Oxygen Motion and Electroresistance Observed in a Bilayer Manganite

Oxygen defects and migration are thought to play key roles in electroresistive oxide devices$^{1,2}$. Scanning Tunnelling Microscopy (STM) can be used to study the dynamics of individual oxygen adatoms and vacancies at the oxide surface. We have identified a material, PrSr$_2$Mn$_2$O$_7$ which is suitable for STM study and also displays room temperature electroresistance. We have observed surface oxygen adatoms and vacancies in atomic-resolution STM images and tunnelling spectra. Time dependent STM imaging shows the dynamics of adatoms and vacancies, including adatom hopping and vacancy-adatom recombination. Bistable current-voltage characteristics are found for single oxygen adatoms. We suggest that the bulk material may be modelled as a network of electroresistive junctions. \footnotetext[1]{Nian, Y. B. et. al., Physical Review Letters 98, 146403 (2007).} \footnotetext[2]{Shono, K. et. al., Applied Physics Express 1, 055002 (2008).}