Spectroscopic evidence for an unrealized heavy-electron state in CeAl2

The compound CeAl2 has been studied at low temperature (15 K) by high-resolution (<20 meV) photoemission using He I and He II excitation sources. The spectra analysis within the Anderson single-impurity model for T = 0 reveals that the extrapolated low-energy parameter δ = 0.2 meV is consistent with the analysis of the specific heat performed within the same formalism. The extreme narrowness of the density of low-lying excitations predicted for T = 0 indicates that CeAl2 would be a heavy-electron metal if the magnetic ordering below 4 K did not prevent the formation of a coherent Kondo lattice