Damping of Landau levels in neutral graphene at low magnetic fields: A phonon Raman scattering study

TL;DR

This study investigates Landau level broadening in neutral graphene using magneto-Raman spectroscopy, revealing that strain-induced pseudomagnetic fields significantly dampen low-field resonances in single-layer graphene.

Contribution

It provides a quantitative analysis of Landau level broadening due to strain-induced pseudomagnetic fields in neutral graphene, highlighting differences from multilayer graphene.

Findings

Single-layer graphene shows strong damping of low-field Landau level resonances.

Strain induces a pseudomagnetic field distribution of 1.0-1.7 T in single-layer samples.

Multilayer graphene exhibits less Landau level broadening at low fields.

Abstract

Landau level broadening mechanisms in electrically neutral and quasineutral graphene were investigated through micro-magneto-Raman experiments in three different samples, namely, a natural single-layer graphene flake and a back-gated single-layer device, both deposited over Si/SiO2 substrates, and a multilayer epitaxial graphene employed as a reference sample. Interband Landau level transition widths were estimated through a quantitative analysis of the magnetophonon resonances associated with optically active Landau level transitions crossing the energy of the E_2g Raman-active phonon. Contrary to multilayer graphene, the single-layer graphene samples show a strong damping of the low-field resonances, consistent with an additional broadening contribution of the Landau level energies arising from a random strain field. This extra contribution is properly quantified in terms of a pseudomagnetic field distribution Delta_B = 1.0-1.7 T in our single-layer samples.