An analytical form of screened impurity potential is derived, taking into account the presence of a bound electron exhibiting a hydrogenic wave function. A subsequent calculation of the impurity level as a function of the screening parameter then shows that the impact of screening can become very different, depending on whether the impurity was initially occupied or empty. When the screening parameter exceeds the (unscreened) reciprocal Bohr radius, there is no empty impurity state, whereas if an electron is trapped there remains a localized state, the level of which saturates around 0.39 Ry. Possible implications of this result are discussed, regarding either neutral impurity scattering, the Metal-Insulator Transition or the possibility to get bistable impurity states.

Stationary Occupied State in a Coulomb Potential with Electron Screening

In plasmas with helium-like bound states electrostatic screening inside the atom gives rise to deviations from the Debye-Huckel chemical potential. Assuming a variational solution for the ground state of the helium-like atom the corresponding Free Energy is explicitely given. The result provides a simple means to describe the forming of bound states in consistency with the surrounding plasma and surpasses in this sense perturbation theories.

H. Lehmann

Papers

Bound states structure in the critical region of a Thomas-Fermi symmetrical quantum plasma