Fate of the half-filled, strongly correlated topological flat band in 1T-TaS2

Ascertain the fate of electrons in the half-filled flat miniband of 1T-TaS2 under strong correlations when the band carries a non-trivial Z2 topological index, i.e., opposite inversion eigenvalues at the Γ and M points that obstruct a time-reversal-invariant localized Wannier representation; determine the resulting many-body ground state or correlated phase in this regime.

Background

The paper constructs a microscopic tight-binding model for 1T-TaS2 that includes spin-orbit coupling and the commensurate star-of-David charge-density wave, showing that an isolated, half-filled flat band is a robust feature across broad parameter ranges. By viewing the CDW phase as a superlattice of weakly coupled clusters, the authors classify possible flat-band scenarios and identify conditions under which the flat band acquires a non-trivial Z2 topology based on inversion eigenvalues at Γ and M.

In the topologically non-trivial regime, the band lacks a time-reversal-invariant localized Wannier representation, which complicates the understanding of correlation-driven phenomena at half filling. This obstruction raises a fundamental unresolved question regarding the many-body ground state and correlated phases that can emerge from strong electron interactions in such a band, with prior literature indicating nontrivial possibilities but no definitive resolution.