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Electronic structure of MgB$_2$ from angle-resolved photoemission spectroscopy

The first angle-resolved photoemission spectroscopy results from MgB$_2$ single crystals are reported. Close to the $Γ$K and $Γ$M directions, three distinct dispersions are observed approaching the Fermi energy, as can be assigned to the theoretically predicted $σ$ (B $2p_{x,y}$) and $π$ (B $2p_z$) bands. In addition, we also observed a small parabolic-like band centered around $Γ$, and attributed it to a surface-derived state. Good agreement between our results and the band calculations suggests that the electronic structure of MgB$_2$ is of a conventional nature, thus implying that electron correlations are weak, and may be of little importance to the superconductivity in this system.