Spin Wave in Solid ³He

Abstract

Using the spin wave theory a few thermodynamic quantities of solid ³He in the “uudd” phase are calculated. In the first approximation, in which higher terms than the fourth power of Holstein-Primakoff operators are neglected, the contraction of the spin is not small and the gain of the energy at 0 K due to the zero point motion of spins is comparable to the energy associated with the molecular field approximation. If only j_t and K_P are not zero, this approximation does not explain the experimental results. In the second approximation, in which the contribution due to the fourth power terms is taken into account, the “uudd” phase becomes stable or metastable because of large zero point motion of spins even when J₂–K_F<0, and the exchanges that only j_t and K_P are not zero, can explain the experimental results, where j_t, K_P and K_F are the triple, planar and folded type cyclic four spin exchanges.