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S. Khmelevskyi:
"Correlated excited states in the narrow band gap semiconductor FeSi and antiferromagnetic screening of local spin moments";
Physical Review B, 98 (2018), S. 125201 - 125208.

The physical properties of the semiconductor FeSi with very narrow band gap, anomalous behavior of
the magnetic susceptibility and metal-insulator transition at elevated temperatures attract great interest due to the
still controversial theoretical understanding of their origin. On one side the purely bandlike mechanism of the
gap formation in FeSi at low temperature is well established; on the other side a number of experiments and their
theoretical interpretation suggest a rich physics of strong correlations at finite temperature. In this work we use an
ab initio scheme based on the random-phase approximation and local spin-density approximation (RPA@LSDA)
to reveal the role of the electron correlation effects in FeSi extending it by applying a fixed spin moment constraint.
In the parameter-free framework we show that correlation effects essentially alter the one-electron LSDA
results leading to the formation of an additional state with finite magnetic moment on Fe, whose energy is almost
degenerate with the nonmagnetic ground state. This explains the results of high-field experiments, which found
a first-order metamagnetic phase transition into a metallic ferromagnetic state. Our results suggest a strongly
correlated nature of the low-energy excitations in FeSi. From our supercells calculations we reveal that these
excitations are local and exhibit a Kondo-like behavior since a strong antiferromagnetic screening is present.