Disordered systems and the metal-insulator Transition: A super universality class

The critical behaviour of three-dimensional disordered systems is investigated by analysing the spectral fluctuations of the energy spectrum. Our results suggest that the initial symmetries (orthogonal, unitary and symplectic) are broken by the disorder at the critical point. The critical behaviour, determinedby the symmetry at the critical point, should therefore be independent of the previous invariances and be described by a ``super'' universality class. This result is strongly supported by the fact that we obtain the same critical exponent $\nu \simeq 1.35$ in the three cases: orthogonal, unitary and symplectic.