The differential resistance dV/dI versus voltage characteristics were studied for point contacts between a LaB6-needle on one hand and a LaB6(100)-cleavage surface on the other. A technique of automatic in situ cleaning was used to clean the sample surface. The spectra of pure metal point contacts were contrary to that of the tunneling contacts interposed by the oxide layer. That is, the former was for the barrierless junction of a sufficiently clean surface and the latter was for the barrier-type junction of an intentionally oxidized surface. Measurements of the second derivative, d2K/dI2, furnished information on the phonon density of states of LaB6. The peaks in the phonon density of states were situated at 12, 24, 38 and 50meV.

Phonon Structure of LaB6 by Point-Contact Spectroscopy. Kunii, S.: Journal of the Physical Society of Japan, 1988, 57[1], 361-6