  p-d hybridization of transition metal impurities in a semiconductor host is
the mechanism that couples valence-band electrons and localized spins. We use
scanning tunneling microscopy and spectroscopy combined with density functional
theory to probe at the atomic scale hybridization of Cr single impurities with
GaAs host. Combining spatial density of states mapping and in-gap states
spectroscopy of the Cr substituted at the surface of the semiconductor, we give
a detailed picture of the spatial extension and the electronic structure of the
strongly anisotropic wave function of Cr on GaAs(110). First principles
calculations allow to identify electronic character and origin of each states
and show that the main resonance peaks and the wave function with "drop-eyes"
lobes experimentally observed for 3d metal impurities in III-V semiconductor
are direct local evidences of the p-d hybridization.
