Out-of-Equilibrium Electrons and Record Thermionic Emission in LaB6

To understand mechanisms of high thermionic emission of LaB
₆
we use infrared spectroscopy, DC resistivity and Hall-effect techniques to study conduction electrons state in LaB6 single crystals with different contents of
¹⁰
B and
¹¹
B isotopes. We find that up to 70% of conduction electrons are strongly non-equilibrium due to involvement in the collective oscillations of electron density coupled to vibrations of Jahn-Teller unstable boron cage and rattling modes of La-ions. We claim that these non-equilibrium electrons determine the extraordinary low work function of thermoemission in LaB
₆
.