Reconciling the bulk metallic and surface insulating state in 1T−TaSe2

Abstract

The transition metal dichalcogenides 1T -TaS2 and 1T -TaSe2 have been extensively studied for the complicated correlated electronic properties. The origin of different surface electronic states remains controversial. We apply scanning tunneling microscopy and spectroscopy to restudy the surface electronic state of bulk 1T -TaSe2. Both insulating and metallic states are identified in different areas of the same sample. The insulating state is similar to that in 1T -TaS2, concerning both the dI/dV spectrum and the orbital texture. With further investigations on single-step areas, the discrepancy of electronic states is found to be associated with different stacking orders. The insulating state is most possibly a single layer property, modulated to a metallic state in some particular stacking orders. The metallic spectrum and corresponding stacking orders are dominant in 1T-TaSe2, consistent with the metallic transport measurement. We then reconcile the bulk metallic and surface insulating state in 1T -TaSe2. The rich phenomena in 1T -TaSe2 deepens our understanding of the correlated electronic state on bulk 1T -TaSe2 and 1T -TaS2.

Charge density waves in two-dimensional transition metal dichalcogenides

“…Although the surface states with larger/smaller bandgaps have been suggested to arise from interlayer dimerization/Coulomb repulsion U, respectively [165,166], a recent study shows that the surface electronic structure is not solely determined by the stacking of the top two CDW layers [169]. A similar complication was observed at bulk 1T-TaSe 2 surface [170],…”

“…where the surface states can even range from insulating to weakly metallic to strongly metallic [170,171]. These complications create difficulty in reaching a one-to-one correspondence between stacking orders and electronic structures in related materials.…”

Exploring the Charge Density Wave Phase of1T−TaSe2: Mott or Charge-Transfer Gap?

“…The nature of this gap was discussed considering Mott electron correlations in density-functional theory (DFT) calculations combined with the Hubbard correction (DFT þ U) [16][17][18]. Reports of electronic gaps up to ∼0.5 eV in bulk samples by ARPES and STS have been interpreted assuming Mott physics confined to the crystal surface [15,19,20]. Such experimental techniques alone cannot describe the nature of the gap and, while ARPES offers the possibility of a comparison with the calculated band structure, it fails to probe unoccupied bands, which are necessary to estimate gaps across the Fermi surface.…”

Large-Area Epitaxial Mott Insulating 1T-TaSe2 Monolayer on GaP(111)B

“…As this interaction can strongly modify the Mott gap, , tunneling spectroscopy was further performed. Figure a exhibits typical spectra.…”