Anisotropic thermal conduction in the antiferromagnetic spin-ordered phase of solid He3

The thermal conductivity κ of single crystals of solid He3 was measured using NMR techniques in the low-field spin-ordered phase where magnons are the dominant heat carriers. In the umklapp scattering regime, the thermal conduction in monodomain samples is found to be anisotropic, consistent with κ varying by a factor of 18 between the two symmetry directions of the ordered state, in good agreement with theoretical expectations. In the defect scattering regime, evidence is found in one crystal for a Poiseuille flow of magnons, suggesting that magnon second sound may be observable in this system.