Carrier localization in perovskite nickelates from oxygen vacancies

Significance Oxygen vacancies and their associated electrons, ubiquitous in oxide materials, can lead to emergent phenomena. Control of these vacancies allows the manipulation and exploitation of such properties. Using an ultralow oxygen partial pressure environment, we are able to systematically control the oxygen vacancy concentration in thin films of rare-earth nickelates. We find that oxygen vacancies lead to strong carrier localization arising from Ni valence reduction to 2+, resulting in an increase of room-temperature electrical resistivity by several orders of magnitude while maintaining the perovskite structure throughout. The oxygen vacancies can be redistributed by electric fields, leading to analog resistance behavior.