Thermal Conductivity Of YBa2Cu3O7 Research Articles

Role of defects, resonances, anharmonicities and electron–phonon scattering processes on thermal conductivity of YBa2Cu3O7−δ

In this work, thermal conductivity of high temperature superconductors (HTS) has been analyzed on the basis of modified Callaway model. In the new formulation, the relaxation times of various contributing processes have been observed in newer perspectives of electron and phonon line widths. To obtain line widths, the quantum dynamics of electron and phonon is carried out by using double time thermodynamic Green’s functions method via a general Hamiltonian. The outcome of this heuristic approach is utilized to successfully explain the spectacular behavior of thermal conductivity of HTS, and particularly in the vicinity of transition temperature.

Investigating the Effect of the Magnetic Field on the Thermal Conductivity of a Single Crystal of YBa 2 Cu 3 O 7−δ

The effect of the magnetic field on thermal conductivity of a single crystal of YBa2Cu3 O 7 − δ was investigated using London’s equation. The result of the study shows that the thermal conductivity of YBa2Cu3 O 7 − δ decreases exponentially as the applied magnetic field increases at a uniform temperature and then ‘saturates’. This indicates that magneto-thermal conductivity of YBa2Cu3 O 7 − δ is necessitated by electrons which are scattered by the core of vortices in the mixed state.

Evidence of d-wave pairing in the thermal conductivity of YBa2Cu3O7−d and Bi2Sr2CaCu2O8 single crystals

The electronic contribution to the thermal conductivity of a d x 2−y 2-wave superconductor is calculated within a variational method. By considering the scattering of electrons by point defects and acoustic phonons, the behavior of the thermal conductivity of YBa2Cu3O7−δ and Bi2Sr2CaCu2O8 single crystals can be well described with realistic values of the physical parameters. Besides, the values obtained for the transport electron-phonon coupling constant λ tr lie in the same range of magnitude than those derived from electrical resistivity measurements. b]References

Theoretical analysis of the thermal conductivity of high-temperature superconductors

The thermal conductivity of YBa2Cu3O7−δ high-T c superconductor is analysed self-consistently on both normal and superconducting states on the base of the Bardeen-Rickayzen-Tewordt extended theory to take into account the effects of magnetic field and superconducting fluctuations. It is shown that experimental data are in a quantitative agreement with theory even if the number and variation intervals of adjustable parameters are substantially reduced in comparison with previous works. Phonon relaxation rates due to different mechanisms of phonon scattering as well as the parameters of electron-phonon interaction are estimated. It is shown that thermal conductivity in YBa2Cu3O7−δ is consistent with the BCS model with intermediate electron-phonon coupling λ=1–3 the phonon-electron and electron-phonon relaxation times near critical temperature are evaluated to be 10−10s and 10−12s, respectively.

Thermal conductivity of YBa2Cu3O7 from 7 K to 260 K

Thermal conductivity of YBa2Cu3O7 has been measured on samples of a few mm thickness. AboveT c thermal conductivity is found to decrease with increase in temperature, pointing towards a contribution to thermal resistivity from three-phonon Umklapp processes. BelowT c thermal conductivity increases rapidly before reaching a maximum at about 50 K and then falls towards zero at lower temperatures. The experimental set up is described and results discussed.

Anisotropic low-temperature heat transport in YBa2Cu3O6.9 single crystal

We report measurements of the low-temperature thermal conductivity of YBa2Cu3O7−δ (δ≃0.1) single crystals (Tc=84 K) both parallel (κa, b) and perpendicular (κc) to the CuO2 planes. Whereasκc (T) is found to be identical, within experimental resolution, with the phonon contributionκph (T),κa, b (T) contains an additional term linear in temperature,AT. We ascribeAT to the contribution of unpaired electronic carriers residing in the “chain layers”. Measurements performed in external magnetic fieldsB≦8 T support this interpretation. Our observations can be explained by an “internal multilayer” (IML) model in which it is assumed that strong superconductivity is generated within the CuO2 layers and weak superconductivity is induced in the “chain layers” by the proximity effect. The fit of the experimental results to the IML model reveals that approximately 15% of the electronic carriers remain unpaired in YBa2Cu3O7 belowT=1 K.

Effect of magnetic field on thermal conductivity of YBa2Cu3O7- delta single crystals.

We report measurements of the thermal conductivity in a magnetic field on single crystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$. Unlike in sintered samples, the zero-field thermal conductivity of these crystals above the superconducting transition temperature shows a marked decrease with increasing temperature, demonstrating the importance of phonon-phonon processes and the high quality of the crystals. We find that the thermal conductivity \ensuremath{\kappa} is very sensitive to the presence of fluxoids which are strong scatterers of phonons. The degradation of \ensuremath{\kappa} is particularly large when the magnetic field H is oriented perpendicular to the Cu-O planes. The anisotropic behavior of \ensuremath{\kappa}(H) is in qualitative agreement with a geometric argument based on the anisotropy of the superconducting coherence length. We detect hysteresis at the level of several percent in the dependence of \ensuremath{\kappa} on the field.