ON-SITE COULOMB REPULSION IN THE SMALL POLARON SYSTEM LA1-XCAXMNO3

Conductivity measurements from 300 to 1200 K of La1-xCaxMnO3 thin film s, with doping from x=0 to x=1, show that the entire doping range fits the adiabatic small polaron model sigma=(A/T)exp(-E-a/kT). Furthermor e the x dependence of A explicitly shows the effects of on-site Coulom b repulsion, i.e., a polaron cannot hop into an occupied site. Instead of increasing monotonically as more carriers are introduced, A starts to decrease at x=0.2 and, as expected for Hubbard band splitting, is reduced to almost zero when the lattice is full.