Fermi surface shrinking, band shifts and interband coupling in iron-based pnictides

Band shifts are systematically observed in pnictides using de Hass-van Alphen and ARPES techniques.Most interesting, such shifts result to be band-sensitive, so that hole-like bands are shifted downwardswhile electron-like ones are shifted upwards. In this contribution we present a comprehensive explanationfor the origin of such band shifts. Using a four band Eliashberg analysis, we show that they are a naturalconsequence of the multiband character of these systems and of the strong particle-hole asymmetryof the bands. We also show that the relative sign of such shifts provides a direct experimental evidence ofa dominant interband scattering. A quantitative analysis in LaFePO yields a spin-mediated interband couplingof the order V 0.46 eV which corresponds to a mass enhancement Z 1:5.