THERMAL CONDUCTIVITY OF ORIENTED SINGLE CRYSTALS OF HEXAGONAL CLOSE-PACKED HELIUM 4

Thermal conductivity measurements have been made on hcp single crystals of helium 4 between 0.36K and 1.6K. Data on crystals grown at 53.4, 85, and 125.8 atm exhibit a strong orientation dependence in the umklapp region, and Poiseuille flow at temperatures below the thermal conductivity maximum. In the umklapp region, the data are described by two thermal conductivities, K=Aexp(ΘD2.58T) and K=Aexp(ΘD4.62T), the components of the thermal conductivity tensor perpendicular and parallel to the c axis. At 85 atm, A=1.12×10-5 W/cm K and A=2.31×10-4 W/cm K. The umklapp data permit one to determine the orientation of the single crystals. The thermal conductivity in the Poiseuille region is proportional to d2T6, where d is the sample diameter. The normal-process relaxation time determined from these data, τN=(2.1±0.4)(ΘDT)3×10-12 sec, is in good agreement with the results of second-sound experiments. © 1969 The American Physical Society.