Temperature and pressure dependences of the electronic structure of the heavy-fermion system CePd${}_2$Si${}_2$ have been investigated using partial fluorescence yield x-ray absorption spectroscopy and resonant x-ray emission spectroscopy at the Ce $L_3$ edge. The temperature dependence has also been measured for CeRh${}_2$Si${}_2$ for comparison. In both compounds Ce is in a weakly mixed valence state at ambient pressure, mostly $f^1$ with a small contribution from the $f^0$ component. No temperature dependence of the Ce valence is observed at temperatures as low as 8 K. In CePd${}_2$Si${}_2$ at 19 K, however, the Ce valence shows a continuous increase with pressure, indicating pressure-induced delocalization of the $4f$ states. Theoretical calculations based on the single impurity Anderson model reproduce the experimental results well. Pressure dependence of the difference between the ground state valence and the measured valence including the final state effect is also discussed.

• Received 4 September 2012

DOI:https://doi.org/10.1103/PhysRevB.86.235131