Strain-induced orders-of-magnitude reduction of hopping conductivity in epitaxial SrTiO3 films

Rational control of the electronic properties, including charge transport, is essential for nearly all applications of ABO3 ferroelectrics. Whereas such control is critical for advanced devices using thin epitaxial films, the effects of epitaxy on the electrical conductivity are not fully acknowledged. Here, an unprecedented orders-of-magnitude decrease in conductivity with increasing substrate-induced strain to less than 1% is demonstrated in epitaxial films of pure archetypal representative perovskite SrTiO3 as well as of (Mn, Fe, Co, Ni)-doped SrTiO3. The effect is analyzed in terms of small-polaron localization and hopping. The experimental evidence for hopping and the theoretical justification for the strain-induced fall of the hopping mobility are presented. The discovered massive epitaxial suppression of the electrical hopping conductivity is anticipated for many ABO3 films in general.