Electronic band structures of FeGe driven by thermal-fluctuation

Fluctuation-induced first-order transitions have been discussed in superconductors, liquid crystals, and magnetic materials. Recently, chiral magnet, such as FeGe, were found thermal-fluctuation first-order transition above T_C, which forms fluctuation disordered state (FD) of magnetic structure. Here, we unveil the Fermi surface symmetry and the evolution of electronic structures across the transition temperature of helimagnetic-paramagnetic phase at T_C~274K by means of angle-resolved photoemission spectroscopy (ARPES) on high-quality FeGe(111) films epitaxially grown on Si(111) substrate. The evolution of electronic structures with temperature suggest that FeGe is a Stoner itinerant magnetism. In contrast to ordinary ferromagnetism, a small kink in the integral energy distribution curve (IEDC) at binding energy of 0.5eV in the regime of 274K≤T_C≤276K can be identified. This temperature range is the same with the range of FD measured by AC magnetic susceptibility. Therefore, the small kinks on IEDCs imply the contribution of Dzyaloshinskii-Moriya interaction (DMI) on electronic band structure. Our finding paves the path for the theory of the relationship between freedom of spin and electron in itinerant DM helimagnet.