Motion-enhanced magnetic moments of excitons in ZnSe

Abstract

Recent studies of excitons in wide quantum wells have shown that the magnetic properties are strongly affected as the excitons acquire kinetic energy. In the center of mass approximation, these motion-induced changes are ascribed to mixing between the 1S exciton ground state and the higher lying nP states. The origin of the mixing is due to the dispersion curves for the valence band not being of simple parabolic form. Detailed previous studies of excitons in CdTe have resulted in excellent agreement between experiment and the predic tions of this model. One consequence of the mixing is that the magnetic moment of the exciton is not simply the sum of the magnetic moments of the electron and hole, but contains motion-induced contributions, which can easily dominate the contributions from the individual charge carriers. To confirm the validity of the model, we have carried out detailed investigations of the magnetic properties of center of mass excitons in a second semiconductor, ZnSe, for which the magneto-optical properties of the individual charge carriers are completely different from those of CdTe. Excellent agreement is obtained between theory and experiment with a choice of the Luttinger parameter � 3 = 0.98, in close agreement with the value determined independently by two-photon magnetoabsorption experiments. The success of the model when applied to both materials provides strong evidence that motion-induced changes in magnetism are a universal feature in zinc-blende semiconductors.

Excitons in motion in II–VI semiconductors

“…To answer this question is not easy, since the usual method of investigating the structure of excitons is to use optical spectroscopy and, unfortunately, the small wavevector of photons means that only excitons with low values of their translational wavevectors can conventionally be studied. To overcome this difficulty, we have in a series of recent investigations [1][2][3][4][5][6] studied excitons in potential wells which are sufficiently wide for quantum confinement energies to be smaller than the exciton binding energy. In such quantum wells, the exciton can be described in the adiabatic or centre of mass (CoM) approximation [7,8], in which it is considered as a composite particle formed from the electron and the hole mutually orbiting each other.…”

Inversion of Zeeman splitting of exciton states in InGaAs quantum wells

“…6 is observed not only for QWs of varying widths but also for the excited exciton states in the QWs. We should note that monotonic dependence of the exciton g-factor on the effective wave vector has been observed previously only for the wide QWs [28][29][30]. …”

“…Similar technique has been used in several publications, see, e.g., Refs. [28,29,31,[37][38][39] resonantly using a Ti-sapphire or a He-Ne laser. Spectral resolution of the setup was sufficiently better than the typical width of features in the PL spectra.…”

“…Large variation of exciton g-factor for different quantum-confined exciton states has been experimentally observed in several heterostructures with wide QWs [27][28][29][30]. Effect of the quantum confinement of excitons in the QWs gives rise to quasiperiodic peculiarities in optical spectra corresponding to the quantization of the centerof-mass exciton motion [31,32].…”

“…This fact strongly simplifies theoretical analysis. The gfactor modification has been treated as the mixing of the relative motion of electron and hole in the exciton and the motion of the exciton as the whole [28,29].…”