Spin Wave Theory and Green Function Theory of Ferromagnetic State of HCP Solid ³He

抄録

There are two sublattices A and B in hcp ³He in spite of the ferromagnetic state, because the hcp structure consists of two interpenetrating simple hexagonal Bravais lattices. We obtain the magnon excitation energy, and calculate ⟨S_z⟩, the specific heat and so on near T=0 by the spin wave theory. To extend the calculation for finite temperatures not near T=0, the Green functions G_AA and G_BA are introduced. We derive a self consistent equation for ⟨S_z⟩, using the spectral theorem, and compute ⟨S_z⟩ and the Curie temperature T_c, using RPA.