Strong electron correlations in the normal state of FeSe0.42Te0.58

We investigate the normal state of the ‘11’ iron-based superconductor FeSe0.42Te0.58 by angle resolved photoemission. Our data reveal a highly renormalized quasiparticle dispersion characteristic of a strongly correlated metal. We find sheet dependent effective carrier masses between ~ 3 - 16 m_e corresponding to a mass enhancement over band structure values of m*/m_band ~ 6

• 20. This is nearly an order of magnitude higher than the renormalization reported previously for iron-arsenide superconductors of the ‘1111’ and ‘122’ families but fully consistent with the bulk specific heat.