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.
Categories: cond-mat.mtrl-sci physics.comp-ph