Double photo-ionization of two-electron impurity centers in quasi-zero-dimensional structures in an external magnetic field

Background. Impurity atoms with two electrons are the simplest systems in which double ionization by a single photon is possible. In this case, influence of an external magnetic field on the double photoionization spectra can lead to new effects associated with the optical absorption dichroism. The aim of this work is to take into account influence of an external magnetic field on the first ionization potential of a two-electron impurity center in a quantum dot, as well as theoretical study of the double photoionization features for two-electron impurity centers in a quasi-zero-dimensional structure in an external magnetic field. Materials and methods. Influence of an external magnetic field has been taken into account in framework of the perturbation theory. Calculation of the binding energy and the first ionization potential of a two-electron atom has been carried out by a variational method, where the second ionization potential has been taken as an empirical parameter. Expressions for the light impurity absorption coefficients are obtained in the dipole approximation taking into account the quantum dots radius dispersion. Results. An analytical expression for the first ionization potential of a two-electron impurity center under an external magnetic field is obtained by a variational method within the semi-empirical model framework. Coefficients of the light impurity absorption have been calculated in the dipole approximation, in cases of the light longitudinal and transverse polarization with respect to the magnetic field direction, during photoionization of a two-electron impurity by a single photon. Conclusions. It is shown that magnetic field has a stabilizing effect on two-electron impurity centers in a semiconductor quantum dot. Dichroism of the optical absorption has been appeared in the absorption band edge shift and in appearance of the additional peaks in the absorption spectral curve in case of the light polarization transverse to the external magnetic field direction ($\vec{e}\bot \vec{B}$) as also in disappearance of the double-hump profile in case of the longitudinal light polarization ($\vec{e} \| \vec{B}$).