Anisotropic penetration depth and optical sum rule violation in   La_(2-x)Sr_xCuO_4
  We calculate the doping dependence of the penetration depths and optical sum rule violation in La_(2-x)Sr_xCuO_4 within the model of hole superconductivity. In the clean limit the predicted in-plane sum rule violation is larger than the c-axis one, however in the presence of disorder the latter one becomes very substantially enhanced. 
F. Marsiglio and J.E. Hirsch