Non-linear dielectric response by protons in amorphous insulators

Nonlinear relaxational polarization effects at high electric field strengths in amorphous or polycrystalline aluminum oxide have been observed. The experiments are described using an asymmetric two-level system. The asymmetry is intrinsic, present even without external field. In the molecular model protons fluctuate between two equilibrium positions located at neighboring negative (oxygen) ions. The built-in asymmetry results from a slight variation of the distances to the next positive (aluminum) ions. This picture is developed in detail and compared with experiments. The correspondence between experiments and the theoretical results confirms the proposed model