Vibrational Spectra of Pb2Bi2Te3, PbBi2Te4 and PbBi4Te7 Topological Insulators: Temperature Dependent Raman and Theoretical Insight from DFT Simulations

TL;DR

This study investigates temperature-dependent vibrational spectra of layered topological insulators Pb2Bi2Te3, PbBi2Te4, and PbBi4Te7 using Raman spectroscopy and DFT simulations, revealing how atomic layer insertion affects phonon modes and lattice interactions.

Contribution

It provides new insights into the vibrational properties of layered topological insulators with atomic layer insertion, combining experimental Raman data with theoretical DFT calculations.

Findings

Raman modes shift with temperature, indicating anharmonic lattice vibrations.

Pb and PbTe layer insertion modifies interlayer interactions and phonon modes.

Experimental and computational data show good agreement, elucidating lattice dynamics.

Abstract

We present temperature dependent frequency shift and line broadening of phonon modes by insertion of atomic layers of Pb and PbTe in the prototype 3D topological insulator Bi2Te3, using Raman spectroscopy. Good quality single crystals of Pb2Bi2Te3, PbBi2Te4 and PbBi4Te7 are grown using the modified Bridgman technique. The Raman modes show progressive blue shift with the decrease in temperature from 298 K to 93 K in Pb2Bi2Te3, PbBi2Te4 and PbBi4Te7 is due to anharmonic vibrations of the lattice as well as increasing strength of Bi-Te covalent interactions. Experimental results are complemented by extensive density functional theory calculations where a reasonable matching between experimental and computational data is found. Chemical pressure, induces by the insertion of Pb and PbTe layers in Bi2Te3, modifies the interactions at the boundaries of the quintuple-layers which is evident from the evolution of mode. The enhancement of out-of-plane Bi-Te vibrations with respect to in-plane Bi-Te vibrations are observed at low temperatures.