Effect of disorder on superconductivity in the boson-fermion model

We study how a randomness of either boson or fermion site energies affects the superconducting phase of the boson fermion model. We find that, contrary to what is expected for s-wave superconductors, the nonmagnetic disorder is detrimental to the s-wave superconductivity. However, depending on which subsystem the disorder is located, we can observe different channels being affected. Weak disorder of the fermion subsystem is mainly responsible for the renormalization of the single-particle density of states, while disorder in the boson subsystem leads directly to fluctuations of the strength of the effective pairing between fermions.