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

Abstract

If a material with an odd number of electrons per unit-cell is insulating, Mott localisation may be invoked as an explanation. This is widely accepted for the layered compound 1T-TaS 2 , which has a low-temperature insulating phase comprising charge order clusters with 13 unpaired orbitals each. But if the stacking of layers doubles the unit-cell to include an even number of orbitals, the nature of the insulating state is ambiguous. Here, scanning tunnelling microscopy reveals two distinct terminations of the charge order in 1T-TaS 2 , the sign of such a double-layer stacking pattern. However, spectroscopy at both terminations allows us to disentangle unit-cell doubling effects and determine that Mott localisation alone can drive gap formation. We also observe the collapse of Mottness at an extrinsically re-stacked termination, demonstrating that the microscopic mechanism of insulator-metal transitions lies in degrees of freedom of inter-layer stacking.

Revealing the Charge Density Wave Proximity Effect in Graphene on 1T-TaS2

“…We note that taking a unit cell consisting of two layers of 1T-TaS2 results in dimerization between layers, as suggested by recent theoretical and experimental works [27][28][29][30] . In this case, 1T-TaS2 is no longer best described as a two-dimensional Mott insulator with magnetic ordering, but rather a band insulator, as the formation of interlayer dimer singlets suppresses magnetism.…”

Toward nonthermal control of excited quantum materials: framework and investigations by ultrafast electron scattering and imaging

“…Interestingly, this relevant length scale matches the characteristic length scale of the HCDW structure revealed by STM [169], which also suggests the structure as chiral. A recent X-ray diffraction investigation of HCDW also indicated a ϕ-shift and correlated the change with the loss of interlayer dimerization [172]-which the authors attribute as a defining factor introducing the insulating behavior in the C-CDW phase [195], although the relative roles of interlayer stacking and the Mott physics for the insulator-metal transition in TaS 2 are still debated [165,171,[196][197][198][199]. The three independent measurements give a similar laser threshold ∼1 mJ/cm 2 , for the light-induced phase transition.…”

Van Der Waals Heterostructures Based on Atomically‐Thin Superconductors

“…[9]—favors a metallic one. [ 10 ] Nonetheless, other scenarios such as the formation of emergent domain wall networks, [ 11 ] the out‐of‐plane dimerization [ 12 ] or the Mott picture, [ 8 ] among others, [ 6 ] are also under consideration.…”