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| VOLUME 110 (2019) | ISSUE 1 | PAGE 70 |
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Boron 10B-11B isotope substitution as a probe of mechanism responsible for the record thermionic emission in LaB 6 with the Jahn-Teller instability
E. S. Zhukova+*, B. P. Gorshunov+*, M. Dressel+×, G. A. Komandin*, M. A. Belyanchikov+, Z. V. Bedran+, A. V. Muratov°, Y. A. Aleshchenko°, M. A. Anisimov*, N. Yu. Shitsevalova∇, A. V. Dukhnenko∇, V. B. Filipov∇, V. V. Voronov*, N. E. Sluchanko+* 1)
+Moscow Institute of Physics and Technology, 141700 Dolgoprudny, Russia *Prokhorov General Physics Institute of the Russian Academy of Sciences, 119991 Moscow, Russia ×1.Physikalisches Institut, Universität Stuttgart, D-70569 Stuttgart, Germany °Lebedev Physical Institute of Russian Academy of Sciences, 119991 Moscow, Russia ∇Frantsevich Institute for Problems of Materials Science, NASU, 03680 Kiev, Ukraine
Abstract
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. |