Anharmonicity of Phonon Modes in MBE-Grown Bi2Te3 Thin Films: A Temperature-Dependent Raman Study

 https://doi.org/10.1002/jrs.70001

This study examines the temperature-dependent Raman spectra of MBE-grown bismuth telluride (Bi₂Te₃) thin films, analyzing Stokes, and anti-Stokes scattering in two polarizations to resolve symmetry-dependent mode strengths. Density functional theory simulations of Stokes spectra identified the fundamental vibrational modes and anharmonic decay. The temperature evolution of phonon wavenumbers and linewidths revealed the role of anharmonicity: the real part of the phonon self-energy governs the wavenumber shift (redshift) of the A1⁢�2 mode, while its imaginary part drives the linewidth broadening, both arising from cubic and quartic anharmonic processes which is associated to energy and symmetry of the mode. In contrast, the lower wavenumber A1⁢�1 and E�2 modes exhibited weaker coupling to thermal decay channels, reflected in smaller changes to their self-energy components and longer lifetimes. The intensity of A1⁢�2 mode decreased significantly with temperature due to multi-phonon decay, whereas A1⁢�1 and E�2 intensities remained stable. These results quantify the distinct mediation of wavenumber renormalization and lifetime effects in Bi₂Te₃ by the real and imaginary components of the phonon self-energy.