  The single-site two-electron exchange amplitude J_sd between the Cu 4s and Cu
3d_{x^2-y^2} states is found to be the pairing mechanism of high-T_c overdoped
cuprates. The noninteracting part of the Hamiltonian spans the copper Cu 4s, Cu
3d_{x^2-y^2} and oxygen O 2p_x and O 2p_y states. Within the standard BCS
treatment an explicit expression for the momentum dependence of the gap Delta_p
is derived and shown to fit the angle-resolved photoemission spectroscopy
(ARPES) data. The basic thermodynamic and electrodynamic properties of the
model (specific heat C(T), London penetration depth lambda(T)) are analytically
derived. These are directly applicable to cuprates without complicating
structural accessories (chains, double CuO_2 planes, etc.). We advocate that
the pairing mechanism of overdoped and underdoped cuprates is the same, as T_c
displays smooth doping dependence. Thus, a long-standing puzzle in physics is
possibly solved.
