Attractive critical point from weak antilocalization on fractals

We report an attractive critical point occurring in the Anderson localization scaling flow of symplectic models on fractals. The scaling theory of Anderson localization predicts that in disordered symplectic two-dimensional systems weak-antilocalization effects lead to a metal-insulator transition. This transition is characterized by a repulsive critical point above which the system becomes metallic. Fractals possess a noninteger scaling of conductance in the classical limit which can be continuously tuned by changing the fractal structure. We demonstrate that in disordered symplectic Hamiltonians defined on fractals with classical conductance scaling g~L^-ε, for 0<ε<βₘₐₓ≈0.15, the metallic phase is replaced by a critical phase with a scale-invariant conductance dependent on the fractal dimensionality. Our results show that disordered fractals allow an explicit construction and verification of the ε expansion.