Energy level statistics in weakly-disordered systems: from quantum to diffusive regime

We calculate two-point energy level correlation function in weakly disordered metallic grain by taking account of localization corrections to the universal random matrix result. Using supersymmetric nonlinear sigma model and exactly integrating spatially, homogeneous modes, we derive the expression valid for arbitrary energy differences from quantum to diffusive regime for the system with broken time reversal symmetry. Our result coincides with that obtained by Andreev and Altshuler (1995 Phys. Rev. Lett. 72 902) where homogeneous modes are perturbatively treated.