ANALYSIS OF PROTON TUNNELLING IN KDP USING A REALISTIC PROTON POTENTIAL

Abstract

The authors argue that because of the skewness of the double-minimum proton potential and the magnitude of the ground-state splitting it is not possible to construct fully localised single-particle proton states in KDP. It follows the proton-proton interactions differ according to whether each proton is in its lowest symmetrical or antisymmetrical state, and that the transverse-field Ising-model Hamiltonian must be supplemented by a further interaction term bilinear in the pseudospin operator Sx. This argument is strongly supported in the crystallographic studies by Nelmes (1980) of the temperature variation of the atom positions in KDP and DKDP.