We have measured the uranium L3 absorption and resonant emission spectra in the localized magnetic compound U Pd3 and heavy fermion U Pd2 Al3 as a function of pressure. The spectral line shape of the absorption edge is found to vary rapidly in U Pd2 Al3 with a notable broadening of the white line above the structural transition around 25 GPa while it shows a more gradual variation in U Pd3 over the considered pressure range (0-40 GPa), indicating different responses of the f-d electrons to the compressed lattice in the two compounds. The U L3 absorption spectra in both U Pd3 and U Pd2 Al3 and their pressure dependence were further simulated via first-principles band calculations within the linear muffin-tin orbital approach. The calculations reproduce the main features of the experimental absorption edges. The calculated pressure dependence of the f charge reveals a stronger localization of the f electrons in U Pd3 which shows a remarkably stable valency under pressure, close the nominal value of 4. On the contrary, our results point to a mixed valent U4-δ ground state in U Pd2 Al3 at ambient conditions, evolving into a U4+ (or possibly U4+δ) configuration at high pressure. The f -electron delocalization could be responsible for the known structural transition in U Pd2 Al3.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - aug. 10 2007|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics