W. Nolting et al., MAGNETIC POLARON IN FERROMAGNETIC AND ANTIFERROMAGNETIC SEMICONDUCTORS, Physical review. B, Condensed matter, 54(20), 1996, pp. 14455-14466
The temperature-dependent quasiparticle spectrum of a single conductio
n electron exchange coupled to a ferro- or antiferromagnetically order
ed localized-spin system (e.g., EuO, EuTe) is calculated by a moment-c
onserving Green function technique. In the weak coupling regime the ex
change interaction leads to an almost rigid shift of the Bloch dispers
ion. The induced spin splitting of the conduction band states is propo
rtional to the magnetization [S-Z] of the localized-spin system. As so
on as the coupling constant exceeds a critical value an additional spl
itting of the quasiparticle dispersion for each spin projection sets i
n due to different elementary excitations. One is based on a repeated
emission and reabsorption of a magnon by the conduction electron resul
ting in an effective attraction between magnon and electron. This give
s rise to a polaronlike quasiparticle (''magnetic polaron''). Another
excitation is due to a direct magnon emission or absorption by the ele
ctron thereby flipping its own spin (''scattering states''). For the e
xactly calculable special case of a ferromagnetically saturated spin s
ystem (T=0 K), the magnetic polaron appears only in the down arrow spe
ctrum and turns out to be a stable quasiparticle. For finite temperatu
res it gets a finite Lifetime. In antiferromagnetic systems each quasi
particle band exhibits an additional ''Slater splitting'' due to the r
educed magnetic Brillouin zone. The predicted strong correlation effec
ts in the excitation spectrum require unconventional interpretations o
f respective inverse photoemission experiments.