Infrared-active phonons in one-dimensional materials and their spectroscopic signatures

TL;DR

This paper extends the theory of infrared-active phonons to one-dimensional materials, revealing how their dielectric properties influence spectroscopic signatures and enabling new IR and Raman characterization methods.

Contribution

It introduces a theoretical framework combining analytical models and density-functional perturbation theory for 1D materials, explaining phonon dispersion and dielectric splitting behavior.

Findings

Dielectric splitting in 1D phonons collapses logarithmically at zone center.

The dielectric properties are linked to the physical radius of 1D materials.

New spectroscopic signatures can be used for IR and Raman characterization.

Abstract

Dimensionality provides a clear fingerprint on the dispersion of infrared-active, polar-optical phonons. For these phonons, the local dipoles parametrized by the Born effective charges drive the LO-TO splitting of bulk materials; this splitting actually breaks down in two-dimensional materials. Here, we extend the existing theory to the one-dimensional (1D) case. Combining an analytical model with the implementation of density-functional perturbation theory in 1D boundary conditions, we show that the dielectric splitting in the dispersion relations collapses logarithmically at the zone center. The dielectric properties and the radius of the 1D materials are linked by the present work to these red shifts, opening novel IR and Raman characterization avenues.