Energy gap of intermediate-valent SmB6 studied by point-contact spectroscopy - art. no. 085104

We have investigated the intermediate valence narrow-gap semiconductor SmB6 at low temperatures using both conventional spear-anvil type point contact s as well as mechanically controllable break junctions. The zero-bias condu ctance varied between less than 0.01 muS and up to 1 mS. The position of th e spectral anomalies, which are related to the different activation energie s and band gaps of SmB6, did not depend on the the contact size. Two differ ent regimes of charge transport could be distinguished: Contacts with large zero-bias conductance are in the diffusive Maxwell regime. They had spectr a with only small nonlinearities. Contacts with small zero-bias conductance are in the tunneling regime. They had larger anomalies, but still indicati ng a finite 45% residual quasiparticle density of states at the Fermi level at low temperatures of T=0.1 K. The density of states derived from the tun eling spectra can be decomposed into two energy-dependent parts with Eg = 2 1 meV and E-d = 4.5 meV wide gaps, respectively.