Wick and Goldstone Theorems for General Spin; Antiferromagnetic Spin Waves II

摘要

The analogues of Wick's theorem and of Goldstone's theorem, proved in the preceding paper for spin 1/2, are generalized to arbitrary spin. The proof Is based on the Schwinger coupled-boson representation of spin operators. Quantum corrections to the spin wave modes in antiferromagnets are again considered and it is shown that these corrections can be expanded in powers of 1 2Sz where z is the number of nearest neighbors. For large S the l/S factor presumably provides convergence, as assumed by Ouchy, whereas for S = 1/2 the expansion parameter reduces to l/z, as discussed In the preceding paper.