A WICK'S THEOREM FOR SPIN OPERATORS, WITH AN APPLICATION TO SPIN WAVES IN ANTIFERROMAGNETS.
Abstract
An analogue of Wick's theorem is developed for spin-1/2 operators, and a linked diagram expansion for spin Green functions is derived. As an application the familiar Anderson approximation is derived for spin waves in antiferromagnets, and the leading dynamical and kinematical corrections to that approximation are obtained. The Oguchi form of correction, usually obtained by a formal expansion in 1/S extrapolated to S = 1/2, is found here as the leading term of an expansion in powers of 1/z, where z is the number of nearest neighbors. However, the Oguchi result is here found to be valid only for spin waves with wave lengths greater than two or three inter-spin distances. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1965
- Accession Number
- AD0624720
Entities
People
- Herbert Callen
- S. Shtrikman
- Yung-li Wang
Organizations
- University of Pennsylvania