Phonon spectrum and bonding properties of Bi$_{2}$Se$_{3}$: Role of strong spin-orbit interaction

TL;DR

This study investigates how strong spin-orbit interaction affects phonon spectra and bonding in Bi$_{2}$Se$_{3}$, revealing phonon instabilities and enhanced van der Waals forces due to SOI.

Contribution

It provides the first detailed analysis of the impact of spin-orbit interaction on phonon dispersions and bonding properties in Bi$_{2}$Se$_{3}$ using density functional theory.

Findings

Imaginary phonon frequencies appear with SOI in certain directions.

SOI strengthens van der Waals forces between Se layers.

Similar phonon behavior observed in Bi$_{2}$Te$_{3}$.

Abstract

Phonon dispersions of one typical three-dimensional topological insulator Bi$_{2}$Se$_{3}$ have been studied within density functional theory. The soft modes of two acoustic branches along the $Z$$-$$F$ and $\Gamma$$-$$F$ directions within the pure local density approximation will transit to show imaginary frequency oscillating after including the spin-orbit interaction (SOI). Similar phenomenon has also been observed for Bi$_{2}$Te$_{3}$. Besides, we have found that the weak van der Waals forces between two Se1 layers in Bi$_{2}$Se$_{3}$ are strengthened by turning on the SOI.