1,721,217 research outputs found
Polaronic Effects on Exciton States with Different Angular Momenta
No full textIt is shown that exciton states with various total angular momenta (L = 0, 1, 2, 3) are differently affected by the interaction with LO phonons in polar materials. In particular, a dependence is found of the binding energy on the value of L not expected on the basis of the statically screened electron-hole attraction. Calculations for CuCl and other ionic compounds show that the lowest L = 1 state (n = 2) is less bound than the corresponding exciton state with static screening. This effect, which is opposite to the polaronic effect on the ground state, is still present for L ≧ 2 but it decreases with increasing L. The computed binding energies of 2p excitons compare favorably with the available experimental data. The method is also applied to the calculation of bipolaron binding energies
POLARITONS IN ANISOTROPIC SEMICONDUCTORS
No full textWe show how to compute the optical properties (reflection and absorption) of anisotropic semiconductors in the exciton energy region, taking into account polariton and electron-hole coherence effects. The method is applied to a GaAs/Ga1-xAlxAs superlattice, and the modifications in the optical properties with respect to GaAs are related to the anisotropy
Polaritonic effects in superlattices
No full textWe present a method to compute the optical functions of superlattices in the excitonic energy region including the effect of the coherence between the electron-hole pair and the electromagnetic field. The electron-hole screened Coulomb potential is adopted and the valence-band structure is taken into account in the cylindrical approximation, thus separating light- and heavy-hole motions. The: calculated optical functions have poles in correspondence to the polariton eigenvalues for a multiplicity of excitonic states. We also calculate the amplitudes of higher polariton branches and the line shapes of the optical functions. Numerical examples appropriate to GaAs/Ga1-xAlxAs superlattices are given and the effect of coherence is displayed in the line shape of the excitation spectrum
BULK EXCITON POLARITONS IN GAAS MICROCAVITIES
No full textThe optical properties of excitons in thin layers are significantly different from those in bulk crystals. In particular, we study the case of a bulk material of thickness comparable with the wavelength of the excitonic transition confined on one or on both sides by appropriate Bragg reflectors. If-the cavity resonance quasimode is carefully tuned on the excitonic transition, strong exciton-photon coupling takes place and produces a Rabi-like splitting as large as that observed in quantum-well-implanted microcavities and comparable optical absorption. In addition, the polaritonic spatial dispersion and the quantization of the exciton center-of-mass motion introduce remarkable fine structures which are absent in the quantum-well case. We demonstrate the above effects from a spectroscopic analysis of GaAs cavities and compare them with those displayed by quantum-well-implanted microcavities
Optical response of a GaAs microcavity near the exciton resonance
No full textOptical response of semiconductor microcavities is particularly interesting near the exciton resonance because of the strong mode coupling between exciton and photons. In the simplest case where the cavity core is made of a bulk material, bounded by appropriate Bragg mirrors, a large Rabi-like mode splitting is observed under resonance condition (the radiation mode tuned on the excitonic transition of the bulk). This is comparable to the recent findings of quantum well embedded microcavities. In addition, a satellite structure is evidenced which can be attributed to the nonlocal susceptibility of the cavity core and the resulting center-of-mass quantization of the exciton motion. Finally, we describe a theoretical calculation which allows a close comparison with the experimental data
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