Coexistence of s-wave Superconductivity and Antiferromagnetism

We study the phase diagram of a new model that exhibits a first order transition between s-wave superconducting and antiferromagnetic phases. The model, a generalized Hubbard model augmented with competing spin-spin and pair-pair interactions, was investigated using the projector Quantum Monte Carlo method. Upon varying the Hubbard $U$ from attractive to repulsive we find a first order phase transition between superconducting and antiferromagnetic states.