Sharp lines in the absorption edge of EuTe and Pb$_{0.1}$Eu$_{0.9}$Te in high magnetic fields

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