Many-body effects in suspended graphene probed through magneto-phonon resonances

TL;DR

This study uses magneto-Raman spectroscopy to investigate many-body effects in suspended graphene by analyzing magneto-phonon resonances, revealing significant velocity enhancements in monolayer graphene indicative of strong many-body interactions.

Contribution

It demonstrates how magneto-phonon resonances can be used to probe many-body effects and extract electronic velocity parameters in multilayer and monolayer graphene.

Findings

Velocity parameter slightly above bulk graphite in multilayer graphene.

Significant increase in velocity parameter in monolayer graphene.

Enhanced many-body effects observed in unscreened graphene.

Abstract

We make use of micro-magneto Raman scattering spectroscopy to probe magneto-phonon resonances (MPR) in suspended mono- to penta-layer graphene. MPR correspond to avoided crossings between zone-center optical phonons (G-mode) and optically-active inter Landau level (LL) transitions and provide a tool to perform LL spectroscopy at a fixed energy ($\approx 197~\rm{meV}$) set by the G-mode phonon. Using a single-particle effective bilayer model, we readily extract the velocity parameter associated with each MPR. A single velocity parameter slightly above the bulk graphite value suffices to fit all MPR for $N\geq2$ layer systems. In contrast, in monolayer graphene, we find that the velocity parameter increases significantly from $(1.23\pm 0.01) \times 10^6~\mathrm{m.s^{-1}}$ up to $(1.45\pm0.02) \times 10^6~\mathrm{m.s^{-1}}$ as the first to third optically-active inter LL transition couple to the G-mode phonon. This result is understood as a signature of enhanced many-body effects in unscreened graphene.