Exploring the Charge Density Wave Phase of 1T-TaSe_{2}: Mott or Charge-Transfer Gap?

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Physics

Background:

• 1T-TaSe2 is thought to exhibit a Mott metal-insulator transition within its charge density wave (CDW) phase.
• Previous studies suggested Mott physics was confined to the surface of bulk samples.
• Thin film studies indicated Mott-like behavior diminishes rapidly with increasing thickness.

Purpose of the Study:

• To investigate the electronic structure of 1T-TaSe2 using combined experimental and theoretical methods.
• To clarify the origin of the observed band gap and the state above the Fermi level (EF).
• To determine if Mott correlation effects are necessary to explain the electronic properties of 1T-TaSe2.

Main Methods:

• Combined time- and angle-resolved photoemission spectroscopy (TR-ARPES).
• Theoretical investigations using density functional theory (DFT) calculations.
• Analysis of electronic band structure modifications.

Main Results:

• Experimental confirmation of a state above EF and a band gap of ~0.7 eV at the Γ point.
• DFT calculations revealed band structure modifications induced by the CDW phase.
• Demonstrated that these modifications alone explain the observed electronic state and band gap.

Conclusions:

• The observed band gap and state above EF in 1T-TaSe2 are primarily due to CDW-induced band structure changes.
• Mott correlation effects are not required to explain these electronic properties.
• This work reframes the understanding of electronic transitions in 1T-TaSe2.