(2) spectra is well described by using a model of 1D correlations of the charge and spin distribution in the CuO2 planes (stripe correlations). In the undoped superconductors the charge-spin stripe structure moves fast in the CuO2 planes, but doping the YBa2Cu3O7 lattice with praseodymium slows this motion down.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567452
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  • 8
    Electronic Resource
    Electronic Resource
    Nature of the microwave response of a YBaCuO Josephson junction on a bicrystalline substrate (1996)
    Springer
    JETP letters 64 (1996), S. 454-459 
    Details
    ISSN: 1090-6487
    Keywords: 74.60.+r ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The response of YBaCuO Josephson junctions on a bicrystalline substrate to the action of microwave radiation is found to contain, besides the Josephson response, a contribution associated with the tunneling of quasiparticles through channels formed by localized states in the region of the Josephson junction. It is shown that this contribution is associated with an increase in the conduction through these channels under the action of the radiation on the junction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567219
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  • 9
    Electronic Resource
    Electronic Resource
    Anomalies of the electronic spin-lattice relaxation of Gd3+ in YBa2Cu4O8 and YBa2Cu3O6+x near 200 K (1999)
    Springer
    JETP letters 69 (1999), S. 610-615 
    Details
    ISSN: 1090-6487
    Keywords: 74.72.Bk ; 76.60.Es
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A sharp kink in the temperature dependence of the electronic spin-lattice relaxation rate near 200 K was found in the high-temperature superconductors YBa2Cu4O8 and YBa2Cu3O6+x . The effect is correlated with opening of a spin gap and microscopic phase separation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567968
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  • 10
    Electronic Resource
    Electronic Resource
    Characteristic features of the temperature dependence of the surface impedance of YBa2Cu3O6.95 single crystals (1997)
    Springer
    JETP letters 65 (1997), S. 938-944 
    Details
    ISSN: 1090-6487
    Keywords: 74.25.Nf ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The real and imaginary parts of the surface impedance Z s =R s +iX s of YBa2Cu3O6.95 single crystals are measured at a frequency ω/π=9.4 GHz. The quantities R s (T) and X s (T) are linear functions of temperature for T〈0.3T c (T c =93.5 K). A maximum of R s (T) and a plateau of X s (T) are observed in the interval 35〈T〈65 K. Our experimental data, just as all recent measurements of R s (T) in YBa2Cu3O6.95 single crystals in the temperature range 0〈T〈1.3T c , are described well in a two-fluid model which assumes electron-phonon scattering of quasiparticles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567453
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  • 11
    Electronic Resource
    Electronic Resource
    Spin susceptibility of neutron-irradiation-disordered YBa2Cu3O6.9 in the normal and superconducting states (1998)
    Springer
    JETP letters 67 (1998), S. 182-188 
    Details
    ISSN: 1090-6487
    Keywords: 61.80.Hg ; 76.60.Es ; 74.72.Bk ; 74.25.Nf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The spin-spin relaxation rate 63 T 2 −1 of 63Cu nuclei in CuO2 layers is measured in the normal and superconducting states of the compound YBa2Cu3O6.9 (T c onset =94 K) subjected to radiation-induced disordering by a fast-neutron flux Φ to T c onset =68 K (Φ=7×1018 cm−2) and T c onset 〈4 K (Φ=12×1018 cm−2). It is found that as the structural disorder increases, the contribution of the indirect spin-spin interaction 63 T 2G −1 , which is related to the value of the spin susceptibility at the boundary of the Brillouin zone of the copper planes χs(q={π/a; π/a}), decreases slightly at the transition to the superconducting state for the initial sample and remains unchanged for the weakly disordered sample. This behavior of the short-wavelength contribution to the spin susceptibility attests to the stability of the x 2−y 2 symmetry of the energy gap against structural disorder, in accordance with proposed theoretical models of Cooper pairing for high-T c cuprates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567648
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  • 12
    Electronic Resource
    Electronic Resource
    Antiferromagnetism in hydrated 123 compounds (1999)
    Springer
    JETP letters 69 (1999), S. 792-797 
    Details
    ISSN: 1090-6487
    Keywords: 74.72.Bk ; 74.25.Ha ; 75.50.Gg ; 76.60.Gv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Copper nuclear quadrupole resonance and zero-field nuclear magnetic resonance (ZFNMR) studies of YBa2Cu3O6.5 show that a magnetic phase appears in underdoped 123 superconductors treated in ambient moist air. The studies give convincing evidence that the “empty” CuO chains play the role of easy water insertion channels. The reaction occurs first in ordered regions of the crystallites. The final product of the reaction is a nonsuperconducting antiferromagnetic compound characterized by at least two types of magnetically ordered copper ions, with ZFNMR spectra in the frequency ranges 46–96 and 96–135 MHz, respectively. Even for powder samples fixed in an epoxy resin, this reaction is found to have partially occurred after a few years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.568092
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  • 13
    Electronic Resource
    Electronic Resource
    Effect of asymmetry of CuO2 layers in copper oxides on the anomalous neutron scattering near T c (1999)
    Springer
    JETP letters 69 (1999), S. 392-397 
    Details
    ISSN: 1090-6487
    Keywords: 74.72.Bk ; 61.12.Ex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Reasons for critical magnetic scattering of neutrons near T c in copper oxides with CuO2 layers whose nearest environment has no “up-down” symmetry are discussed. The intracrystalline electric field, which threads the CuO2 planes on account of the asymmetry, induces coupling between the spin and momentum of the current carriers. This coupling is shown to result in a manifestation of virtual Cooper pairs in the imaginary part of the spin susceptibility. Thus spin density fluctuations as well as current fluctuations should participate in the scattering. A way of experimentally distinguishing between the two mechanisms is pointed out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.568040
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  • 14
    Electronic Resource
    Electronic Resource
    Anomalous behavior of the structural parameters of YBa2Cu4O8 single crystals at the transition to the superconducting state (1997)
    Springer
    JETP letters 66 (1997), S. 534-539 
    Details
    ISSN: 1090-6487
    Keywords: 61.50.Ks ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract High-precision x-ray crystallographic studies of YBa2Cu4O8 single crystals (T c =70 K) are performed at eight temperatures in the interval 20–295 K. It is found that a number of structural parameters exhibit anomalous behavior near the superconducting transition of the crystal. A characteristic effect near the phase transition is the displacement of the O1 bridge atom that joins the Cu1 atom of the cuprate chain to the Cu2 atom of the cuprate plane. The shift of this oxygen toward the Cu2 atom is indicative of a change in the Cu2-O1 chemical bond and of charge transfer to the cuprate plane in the process of the transition of the crystal to the superconducting state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567560
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  • 15
    Electronic Resource
    Electronic Resource
    Theory of the pseudogap in the elementary excitation spectrum of the normal phase of bilayer cuprates (1997)
    Springer
    JETP letters 66 (1997), S. 569-574 
    Details
    ISSN: 1090-6487
    Keywords: 74.25.Jb ; 74.25.Gz ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Solutions of the integral equations for the pseudogap in the elementary excitation spectrum of current carriers in bilayer cuprates are found. In the general case, the pseudogap possesses s + id symmetry, where the s component is determined by the interaction of holes via the phonon field and the d component is due to the superexchange interaction of the copper spins and the Coulomb-repulsion screened holes. The s and d components exhibit different temperature dependences. This fact enabled us to explain the characteristic features of the temperature behavior of the normal-phase spin susceptibility of lightly doped cuprates, specifically, for the compound YBa2Cu4O8 in the entire temperature interval T〉T c . The wave-number dependence of the pseudogap agrees with the photoemission data for Bi2Sr2CaCu2O8+y .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567547
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  • 16
    Electronic Resource
    Electronic Resource
    Comparative studies of the NMR of thulium in Tm123 and Tm124 compounds: Evidence for structural and electronic phase separation (1996)
    Springer
    JETP letters 64 (1996), S. 398-403 
    Details
    ISSN: 1090-6487
    Keywords: 61.72.Hh ; 74.72.Bk ; 74.80.Bj ; 76.60.Lz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The nuclear magnetic relaxation of 169Tm in TmBa2Cu3O6+x (x=0.1–1.0, Δ x=0.1) and TmBa2Cu4O8 is studied at temperatures below 5 K. In all the samples, the Tm spin-lattice relaxation proceeds via intrinsic paramagnetic centers (PCs) like Cu2+ or copper-oxygen spin-polarized clusters. The experimental data for TmBa2Cu3O6+x support the idea of the structural (chemical) micro-phase separation in oxygen-deficient 123 compounds. Apparently, the samples with x⩾0.4 contain hole-poor nonsuperconducting regions, enriched with PCs, and hole-rich (PC-poor) superconducting regions. The volume fraction f n of the PC-rich phase reaches a maximum value of 0.85 at x=0.4 and decreases monotonically with increasing x (f n=0.5, 0.3, and 0.25 at x=0.5, 0.6, and 0.7, respectively). The Tm spin-lattice relaxation in the underdoped TmBa2Cu4O8 compound indicates that this sample, in contrast to oxygen-deficient TmBa2Cu3O6+x , has a homogeneous composition. However, the Tm spin-spin relaxation measurements reveal two sorts of the Tm nuclear spins in Tm124, having different NMR spectra and different relaxation times T 2. The latter result is evidence of electronic phase separation in CuO2 phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567210
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  • 17
    Electronic Resource
    Electronic Resource
    Commensurability oscillations and a new phase transition in YBa2Cu3Oy single crystals (1999)
    Springer
    JETP letters 69 (1999), S. 881-886 
    Details
    ISSN: 1090-6487
    Keywords: 74.72.Bk ; 75.60.Ej ; 74.25.Ha
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Magnetization oscillations due to the commensurability of the vortex and crystal lattice periods in YBa2Cu3Oy (y=6.97±0.02) single crystals are investigated using a high angular resolution magnetometer. A sharp peak in the temperature dependence of the oscillation amplitude as well as other features in the behavior of the oscillation amplitude and of the irreversible magnetization are observed at T f ∼60 K. It is inferred that T f is the temperature of a transition of the solid vortex state to a smectic phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.568106
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  • 18
    Electronic Resource
    Electronic Resource
    Transport and Cu NMR studies of charge and spin dynamics in PrBa2Cu4O8 (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 437-442 
    Details
    ISSN: 1573-7357
    Keywords: 74.72.Bk ; 72.15.−v ; 76.60.−k
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The charge and spin dynamics in PrBa2Cu4O8 are investigated by means of transport and Cu NMR measurements. The magnetoresistance was found to be very small at high temperatures and increase rapidly with decreasing temperature below ∼100 K, which may be ascribed to the dimensional crossover from one to two dimensions in the charge transport in the CuO double chains. While the NMR signal from the chain Cu sites persists down to 4.2 K without any appreciable line broadening, the signal from the planar Ce sites disappears below ∼250 K indicating the long-range antiferromagnetic order of plane Cu moments. This is consistent with the view of metallic conduction along the quasi one-dimensional CuO chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00768425
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  • 19
    Electronic Resource
    Electronic Resource
    On atoms charge states in RBa2Cu3Ox high-temperature superconductors (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 359-364 
    Details
    ISSN: 1573-7357
    Keywords: 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The distribution of charge states of all atoms in the unit cell of RBa2Cu3Ox; x=6,7 (R = Yb, Er, Ho, Y, Gd, Eu, Sm, Nd, Pr) is determined on the basis of comparison of the theoretical calculated electric field gradient tensor and existing experimental data. The variation of the charge states of the atoms as a function of the ionic radius is analyzed.
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    URL: http://dx.doi.org/10.1007/BF00768412
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  • 20
    Electronic Resource
    Electronic Resource
    Dynamical structural instability in YBa2Cu3O6.6 (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 837-842 
    Details
    ISSN: 1573-7357
    Keywords: 74.72−h ; 74.72.Bk ; 87.64.Bx ; 74.25.Kc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have performed inelastic neutron scattering and total neutron scattering experiments on the under-doped superconductor YBa2Cu3O6.6. We have found that the dynamical structure and the local structure concerned about the CuO2 plane has an anomalous temperature dependence at Tc (=57K) and well above Tc (TSG∼150K), which may be explained by a spin-gap opening.
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    URL: http://dx.doi.org/10.1007/BF00768487
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  • 21
    Electronic Resource
    Electronic Resource
    Influence of micro-structure in the low temperature critical currents of YBa2Cu3O7−δ thin films (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1017-1022 
    Details
    ISSN: 1573-7357
    Keywords: 74.60Jg ; 74.72.Bk ; 74.76.Bz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Epitaxial YBa2Cu3O7−δ films nucleate in c-axis oriented single-crystalline islands. The surface of the single-crystalline SrTiO3 substrates exhibit steps of one third of the YBa2Cu3O7−δ c-axis. These steps generate a mismatch in the island boundaries between the CuO2 superconducting blocks. We show that these defect regions are strong candidates for being the pinning centers responsible for the large critical currents observed in Laser Ablated and Sputtered thin films.
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    URL: http://dx.doi.org/10.1007/BF00768516
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  • 22
    Electronic Resource
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    Electronic transport and specific heat of Ca-doped YBa2Cu3Ox-single crystals (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 909-914 
    Details
    ISSN: 1573-7357
    Keywords: 74.25.Bt ; 74.25.Fy ; 74.62.Dk ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Measurements of the anisotropic electrical resistivity, the Hall Effect, and the specific heat anomaly at Tc of Ca-doped YBa2Cu3Ox single crystals of various Ca and O contents are presented. The transport properties are discussed in terms of charge and spin separated quasiparticles and confirm that by doping Ca onto Y sites the hole concentration, nh, can be extended beyond the value achieved with O-doping alone at x=7.0. The jump in the specific heat at Tc which increases monotonously with x up to x=7.0 in Ca-free crystals displays a maximum in highly oxygenated Ca-doped crystals. This maximum, however, is displaced from the Tc(nh) maximum to higher values of nh, consistent with the model of induced superconductivity in the CuO chains.
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    URL: http://dx.doi.org/10.1007/BF00768498
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  • 23
    Electronic Resource
    Electronic Resource
    Cu-O bond-stretching vibrations in YBa2Cu3O7 studied by inelastic neutron scattering (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 807-812 
    Details
    ISSN: 1573-7357
    Keywords: 74.72.Bk ; 74.25.Ke ; 63.20.Kr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Inelastic neutron experiments confirm the previously reported anomalous nature of the planar oxygen bond-stretching vibrations and furnish further details. It is shown that the frequency of the linear breathing mode is renormalized by 5 THz compared to insulating YBa2Cu3O6. Studies of the Cu1-apical O bond-stretching vibrations demonstrate that frequencies, line-widths and phonon intensities can well be understood within the framework of a harmonic lattice dynamical model. This rules out predictions of a double well potential and strong anharmonitity for this type of vibration.
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    URL: http://dx.doi.org/10.1007/BF00768482
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  • 24
    Electronic Resource
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    Ion-channeling studies of lattice anomalies well aboveT c in YBa2CU3O7−y (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 831-836 
    Details
    ISSN: 1573-7357
    Keywords: 61.85.+p ; 74.20.Mn ; 74.25.Kc ; 74.62. Bf ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Backscattering yields in the 〈001〉 axial channeling mode using D+ ions have been measured for YBa2Cu3O7−y single crystals with Tc=59K. 68K and 91K at temperatures between 40K and 295K. In 60 K-class YBa2Cu3O7−y with significant anomalies associated with the spin gap, it is found that the channeling anomalies are observed at 130–140 K(Tpa) in addition to anomalies at Tc. The channeling anomalies at Tc follow to the shift of Tc, suggesting the phonon anomalies induced by the superconducting-gap opening. On the other hand, Tpa is found to be almost unchanged for varying Tc, although Tpa appears near the temperature where the spin gap is opened. This leads a question whether the channeling anomalies at Tpa is directly related to the phonon anomalies induced by the spin-gap opening. The existence of lattice instability is suggested as one of possible explanations for the anomalies at Tpa.
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    Transport results from untwinned YBCO: Washboard frequency of the vortex lattice, and the quasiparticle mean free path (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 877-886 
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    ISSN: 1573-7357
    Keywords: 74.60.Ge ; 72.15.Lh ; 74.72.−h ; 72.15.Gd ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The “washboard frequency” ω of the moving vortex lattice in untwinned YBa2 Cu3 O6.93 may be observed through mode-locking to an externally applied ac current of frequency ωext. The interference between ω and ωext results in jumps in the dc current-voltage characteristics when ω and ωext are harmonically related1. The interference effect disappears in the vortex liquid state. The Hall conductivity σxy below Tc in YBCO contains contributions2 from a positive quasiparticle (qp) term (∼H) and a negative vortex term (∼1/H). The qp term is surprisingly large well below Tc and implies a large gap anisotropy and a long qp mean free path (mfp). The thermal Hall effect3 κxy is closely related to the qp σxy; κxy is produced by asymmetric scattering of qp by pinned vortices. The qp mfp at H = 0, extracted from σxy and extended to low T by κxy, increases remarkably from 90 Å at Tc to more than 0.5μm at 22 K.
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    Raman scattering by electronic excitations in semiconductors and in highT c superconductors (1995)
    Springer
    Journal of low temperature physics 99 (1995), S. 205-221 
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    ISSN: 1573-7357
    Keywords: 74.25.Gz ; 74.72.Bk ; 78.30.Er ; 71.25.−s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Raman scattering by electronic excitations in normal and superconducting metals with complex Fermi surfaces is discussed. The theoretical results are applied to the case of high Tc superconductors. The possible implications of measurements of this scattering concerning the symmetry of the gap function is dealt with.
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    URL: http://dx.doi.org/10.1007/BF00752289
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    Photoinduced enhancement of the Josephson effect in YBaCuO grain boundary junctions (1997)
    Springer
    Journal of low temperature physics 106 (1997), S. 255-264 
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    ISSN: 1573-7357
    Keywords: 73.50.Pz ; 74.50.+r ; 74.72.Bk
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    Topics: Physics
    Notes: Abstract Experiments of persistent photoinduced enhancement of the Josephson effect in YBaCuO junctions are reviewed in this paper. These experiments show that the critical current and the conductivity of these Josephson junctions can be increased after illumination. This effect is due to photodoping of the oxygen depleted region in the weak link.
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    URL: http://dx.doi.org/10.1007/BF02399623
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    The influence of external bias voltage on electrical properties of YBa2Cu3O7−x /metal point contact interface (1997)
    Springer
    Journal of low temperature physics 106 (1997), S. 277-283 
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    ISSN: 1573-7357
    Keywords: 74.72.Bk ; 74.50.+r ; 74.80.Fp ; 73.40.Cg ; 73.40.Gk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have investigated a change of electrical properties of YBa2Cu3O7−δ/metal point contact immediately after its preparation depending on time, temperature as well as external bias voltage. The increase of the point contact differential resistance in time was experimentally observed at temperature above 200 K even if no external bias voltage was applied. The low external bias voltage considerably influences the time increase of the differential resistance indicating an important role of oxygen diffusion. It is shown on differential characteristics that for Au, In the parameters of tunneling barrier such as the average height and width are constant in time whereas for Al, Pb an evolution of the tunneling barrier was observed because of oxidation of Al and Pb. Applying of higher bias voltage (up to 1 V) enables the transport of oxygen even below 200 K (down to 4.2 K) and changes the electrical properties of YBCO/metal point contact interface. The differential characteristics change their behaviour from that typical for NIS contact with strong tunneling barrier to NS contact with a high transparency of the interface. All the above changes are reversible upon changing the bias voltage polarity.
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    Experimental study of the intergranular weak link structures YBa2Cu3O7−x with the help of magnetization measurements (1997)
    Springer
    Journal of low temperature physics 106 (1997), S. 447-452 
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    ISSN: 1573-7357
    Keywords: 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract AC and DC virgin magnetizations of sintered YBa2Cu3O7−x samples have been measured in dependence of the sintering temperature. The samples were prepared by solid state reaction of stoichiometric decarbonated mixture of Y2O3, BaCO3 and CuO components. Magnetization curves were measured at 77K in the range of magnetic field (10−1−2×104 Am −1). The temperature of sintering was being changed in the range 910°C up to 950°C. In the range of weak magnetization fields the magnetization curves are affected by properties of the intergranular medium — the intergranular weak links. The parameters H 1 w1 , H 2 w1 and H 1 g characterising the flux penetration into intergrain and intragrain medium were estimated from the magnetization measurements.
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    Granular nature and superconductive coupling of YBa2Cu3O7 polycrystals observed by microwave absorption measurements (1997)
    Springer
    Journal of low temperature physics 106 (1997), S. 469-474 
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    ISSN: 1573-7357
    Keywords: 74.80.Bj ; 74.72.Bk ; 74.50.+r ; 78.70.Gq
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The results of measurements of the H-modulated microwave absorption of of YBa2Cu3O7 ceramic in the transition temperature region and with fields in the range 0–10 kOe are presented. They give clear evidence of the weak-link inter-grain nature of the gross part of the dissipation and support the idea of stronger links, or microbridges of a more intrinsic species, involved in the high-field intra-grain absorption component. A semiquantitative analysis of the absorption process is suggested and applied to the derivative spectra in the T-swept form (at fixed external field). It allows to deduce information about Tc, the superconductive coupling, and the H- and T-dependences of the critical currents involved in the inter- and intra-grain regions. When applied to YBa2Cu3O7 powders, obtained by finely grinding a ceramic pellet, it gives also evidence of a generalized suppression of coupling induced by the grinding process
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    Upward curvature of the microwave surface resistance vs. field in YBCO films and the Clem's Rs model (1997)
    Springer
    Journal of low temperature physics 106 (1997), S. 487-492 
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    ISSN: 1573-7357
    Keywords: 74.25.Nf ; 74.60.Ge ; 74.72.Bk ; 78.70.Gq
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The recent experimental data by I. S. Ghosh et al. (1994) on microwave losses induced by flux motion in YBCO thin films are discussed, which seem to contradict a generalized use of the surface resistance model proposed by Coffey and Clem (1992) in the field range 0–8 Tesla. It is found that the necessary condition, in order to reproduce the upward curvature vs. field observed for B‖BMW‖ film surface, is to assume that the Campbell penetration depth is governed by a critical field dependence reminishent of the well known Bc∝(1−t)3/2 expression. Nevertheless, the experimental data for the perpendicular case B⊥BMW and the behaviours in very low fields for both orientations cannot be satisfactorily explained in this view. It is shown that the discrepancies may be rationalized in a quite natural way as due to losses in a network of Josephson junctions of an intrinsic species, located in the intragrain region of the film.
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    Spin dynamics by inelastic neutron scattering in YBCO (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 377-382 
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    ISSN: 1573-7357
    Keywords: 74.20.Mn ; 25.40.Fq ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Key features of Inelastic neutron scattering experiments in YBCO-based cuprates are discussed. We underline the importance of precise oxygen content determination in samples having similar TC as well as the resolution configuration used. This may explain the apparent contradictory results recently obtained by different groups.
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    c-axis infrared reflectivity of magnetically aligned YBa2Cu3O7−δ as a function of doping (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 773-778 
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    ISSN: 1573-7357
    Keywords: 78.30.Hv ; 74.72.Bk ; 74.25.Gz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Dense polycrystalline samples of YBa2Cu3O7−δ with a high degree of c-axis texture in the plane of the sample were prepared by magnetic alignment. The c-axis infrared reflectivity was measured between 300 and 6K on polished surfaces. Spectra compare well with measurements on single crystals indicating that magnetically aligned samples are a reliable alternative to single crystals for c-axis measurements.
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    Macroscopic symmetry group describes Josephson tunneling in twinned crystals (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 483-488 
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    Keywords: 74.20.De ; 74-50.+r ; 74.72.Bk ; 74.62.Bf
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    Topics: Physics
    Notes: Abstract A macroscopic symmetry group describing the superconducting state of an orthorhombically twinned crystal of YBCO is introduced. This macroscopic symmetry group is different for different symmetries of twin boundaries. Josephson tunneling experiments performed on twinned crystals of YBCO determine this macroscopic symmetry group and hence determine the twin boundary symmetry (but do not experimentally determine whether the microscopic order parameter is primarily d- or s-wave). A consequence of the odd-symmetry twin boundaries in YBCO is the stability of 1/2 Φo vortices at the intersection of a twin boundary and certain grain boundaries.
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    Fluctuation-induced in-plane magnetoconductivity in bilayered superconductors (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 681-686 
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    Keywords: 74.25.Fy ; 74.25.Ha ; 74.40.+k ; 74.50.+r ; 74.72.Bk
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    Topics: Physics
    Notes: Abstract In this paper we summarize some of our theoretical results for the paraconductivity and for the fluctuation-induced in-plane magnetoconductivity in the weak magnetic field limit of layered superconductors with several interlayer separations. Also, we briefly discuss the existing experimental data obtained in untwinned Y Ba2Cu3O7-δ crystals.
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    Zn-substitution effects on the normal optical conductivity and the superconducting gap (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 743-748 
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    ISSN: 1573-7357
    Keywords: 74.72.Bk ; 74.25.Gz ; 74.62.Dh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Zn-substitution effects on the c-axis optical spectra have been investigated for highly oxygenated YBa2 Cu3Oy crystals with y = 6.88 – 6.92. In the normal state, the Zn-substitution does not affect the high frequency conductivity but changes the ω-dependence of the scattering rate at low frequencies, leading to the increase in the dc resistivity in the c-direction. In the superconducting state, we observed a pronounced effect of Zn-substitution that a large number of unpaired carriers form a Drude-like absorption band within the gap, keeping the maximum gap amplitude unchanged. The missing area which gives the superfluid density is found to correlate with Tc.
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    Optical study of the Zn-substitution effect on phonon anomalies and spin gap in underdoped YBa2Cu3Oy (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 779-784 
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    ISSN: 1573-7357
    Keywords: 74.25.Gz ; 74.72.Bk ; 78.30.Er ; 63.20.Kr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Performing optical reflectivity measurements with the electric field vector parallel to the c-axis of Zn-substituted, oxygen deficient YBa2Cu3Oy single crystals, we find a strong Zn-substitution effect on the anomaly of the inplane oxygen bending mode at 320 cm−1 and the new absorption band at 450 cm−1, which are observed in underdoped, non-substituted crystals. Contrary to that, the low-frequency suppression of the conductivity is almost not affected. We conclude that the phonon anomaly and the absorption band are related to each other, but that the suppression of the conductivity is an independent phenomenon. Moreover, the present work could be strong evidence for a model where some phonons couple to antiferromagnetic fluctuations at the (π, π)-point leading to anomalous behaviour of these phonons when a spin gap opens.
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    Melting of the flux line lattice observed by specific heat experiments in YBa2Cu3O7−δ (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1099-1104 
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    ISSN: 1573-7357
    Keywords: 74.25.Bt ; 74.60.Ge ; 74.72.Bk
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    Topics: Physics
    Notes: Abstract High resolution adiabatic specific heat experiments on YBa2Cu3O7−δ (0≤δ≤0.05) are performed in magnetic fields from 0 to 14 T (B∥c and B⊥c). In a 0.3 gram, twinned crystal with strong pinning, a step is consistently observed at the melting temperature Tm of the vortex solid up to a critical point that depends on δ. The field Bm and step temperature Tm obey the relation Bm=Bmo(δ)(1−Tm/Tc)≈4/3. The anisotropy of Bm and that of the upper critical field Bc2 are found to be equal. Alternatively, in a 18 mg, twinned crystal of high purity with low pinning, first-order-like specific heat peaks are observed on the melting line from 8 to 14 T. The entropy under these peaks is ≈0.5 kB /vortex/bilayer. These characteristic features are attributed to the melting of a vortex glass in the former case and that of a vortex lattice in the latter case.
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    Gap symmetry and intrinsic intraplane pinning of untwinned YBa2Cu3O7 single crystals (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1165-1170 
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    ISSN: 1573-7357
    Keywords: 76.60.Ge ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The interplane (cb) and intraplane (ab) anisotropy of untwinned YBa2 Cu307 single crystals has been investigated by means of the torque magnetometry. To extract the reversible and irreversible components, the torque was measured as a function of increasing angle as well as decreasing angle. The interplane irreversible torque Γirr shows two-fold peaks at θc =90 ° and270 ° (of half width11 ° at77 K) due to the well-known intrinsic interplane pinning. A novel intrinsic pinning has been discovered in the intraplane irreversible torque, i.e., Γirr shows four-fold peaks of half width20° at77 K when θa =0 °, 90 °, 180 ° and270 °. We argue that the intrinsic intraplane pinning comes from the four-fold nature of the gap parameter.
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    Energy gap symmetry and thermal conductivity of YBa2Cu3O7 (1997)
    Springer
    Journal of low temperature physics 107 (1997), S. 467-472 
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    Keywords: 74.25.Fy ; 74.72.Bk ; 74.25.Jb
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    Topics: Physics
    Notes: Abstract The characteristic enhancement in the heat conduction below Tc is analyzed on sintered YBa2Cu3O7 from viewpoints of both d-wave and s-wave coupling. Assuming the existence of a large energy gap Δ0(≥1.5Δ BCS ), only d-wave coupling is consistent with experimental observation. It is found that the most reasonable explanation for the enhancement is provided by the weak-coupling phonon conduction model under d-wave energy gap.
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    Evidence for vortex lattice melting and softening in untwinned YBa2Cu3O7 single crystal (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1171-1176 
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    Keywords: 74.60.Ge ; 74.72.Bk
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    Topics: Physics
    Notes: Abstract Real part of the ac susceptibility X′1 of an untwinned YBa2 Cu3O7 single crystal jumps at the onset temperature in the narrow width (0.1 K in 0.7 T), suggesting the first-order melting transition. A sharp X′1 dip and a sharp X″ peak can be interpreted as synchronous trapping of vortices due to lattice softening prior to melting. At lower temperatures, the X′1-X″1 chart shows a single-parameter behavior while the melting occurs as a strong deviation from this.
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    Effect of correlated and point-like disorder on transport properties of YBa2Cu3O7−δ single crystals (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1177-1182 
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    Keywords: 74.25.Fy ; 74.40.+k ; 74.60.Ge ; 74.72.Bk
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    Topics: Physics
    Notes: Abstract Pinning by point-like defects and twin boundaries in single-crystalline YBa2Cu3O7−δ has been investigated by measuring resistance and current-voltage characteristics in fields up to 5 T. A number of untwinned and twinned samples with different densities of point-like defects were studied. The experimental results are compared within the framework of vortex-entanglement.
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    Photodoping and relaxation of persistent photoconductivity in YBa2Cu3Ox studied byin-situ transport measurements (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1403-1408 
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    Keywords: 73.50.Jt ; 73.5O.Pz ; 74.72.Bk ; 74.76.Bz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on in-situ resistivity and Hall-effect studies of partially oxygen-depleted YBa2Cu3Ox thin films during white light illumination. The measurements were performed at various temperatures between the superconducting transition and room temperature. At all temperatures the resistivity and the Hall coefficient decreased as a function of the illumination time. The Hall number pH and the Hall mobility μH, calculated within a simple one-band model, showed an increase of pH during the illumination without a saturation. At low temperatures, μH behaved similarly to pH. At 200 K, however, μH became constant after several hours of illumination, while at 260 K and 290 K, we observed a short increase of μH followed by a long-term decrease. From the different time dependences of μH and pH, we conclude that two mechanisms contribute to the photodoping effect. Additionally, we observed that after termination of the illumination at 290 K the photodoped values of pH and μH relaxed with substantially different time constants.
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    Scanning tunneling spectroscopy studies on YBa2Cu3O7−δ (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1129-1134 
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    Keywords: 74.60.Ge ; 71.20.−b ; 74.50.+r ; 74.72.Bk
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    Topics: Physics
    Notes: Abstract Scanning Tunneling Spectroscopy (STS) measurements have been carried out on the high Tc superconductor (HTS) YBa2Cu3O7−δ (YBCO). Using very high quality single crystals as well as hard tips, we obtained differential conductance spectra which showed various conductance features in agreement with other spectroscopic techniques. The reproducibility of our spectra allowed us to map for the first time the vortex lattice on a HTS using a STS technique1. The vortices are arranged in a short range order oblique lattice, while the cores of the flux lines show an anisotropic shape. These observations can be related to the in-plane anisotropy of YBCO.
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    Novel vortex dynamics in untwinned YBa2Cu3O7−δ single crystals (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1147-1152 
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    Keywords: 74.25.Fy ; 74.40.+k ; 74.60.Ge ; 74.72.Bk
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    Topics: Physics
    Notes: Abstract Magnetotransport measurements on a clean, untwinned YBa2Cu3O7−δ single crystal show that the vortex dynamics at temperatures just below the vortex lattice melting transition are highly dependent on the type of modulation of the probing current. While in the case of DC current the flux flow is disordered, the “shaking” of the vortex lattice by a square-wave current leads to a more uniform vortex motion. A small asymmetry (∼10%) in the durations of the positive and negative parts of the square-wave period induces periodical oscillations of the voltage response amplitude. The period of oscillations (∼100 s) is the same order of magnitude as the time needed for vortices to cross the sample (transit time). We relate the observed voltage oscillations to a periodically ordered vortex motion.
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    Phase sensitive measurements of the pairing state symmetries of cuprate superconductors using tricrystal microbridges (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 527-532 
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    Keywords: 74.50.+r ; 74.72.Bk ; 74.76.Bz ; 85.25.Cp
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    Topics: Physics
    Notes: Abstract Measurements of the field-modulated critical currents of cuprate thin film microbridges on tricrystal substrates are reported. Two central peaks of equal height are observed in the field-dependent critical currents of YBCO tricrystal microbridges. However, the critical current is nonvanishing at zero field for YBCO, consistent with an orthorhombically distorted d-wave order parameter. An ion-irradiated YBCO tricrystal microbridge has also been measured, and has been found to exhibit more ideal dx2−y2-like behavior with increasing irradiation dosage.
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    Preparation of long Y123 superconducting filament by solution spinning (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1421-1426 
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    Keywords: 74.72.Bk ; 74.60.Jg ; 74.80.Bj
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    Topics: Physics
    Notes: Abstract The preparation of a long superconducting Y123 filaments is developed by using solution spinning for the precursor of the oxide. Long precursor filaments are prepared by dry spinning with a starting homogeneous aqueous PVA solution containing Y, Ba and Cu acetates. The as-drawn filament with 250 μm in diameter and 300 mm in length is pyrolyzed and partial-melted by using a tube furnace with a constant heating zone of 500 mm. A superconducting filament of 60 μm in diameter and 200 mm in length with high Jc of more than 104A/cm2 at 77 K and 0 T is obtained by controlling the partial melting.
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    Determination of pairing symmetry using phase-sensitive tunneling in tricrystal cuprates (1997)
    Springer
    Journal of low temperature physics 107 (1997), S. 445-454 
    Details
    ISSN: 1573-7357
    Keywords: 74.72.Bk ; 74.60. Ge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An unambiguous determination of the pairing symmetry in cuprate superconductors is important in order to understand the origin of high-temperature superconductivity. By making use of the effects of pair tunneling and flux quantization, we have designed and implemented several tricrystal experiments for phase-sensitive determination of the order parameter symmetry in high-Tc superconductors such as YBa2Cu3O7 Tl2Ba2CuO6, GdBa2Cu3O7, and Bi2Sr2CaCu2O8. By using a high-resolution scanning SQUID microscope, we have made the first direct observation of spontaneously generated half-flux quanta at the tricrystal point. The half-integer flux quantum effect in various specially designed tricrystal cuprate systems provides strong evidence for d-wave pairing in high-Tc cuprates. Our various tricrystal experiments have demonstrated that this effect can be used as a general probe of the microscopic phase of the pair wavefunction in unconventional superconductors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02397226
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  • 49
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    Electronic Resource
    Non-isovalent alkali metal “substitution” in YBa2Cu3O7−y granular ceramics (1995)
    Springer
    The European physical journal 96 (1995), S. 319-324 
    Details
    ISSN: 1434-6036
    Keywords: 74.72.Bk ; 74.62.Bf ; 74.72.Dh ; 74.25.Fy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The aim of this paper is to study the influence of non-isovalent “doping” in YBa2Cu3O7−y in particular on its synthesis conditions and on the resistive properties both with and without a magnetic field. We concentrate on the study of possible alkali ions (Na, K, Cs) “substitution” at the barium sites. A low temperature sintering process is used in order to induce a reactive liquid phase. The final chemical composition is discussed as a function of the amount of the liquid phase. No alkali ion is substituted. Carbonate layers are present. However, this (lack of) “substitution” leads to induced vacancies and improved electrical transport properties which are as good as in highly pure materials. For conciseness the case of Na “substitution” only is illustrated. The use of such data in order to probe the microstructure is emphasized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313053
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  • 50
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    Electronic Resource
    Anisotropic magnetoresistance in the normal state of oxygen-deficient YBa2Cu3O7−δ thin films induced by superconducting fluctuations (1995)
    Springer
    The European physical journal 98 (1995), S. 453-456 
    Details
    ISSN: 1434-6036
    Keywords: 74.25.Fy ; 74.40.+k ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have investigated both the transverse and the longitudinal magnetoresistance of oxygen-deficient YBa2Cu3O7−δ thin films above their critical temperatureT c =55 K. The magnetoresistance is solely caused by the magnetic-field suppression of superconducting orderparameter fluctuations, existing in the films up to 143 K, i.e. 2.6T c . The fluctuation effect provides a reliable determination of the Ginzburg-Landau coherence lengths, ξ ab = 2.5 nm and ξ c = 0.09 nm, with the anisotropy enhanced by oxygen depletion. No signature of the Maki-Thompson fluctuation process or a magnetoresistance resulting from the cyclotron motion of the normalstate quasiparticles was found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320845
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