Flat band Engineering in (Co0.2Fe0.8)5GeTe2 and Fe5GeTe2

Flat band engineering is crucial after the discoveries of the flat band sitting close to the Fermi level, leading to superconductivity and charge fractionalization. This proposal explores the path to create/annihilate this flat band in (Co0.2Fe0.8)5GeTe2, where it has been shown in its original parent Fe5GeTe2 through ARPES. This family is known to undergo a different site ordering depending on the temperature cycle: whether the temperature is quickly quenched or is slowly cooled (a flat band appears in the quickly quenched sample). This proposal will answer if the destructive interference by the clover-like Fe site still survives to create the flat band if the elements are changed partially into Cobalt in the quickly quenched sample. The temperature cycle is also proposed to confirm the engineering path to destroy the flat band on the originally quenched sample by slowly cooling it in situ after annealing up to 700 K. The parent compound will also be studied as the reference of this study.