Excitonic Molecule in CuCl Crystal

Abstract

The electronic structure of a biexciton is discussed while taking into account the detailed band structure of CuCl. The fine structure of the excitonic molecule is clarified with the effective electron-hole exchange effect taken into account beyond the effective mass approximation. The electron-hole exchange interaction mixes the states of opposite parities with respect to the permutation of electrons and holes. Two trial envelope functions, symmetric and antisymmetric under the permutation of two electrons or two holes, were used in the numerical minimization of the ground state energy of the biexciton. The obtained binding energy of the biexciton, as well as, the ratio of the mixing of the trial envelope functions of opposite parities are presented.

Excitonic Molecule in Wurtzite Crystals

“…The present paper is a continuation of the work about biexcitons in CuCl crystal [4]. The structure of the valence band Bloch functions at k= O for wurtzite crystals differs from that for CuCl and the exciton exchange splitting in wurtzite CdS and ZnS is much greater than in CuCl.…”

“…We adopt Dirac &functions since the exchange interaction is assumed to be of short-range effective only in the volume Q of the unit cell. Equation (22) differs from that for CuCI by factors in front of electron-hole exchange terms d [4].…”

“…The electron-hole exchange interaction mixes two singlet states of opposite parity, therefore the ground state of the biexciton has no definite parity under separate permutation of the spatial and the spin coordinates of identical particles, two electrons and two holes, respectively. It was shown by Ungier [1,2] and Hayashi [3] in previous papers that in the simple band structure (without total angular momentum classification according to spin-orbit interaction) the ground state of the biexciton should be described by a two component, symmetric and antisymmetric, spatial envelope function, but not only the symmetric one.…”