Thermal conductivity of CeB6 and LaB6

Abstract The thermal conductivity of the dense Kondo system CeB6 and of the non-magnetic metal LaB6 have been measured over a wide range of temperature and magnetic fields. In addition, electrical resistivity and thermoelectric power measurements have also been performed on the same single crystals. The behaviour of LaB6 is typical for a non-magnetic metal, but for CeB6 a large deviation from the Wiedemann-Franz law is observed in a large temperature range, and vanishes only below the Neel temperature. This discrepancy suggests that the phonon contribution could be as large as the electronic one in the Kondo regime. Scattering of phonons by conduction electrons mainly determines the phonon conductivity and there is no evidence of a Jahn-Teller effect in the Γ8 ground state. Below the transition temperature TQ, the strong enhancement of the thermal conductivity by applying magnetic fields up to 7 T is in agreement with the corresponding decrease of the Kondo scattering for the conduction electrons and the phonon conductivity is negligible.

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