ISSN:
1434-6036
Keywords:
PACS. 74.72.-h High Tc compounds – 74.25.Fy Transport properties (electric and thermal conductivity, thermoelectric effects, etc.)
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract: Measurements of the thermal conductivity (kxx) and the thermal Hall effect (kxy) in high magnetic fields in Y- and Bi-based high-T c superconductors are presented. We describe the experimental technique and test measurements on a simple metal (niobium). In the high-T c superconductors kxx and kxy increase below T c and show a maximum in their temperature dependence. kxx has contributions from phonons and quasiparticle (QP) excitations, whereas kxy is purely electronic. The strong increase of kxy below T c gives direct evidence for a strong enhancement of the QP contribution to the heat current and thus for a strong increase of the QP mean free path. Using kxy and the magnetic field dependence of kxx we separate the electronic thermal conductivity ( k xx el ) of the CuO 2 -planes from the phononic thermal conductivity ( k xx ph ). In YBa2Cu3O 7 - δ k xx el shows a pronounced maximum in the superconducting state. This maximum is much weaker in Bi2Sr2CaCu2O 8 + δ , due to stronger impurity scattering. The maximum of k xx el is strongly suppressed by a magnetic field, which we attribute to the scattering of QPs on vortices. An additional magnetic field independent contribution to the maximum of kxx occurs in YBa2Cu3O 7 - δ , reminiscent of the contribution of the CuO-chains, as determined from the anisotropy in untwined single crystals. Our data analysis reveals that below T c as in the normal state a transport (τ) and a Hall ( ) relaxation time must be distinguished: The inelastic (i.e. temperature dependent) contribution to τ is strongly enhanced in the superconducting state, whereas displays the same temperature dependence as above T c . We determine also the electronic thermal conductivity in the normal state from kxy and the electrical Hall angle. It shows an unusual linear increase with temperature.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/PL00011098
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