1T-TaS2 undergoes successive phase transitions upon cooling and eventually enters an insulating state of mysterious origin. Some consider this state to be a band insulator with interlayer stacking order, yet others attribute it to Mott physics that support a quantum spin liquid state.Here, we determine the electronic and structural properties of 1T-TaS2 using angle-resolved photoemission spectroscopy and X-Ray diffraction. At low temperatures, the 2π/2c-periodic band dispersion, along with half-integer-indexed diffraction peaks along the c axis, unambiguously indicates that the ground state of 1T-TaS2 is a band insulator with interlayer dimerization. Upon heating, however, the system undergoes a transition into a Mott insulating state, which only exists in a narrow temperature window. Our results refute the idea of searching for quantum magnetism in 1T-TaS2 only at low temperatures, and highlight the competition between on-site Coulomb repulsion and interlayer hopping as a crucial aspect for understanding the material's electronic properties.
@article{arxiv.2008.11001,
title = {Band insulator to Mott insulator transition in 1T-TaS$_2$},
author = {Y. D. Wang and W. L. Yao and Z. M. Xin and T. T. Han and Z. G. Wang and L. Chen and C. Cai and Yuan Li and Y. Zhang},
journal= {arXiv preprint arXiv:2008.11001},
year = {2020}
}