Spin excitations of the correlated semiconductor FeSi probed by THz radiation

TL;DR

This study investigates the spin excitations in FeSi using THz radiation, revealing spin-polaronic states and their relation to magnetic properties and spin fluctuations in this correlated semiconductor.

Contribution

It provides direct optical evidence of spin-polaronic states in FeSi and links their formation to spin fluctuations and magnetic phase behavior.

Findings

Broad absorption peak at 32 cm^{-1} develops below 20 K

Spin excitations split by an exchange field of 34 T

Spin fluctuations influence the magnetic phase diagram

Abstract

By direct measurements of the complex optical conductivity $\sigma(\nu)$ of FeSi we have discovered a broad absorption peak centered at frequency $\nu_{0}(4.2 K) \approx 32 cm^{-1}$ that develops at temperatures below 20 K. This feature is caused by spin-polaronic states formed in the middle of the gap in the electronic density of states. We observe the spin excitations between the electronic levels split by the exchange field of $H_{e}=34\pm 6 T$. Spin fluctuations are identified as the main factor determining the formation of the spin polarons and the rich magnetic phase diagram of FeSi.