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. 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. 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.