Photoemission Evidence of a Novel Charge Order in Kagome Metal FeGe

Abstract A charge order has been discovered to emerge deep into the antiferromagnetic phase of the kagome metal FeGe. However, due to the existence of defects, the as-grown FeGe sample shows a nano-scale phase separation with a short range charge order behavior and this can be removed by annealing procedure where long range charge order phase will be stabilized. Thus, to study its intrinsic origin, the evolution of the low-lying electronic structure across the charge order phase transition of the annealed FeGe sample is investigated with angle-resolved photoemission spectroscopy. We do not find signatures supporting nesting mechanism between Fermi surface sections or van-Hove singularities for the charge order formation in FeGe. However, two obvious changes in the band structure have been detected, i.e., one electron-like band around the K point and another one around the A point move upward in energy position when the charge order forms. These features can be well reproduced by our density-functional theory calculations, where the charge order is primarily driven by magnetic energy saving via large dimerizations of a quarter of Ge1-sites (in the kagome plane) along the c-axis. Our results provide strong support for this novel charge order formation mechanism in FeGe, in contrast to the conventional nesting mechanism.