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VOLUME 110 | ISSUE 1 | PAGE 70
Boron 10B-11B isotope substitution as a probe of mechanism responsible for the record thermionic emission in LaB 6 with the Jahn-Teller instability
We have tested the conduction band electrons of lanthanum hexaboride that is among the most effective electron-beam sources with one of the highest brightness of thermionic emission. We performed infrared spectroscopic, DC ( direct current) resistivity and Hall-effect studies of LaB6 single crystals with various 10B and 11B isotope content. We find that only a small amount of conduction electrons behave as Drude-type charge carriers while about 70 % of the electrons are involved in collective oscillations of electron density coupled to vibrations of both the Jahn-Teller unstable rigid boron cage and rattling modes of La-ions loosely bound to the lattice. We suggest that exactly these non-equilibrium conduction electrons determine the extraordinary low work function of thermoemission in LaB6.