Mottness collapse without metallization in the domain wall of the triangular-lattice Mott insulator1T−TaS2

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 zigzag 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.The interplay between superconductivity (SC) and correlated insulating phases, such as Mott insulators and charge density waves (CDW), is one of the central problems in condensed-matter physics. Remarkably, their combination can be found even in simple material systems, such as transition metal dichalcogenide (TMD) van der Waals compound 1T-TaS 2 . The ground state is a Mott insulator[1-3] with CDW[4] and unconventional quantum spin liquid behavior [5][6][7][8][9][10]. Upon Se substitution[11], Fe intercalation [12], or by applying pressure[13] it becomes superconducting, with both CDW and correlated behavior still present. Further control over electronic properties is possible through non-equilibrium charge injection via ultrafast optical or electrical pulses [14][15][16][17][18][19][20][21], which lead to drastic insulator to metastable metal transition. The long-standing hypothesis for metallisation and SC onset is linked to the formation of CDW domain walls, seen in multiple TMDs with different techniques [22][23][24]. Recently, it was challenged experimentally with scanning tunneling spectroscopy (STS) [25], which showed the absence of metallisation in certain types of walls. First-principles calculations revealed that atomic reconstruction in the walls may cause the formation of bound states[25] and band reconstruction [24], but the correlation effects were left out of scope. Thus, the crucial question of whether the CDW distortion inside the wall can lead to Mottness collapse remains open. In this paper we combine STS and dynamical mean field theory (DMFT) calculations to study the behavior of the Mott gap in CDW domain walls, finding Mottness collapse without metallisation.In 1T-TaS 2 , each layer is periodically modulated to form a √ 13 × √ 13 superlattice of David star deformations [4], resulting in a commensurate CDW state with a single half-filled electron band at the Fermi level [26,27]. The Coulomb repulsion opens a charge gap in this band, resulting in a Mott insulating ground state [2...

Mottness versus unit-cell doubling as the driver of the insulating state in 1T-TaS2

“…For samples cooled through the C-CDW transition only after cleavage, a surface that retains information about the bulk stacking order may not be expected, since the presence of the surface may set boundary conditions on the CDW formation. In most previous STM reports showing dI/dV data that can be compared against those presented here, the temperature of cleavage was either reported to be room temperature 29,30,35 , or else was unspecified 28,36 . To our knowledge, only in one work was it specified that the cleavage temperature was below the transition temperature into the C-CDW phase 9 , and there a spectrum was shown that appears very similar to the the Type 1 spectrum presented in the current work (Fig.…”

Intertwined chiral charge orders and topological stabilization of the light-induced state of a prototypical transition metal dichalcogenide

“…S13 for opt-H spectrum) to the Mottness collapse caused by the structural distortion in DWs, 29 however recent studies show that dimerization inside DW precludes metallization. 48 Further spectroscopic studies are thus necessary to build a coherent picture of the transition to the H state from this viewpoint.…”

Stable Flatbands, Topology, and Superconductivity of Magic Honeycomb Networks

“…This can lead to the emergent corner states at the tri-junctions and corners of the sample boundary, which are akin to those of higher-order topological insulators. [37][38][39] Motivated by references 61,62 where the nature of the insulating domain walls of C-CDW 1T-TaS 2 were discussed, we consider the half-filled wires which can develop a period-2 charge density modulation. When the tri-junction frustrates the charge order and traps solitons, we can show that there is an associated crystal symmetry-protected bound state at the junction (In SI, 41 we provide a few concrete realizations.).…”