Anharmonicity and Doping Melt the Charge Density Wave in Single-Layer TiSe₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• 2D Materials

Background:

• Low-dimensional systems with vanishing band gaps are theoretically prone to exciton formation.
• Excitonic insulators are predicted to be more stable in 2D than 3D due to increased exciton binding energy.

Purpose of the Study:

• Investigate the role of electron-hole interaction and anharmonicity in single-layer TiSe2.
• Re-evaluate the stability of excitonic insulators in 2D systems.
• Explain the experimentally observed charge density wave behavior in single-layer TiSe2.

Main Methods:

• Stochastic self-consistent harmonic approximation to calculate anharmonic phonon spectra.
• Theoretical modeling of electron-hole interactions in 2D vs. 3D systems.
• Analysis of doping effects on charge density wave stability.

Main Results:

• Electron-hole exchange interaction in 2D TiSe2 is significantly smaller than in 3D.
• Weak influence of electron-hole interaction on phonon spectra in single-layer TiSe2.
• Calculated charge density wave transition temperatures (TCDW) of ~440 K (undoped) and ~364 K (doped).

Conclusions:

• Anharmonicity and electron doping are key factors in melting the charge density wave in single-layer TiSe2.
• Findings challenge conventional understanding of excitonic insulator stability in 2D.
• The theoretical TCDW values align with experimental observations for supported single-layer TiSe2 samples.