Excitons in Solids

Abstract

The lectures here are concerned with excitations to the N-body system instead of the N±1-body system which is the normal result of an energy band calculation. Thus one has to investigate the two-body Green’s function formation and not stop with the single-particle function. In the first two lectures the Green’s function formalism is used to construct a set of Bethe-Salpeter equations from which the excitation energies and corresponding Bethe-Salpeter amplitudes are deduced [1]. The third part will describe one of the excited states that can be obtained using a laser beam on a semiconductor, namely the quantum mechanical fluid composed entirely of electrons and holes [2]. The exciton mechanism of superconductivity [3] and experimental evidence [4] are the subjects of the last lecture. This last part is still under study and the lecture will point out the current situation.