Electronic flat bands serve as a unique platform to achieve strongly-correlated phases. The emergence of a flat band around the Fermi level in 1T-TaS2 in accompany with the development of a 13×13 charge density wave (CDW) superlattice has long been noticed experimentally, but a transparent theoretical understanding remains elusive. We show that without CDW, the primary feature of the 1×1 bands can be fitted by a simple trigonometric function, and physically understood by choosing a rotated t~2g basis with the principle axes aligning to the tilted TaS6 octahedron. Using this basis, we trace the band evolution in the 13×13 superlattice by progressively including different CDW effects. We point out that CDW strongly rehybridizes the three t~2g orbitals, which leads to the formation of a well-localized molecular orbital and spawns the flat band.
@article{arxiv.2109.05672,
title = {Understanding the flat band in 1T-TaS2 using a rotated basis},
author = {Li Cheng and Xuanyu Long and Xiaobin Chen and Xiaolong Zou and Zheng Liu},
journal= {arXiv preprint arXiv:2109.05672},
year = {2022}
}