Correlated Electronic Structure Of Colossal Thermopower Fesb2: An Arpes And Ab Initio Study

Iron antimonide (FeSb2) with peculiar colossal thermopower of about -45 mV/K at 10 K is a mysterious material, and a unified microscopic description of this phenomenon is far from being achieved. Combining angle-resolved photoemission spectroscopy (ARPES) and ab initio calculations, we find that the intricate electronic structure of FeSb2 consists of two bands near the Fermi energy: the weakly dispersing strongly renormalized a band and the holelike beta band that intersect at Gamma and Y points of the Brillouin zone. In addition, we found the surface state originated from the bulk beta band. While both bulk bands upshift towards the Fermi level upon raising of the temperature, the weakly dispersing surface states vanish above 100 K. The structural distortions and/or a mixture of the localized low-spin state with the delocalized high-spin state populated with temperature could be responsible for this temperature dependence. Our study reveals that the sizable renormalization of the nondispersing a band and the hybridization with the holelike beta band cause the local increase of the density of states, consequently raising the colossal thermopower in FeSb2.