  We investigate the electronic structure of an antiferromagnetic Kondo lattice
system CeAgAs2 employing hard x-ray photoemission spectroscopy. CeAgAs2, an
orthorhombic variant of HfCuSi2 structure, exhibits antiferromagnetic ground
state, Kondo like resistivity upturn and compensation of magnetic moments at
low temperatures. The photoemission spectra obtained at different photon
energies suggest termination of the cleaved surface at cis-trans-As layers. The
depth-resolved data show significant surface-bulk differences in the As and Ce
core level spectra. The As 2p bulk spectrum shows distinct two peaks
corresponding to two different As layers. The peak at higher binding energy
correspond to cis-trans-As layers and is weakly hybridized with the adjacent Ce
layers. The As layers between Ce and Ag-layers possess close to trivalent
configuration due to strong hybridization with the neighboring atoms and the
corresponding feature appear at lower binding energy. Ce 3d core level spectra
show multiple features reflecting strong Ce-As hybridization and strong
correlation. Intense f0 peak is observed in the surface spectrum while it is
insignificant in the bulk. In addition, we observe a features at binding energy
lower than the well-screened feature indicating the presence of additional
interactions. This feature becomes more intense in the bulk spectra suggesting
it to be a bulk property. Increase in temperature leads to a spectral weight
transfer to higher binding energies in the core level spectra and a depletion
of spectral intensity at the Fermi level as expected in a Kondo material. These
results reveal interesting surface-bulk differences, complex interplay of
intra- and inter-layer covalency, and electron correlation in the electronic
structure of this novel Kondo lattice system.
