Chemical strain-dependent two-dimensional transport at RAlO3/SrTiO3 interfaces (R=La,Nd,Sm,and Gd)

Perovskite RAlO₃ (R = La, Nd, Sm, and Gd) films have been deposited epitaxially on (001) TiO₂-terminated SrTiO₃ substrates. In this paper, it is observed that the two-dimensional transport characteristics at the RAlO₃/SrTiO₃ interfaces are very sensitive to the species of rare-earth element, that is to chemical strain. Although electron energy loss spectroscopy measurements show that electron transfer occurs in all the four polar/nonpolar heterostructures, the amount of electrons transferred across SmAlO₃/SrTiO₃ and GdAlO₃/SrTiO₃ interfaces are much less than those across LaAlO₃/SrTiO₃ and NdAlO₃/SrTiO₃ interfaces. First-principles calculations reveal the competition between ionic polarization and electronic polarization in the polar layers in compensating the build-in polarization due to the polar discontinuity at the interface. Finally, in particular, a large ionic polarization is found in SmAlO₃/SrTiO₃ and GdAlO₃/SrTiO₃ systems (which experience the largest tensile epitaxial strain), hence reducing the amount of electrons transferred.