Quantum interference in exciton-Mn spin interactions in a CdTe semiconductor quantum dot

We show theoretically and experimentally the existence of a new quantum interference(QI) effect between the electron-hole interactions and the scattering by a single Mn impurity. Theoretical model, including electron-valence hole correlations, the short and long range exchange interaction of Mn ion with the heavy hole and with electron and anisotropy of the quantum dot, is compared with photoluminescence spectroscopy of CdTe dots with single magnetic ions. We show how design of the electronic levels of a quantum dot enable the design of an exciton, control of the quantum interference and hence engineering of light-Mn interaction.Comment: 11 pages, 4 figures, submitted to PR

Optical readout of charge and spin in a self-assembled quantum dot in a strong magnetic field

We present a theory and experiment demonstrating optical readout of charge and spin in a single InAs/GaAs self-assembled quantum dot. By applying a magnetic field we create the filling factor 2 quantum Hall singlet phase of the charged exciton. Increasing or decreasing the magnetic field leads to electronic spin-flip transitions and increasing spin polarization. The increasing total spin of electrons appears as a manifold of closely spaced emission lines, while spin flips appear as discontinuities of emission lines. The number of multiplets and discontinuities measures the number of carriers and their spin. We present a complete analysis of the emission spectrum of a single quantum dot with N=4 electrons and a single hole, calculated and measured in magnetic fields up to 23 Tesla.Comment: 9 pages, 3 figures, submitted to Europhysics Letter

A micro-magneto-Raman scattering study of graphene on a bulk graphite substrate

We report on a magneto-Raman scattering study of graphene flakes located on the surface of a bulk graphite substrate. By spatially mapping the Raman scattering response of the surface of bulk graphite with an applied magnetic field, we pinpoint specific locations which show the electronic excitation spectrum of graphene. We present the characteristic Raman scattering signatures of these specific locations. We show that such flakes can be superimposed with another flake and still exhibit a graphene-like excitation spectrum. Two different excitation laser energies (514.5 and 720 nm) are used to investigate the excitation wavelength dependence of the electronic Raman scattering signal.Comment: 6 pages, 5 figure

Multiple magneto-phonon resonances in graphene

Our low-temperature magneto-Raman scattering measurements performed on graphene-like locations on the surface of bulk graphite reveal a new series of magneto-phonon resonances involving both K-point and Gamma-point phonons. In particular, we observe for the first time the resonant splitting of three crossing excitation branches. We give a detailed theoretical analysis of these new resonances. Our results highlight the role of combined excitations and the importance of multi-phonon processes (from both K and Gamma points) for the relaxation of hot carriers in graphene.Comment: 20 pages, 11 figure

Circular dichroism of magneto-phonon resonance in doped graphene

Polarization resolved, Raman scattering response due to E$_{2g}$ phonon in monolayer graphene has been investigated in magnetic fields up to 29 T. The hybridization of the E$_{2g}$ phonon with only the fundamental inter Landau level excitation (involving the n=0 Landau level) is observed and only in one of the two configurations of the circularly crossed polarized excitation and scattered light. This polarization anisotropy of the magneto-phonon resonance is shown to be inherent to relatively strongly doped graphene samples, with carrier concentration typical for graphene deposited on SiO$_2$

Tuning the electron-phonon coupling in multilayer graphene with magnetic fields

Magneto Raman scattering study of the E$_{2g}$ optical phonons in multi-layer epitaxial graphene grown on a carbon face of SiC are presented. At 4.2K in magnetic field up to 33 T, we observe a series of well pronounced avoided crossings each time the optically active inter Landau level transition is tuned in resonance with the E$_{2g}$ phonon excitation (at 196 meV). The width of the phonon Raman scattering response also shows pronounced variations and is enhanced in conditions of resonance. The experimental results are well reproduced by a model that gives directly the strength of the electron-phonon interaction.Comment: 4 pages, 3 figure

Probing the band structure of quadri-layer graphene with magneto-phonon resonance

We show how the magneto-phonon resonance, particularly pronounced in sp2 carbon allotropes, can be used as a tool to probe the band structure of multilayer graphene specimens. Even when electronic excitations cannot be directly observed, their coupling to the E2g phonon leads to pronounced oscillations of the phonon feature observed through Raman scattering experiments with multiple periods and amplitudes detemined by the electronic excitation spectrum. Such experiment and analysis have been performed up to 28T on an exfoliated 4-layer graphene specimen deposited on SiO2, and the observed oscillations correspond to the specific AB stacked 4-layer graphene electronic excitation spectrum.Comment: 11 pages, 5 Fi