Magnetic-field dependence of electrothermal conductivity in YBCO (original) (raw)
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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.
1999
Temperature and magnetic field dependences of the conductivity of YBaCuO films in the transition region are analyzed taking into account spatial inhomogeneity in transition temperature, Tc. (i) An expression for the superconducting contribution to conductivity, \sigma_s(T,H,Tc), of a homogeneous superconductor for H<<Hc2(T=0) is obtained using the solution of the Ginzburg-Landau equation in form of perturbation expansions [S.Ullah, A.T.Dorsey, PRB 44, 262 (1991)]. (ii) The error in \sigma_s(T,H,Tc) occurring due to the presence of Tc-inhomogeneity is calculated and plotted on an H-T plane diagram. These calculations use an effective medium approximation and a Gaussian distribution of Tc. (iii) Measuring the temperature dependences of a voltage, induced by a focused electron beam, we determine spatial distributions of the critical temperature for YBaCuO microbridges with a 2 micron resolution. A typical Tc-distribution dispersion is found to be approximately 1K. For such disper...
2001
Experimental studies of the electric and heat currents in the normal, superconducting and mixed states of high T c superconductors (HTcS) lead to characterization, complementary to data obtained from equilibrium property based techniques. A magnetic field superimposed on the superconducting sample generates magneto-transport phenomena, from which an excess electrical resistivity, an excess thermoelectric power, the Hall or the Nernst effect. Different behavioral effects allow one to distinguish various dissipation mechanisms, like quasi particle scattering, vortex motion dissipation and superconductivity fluctuations, in particular when the Corbino geometry is used. Moreover bulk measurements of the thermal conductivity and the electrothermal conductivity in a magnetic field give us sure indications of the order parameter symmetry. The location of the mixed state phase transition lines in the technological phase diagram of HTcS are briefly pointed out through precise measurements performed over broad temperature and magnetic field ranges. The results are mainly reviewed with the aim of defining further investigation lines.
Conductivity of anisotropic inhomogeneous superconductors above the critical temperature
Physical Review B, 2018
We propose a model and derive analytical expressions for conductivity in heterogeneous fully anisotropic conductors with ellipsoid superconducting inclusions. This model and calculations are useful to analyze the observed temperature dependence of conductivity anisotropy in various anisotropic superconductors, where superconductivity onset happens inhomogeneously in the form of isolated superconducting islands. The results are applied to explain the experimental data on resistivity above the transition temperature Tc in the high-temperature superconductor YBa2Cu4O8 and in the organic superconductor β-(BEDT-TTF)2I3. The comparison of resistivity data and diamagnetic response in β-(BEDT-TTF)2I3 allows us to estimate the size of superconducting inclusions as d ∼ 1µm.
Rule-based technique to measure conductivity of Yba2Cu3O7 superconductors
2012 CSI Sixth International Conference on Software Engineering (CONSEG), 2012
With the emergence of digital computing, new approaches have been attempted to solve the computationally intensive problems by selecting the suitable model and getting the inferences via controlled simulation technique close to the actual experimental observations. This provides a test-bed for preexperimental setup and also reduces resources. With the concept, the present work is numerically experimented on such a problem in measuring the thermal conductivity for the Yba 2 Cu 3 O 7 superconductors; which has been an interesting research area for its wide industrial applications. Measuring the conductivity of this type of material becomes complex when derived as a function of wide range of temperature considering impact of existing interactions between various scattering processes involved during the thermal conduction. The outcome of the present approach does not much deviate from the experimental results. In addition, inferences at higher temperature regions have also been obtained to uncover the impact of scattering process individual or combined.
Physica C: Superconductivity, 2010
Fluctuations on the electrical conductivity of polycrystalline YBa 2 Cu 3 O 7Àd + xBaZrO 3 (x = 1.0, 2.5, 5.0 and 10.0 wt.%) superconductors were investigated from the resistivity vs. temperature data for zero field and 8 T (Tesla) external magnetic fields. Attempts have been made to identify the optimum inclusion of BaZrO 3 (BZO) in YBa 2 Cu 3 O 7Àd (YBCO) superconductors. The phase formation, texture and grain alignments were analyzed by XRD and SEM techniques. Then the effects of superconducting fluctuations on the electrical conductivity of granular composite superconductors were studied for zero field and 8 T external magnetic fields. Though inclusions of BZO sub-micron particles are not expected to influence superconducting order-parameter fluctuation (SCOPF) much, the transition from 2D to 3D of the order parameter in the mean-field region depends on the BZO content in the composites. It has been observed that BZO residing at the grain boundary of YBCO matrix influences the tailing region without having significant change in the mean-field critical temperature. In the present work, attention has been focused mostly in the experimental domain relatively above the T c. It reveals that, 1 wt.% composite exhibits a better superconducting property in comparison with pure YBCO.
Materials Science and Engineering: B, 1998
High transport currents along the (a,b) planes and along the c-axis have been measured in pulsed current of different pseudo-frequencies. Self field losses and transport current of 8000 A (20000 A cm -') have been measured in Y ,Ba,Cu,O, _ 6 bars textured by the melting zone technique. Critical currents as high as 500 A (90000 A cm-') along the (n,b) planes or 3000 A (7500 A cm-') along the c-axis have been measured. For both orientations, the transition from the normal state to the superconducting state has been observed. Electric field of 1000 V m-' and study of the superconducting state recovery are reported. 0 1998 Elsevier Science S.A. All rights reserved.
Physical Review B, 1996
We calculate the influence of a magnetic field on a transport property like the electrothermal conductivity P of high-T c superconductors for either an anisotropic ͑or not͒ s-wave or a d x 2 Ϫy 2-wave gap parameter. The field dependence of the electrothermal conductivity of Bi 2 Sr 2 CaCu 2 O 8 , (BiPb͒ 2 Sr 2 Ca 2 Cu 3 O 10 , and Tl 2 Ba 2 CaCu 2 O 8 compounds near T c is then analyzed. It is shown that the behavior is consistent with a gap parameter of d x 2 Ϫy 2-wave type for reasonable values of the physical parameters and excludes an anisotropic ͑or not͒ s-wave symmetry over a temperature range extending up to T c. ͓S0163-1829͑96͒52542-7͔
Excess conductivity of Cu0.5Tl0.5Ba2Ca3Cu4−yZnyO12−δ superconductors
Low Temperature Physics, 2012
Oxide high-T c superconductors (HTSC) are anisotropic in character since the charge carriers have free moment in the conducting CuO 2 planes [1] whereas their motion is impeded by insulating/partially insulating MBa 2 O 4-δ (M = Y, Bi, Hg, Tl, CuTl, etc.) charge reservoir layers. In the transport process the charge carriers have to tunnel across insulating/partially insulating barriers along the c-axis and across the grain boundaries, which promote a fluctuation in the order parameter and in turn to the conductivity of the carriers. The studies of such fluctuation conductivity (FIC) may help in understanding the intrinsic mechanism of superconductivity. Here the electrical resistivity ρ(T) versus temperature data of as-prepared and oxygen post-annealed Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4-y Zn y O 12-δ (y = 0, 0.5, 1.5, 2.5) samples is studied for FIC analyses in the temperature regime well above the critical temperature; such analyses have been carried out by employing Lawrence and Doniach (LD) and Maki-Thompson (MT) models. The coherence length, inter-plane coupling, exponent, dimensionality of fluctuations and the phase relaxation time of the carriers are determined from such analyses. It is observed that the crossover temperature associated with two distinct exponents fits very well with the two-dimensional (2D) and three-dimensional (3D) LD equations. The crossover temperature T 0 is shifted to higher temperatures with enhanced Zn doping. The 3D LD region is shifted to higher temperature with the increased Zn doping. We have elucidated from these analyses that lower Tl content in the final compound may increase the charge carrier's doping efficiency of MBa 2 O 4-δ charge reservoir layer, resulting into an increase in the coherence length along the c-axis and superconductivity parameters. A small decrease in the coherence length along the c-axis ξ c (0) is observed in the samples with Zn doping of y = 1.5 whereas ξ c (0) increases in the samples y = 0.5, 2.5. In comparison with as-prepared samples, the ξ c (0) decreases after post-annealing in oxygen atmosphere. It is most likely that a decrease in the density of charge carrier's is promoted by oxygen diffusion in the unit cell may suppress the ξ c (0). The increase oxygen diffusion is evidenced from the softening of phonon modes after postannealing in oxygen atmosphere. The decreased population of small spins of Cu atoms induced by doping of Zn is viewed in the terms of suppression of spin gap and hence the pseudo-gap in Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4-y Zn y O 12-δ (y = 0, 0.5, 1.5, 2.5) samples.
Solid State Communications, 1993
The behavior of the thermal conductivity ~; of twinned YBa2Cu307_ x and tweeded YBa2(Cu0.95Fe0.05)307_x polycrystals in a magnetic field up to 5 T is presented. Data as a function of field are shown to depart from the usual linear behavior of thermal magnetoresistivity (TMR) n-l(B) for conventional superconductors. A set of stretched exponential laws, of the form n-l (B) -~;-I(0) = CBexp(-pB q) has been found to describe our data with q decreasing with temperature from 1 to 1 and from ~ to ¼ for pure and iron-doped samples, respectively/in contrast to'the unique interpolation formula (q = ¼) for TMR proposed recently by Richardson et al.