Thermal transport in YBa{sub 2}Cu{sub 3}O{sub 6+x}: Doping dependence across the phase diagram

A systematic study of the temperature and oxygen-doping dependence of thermal conductivity ({kappa}) and thermoelectric power (S) in polycrystal YBa{sub 2}Cu{sub 3}O{sub 6+x} is reported for compositions spanning the phase diagram (0{lt}x{lt}1). {kappa}(x) is nonmonotonic with apparent enhancements near x=0.1, 0.3, and 0.6. Thermal hysteresis in {kappa} and S with a common temperature dependence is observed for all x, and is substantially enhanced at these same compositions. These features are likely related to the oxygen order and associated changes in the local structure. The superconducting-state enhancement of {kappa} is parametrized by its change in slope at the superconducting transition. The doping dependence of this quantity agrees with that of the in-plane thermal conductivity in single crystals, and confirms that the enhancement scales with the superconducting condensate density throughout the underdoped regime. {copyright} {ital 1997} {ital The American Physical Society

Local lattice distortions and thermal transport in perovskite manganites

Measurements of thermal conductivity versus temperature and magnetic field are reported for perovskite manganites that exhibit ferromagnetic (FM), charge-ordering (CO), antiferromagnetic, and/or structural phase transitions. The data reveal a dominant lattice contribution to the heat conductivity with {kappa}{approximately}1{minus}2 W/mK near room temperature. The rather low values, implying a phonon mean free path on the order of a lattice spacing, are shown to correlate with static local distortions of the MnO{sub 6} octahedra. Modifications of the local structure are responsible for abrupt anomalies in the zero-field {kappa} at the FM, CO, and structural transitions, and for colossal magnetothermal resistance near the FM transition. {copyright} {ital 1997} {ital The American Physical Society