Sharp lines in the absorption edge of EuTe and Pb0.1Eu0.9Te in high magnetic fields

The optical absorption spectra in the region of the transition energies of epitaxial layers of of EuTe and , grown by molecular beam epitaxy, were studied using circularly polarized light, in the Faraday configuration. Under polarization a sharp symmetric absorption line (full width at half-maximum 0.041 eV) emerges at the low energy side of the band-edge absorption, for magnetic fields intensities greater than 6 T. The absorption line shows a huge red shift (35 meV/T) with increasing magnetic fields. The peak position of the absorption line as a function of magnetic field is dominated by the { d-f} exchange interaction of the excited electron and the spins in the lattice. The { d-f} exchange interaction energy was estimated to be JdfS=0.15± 0.01 eV. In the same absorption line is detected, but it is broader, due to alloy disorder, indicating that the excitation is localized within a finite radius. From a comparison of the absorption spectra in EuTe and the characteristic radius of the excitation is estimated to be ~ 10.