Photoemission from Ferromagnetic Uranium Salts
Photoelectric emission has proved to be a powerful spectro-scopic technique to investigate the electronic structure of condensed matter1. Measurement of the kinetic energy distribution curves (EDC’s) of excited electrons at a given photon energy hv gives information about the density of electronic states prior to excitation. Variations in the structure of EDC’s for different hv help one to identify different angular momentum contributions to the measured spectra2. An application to sulfides of several lanthanoid elements in the region of 20 < hv < 80 eV has revealed emission from s, p, d, and f states. In these materials anion derived s and p electrons form the bonding orbitals and show up in the spectra as 4 eV wide valence bands about 5 eV below the Fermi level, EF 3. The 5d electrons, whenever present, contribute to conduction and thus make the material, e. g., NdS, DyS, ErS, metallic; they are located at EF. In SmS and EuS the 5d states are empty and hence SmS and EuS are insulating. 4f electrons form atom-like localized states and are responsible for the magnetic properties. Since the time required for photoemission is very short (10−16 sec), even shorter than the lifetime of the ion core left behind after an electron is photoemitted, the probability of observing the 4fn ground state is rather small. Instead, the spectrum constains the multiplett-split 4fn−1 final state manifold4. It is interesting that these states can be well below EF but nevertheless only partially filled. In some cases their binding energies are smaller than that of the uncorrelated valence band and under certain circumstances these materials show valence instabilities5.
KeywordsValence Band Electron Spin Polarization Uranium Compound Exciting Photon Energy Electronic Specific Heat Coefficient
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