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

TL;DR

This study investigates sharp absorption lines in EuTe and Pb$_{0.1}$Eu$_{0.9}$Te under high magnetic fields, revealing a strong d-f exchange interaction and localized excitations with implications for magnetic and optical properties.

Contribution

The paper reports the observation of a sharp, field-dependent absorption line in EuTe and PbEuTe, quantifies the d-f exchange interaction, and estimates the excitation radius, advancing understanding of magnetic semiconductors.

Findings

Sharp absorption line appears above 6 T in EuTe.

The absorption line shifts by 35 meV/T with magnetic field.

Excitation radius estimated to be around 10 Å.

Abstract

The optical absorption spectra in the region of the \fd transition energies of epitaxial layers of of EuTe and \PbEuTe, grown by molecular beam epitaxy, were studied using circularly polarized light, in the Faraday configuration. Under \sigmam 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 {\em d-f} exchange interaction of the excited electron and the \Euion spins in the lattice. The {\em d-f} exchange interaction energy was estimated to be $J_{df}S=0.15\pm 0.01$ eV. In \PbEuTe 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 \PbEuTe the characteristic radius of the excitation is estimated to be $\sim 10$\AA.