Large physical spin approach for strongly correlated electrons

We present a novel approach for a systematic large-spin expansion of the t-J Hamiltonian which enables us to work without the constraint of no double occupancy. In our scheme we can perform the large-spin limit ensuring that the low energy spin excitations are in exact correspondence with the physical excitations of the s = 1/2 Hilbert space. As a consequence, we expect a smooth dependence of the physical quantities on the expansion parameter 1/s. As a first application of the method we study the case of a single hole in a Neel background. A systematic expansion in fluctuations about this stable solution indicates that by increasing t/J the quasiparticle weight strongly depends on the momentum carried by the hole. Results, obtained on small lattice sizes, are found in excellent agreement with exact diagonalization data.