Orbital-dependent electron correlation effect on the two- and   three-dimensional Fermi surfaces in KFe2As2 revealed by angle-resolved   photoemission spectroscopy
  We have performed an angle-resolved photoemission study of the hole-overdoped iron pnictide superconductor KFe2As2, which shows a low Tc of ~4 K. Most of the observed Fermi surfaces show nearly two-dimensional shapes, while a band near the Fermi level shows a strong dispersion along the kz direction and forms a small three-dimensional hole pocket centered at the Z point, as predicted by band-structure calculation. However, hole Fermi surfaces of yz and zx orbital character centered at the \Gamma point of the two-dimensional Brillouin zone are smaller than those predicted by the calculation while the other hole Fermi surfaces of xy orbital character is much larger. Clover-shaped hole Fermi surfaces around the corner of the 2D BZ are also larger than those predicted by the calculation. These observations are consistent with the de Haas-van Alphen measurement and indicate orbital-dependent electron correlation effects. The effective masses of the energy bands show moderate to strong enhancement, partly due to electron correlation and partly due to energy shifts from the calculated band structure. 
T. Yoshida, S. Ideta, I. Nishi, A. Fujimori, M. Yi, R. G. Moore, S. K.   Mo, D.-H. Lu, Z.-X. Shen, Z. Hussain, K. Kihou, P. ...
cond-mat.str-el cond-mat.supr-con