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arXiv · 2405.06132

Moir\'e polar vortex, flat bands and Lieb lattice in twisted bilayer BaTiO$_3$

Seungjun Lee·D. J. P. de Sousa·Bharat Jalan·Tony Low
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Abstract

Advances in material fabrication techniques and growth methods have opened up a new chapter for twistronics, in the form of twisted freestanding three-dimensional material membranes. Through first-principles calculations based on density functional theory, we investigate the crystal and electronic structures of twisted bilayer BaTiO$_3$. Our findings reveal that large stacking fault energy leads to chiral in-plane vortex pattern that was recently observed in experiments. Moreover, we also found non-zero out-of-plane local dipole moments, indicating that the strong interlayer interaction might offer promising strategy to stabilize ferroelectric order in the two-dimensional limit. Remarkably, the vortex pattern in the twisted BaTiO$_3$ bilayer support localized electronic states with quasi-flat bands, associated with the interlayer hybridization of oxygen $p_z$ orbitals. We found that the associated band width reaches a minimum at $\sim$19$^{\circ}$ twisting, configuring the largest magic angle in moir\'e systems reported so far. Further, the moir\'e vortex pattern bears a striking resemblance to two interpenetrating Lieb lattices and corresponding tight-binding model provides a comprehensive description of the evolution the moir\'e bands with twist angle and reveals the topological nature of these states.

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Seungjun Lee, D. J. P. de Sousa, Bharat Jalan, Tony Low. 2024-05-09. Moir\'e polar vortex, flat bands and Lieb lattice in twisted bilayer BaTiO$_3$. https://doi.org/10.1126/sciadv.adq0293

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