On the resistance minimum in LaAlO$_3$/Eu$_{1-x}$La$_x$TiO$_3$/SrTiO$_3$ heterostructures

TL;DR

This study investigates LaAlO₃/Eu₁₋ₓLaₓTiO₃/SrTiO₃ heterostructures, revealing a resistance minimum influenced by SrTiO₃ properties and charge trapping, distinct from Kondo effect explanations.

Contribution

It provides new insights into the resistance minimum phenomenon in these heterostructures, emphasizing the role of SrTiO₃ and charge trapping over magnetic Kondo effects.

Findings

Observation of a resistance minimum below the Lifshitz point.

Identification of charge trapping and SrTiO₃ effects as causes of the resistance minimum.

Confirmation of similar properties to other oxide interfaces like LaAlO₃/EuTiO₃/SrTiO₃.

Abstract

In this paper we study LaAlO$_3$/Eu$_{1-x}$La$_x$TiO$_3$/SrTiO$_3$ structures with nominally x = 0, 0.1 and different thicknesses of the Eu$_{1-x}$La$_x$TiO$_3$ layer. We observe that both systems have many properties similar to previously studied LaAlO$_3$/EuTiO$_3$/SrTiO$_3$ and other oxide interfaces, such as the formation of a 2D electron liquid for 1 or 2 unit cells of Eu$_{1-x}$La$_x$TiO$_3$; a metal-insulator transition driven by the thickness increase of Eu$_{1-x}$La$_x$TiO$_3$ layer; the presence of an Anomalous Hall effect (AHE) when driving the systems above the Lifshitz point with a backgate 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 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 SrTiO$_3$ crystal and the inevitable effects of charge trapping when using back gates.