4 research outputs found
The Expansion and Spin Correlations in Constrained Wavefunctions
We develop a large-N expansion for Gutzwiller projected spin states. We
consider valence bonds singlets, constructed by Schwinger bosons or fermions,
which are variational ground states for quantum antiferromagnets. This
expansion is simpler than the familiar expansions of the quantum Heisenberg
model, and thus more instructive. The diagrammatic rules of this expansion
allow us to prove certain identities to all orders in 1/N. We derive the
on-site spin fluctuations sum rule for arbitrary N. We calculate the
correlations of the one dimensional Valence Bonds Solid states and the
Gutzwiller Projected Fermi Gas upto order 1/N. For the bosons case, we are
surprised to find that the mean field, the order 1/N and the exact correlations
are simply proportional. For the fermions case, the 1/N correction enhances the
zone edge singularity. The comparison of our leading order terms to known
results for N=2, enhances our understanding of large-N approximations in
general.Comment: 36 pages, LaTe