Article

# Excitonic Molecule. III. Electronic Structure

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## Abstract

The electronic structure of excitonic molecule is discussed by taking into account the detailed band structure of CuCl, CuBr, CdS, CdSe and ZnO. Especially the excitonic molecule in CuBr is interesting due to the less simple valence band. The fine structure of the excitonic molecule is clarified under the effective electron-hole exchange effect and the interband hole-hole scattering beyond the effective mass approximation.

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... Similar results can be observed in Fig. 6(b,d) for Au and Ag NCs, respectively. A fingerprint of biexciton emission can be obtained by using right (σ+) and left (σ−) circularly polarized beam laser excitation 55,61,64 . However, when using circularly polarized light, the samples studied in this work did not exhibit any significant change in spectral PL emission, as shown in Fig. 7. Then the superlinear behavior cannot been unambigously adscribed to biexciton emissions, and instead the carrier dynamic is probably dominated by uncorrelated electrons and holes pairs. ...
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Bose-condensation of the excitonic molecule gas is expected from the large quantum effect and the boson character of the particles. It is discussed how to accumulate the Bose-condensed system of excitonic molecules directly and how to observe evidence of the Bose-condensation of excitonic molecules in the luminescence spectrum.
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Specific features of two-photon nutation in a system of coherent biexcitons in CuCl-type semiconductors are studied. It is shown that, depending on the parameters of the system, nutation represents a process of periodic conversion of photon pairs into biexcitons and vice versa. The possibility of phase control of optical nutation is predicted.
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Article
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Article
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Article
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Article
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Article
The excitonic polariton dispersion in wide k-space for k∥[111] is measured through the two-photon-resonant Raman scattering with the use of the double beam excitation technique. The k-linear effect, the heavy and light masses and the polariton effect of the Z1,2 exciton are clarified.
Article
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Article
The behavior of the semiconductor dielectric susceptibility under the action of a strong laser pulse in the range of the luminescent M band and two-photon probe of a biexciton level is investigated. It is shown that the pronounced Autler-Towns effect occurs at the two-photon transition. The position of the absorption peaks is essentially determined by the amplitude and frequency of the pump field.
Article
We report on symmetry-based calculations of the spin structure of excitons and biexcitons in quantum wells. Depending on the point-group symmetry of the material and the growth directions of the quantum wells, we derive Hamiltonians appropriate for the description of excitons and biexcitons. We show possible paths of coherent spin-flip processes of a particle and their consequences for experimental observations.
Article
The theory of the electronic excitations in a highly excited semiconductor is presented. The relaxation processes, the formation of excitons and excitonic molecules, the interaction among the various forms of electronic excitations, as well as their optical and thermodynamical properties are analyzed. At low temperatures one expects condensations into the quantum statistically degenerate phases of the excitonic molecules and of the electron-hole plasma. The physical properties of these low temperature phases are investigated. Possibilities and previous attempts to observe the Bose-Einstein condensation in excitonic systems are discussed critically. The experimental observations of the electron-hole liquid phase transition are reviewed.
Article
The binding energy of the excitonic molecule, a complex consisting of two electrons and two positive holes, is calculated as a function of the mass ratio me/mh by avariational method. It is shown that the excitonic molecule is stable for any value of the mass ratio. For me{=}mh, the binding energy is estimated to be 0.00684 mee4/\varepsilon{0}2\hslash2. Some results about the wave function are also presented.
Article
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Article
The binding energy of the excitonic molecule is calculated as a function of the mass ratio . It is found that the excitonic molecule should be stable for any value of the mass ratio.ZusammenfassungDie Bindungsenergie des Exzitonenmoleküls wird als Funktion vom Verhältnis der Elektronenmasse zur Lochmasse berechnet. Es zeigt sich, dass das Exzitonenmolekül füf jeden Wert vom Masseverhältnis stabil sein sollte.
Article
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Article
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Article
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Article
In this paper the energetics of the formation of electron-hole metallic liquids in semiconductors is examined. The ground-state energies of electron-hole metals are calculated using Hubbard's approximate treatment of the electron gas for the following cases: (a) germanium, (b) germanium with a large (111) strain, (c) silicon, and (d) GaAs. The simple case of a single isotropic maximum for the valence band and a single minimum for the conduction band is also treated. It is shown that for both Si and Ge, the binding energy of the metallic state relative to free excitons is 5.7 and 1.7 meV, respectively. These values and the values of the equilibrium density are in good agreement with experiment. In the isotropic model the metallic state is not bound while for GaAs and strained Ge the metallic-state energy per electron is essentially equal to that for a gas of free excitons. The low-density limit of the isotropic band model is examined and the ground state for this system is predicted to be a dilute gas of molecules. It is argued that the forces between molecules are repulsive and will cause this state to break up at relatively low densities. If the density is increased, the system will undergo a first-order transition to the metallic state. The relevance of these calculations to the metal-insulator transition problem is discussed. It is pointed out that the fact that anisotropic and many-valleyed bands favor the metallic state means that the metal-insulator transition must ultimately be first order.
Article
The states of the biexciton molecule are related to the band structure of the crystal and effects due to spin–orbit interaction and to electron–hole exchange are taken into account. The cases of CuCl and CdS are explicitly studied and the possible bound states are given. Optical luminescence decay processes and two-photon excitation processes are discussed and related selection rules are given. In the case of CdS all decay processes are shown to produce polarized photons. Experimental results are analyzed and are compared with theoretical calculations of the biexciton ground state energy.Les états de la molécule biexcitonique sont reliés à la structure de bande du cristal en tenant compte des effets dǔs à l'interaction spin–orbite et à l'échange électron-trou. Les cas de CuCl et de CdS sont étudiés en détail et on donne les états liés possibles. On discute les processus de recombinaison luminescente et d'excitation optique à deux photons, avec leurs règles de sélection. Dans le cas du CdS, on montre que toutes les recombinaisons radiatives produisent des photons polarisés. Les résultats expérimentaux sont discutés et comparés aux calculs théoriques de l'énergie de l'état fondamental du biexciton.
Article
The interaction of excitons in Ge and Si was recently investigated in a large number of experimental studies. All these results may be explained if one assumes that after reaching the threshold temperature and excitation level the condensed phase of non-equilibrium carriers appears. There is a direct confirmation of the existence of collective substances, which consist of a large number of non-equilibrium carriers.
Article
The exciton spectra of CuCl have been investigated in the presence of high transient magnetic fields up to 180 kG.The Zeeman splitting of the broad orthoexciton line ν1f (25,865 cm−1 at 4.2°K) is unresolved because of a too small effective g factor (g = 0.9). The paraexciton line ν1 (25,814 cm−1 at 4.2°K) is detected in magnetic field. The mixing of the ortho and paraexciton states T15 and T2 in magnetic fields is discussed.The bound exciton line ν2 (25,654 cm−1 at 4.2°K) splits in four components in magnetic field, both in absorption and in emission. The sharp line ν21 (25,665 cm−1 at 4.2°K) behaves similarly. The g factors of both the ground and excited states are obtained from the temperature variation between 1.9° and 20°K of the intensities of the absorption lines. This allows us to ascribe the above lines to excitonneutral acceptor complexes.