Pressure and temperature dependences of the electronic structure of CeIrSi3 probed by resonant X-ray emission spectroscopy

Pressure and temperature dependences of the electronic structure of the heavy-fermion superconductor CeIrSi₃ have been investigated using partial fluorescence yield x-ray absorption spectroscopy and resonant x-ray emission spectroscopy at the Ce L₃ edge. Ce is in a weakly mixed valence state at ambient pressure, mostly f¹ with a small contribution from the f⁰ component. Pressure-induced increase of the Ce valence becomes apparent above 4 GPa, concomitantly with the disappearance of the superconductivity. No temperature dependence of the Ce valence is observed within the measured temperature range down to 24 K.