Interlayer Coupling Induced Phonon-Glass-Electron-Crystal Behavior in van der Waals Heterostructure PtSe₂/γ-GeSe

We report the electronic band structure and interlayer coupling induced phonon-glass-electron-crystal behavior in the van der Waals heterostructure PtSe₂/γ-GeSe. The heterostructure is dynamically stable and possesses an indirect band gap of 0.63 eV (at the Heyd-Scuseria-Ernzerhof functional level) with type II band alignment. A low conduction band offset of 0.20 eV compared to the valence band offset of 0.92 eV suggests fluent electrons drive from γ-GeSe to PtSe₂. Interlayer coupling induced strong phonon coupling and a unique "avoided crossing" feature between longitudinal acoustic and low-lying optical phonon modes between K and Γ points. Significant suppression of acoustic phonon modes and giant phonon scattering rates (a maximum value of 73.76 ps^-1) results in a low lattice thermal conductivity of 1.20 W/(m·K) at 300 K after enforcing the mandatory rotational invariance condition. The calculated lattice thermal conductivity is 14-fold smaller than that of monolayer PtSe₂(16.97 W/(m·K)). The lattice thermal conductivity upsurges by 24% as the out-of-plane acoustic phonon dispersion undergoes linear dispersion, indicating the importance of pure quadratic flexural phonon dispersion. Our results disclose a strategy for having the phonon-glass-electron-crystal character in van der Waals heterostructures.