Electronic structure of YbN

Large single crystals of cubic and stoichiometric YbN have been grown. On these crystals we measured the optical reflectivity for photon energies between 1 meV and 12 eV, also at helium temperatures, and performed a Kramers-Kronig analysis to obtain the optical constants. In addition, we measured the Raman effect to obtain further information on the phonon spectra. The electrical conductivity at room and at low temperature and the Hall effect at 300 K served to obtain also the effective mass of the carriers. Also the magnetization and initial susceptibility have been measured. The main important results are that YbN is a self-compensated semimetal with about ${10}^{20}$ carriers per ${\mathrm{cm}}^{\mathrm{-}3}$, the occupied 4${\mathit{f}}^{13}$ state is about 6 eV below ${\mathit{E}}_{\mathit{F}}$, the empty 4${\mathit{f}}^{14}$ state is about 0.2 eV above ${\mathit{E}}_{\mathit{F}}$, and the effective mass of the carriers is about 2.2${\mathit{m}}_{\mathit{e}}$. In other words the material definitely is not a heavy fermion—but more probably a Kondo system. Nonstoichiometric samples tend to show stronger Kondo features.