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

Abstract

Perovskite $R{\mathrm{AlO}}_{3}$ $(R=\mathrm{La},\text{Nd},\text{Sm},\text{and Gd})$ films have been deposited epitaxially on (001) ${\mathrm{TiO}}_{2}\text{-terminated}$ ${\mathrm{SrTiO}}_{3}$ substrates. It is observed that the two-dimensional transport characteristics at the $R{\mathrm{AlO}}_{3}/{\mathrm{SrTiO}}_{3}$ 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 ${\mathrm{SmAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ and ${\mathrm{GdAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ interfaces are much less than those across ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ and ${\mathrm{NdAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ 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 ${\mathrm{SmAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ and ${\mathrm{GdAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ systems (which experience the largest tensile epitaxial strain), hence reducing the amount of electrons transferred.