Collapsed tetragonal phase transition of Ca(Fe_1-xRh _x)₂As₂ studied by photoemission spectroscopy

We have investigated the changes in the band structure and core-level energy of Ca(Fe_1-xRh)₂As₂ across the tetragonal-collapsed tetragonal (T-cT) phase transition using photoemission spectroscopy. Angle-resolved photoemission spectroscopy clearly demonstrates that, at the point in the Brillouin zone, a hole-like band that crosses the Fermi level in the T phase lowers its energy position and is completely filled in the cT phase. This indicates the disappearance of a hole-like Fermi surface around the zone center in the cT phase, which gives rise to the extinction of nesting. The relationship of the present results with the results of previous transport and magnetic studies is discussed. The temperature dependences of the As 3d and Ca 2p core levels show energy shifts toward higher and lower binding energies, respectively. These data constitute the first direct experimental results on electronic structure and chemical states across the T-cT transition.