Anisotropic Correlated Electronic Structure of Colossal Thermopower Marcasite FeSb${}_2$

Abstract

Iron antimonide (FeSb${}_2$) is a mysterious material with peculiar colossal thermopower of about $-45$ mV/K at 10 K. However, a unified microscopic description of this phenomenon is far from being achieved. The understanding of the electronic structure in details is crucial in identifying the microscopic mechanism of FeSb${}_2$ thermopower. Combining angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations we find that the spectrum of FeSb${}_2$ consists of two bands near the Fermi energy: the nondispersive strongly renormalized $\hat{I}\pm$-band, and the hole-like ${\hat{I}}^2$-band that intersects the first one at $\hat{I}“$ and Y points of the Brillouin zone. Our study reveals the presence of sizable correlations, predominantly among electrons derived from Fe-3d states, and considerable anisotropy in the electronic structure of FeSb${}_2$. These key ingredients are of fundamental importance in the description of colossal thermopower in FeSb${}_2$.