Metallic interfaces in a CaTiO3 / LaTiO3 superlattice

Abstract

Apart from a handful of exceptions, all known complex oxide two-dimensional electron gases (2DEGs) are formed in ${\mathrm{SrTiO}}_{3}$-based heterostructures, and microscopic information about non-${\mathrm{SrTiO}}_{3}$ 2DEGs systems is scarce. Here, we report on the realization of metallic conductance in a ${\mathrm{CaTiO}}_{3}$-based system, ${\mathrm{CaTiO}}_{3}$/${\mathrm{LaTiO}}_{3}$ superlattices, epitaxially grown in a layer-by-layer way on a ${\mathrm{NdGaO}}_{3}$(110) substrate by pulsed laser deposition. The high quality of the crystal and electronic structures is characterized by in situ reflection high-energy electron diffraction, x-ray diffraction, scanning transmission electron microscopy, and x-ray photoemission spectroscopy. Electrical transport confirms the formation of metallic interfaces in the ${\mathrm{CaTiO}}_{3}$/${\mathrm{LaTiO}}_{3}$ superlattice. In addition, Hall measurements reveal that in the ${\mathrm{CaTiO}}_{3}$/${\mathrm{LaTiO}}_{3}$ superlattice the room-temperature carrier mobility is nearly three times higher than that of the ${\mathrm{CaTiO}}_{3}$/${\mathrm{YTiO}}_{3}$ superlattice, implying the importance of ${\mathrm{TiO}}_{6}$ octahedral tilts and rotations on the carrier mobility of a 2DEG. Since doped ${\mathrm{CaTiO}}_{3}$ is an A-site polar metal, our results provide a materials system for designing synthetic two-dimensional polar metals.