Fermi surface pockets in iron pnictides revised by screened exchange dynamical mean-field theory*

Until today our understanding of iron based superconductors is hampered by a persistent systematic discrepancy between theory and experiment: the size of the Fermi surface pockets consistently turn out too large in theoretical calculations[1]. Here we show that this puzzle can be solved when taking into account the effect of nonlocal exchange beyond the Density Functional Theory plus dynamical mean-field theory(DFT+DMFT) approach. As it turns out, the nonlocal exchange properties in DFT+DMFT are rather poorly described, leading to an overestimation of the size of Fermi surface pockets. We show that an approximative treatment within screened exchange dynamical mean-field theory gives rise to momentum dependent Fermi surface modifications leading to a significant improvement with experiment. Additionally, we observe a Fermi surface modification in paramagnetic BaFe₂As₂, where the Fe 3d_xy hole pocket in the Brillouin zone center vanishes completely. Reinterpreting existing angle-resolved photoemission (ARPES) experiments, we propose that indeed the Fe 3d_xy states are located below the Fermi level, in contrast to previous belief[2].
[1] A. Kordyuk et al. , J. Supercond. Nov. Magn. 26, 2837 (2013)
[2] S. Backes, A. van Roekeghem, S. Biermann, (in preparation)