Interband energy transfer

Elliott-Yafet time relaxation behavior observed in virtually any metal. These effects can be described in terms of an interband energy transfer process mediated by the anomanously broadened E2g phonon [20]. 

The most fundamental transition that can take place is the transfer of an electron from the valence band to the conduction band. This creates a mobile electron and a mobile hole, both of which can often be treated as defects. Transitions of this type, and the reverse, when an electron in the conduction band drops to the valence band, eliminating a hole in the process and liberating energy, are called interband transitions. Apart from the electrons and holes themselves, interband transitions do not involve defects. All other transitions do. 

With small dimensions of the forbidden band the electron transfer of the impurity or of the main substance to the conduction band may take place. The most important luminescent minerals of this kind are ZnS and silver bromides. With the interband spacing of 3-4 eV a UV irradiation with a wavelength of less than 300 nm has enough energy to detach electrons and transfer them from the filled valence band into an empty conduction... 

The main scheme is shown in Fig. 17. The photogenerated electron hole pairs transfer to the soliton-antisoliton pairs in 10 13s. Two kinks appeared in the polymer structure, which separates the degenerated regions. Due to the degeneration, two charged solitons may move without energy dissipation in the electric field and cause the photoconductivity. The size of the soliton was defined as 15 monomer links with the mass equal to the mass of the free electron. In the scheme in Fig. 17, the localized electron levels in the forbidden gap correspond to the free ( + ) and twice occupied ( — ) solitons. The theory shows the suppression of the interband transitions in the presence of the soliton. For cis-(CH)n the degeneration is absent, the soliton cannot be formed and photoconductivity practically does not exist. 

Pair transfer interaction between the states of an electron system components can cause the gauge symmetry breaking realized in superconductivity. This circumstance forms the basis of the two-band model of superconductivity known already during a considerable time [1,2], The basic advantage of such approaches consists in the possibility to reach pairing by a repulsive interband interaction which operates in a considerable volume of the momentum space. An electronic energy scale is... 

The photo-induced spectra in the superconducting state and the ESR data in the normal state can be understood in terms of an interband scattering process. When talking about interband scattering, one may think in terms of transfer of quasiparticles or, alternatively, transfer of the energy of quasiparticles. The latter process can be viewed as a process in which excited quasiparticles in one band relax emitting phonons which can excite quasiparticles in the other band. There is no transfer of the actual quasiparticles but rather of their energy. 

Fig. 9.18 Evolution of the optical absorption of a one-dimensional chain as the binding energy of an exciton located below the conduction band increases. Initially (at the rear) no exciton occurs and the absorption is due to the interband transition, shown shaded. This decreases as the transition moment is transferred to the exciton, shown by the solid vertical line.

In polydiacetylene single crystals electroreflectance revealed the weak interband transitions, hidden under the stronger vibronic excitons (2). The data yield the band gap, the exciton binding energy and derive in case of DCHD a surprisingly small effective mass m = 0.05 m (3). Charge transfer excitons too respond to an external... 

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