The interplay of lattice dynamics, stacking effects and Mott physics ‌in charge-density-wave systems

J. Gašperlin,1,2 D. Golež1,2

1Jožef Stefan Institute, 1000 Ljubljana, Slovenia

2Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana, Slovenia

The transition metal dichalcogenide 1T-TaS2 is a layered compound that exhibits a series of increasingly commensurate charge density wave phases with decreasing temperature, including a low-temperature insulating phase. For a single 1T-TaS2 layer, with an odd number of electrons per Star-of-David cluster, the insulating behaviour may be attributed to Mott localisation. However, the stacking arrangement of multiple layers can lead to doubling of the unit cell, where the nature of the insulating state is ambiguous [1, 2]. Furthermore, the various possible stacking terminations lead to surface states with non-trivial interplay between band-insulating and Mott-insulating behaviour. [3].

We propose a minimal model, motivated by the Peierls transition, to investigate the influence of these degrees of freedom. The model describes a (semi-bulk) stack of coupled one-dimensional chains at half-filling. Charge-density-wave order is introduced through Peierls electron-lattice coupling in the transverse direction, and treated at the mean-field level. We present the equilibrium phase diagram of the model, demonstrating regions where, as a result of layer stacking, the trimerized phase is stabilized instead of the expected dimerized phase. We identify a narrow band crossing the Fermi level and opening of the Mott gap due to on-site electron-electron interactions.

1. C. J. Butler et al., Nat. Commun. 11, 2477, (2020)
2. T. Ritschel et al, Phys. Rev. B 98, 195134 (2018)
3. F. Pettochi et al., Phys. Rev. Lett. 129, 016402, (2022)