Excitons and Plasmons: Collective Excitations in Semiconductors
For a simple model consisting of a nondegenerate valence and conduction band, the spectrum of elementary excitations is calculated taking into account the Coulomb interaction between valence and conduction electrons. It contains, as collective excitations, excitons below and a valence plasmon above the continuum of single electron-hole pair excitations.
The importance of the so-called exchange interaction is pointed out as being responsible for the longitudinal-transverse-splitting of the excitonic solutions and for the existence of the plasmon. Using the equation of motion method not only the energy but also the wavefunction of the plasmonic solution is obtained.
Finally, the dielectric function of the model is derived and the exciton-polariton is discussed.
KeywordsDielectric Function Interband Transition Collective Excitation Elementary Excitation Polariton Branch
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