LEVEL CORRELATIONS DRIVEN BY WEAK-LOCALIZATION IN 2D SYSTEMS

We consider the two-level correlation function in two-dimensional disordered systems. In the nonergodic diffusive regime, at energy ε>Ec (Ec is the Thouless energy), it is shown to be completely determined by the weak localization effects, thus being extremely sensitive to time reversal and spin symmetry breaking: It decreases drastically in the presence of magnetic field or magnetic impurities and changes its sign in the presence of a spin-orbit interaction. In contrast to this, the variance of the levels number fluctuations is shown to be almost unaffected by the weak localization effects. © 1995 The American Physical Society.