Resonant photoemission studies of the Kondo-lattice systems CeCu2Si2, CeAg2Si2, CeAu2Si2, and CePd2Si2

Photoemission experiments performed at an incident photon energy of 70 eV provide a clear view of the transition-element-derived $d$ bands in the systems $\mathrm{Ce}{T}_2{\mathrm{Si}}_2$, with $T=\mathrm{C}\mathrm{u},\mathrm{A}\mathrm{g},\mathrm{A}\mathrm{u},\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{P}\mathrm{d}$. Spectra taken at $h\nu =122\mathrm{}$ eV display both a resonant $4f$ emission at 2-3 eV below $E_F$, and a resonant emission near $E_F$. The total intensity of the latter feature, which has been observed in other Ce-based systems and identified as having strong $4f$ character in $\gamma$-cerium and Ce${\mathrm{Al}}_2$, appears to track the intensities of the transition-element-derived $d$ density of states near $E_F$. In superconducting Ce${\mathrm{Cu}}_2$ ${\mathrm{Si}}_2$, the $E_F$ feature has its maximum at 0.25 eV, whereas we find it at significantly higher binding energies (∼0.6 eV) in the three magnetic systems ($T=\mathrm{A}\mathrm{g},\mathrm{A}\mathrm{u},\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{P}\mathrm{d}$). This observation suggests markedly smaller electronic specific-heat ($\gamma$) values in the magnetic compounds as compared with $\gamma \simeq 1$ J ${\mathrm{mole}}^{-1\mathrm{}}$ ${\mathrm{K}}^{-2\mathrm{}}$ generated by heavy fermions in Ce${\mathrm{Cu}}_2$ ${\mathrm{Si}}_2$.