Temperature-dependent pseudogap and electron localization in 1T-TaS2

Time-domain classification of charge-density-wave insulators

“…2a), which occurs at temperatures below 180-200 K (depending on cooling or heating), is rather well understood as a combined Peierls-Mott insulating phase 8,10,24 : the strong periodic lattice distortion, which is coupled to the CDW, splits the occupied part of the lowest-lying Ta 5d band into three subband manifolds so that the uppermost, half-filled manifold becomes susceptible to a Mott-Hubbard-type transition creating a deep pseudogap at E F . The spectroscopic signatures of this scenario are remarkably strong and momentum selective.…”

“…In the ARPES spectral weight distribution depicted in Fig. 2b, the Mott-Hubbard gap (taken here as the distance between E F and the lower Hubbard band) has a size of about 120 meV and is best visible near the Γ point 8 . The CDW reconstruction, on the other hand, seems most pronounced in the clear subband splittings along Γ − M , the strong band backfolding along M K − , and the large spectral gap of about 400 meV that opens at the edge of the original Brillouin zone (midway between M and K ).…”

“…Two prominent examples are 1T-TaS 2 and 1T-TiSe 2 . In these two compounds, the electronic structures [8][9][10][11][12][13][14][15] and ultrafast spectral responses [16][17][18][19] indicate the presence of significant electron correlation effects. In both compounds, electron-electron interactions may in fact have an important role in CDW formation [12][13][14][18][19][20] and in the emergence of superconductivity from CDW states upon intercalation 21 or under pressure 22,23 .…”

Strain tuning of the charge density wave in monolayer and bilayer 1T-TaS2

“…3 Particularly, 1T-TaS 2 has been extensively investigated because of its rich phase behavior as a function of the temperature. 1,3,4,[9][10][11][12] At 540 K an incommensurate CDW develops from the undistorted metallic structure, at 350 K an almost commensurate CDW is adopted, and further cooling to 180 K leads to a commensurate CDW, which exhibits a "Star-of-David" structure with an inplane √13 × √13 periodic lattice distortion. The origin of the CDW, the pseudo-gapped Fermi surface, and the rich phase diagram are some of the topics that have motivated experimental and theoretical studies.…”

“…The origin of the CDW, the pseudo-gapped Fermi surface, and the rich phase diagram are some of the topics that have motivated experimental and theoretical studies. 3,7,[9][10][11][12][13] Recent progress in mechanical 14,15 and chemical 16 exfoliation enables the fabrication of planar 1T-TaS 2 samples as thin as a monolayer, 17 initiating interest in the behavior of the CDW in two-dimensional systems. [18][19][20] It has been suggested that the CDW in the monolayer adopts the same periodic lattice distortion as known from the bulk.…”