Surface Optical and Bulk Acoustic Phonons in the Topological Insulator, Bi2Se2Te

TL;DR

This study investigates phonon behaviors in Bi2Se2Te topological insulator thin films, revealing surface optical phonons and tunable bulk acoustic phonons, with implications for spintronics and quantum computing.

Contribution

It provides a detailed analysis of phonon modes in Bi2Se2Te thin films, highlighting the surface nature of optical phonons and the thickness-dependent tuning of acoustic phonons.

Findings

Optical phonon frequencies are independent of film thickness.

Acoustic phonon frequencies vary with film thickness, indicating standing modes.

Surface optical phonons are intrinsic to the topological insulator surface.

Abstract

We explore the phonon dynamics of thin films of the topological insulator material Bi2Se2Te using ultrafast pump-probe spectroscopy. The time resolved differential reflectivity of the films exhibit fast and slow oscillations. We have given a careful analysis of variation of phonon frequency as a function of film thickness attributing this to existence of standing acoustic modes. However, no variation in the frequency of the optical phonon modes was found with film thickness. This indicates that the optical phonons intrinsically belong to the surface of the topological insulators. The fact that the acoustic phonons can be tuned by changing the film thickness has tremendous potential for room temperature low power spintronic devices and in topological quantum computation.