Raman spectroscopy of magneto-phonon resonances in graphene and graphite

Abstract

The magneto-phonon resonance or MPR occurs in semiconductor materials when the energy spacing between Landau levels is continuously tuned to cross the energy of an optical phonon mode. MPRs have been largely explored in bulk semiconductors, in two-dimensional systems and in quantum dots. Recently there has been significant interest in the MPR interactions of the Dirac fermion magnetoexcitons in graphene, and a rich splitting and anti-crossing phenomena of the even parity E2g long wavelength optical phonon mode have been theoretically proposed and experimentally observed. The MPR has been found to crucially depend on disorder in the graphene layer. This is a feature that creates new venues for the study of interplays between disorder and interactions in the atomic layers. We review here the fundamentals of MRP in graphene and the experimental Raman scattering works that have led to the observation of these phenomena in graphene and graphite.

Giant magneto-optical Raman effect in a layered transition metal compound

“…Furthermore, the fact that similar field-induced modulations are observed in both monolayer and bulk MoS 2 makes interface-related effects implausible. Recent studies of Raman spectra under magnetic fields in graphene revealed that Landau levels are superimposed on original energy bands, which can substantially tune the inter-or intraband transitions and hence cause magneto-phonon resonances (16)(17)(18). In the present work, thermal fluctuations are sufficiently strong to melt the Landau levels formed in the presence of magnetic fields up to 9 T at room temperature (Fig.…”

Impact of Many-Body Effects on Landau Levels in Graphene

“…For our experimental study, we use a current-annealed suspended graphene device offering high carrier mobility, low intrinsic strain, low charge carrier density inhomogeneity, and electron-electron interactions that are not screened by the environment. The device consists of a graphene flake on a Si/SiO 2 substrate which was exfoli- [35], giving rise to a carrier mobility exceeding 400 000 cm 2 /(Vs) and a charge inhomogeneity of less than n * ≈ 10 9 cm −2 (see Supplemental Material [34]), which allow the observation of magneto-phonon resonances below 4 T [22][23][24][25][26][27][28][29][30]. The Si back gate moreover permits the controlled tuning of the charge carrier density.…”

“…1a and b, respectively. We observe the resonant coupling of the Raman G mode phonon [22][23][24][25][26][27][28] to electronic transitions when its bare energy ε ph =hω G (B = 0 T, n el = 0 cm −2 ) ≡hω 0 matches the energy of a transition between the discrete LLs. Most prominently, this coupling results in a decrease of the phonon lifetime due to the excitation of electron-hole pairs, which results in an increased width Γ G of the Raman G peak at resonance.…”

Uniformity of the pseudomagnetic field in strained graphene

“…A particular experiment, in which the strength of a tunable pseudomagnetic field may be directly probed, is the shift of the magneto-phonon resonance (MPR) in Raman spectroscopy [35][36][37][38]. In order to exclude other effects, the pseudomagnetic field must be uniform within the laser spot size in the confocal Raman spectroscopy experiment, which is exactly what we showed and discussed in this paper.…”