Giant tunability of exciton photoluminescence emission in antiferromagnetic EuTe

The photoluminescence properties of antiferromagnetic EuTe layers grown by molecular-beam epitaxy are reported. At low temperatures, two excitonic photoluminescence peaks are observed at 1.92 and 1.88 eV with a full width at half maximum of about 10 meV. With applied magnetic field, these excitonic transitions shift linearly by -34 meV/T to smaller transition energies with a total shift of more than 240 meV at 7.2 T. This is the largest tuning range observed in any semiconductor. The observed magnetic field and temperature dependence of the luminescence lines is explained by the formation of large magnetic polarons due to exchange interactions between the d-like electrons in the conduction band and localized $4f$ spins.