Anisotropic heat conduction in HCP⁴He

The authors have measured the thermal conductivity of single crystals of HCP 4He and have determined their c-axis orientations independently by an optical method. In the Umklapp process dominated region it is found, for a Debye characteristic temperature Theta 0=28.7K, that the conductivities perpendicular and parallel to the c-axis can be represented by: kappa perpendicular to =5.53*10-6 exp( Theta 0/2.53T) W cm-1 K-1 k/sub ///=1.35*10-4 exp( Theta 0/4.64 T) W cm-1 K-1. Simple theories predict that the ratio of the two exponents should be 1.4-1.7, which agrees moderately well with the measured value of 1.8. The results confirm those of Hogan and co-workers. The authors have also investigated the extent to which polycrystalline samples are randomly oriented.

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