C. Benoit A La Guillaume

Coherent effects in pump–probe spectroscopy of excitons

Femtosecond measurements of coherent effects arising from exciton bleaching in bulk GaAs are reported. This phenomenon, which is characterized by spectral oscillatory structures, is general and appears whenever the temporal resolution is shorter than the material coherence time. This is shown to be a manifestation of the uncertainty relation in time-resolved spectroscopy.

Electron-hole drops in doped Ge

Abstract We investigate the radiative recombination of electron-hole drops in As and Sb doped Ge at about 2° K. Their luminescence spectrum exhibits a new zero phonon line whose study in As doped Ge suggests that this impurity gives rise to a virtual bound state in the electron Fermi sea.

Investigation of the radiative recombination of the excitonic molecule in Ge and Si

Abstract We give account of the first experimental observation of the excitonic molecule1) in Ge obtained from the investigation and the comparison of the luminescence spectra at 4.2° K and 1.7° K of pure Ge and Si crystals excited by a GaAs laser and by electron bombardment. These spectra generally show emission lines due to the annihilation of a free exciton (A) and of an excitonic molecule (B) with phonon emission in each case. For low excitations, the kinetics of these lines in both Ge and Si as a function of the excitation J is in good agreement with results previously reported in Si1), i.e.: A ∝ J and B ∝ J2. Moreover, for higher excitations, we observe the following dependences: in Si, A ∝ J1/2 and B ∝ J; in Ge, A ∝ J and B ∝ J. A theoretical study of the kinetics equations allows us to interpret these experimental data in both materials. Additional results relative to the influence of a uniaxial stress on the B line are also presented.

Volume and surface effects in the luminescence decay of electron-hole drops in Ge

Abstract Measurements of the luminescence time decay of electron-hole drops (EHD) in Ge are interpreted by taking into account the EHD volume recombination and the evaporation of free excitons (FE) at the EHD surface. From this study we get the EHD binding energy at T = 0 which is φ(0) = 15 ± 2 K. This result is consistent with the spectroscopic value of φ(0) if one takes into account the exchange splitting of FE.

Electron-hole drops in silicon

Abstract Direct experimental evidence for the existence of electron—hole drops in Si has been obtained from the current pulses produced when they dissociate in the high electric field of a p - n junction. From these results we also determine the drop radius, which is typically about 0.75 μ in this experiment.

Two-dimensional electrons-holes droplets in superlattices

Abstract We show that two dimensional electrons-holes droplets can exist in superlattice having a structural defect such as a layer with an additional atomic plane. This is a new and cleaner way to produce and study a plasma in two dimensions.

Resonant Raman scattering on low energy excited states of Fe2+ in Cd1−xFexSe

Abstract The spectrum of low energy excited states of Fe 2+ in Cd 1− xFex Se has been studied through Raman scattering. (1) The energy position of the first two excited states of symmetry A 2 and E have been determined as a function of the applied magnetic field ⊥ c and ∥| c up to 6 T; they are in very good agreement with a crystal field model. (2) Strong resonant effects on free and bound exciton states have been observed and explained. (3) Above the free exciton level, a cascade process involving mainly n (A 1 →A 2 ) excitations is studied. Backscattering on a face ⊥ c strongly favours crossed linear polarizations at each step of the cascade; a longitudinal magnetic field causes an analog of Hanle effect. Analysis of the data gives access to the polariton lifetime and its probability of inelastic scattering on Fe 2+ ions.

Variational model of bound magnetic Polaron and Raman spin flip line shape

Abstract A variational calculation of bound magnetic polaron in the adiabatic approximation is presented. Variation of size and energy is obtained as a function of temperature and magnetic field. New results about Raman spin flip line shape are predicted. They should be observable in the case of neutral acceptors in CdMnTe.

A Variational Model of Bound Magnetic Polaron

A variational calculation of bound magnetic polaron in the adiabatic approximation is presented. Variation of size and energy is obtained as a function of temperature and magnetic field. New results about Raman spin-flip line shape are predicted.

Electron-hole droplets size at equilibrium

Abstract A finite lifetime τ implies that the liquid phase can only form droplets of finite size. Introducing this finite τ in the usual nucleation theory, one can obtain analytical expressions for the electron-hole droplets size, number and exciton density at steady state, in the limit of large τ. This equilibrium size results, in fact, from a Maxwell construction on an appropriate chemical potential.