We have investigated the electronic structure of ${\mathrm{MgB}}_2$ using x-ray Raman scattering at the boron $K$ edge in a single crystal sample. Using both the direction and the magnitude dependence of the momentum transfer we can identify the spatial orientation of empty electronic states with different symmetries. The local symmetry-resolved electronic structure of ${\mathrm{MgB}}_2$ is analyzed using two independent first-principles computational approaches. We show that near the Fermi level the density of $s$ symmetry states is vanishingly small. We also identify and separate the contributions from boron $p_{xy}(\sigma )$ and $p_z(\pi )$ states, which play an important role in determining the superconducting properties of ${\mathrm{MgB}}_2$.

• Received 27 January 2005

DOI:https://doi.org/10.1103/PhysRevLett.94.247003