Abstract
The recently investigated polymorph of monolayer revealed an insulating behavior suggesting a star-of-David phase with periodicity associated with a Mott insulator, reminiscent of . We examine this novel two-dimensional material from first principles. We find an instability towards the formation of an incommensurate charge density wave (CDW) and establish the star-of-David phase as the most stable commensurate CDW. The Mottness in the star-of-David phase is confirmed and studied at various levels of theory: the spin-polarized generalized gradient approximation (GGA) and its extension involving the on-site Coulomb repulsion (GGA+), as well as the dynamical mean-field theory. Finally, we estimate Heisenberg exchange couplings in this material and find a weak nearest-neighbor ferromagnetic coupling, at odds with most Mott insulators. We point out the close resemblance between this star-of-David phase and flat-band ferromagnetism models.
- Received 29 March 2018
- Revised 4 June 2018
DOI:https://doi.org/10.1103/PhysRevB.98.045114
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