Valence band symmetry

Key words Photoluminescence, magneto-luminescence, Zeeman effect, g-factor, excitons, valence band symmetry... 

Figure 39 Band structure of the (a) fully saturated and (b) partially saturated Si[i]-SiC>2(0 01) SL projected along the two symmetry directions of the 2D Brillouin zone of the (0 01) surface. K and M represent, respectively, the k-points in the corner and in the middle of the side of the 2D Brillouin zone. A self-energy correction of 0.8 eV has been added to the conduction states. Energies (in eV) are referred to the valence band maximum.

Having determined that it is very likely that six electrons are transferred to the C80 molecule - in agreement with the 13C NMR data which suggest Ih symmetry for the carbon cage [6] - it is now interesting to consider the valence band photoemission spectrum of the endohedral to see if the consequences of this high symmetry are visible in the energy distribution of the n-MO s of the system. 

The fact that the Sc3N C80 molecule as a whole has only C3 symmetry (or even is reduced to Ci in the solid state [43]) does not give rise to a lifting of the degeneracy of C80 s molecular orbitals visible above the vibronic broadening, which dominates the width of the individual molecular orbitals in valence band photo emission. 

This high symmetry results in the close grouping of the 7r-MOs and the large binding energy of the valence band onset seen in the photoemission spectrum of the system. 

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