Mottness collapse without metallisation in the domain walls of triangular-lattice Mott insulator 1T-TaS$_2$

TL;DR

This study investigates how domain walls in the Mott insulator 1T-TaS₂ exhibit partial metallicity without full metallization, revealing localized in-gap states and the role of structural dimerization in electronic properties.

Contribution

It demonstrates that domain walls in 1T-TaS₂ show partial gap suppression and localized states, with full metallization prevented by structural dimerization effects.

Findings

Partial suppression of the Mott gap at domain walls

Localized in-gap states at domain-wall sites

Full metallization is prevented by band splitting due to dimerization

Abstract

1T-TaS$_2$ is a charge-density-wave (CDW) compound with a Mott-insulating ground state. The metallic state obtained by doping, substitution or pulsed charge injection is characterized by an emergent CDW domain wall network, while single domain walls can be found in the pristine Mott state. Here we study whether and how the single walls become metallic. Tunneling spectroscopy reveals partial suppression of the Mott gap and the presence of in-gap states strongly localized at the domain-wall sites. Using the real-space dynamical mean field theory description of the strongly correlated quantum-paramagnet ground state we show that the local gap suppression follows from the increased hopping along the connected zig-zag chain of lattice sites forming the domain wall, and that full metallisation is preempted by the splitting of the quasiparticle band into bonding and antibonding sub-bands due to the structural dimerization of the wall, explaining the presence of the in-gap states and the low density of states at the Fermi level.