Importance of Non-Adiabatic Effects on Kohn Anomalies in 1D metals

TL;DR

This paper explores how non-adiabatic effects influence Kohn anomalies in 1D metals, providing a model that predicts phonon behavior and system instability thresholds validated by first-principles calculations.

Contribution

The study introduces a model analyzing non-adiabatic effects on Kohn anomalies in 1D metals and predicts instability thresholds relevant for experimental observations.

Findings

Identification of a coupling strength threshold for instability.

Validation of the model with first-principles calculations on carbon nanotubes.

Insights into the influence of electron effective mass on phonon renormalization.

Abstract

Kohn anomalies are kinks or dips in phonon dispersions which are pronounced in low-dimensional materials. We investigate the effects of non-adiabatic phonon self-energy on Kohn anomalies in one-dimensional metals by developing a model that analyzes how the adiabatic phonon frequency, electron effective mass, and electron-phonon coupling strength influence phonon mode renormalization. We introduce an electron-phonon coupling strength threshold for low-temperature system instability, providing experimentalists with a tool to predict them. Finally, we validate the predictions of our model against first-principles calculations on a 4 {\AA}-diameter carbon nanotube.