Evidence for a correlated insulator to antiferromagnetic metal transition in CrN

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We investigate the electronic structure of Chromium Nitride (CrN) across the first-order magneto-structural transition at Tₙ 286 K. Resonant photoemission spectroscopy shows a gap in the 3d partial density of states at the Fermi level and an On-site Coulomb energy U 4.5 eV, indicating strong electron-electron correlations. Bulk-sensitive high resolution (6 meV) laser photoemission reveals a clear Fermi edge indicating an antiferromagnetic metal below Tₙ. Hard x-ray Cr 2p core-level spectra show T-dependent changes across Tₙ which originate from screening due to coherent states as substantiated by cluster model calculations using the experimentally observed U. The electrical resistivity confirms an insulator above Tₙ (Eg 70 meV) which becomes a disordered metal below Tₙ. The results indicate CrN transforms from a correlated insulator to an antiferromagnetic metal, coupled to the magneto-structural transition.