Correlation between the superconducting transition temperature and Madelung site potential difference in YBa2Cu3OX (original) (raw)
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Physical Review Letters, 2007
Angle-dependent magnetoresistance measurements are used to determine the isotropic and anisotropic components of the transport scattering rate in overdoped Tl2Ba2CuO 6+δ for a range of Tc values between 15K and 35K. The size of the anisotropic scattering term is found to scale linearly with Tc, establishing a link between the superconducting and normal state physics. Comparison with results from angle resolved photoemission spectroscopy indicates that the transport and quasiparticle lifetimes are distinct.
Transport in Ultraclean YBa2Cu3O7: Neither Unitary nor Born Impurity Scattering
Physical Review Letters, 2004
The thermal conductivity of ultraclean YBa2Cu3O7 was measured at very low temperature in magnetic fields up to 13 T. The temperature and field dependence of the electronic heat conductivity show that two widespread assumptions of transport theory applied to unconventional superconductors fail for clean cuprates: impurity scattering cannot be treated in the usual unitary limit (nor indeed in the Born limit), and scattering of quasiparticles off vortices cannot be neglected. Our study also sheds light on the long-standing puzzle of a sudden onset of a "plateau" in the thermal conductivity of Bi-2212 versus field.
Spectral shift of the magnetic cross section in superconducting YBa2Cu3O6+x
Physical review. B, Condensed matter, 1991
A triple-axis neutron-scattering study has been done of the magnetic correlations in three large single crystals of YBa2Cup06+ with x=0.5, 0.8, and 0.9 having T 's of 50, 60, and 80 K, respectively. The frequency dependence of the cross section at Q= (2, 2, l) was found to peak near 5 meV for x=0.45 in an earlier study. Our data confirm that this peak shifts to 30 meV for x=0.5. Moreover, the low-frequency ((40 meV) spectra for x=0.8 and 0.9 become progressively suppressed with respect to those of the less oxygenated samples. These data are consistent with a picture in which the spectral weight of the magnetic scattering shifts to higher energy as the oxygen concentration 2: and carrier density increase.
Chemical activity in YBa2Cu3O7−δ across the normal to superconducting phase transition
Microchemical Journal, 2011
The Gibbs free enthalpy, chemical activity across the transition temperature to superconductivity, T c in YBa 2 Cu 3 O 7-δ is obtained from reciprocally enhanced X-Ray absorbance, XAS and diffraction, XRD data near the Ba L 3,2 edges' energy E a , and orientations in the X-ray beam for preferred Miller indexed [HKL] planes' scattering that are enhanced near T c. The standard enthalpy and entropy for the formation of mixed normal metal/superconducting domains above T c , determined individually across the two Ba L 3,2 edges, to better than a percent accuracy: ∆H ≠ > =-220 meV, and ∆S ≠ > =-2 meV/K when 121>T>92K≈T c1 , indicate there is energy available to form the mixture and the reduced entropy indicates there is also order increase. Below T c the standard enthalpy and entropy to form at least two mixed superconducting phases is halved to ∆H ≠ < =-86 meV, ∆S ≠ < =-1 meV/K when 92K>T>T c2 ≈72K. Thus reciprocal XAS/XRD enhancement at orientations in the X-ray field, of preferred 2D planes, induced by the transition to superconductivity in the layer solid, indicates one, the importance of the 2D-plane electron density scattering near T c , and two, identifies the 2D-plane chemical activity, by the electron density leading to symmetry allowed excitations, a role similar to that of the electron density in linear bonds for molecular activity.
Unexpected transport and magnetic properties in YBaCuO superconductors
physica status solidi (a), 2010
Solid-state reactions of Y 2 O 3 , BaCO 3 , and CuO mixtures at stoichiometric ratios of YBa 4 Cu 6 O x reveal superconducting products having quite interesting and unusual properties. For instance, superconducting transition T c at 90 K even without annealing in oxygen flow could be observed. Existence of a ferromagnetic-like behavior was recognized at low temperatures and magnetic fields greater than 1 T. Critical current densities are higher than the one expected from a polycrystalline superconductor. In addition, intergranular J ct-values obtained from the transport measurements show strong magnetic field dependency. Magnetic fields of $6.4 Oe decrease J ct by about 62% in magnitude. These materials seem to be good candidate for a low field sensor in superconducting gaussmeters.
Superconductor Science and Technology, 2019
We first present detailed measurements of the rounding behavior around the superconducting transition temperature, T c , of the in-plane electrical conductivity, magnetoconductivity and magnetization, including the low and moderate magnetic field regimes, in a high-quality single crystal and a thin film of the prototypical optimally-doped YBa 2 Cu 3 O 7−δ (OPT Y-123), in which the inhomogeneity effects are minimized. Then, it is presented a comparison of these experimental data with the phenomenological Ginzburg-Landau (GL) approach that takes into account the unavoidable contribution of the fluctuating pairs, the only theoretical scenario allowing at present to analyze these roundings at the quantitative level. These analyses demonstrate that the measured rounding effects around T c may be explained quantitative and consistently in terms of the GL scenario, even up to the rounding onset temperatures if the quantum localization, associated with the shrinkage of the superconducting wavefunction, is taken into account. The implications of our results on the pseudogap physics of optimally-doped cuprates are also discussed.
Inelastic neutron scattering has been used to determine the dynamic spin fluctua- tions in an underdoped high-temperature superconductor YBCO6.8 single crystal. The magnetic resonance, that occurs around 40 meV in overdoped samples, is shifted to a lower energy, Er = 34 meV. A constant ratio, Er/k_BT_C = 4.9 ± 0.2, almost independent of the doping level, is found. According to numerous theoretical approaches, this finding supports the idea that the resonance energy is proportional (approximately twice) to the superconducting gap.
Physical Review Letters, 1991
The superconducting contribution to the magnetization and resistivity of twinned and untwinned YBa2Cu307-& crystals which are presented here, as well as to the specific heat (Inderhees et al.) and Ettinghausen coeIIicient (Palstra et al.), displays scaling behavior in the variable lT-T, (H)]/(TH)'t'. This is consistent with Ginzburg-Landau Auctuation theory for a 30 system in a high magnetic field. The scaling property allows for a consistent way of determining the mean-field transition temperature T, (H).