Effect of a magnetic field on the two-phonon Raman scattering in graphene

TL;DR

This study investigates how an external magnetic field affects the two-phonon Raman 2D band in graphene, revealing shifts, broadening, and insights into electron scattering mechanisms through combined experimental and theoretical analysis.

Contribution

It provides a detailed experimental and theoretical analysis of magnetic field effects on the 2D Raman band in graphene, including electron scattering insights.

Findings

The 2D band shifts to lower frequency with increasing magnetic field.

The 2D band broadens as the magnetic field increases.

Electronic scattering accounts for about half of the 2D peak width.

Abstract

We have studied, both experimentally and theoretically, the change of the so-called 2D band of the Raman scattering spectrum of graphene (the two-phonon peak near 2700 cm-1) in an external magnetic field applied perpendicular to the graphene crystal plane at liquid helium temperature. A shift to lower frequency and broadening of this band is observed as the magnetic field is increased from 0 to 33 T. At fields up to 5--10 T the changes are quadratic in the field while they become linear at higher magnetic fields. This effect is explained by the curving of the quasiclassical trajectories of the photo-excited electrons and holes in the magnetic field, which enables us (i) to extract the electron inelastic scattering rate, and (ii) to conclude that electronic scattering accounts for about half of the measured width of the 2D peak.