Spin-Orbit Mediated Interference in the Radiative and Nonradiative Channels of the La 4d Core Resonances

Symmetrical fluorescence yield profiles and asymmetrical electron yield profiles of the preresonances at the La N_IV,V x-ray absorption edge are experimentally observed in LaPO₄ nanoparticles. Theoretical studies show that they are caused by interference effects. The spin-orbit interaction and the giant resonance produce symmetry entangled intermediate states that activate coherent scattering and alter the spectral distribution of the oscillator strength. The scattering amplitudes of the electron and fluorescence decays are further modified by the spin-orbit coupling in the final 5p⁵εl and 5p⁵4f¹ states.