arXiv subjects

C. Faugeras

Publications and source records attributed to C. Faugeras.

79 records · Page 5Linked to original sources

arXiv2008

High-Energy Limit of Massless Dirac Fermions in Multilayer Graphene using Magneto-Optical Transmission Spectroscopy

We have investigated the absorption spectrum of multilayer graphene in high magnetic fields. The low energy part of the spectrum of electrons in graphene is well described by the relativistic Dirac equation with a linear dispersion relation. However, at higher energies (>500 meV) a deviation from the ideal behavior of Dirac particles is observed. At an energy of 1.25 eV, the deviation from linearity is 40 meV. This result is in good agreement with the theoretical model, which includes trigonal warping of the Fermi surface and higher-order band corrections. Polarization-resolved measurements show no observable electron-hole asymmetry.

cond-mat.mes-hall↗

arXiv2008

Dirac fermions at the H point of graphite: Magneto-transmission studies

We report on far infrared magneto-transmission measurements on a thin graphite sample prepared by exfoliation of highly oriented pyrolytic graphite. In magnetic field, absorption lines exhibiting a blue-shift proportional to sqrtB are observed. This is a fingerprint for massless Dirac holes at the H point in bulk graphite. The Fermi velocity is found to be c*=1.02x10^6 m/s and the pseudogap at the H point is estimated to be below 10 meV. Although the holes behave to a first approximation as a strictly 2D gas of Dirac fermions, the full 3D band structure has to be taken into account to explain all the observed spectral features.

cond-mat.mes-hall↗

arXiv2007

Few layer graphene on SiC, pyrolitic graphite and graphene: a Raman scattering study

The results of micro-Raman scattering measurements performed on three different ``graphitic'' materials: micro-structured disks of highly oriented pyrolytic graphite, graphene multi-layers thermally decomposed from carbon terminated surface of 4H-SiC and an exfoliated graphene monolayer are presented. Despite its multi-layer character, most parts of the surface of the graphitized SiC substrates shows a single-component, Lorentzian shape, double resonance Raman feature in striking similarity to the case of a single graphene monolayer. Our observation suggests a very weak electronic coupling between graphitic layers on the SiC surface, which therefore can be considered to be graphene multi-layers with a simple (Dirac-like) band structure.

cond-mat.mes-hall↗

arXiv2006

Radiative quantum efficiency in an InAs/AlSb intersubband transition

The quantum efficiency of an electroluminescent intersubband emitter based on InAs/AlSb has been measured as a function of the magnetic field up to 20T. Two series of oscillations periodic in 1/B are observed, corresponding to the elastic and inelastic scattering of electrons of the upper state of the radiative transitions. Experimental results are accurately reproduced by a calculation of the excited state lifetime as a function of the applied magnetic field. The interpretation of these data gives an exact measure of the relative weight of the scattering mechanisms and allows the extraction of material parameters such as the energy dependent electron effective mass and the optical phonon energy.

cond-mat.mes-hall↗

arXiv2006

Magnetophonon resonance in high density, high mobility quantum well systems

We have investigated the magnetophonon resonance (MPR) effect in a series of single GaAs quantum well samples which are symmetrically modulation doped in the adjacent short period AlAs/GaAs superlattices. Two distinct MPR series are observed originating from the $Γ$ and X electrons interacting with the GaAs and AlAs longitudinal optic (LO) phonons respectively. This confirms unequivocally the presence of X electrons in the AlAs quantum well of the superlattice previously invoked to explain the high electron mobility in these structures (Friedland et al. Phys. Rev. Lett. 77,4616 (1996).

cond-mat.mes-hall↗

arXiv2006

Frohlich mass in GaAs-based structures

The Frohlich interaction is one of the main electron-phonon intrinsic interactions in polar materials originating from the coupling of one itinerant electron with the macroscopic electric field generated by any longitudinal optical (LO) phonon. Infra-red magneto-absorption measurements of doped GaAs quantum wells structures have been carried out in order to test the concept of Frohlich interaction and polaron mass in such systems. These new experimental results lead to question the validity of this concept in a real system.

cond-mat.mes-hall↗

arXiv2006

Electron-phonon coupling in the two phonon mode ternary alloy $Al_{0.25}In_{0.75}As/Ga_{0.25}In_{0.75}As$ quantum well

We have investigated the infrared transmission of a two-dimensional (2DEG) electron gas confined in a $Al_{0.25}In_{0.75}As/Ga_{0.25}In_{0.75}As$ single quantum well in order to study the electron optical phonon interaction in a two phonon mode system. Infrared transmission experiments have been performed in both the perpendicular Faraday (PF) and tilted Faraday (TF) configurations for which the growth axis of the sample is tilted with respect to the incident light propagation direction and to the magnetic field direction. The experimental results lead to question the validity of the concept of polaron mass in a real material.

cond-mat.mes-hall↗