Luminescence properties of magnetic polarons in EuTe: Theoretical description and experiments in magnetic fields up to 28 T

The recent discovery of a polaron-associated zero phonon line in the band-edge photoluminescence of high optical quality EuTe crystals opens up the prospect of answering long-standing questions about the polaron internal structure, thermal stability, and generation efficiency. Here, a Schrodinger eq...

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Bibliographic Details
Published in:Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2014-10, Vol.90 (16), Article 165202
Main Authors: Henriques, A. B., Moraes, F. C. D., Galgano, G. D., Meaney, A. J., Christianen, P. C. M., Maan, J. C., Abramof, E., Rappl, P. H. O.
Format: Article
Language:English
Subjects:
Binding energy
Computing time
Condensed matter
Magnetic fields
Phonons
Photoluminescence
Polarons
Schroedinger equation
Thermal stability
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Summary:The recent discovery of a polaron-associated zero phonon line in the band-edge photoluminescence of high optical quality EuTe crystals opens up the prospect of answering long-standing questions about the polaron internal structure, thermal stability, and generation efficiency. Here, a Schrodinger equation for the polaron was formulated and resolved by using both variational and self-consistent methods. The theory is in good agreement with measurements of the zero phonon line as a function of magnetic field and temperature, and it could be applied to other polaronic systems. It is deduced that, in EuTe, at 0 K, a polaron carries a magnetic moment of 610 mu B, and its binding energy is 27 meV. However, this binding energy does not carry the usual meaning of thermal stability, because it decreases drastically when the sample is warmed up. For instance, at T = 100 K, the binding energy is already reduced to only 6 meV. The thermal destruction of a polaron is brought about by thermal fluctuations of the spin lattice that suppress the electron's self-energy. Photoluminescence excitation spectra of EuTe demonstrate that the photogeneration of polarons becomes increasingly inefficient when the energy of the pumping photon is increased above the band gap.
ISSN:1098-0121
1550-235X
DOI:10.1103/PhysRevB.90.165202