Publications de Daniel Oberli | EPFL Graph Search

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Quantum dots (QDs) of high symmetry (e.g., C3v) have degenerate bright exciton states, unlike QDs of C2v symmetry, making them intrinsically suitable for the generation of entangled photon pairs. Deviations from C3v symmetry are detected in real QDs by pol ...

Periodic photonic structures have attracted much interest due to their versatility for controlling light propagation. The dispersion of photon modes in photonic lattices exhibits an energy band structure analo-gous to the electronic one in crystals. An imp ...

Using femtosecond pump-probe spectroscopy, we identify excitation-induced dephasing as a major mechanism responsible for the breakdown of the strong coupling between excitons and photons in a semiconductor microcavity. The effects of dephasing are observed ...

We demonstrate the existence of a cross Feshbach resonance by strongly driving a lower polariton mode and by monitoring in time the transmission of a short optical pulse at the energy of the upper polariton mode in a semiconductor microcavity. From the sig ...

Negatively and positively charged excitons are identified in the spatially resolved photoluminescence spectra of quantum wires. We demonstrate that charged excitons are weakly localized in disordered quantum wires. As a consequence, the enhancement of the ...

High symmetry epitaxial quantum dots (QDs) with three or more symmetry planes provide a very promising route for the generation of entangled photons for quantum information applications. The great challenge to fabricate nanoscopic high symmetry QDs is furt ...

We have studied the luminescence of narrow quantum wires at photoexcitation densities of up to similar to 3 x 10(6) cm(-1). We show that even at these densities, which are well above the expected Mott density of 8 x 10(5) cm(-1), excitonic recombination dominates over other recombination channels in stark contrast with the behavior of quantum wells and bulk structures at equivalent densities. As we observe no significant shift in the peak energy with density, an upper limit to the band gap renormalization c

We report on a highly efficient growth of graphene using dehydrogenation of acetylene by an oxidative reaction with carbon dioxide. In few seconds, large-area of copper foil used as catalyst of the reaction is fully covered with graphene. The yield of the ...

We review the research done in recent years in our group on the effects of nanostructure symmetry, and outline its relevance both for nanostructure physics and for computations of their electronic and optical properties. The exemples of C3v and C2v quantum ...

We present an experimental study and develop a group theoretical analysis of the Zeeman effect on excitons in pyramidal semiconductor quantum dots possessing the symmetries of the C3v point group. The magnetic field dependence of the emission pattern origi ...

We report on the direct absorption measurement of the polarization selection rules in a V-groove QWR waveguide. Attenuation measurements in a 1 mm long waveguide were performed from 10 K up to room temperature. These measurements yielded the QWR DOS selection rules for lateral (TE) and vertical (TM) confinement directions. 1D heavy-hole like e(n)h(n) subband features were observed in the TE absorption spectra. Effective mass and 4 x 4 k . p models have been used to evaluate the band to band absorption. For

We investigate polariton-polariton interactions in a semiconductor microcavity through two-dimensional Fourier transform (2DFT) spectroscopy. We observe, in addition to the lower-lower and the upper-upper polariton self-interactions, a lower-upper cross in ...

The optical properties of high-quality V-groove GaAs/AlxGa1-xAs quantum wires have been investigated using low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) techniques. We systematically study the evolution of PL and PLE spectra as a function of the wire size. This comparison allows us to analyze the modification of one-dimensional subbands with decreasing win thickness. We clarify the influence of surface corrugation and localization effects on PL and PLE spectra and we observe

The electronic states in the conduction and valence bands of quantum wires are studied by means of the effective mass hamiltonian and the Luttinger hamiltonian. The band mixing effects due to the wire geometry are fully taken into account by an accurate finite element solution of the resulting Schrodinger equations. The quantum wire profiles measured by transmission electron microscopy are used. The comparison of theoretical results with photoluminescence excitation spectra of various nanostructures yields

The role of the confinement potential symmetry on the electronic and optical properties of quantum mires is systematically studied. In a wide class of quantum mires with mirror symmetry we evidence a new set of optical transitions resulting both from band mixing and Ct, symmetry breaking at zone center. Several kinds of quasi-one-dimensional excitons are predicted as well as their specific dipole coupling. Even for ultralow C-1 symmetry we find independent excitons with distinct polarization selection rules

We report on the observation of multiple polariton modes, originating from an electronic coupling between quantum wells inside a planar microcavity. A series of excitonic transitions are measured for a bare quantum well stack and are precisely identified t ...

We report on time-resolved and steady-state photoluminescence studies of GaAs/AlGaAs V-groove quantum wire structures. Steady-state photoluminescence experiments are performed in the temperature range from 8 to 200 It. We evaluate the relation between photoluminescence excitation and absorption and determine experimentally the optical density in order to analyze the temperature dependence of the photoluminescence spectra. We find that, at a temperature above 60 K, the photoexcited electron-hole pairs reach

We demonstrate the occurrence of spatial multistability using laterally confined microcavity exciton-polaritons. By coherently exciting with a blue detuned laser a series of confined polariton modes, we investigate the effects of multistability on the tran ...

We report on the observation of negatively- and positively-charged excitons in the photoluminescence spectra of V-groove quantum wires. The. charged exciton binding energy increases with the strength of the quantum confinement. We demonstrate that fluctuat ...

We investigate the embedded interfaces of GaAs/AlGaAs quantum wells grown by metal organic vapor phase epitaxy on slightly (< 1 degrees)-misoriented (001) substrates using selective etching and atomic force microscopy. Depending on the substrate misorienta ...

Daniel Oberli

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Fine structure of exciton complexes in high-symmetry quantum dots: Effects of symmetry breaking and symmetry elevation

Localized Photon Lasing in a Polaritonic Lattice Landscape

Dephasing effects on coherent exciton-polaritons and the breakdown of the strong coupling regime

Polaritonic Cross Feshbach Resonance

Enhancement of the binding energy of charged excitons in disordered quantum wires

Spectral signatures of high-symmetry quantum dots and effects of symmetry breaking

Coulomb correlation and band gap renormalization at high carrier densities in quantum wires

Functionalized graphene grown by oxidative dehydrogenation chemistry

Nanostructure Symmetry: Relevance for Physics and Computing

Intertwining of Zeeman and Coulomb interactions on excitons in highly symmetric semiconductor quantum dots

Direct observation of new transitions in the absorption spectra of a V-groove quantum wire waveguide

Two-dimensional Fourier transform spectroscopy of exciton-polaritons and their interactions

Effect of lateral confinement on valence-band mixing and polarization anisotropy in quantum wires

Band-mixing and coupling in single and double quantum wire structures

The impact of low symmetry on the electronic and optical properties of quantum wires

Multiple polariton modes originating from the coupling of quantum wells in planar microcavity

Photoluminescence study of V-groove quantum wires: The influence of disorder on the optical spectra and the carrier thermalization

Spatial multistability induced by cross interactions of confined polariton modes

Charged excitons in modulation-doped quantum wires

Correlation between optical properties and interfaces morphology of GaAs/AlGaAs quantum wells