ELECTRON-TUNNELING STUDIES OF THE HEXABORIDE MATERIALS SMB6, EUB6, CEB6, AND SRB6

We present a series of tunneling measurements on the hexaboride materi als SmB6, EuB6, CeB6, and SrB6. In this group, SmB6, EuB6, and CeB6 po ssess magnetic moments, whereas SrB6 is nonmagnetic. Our tunneling mea surements show an asymmetric conductance, exhibiting a background that grows with energy in all four materials. We find evidence of a partia l gap, but with only a small depletion in N(E). Our measurements are c onsistent with a two-band model in which the band overlap is reduced w ith decreasing temperature. [S0163-1829(98)03415-8].