Predicting the Structural, Electronic and Magnetic Properties of Few Atomic-layer Polar Perovskite

TL;DR

This study uses density functional theory to predict how the structural, electronic, and magnetic properties of polar perovskite thin layers vary with thickness and stoichiometry, revealing potential for 2D magnetic and semiconducting behaviors.

Contribution

It provides novel predictions on the properties of few-atomic-layer polar perovskites, highlighting differences between even and odd layers and identifying conditions for ferromagnetism.

Findings

Even AL systems are semiconductors; odd AL systems are half-metals or semiconductors.

Ferromagnetic surface states emerge in EL systems beyond 14 layers.

Unique case of KTa2O5 as a semiconductor due to Peierls distortions.

Abstract

Density functional theory (DFT) calculations are performed to predict the structural, electronic and magnetic properties of electrically neutral or charged few-atomic-layer (AL) oxides whose parent systems are based on polar perovskite $KTaO_{3}$. Their properties vary greatly with the number of ALs ($n_{AL}$) and the stoichiometric ratio. In the few-AL limit ($n_{AL}\leqslant 14$), the even AL (EL) systems with chemical formula $(KTaO_{3})_{n}$ are semiconductors, while the odd AL (OL) systems with formula ($K_{n+1}Ta_{n}O_{3n+1}$ or $K_{n}Ta_{n+1}O_{3n+2}$) are half-metal except for the unique $KTa_{2}O_{5}$ case which is a semiconductor due to the large Peierls distortions. After reaching certain critical thickness ($n_{AL}>14$), the EL systems show ferromagnetic surface states, while ferromagnetism disappears in the OL systems. These predictions from fundamental complexity of polar perovskite when approaching the two-dimensional (2D) limit may be helpful for interpreting experimental observations later.