Resistance minimum in LaAlO3/Eu1−xLaxTiO3/SrTiO3 heterostructures

Abstract

In this paper we study ${\mathrm{LaAlO}}_{3}/{\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{TiO}}_{3}/{\mathrm{SrTiO}}_{3}$ structures with nominally $x=0,0.1$ and different thicknesses of the ${\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{TiO}}_{3}$ layer. We observe that both systems have many properties similar to previously studied ${\mathrm{LaAlO}}_{3}/{\mathrm{EuTiO}}_{3}/{\mathrm{SrTiO}}_{3}$ and other oxide interfaces, such as the formation of a two-dimensional electron liquid for two unit cells of ${\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{TiO}}_{3}$; a metal-insulator transition driven by the increase in thickness of the ${\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{TiO}}_{3}$ layer; the presence of an anomalous Hall effect when driving the systems above the Lifshitz point with a back-gate voltage; and a minimum in the temperature dependence of the sheet resistance below the Lifshitz point in the one-band regime, which becomes more pronounced with increasing negative gate voltage. However, and notwithstanding the likely presence of magnetism in the system, we do not attribute that minimum to the Kondo effect, but rather to the properties of the ${\mathrm{SrTiO}}_{3}$ crystal and the inevitable effects of charge trapping when using back gates.