Intertwining ferroelectricity and two-dimensional electron gas at oxide interfaces*

We report the coexistence of ferroelectricity and two-dimensional electron gas (2DEG) in ferroelectric Ba_xSr_1-xTiO₃ (BST) thin films at the LaAlO₃/Ba_xSr_1-xTiO₃ (LAO/BST) interface using piezoresponse force microscopy (PFM), electrical and optical measurements, scanning transmission electron microscopy (STEM) as well as first-principles calculations. The 2DEG is introduced into ferroelectric BST thin films by the polar discontinuity at LAO/BST interface similar to that of LAO/STO. The ferroelectricity of BST thin film of ~3.2 nm is found to persist with a two-dimensional carrier density of ~0.05 electron per unit cell. Our results demonstrate the coexistence of ferroelectricity and two-dimensional electron gas, which are conventionally regarded as mutually exclusive, in oxide heterostructures.

In collaboration with: S. W. Zeng, C. J. Li, R. Guo, J. X. Xiao, Z. Huang, W. M. Lv, K. Han, P. Yang, C. G. Li, Z. S. Lim, H. Wang, Y. Zhang, S. J. Chua, K. Y. Zeng