Emergent quasi-two-dimensional electron gas betweenLi1±xNbO3andLaAlO3and its prospectively switchable magnetism

Abstract

Oxide interfaces between insulating perovskites can provide a two-dimensional electron gas (2DEG), which was observed initially beneath polar $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ (LAO) grown on $\mathrm{Ti}{\mathrm{O}}_{2}$-terminated $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$(001). Here, we suggest to use a solid electrolyte $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ (LiNO) instead of $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ to create in LAO/LiNO a robustly switchable and magnetic quasi 2DEG (q2DEG). This prospective phenomenon is achieved by charging and discharging lithium niobate while its $n\ensuremath{\rightarrow}p$ doping induces the alteration of magnetic order in LAO/LiNO and, thus, the spin degrees of freedom in q2DEG. On the basis of ab initio calculations and starting from the defectless and insulating LAO/LiNO superlattice, we demonstrate that either a ferromagnetic q2DEG or weakly magnetic quasi-2D hole gas emerge there due to the presence of excessive electrons or holes, respectively. These defects were simulated by one extra Li and a lithium vacancy in LiNO. By varying the $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ thicknesses up to 18 formula units, we found that (i) the spatial extent of q2DEG is 1.5 nm along the stacking direction and that (ii) the dopant position at the Al-terminated interface is energetically preferable by more than 0.5 eV compared to the deep layers. In the context of the advanced design of q2DEG, the out-of-plane electric polarization, which intrinsically appears in multiferroic LAO/LiNO, allows to switch externally the electric-field dependence of the Rashba effect. Moreover, the in-plane charge current via q2DEG may generate there a transverse spin density due to the Rashba-Edelstein effect. We discuss this scenario using the relativistic electronic structures and locally projected density of states which differ remarkably in $\mathrm{L}\mathrm{A}\mathrm{O}/{\mathrm{Li}}_{1+x}\mathrm{N}\mathrm{O}$ and $\mathrm{L}\mathrm{A}\mathrm{O}/{\mathrm{Li}}_{1\ensuremath{-}x}\mathrm{N}\mathrm{O}$.