Strong coupling expansion of the extended Hubbard model with spin-orbit coupling

We study the strong coupling limit of the extended Hubbard model in two dimensions. The model consists of hopping, on-site interaction, nearest-neighbor interaction, spin-orbit coupling, and Zeeman spin splitting. While the study of this model is motivated by a search for topological phases, and in particular, a topological superconductor, the methodology we develop may be useful for a variety of systems. We begin our treatment with a canonical transformation of the Hamiltonian to an effective model, which is appropriate when the (quartic) interaction terms are larger than the (quadratic) kinetic and spin-orbit coupling terms. We proceed by analyzing the strong coupling model variationally. Since we are mostly interested in a superconducting phase, we use a Gutzwiller projected BCS wave function as our variational state. To continue analytically, we employ the Gutzwiller approximation and compare the calculated energy with Monte Carlo calculations. Finally, we determine the topology of the ground state and map out the topology phase diagram.