Abstract
We have investigated the low temperature properties of LuB12 by measuring its magnetic susceptibility, heat capacity, and electrical resistivity, as well as by point-contact spectroscopy using both the spear-anvil type technique and mechanically controllable break junctions. Our specific heat measurements and point - contact spectroscopy results indicate that LuB12 is a simple weak-coupling BCS-type superconductor with TC ≈ 0.4 K, a superconducting energy gap of 2 Δ ≈ 0.12 meV, and a very small critical field BC ≈ 1 mT. From the dU/dI(U) characteristics in the superconducting state, the energy gap 2Δ, the critical current IC and the Andreev-reflection excess current Iex as a function of normal-state point contact resistance RN have been determined. At low RN all three parameters are strongly suppressed, possibly due to the self-magnetic field. At contacts with large RN the model of resistively and capacitively shunted Josephson junctions (RCSJ) allowed us to estimate the superconducting current plasma frequency and the Josephson coupling energy. Moreover, from the d2U/d I2(U) spectra in the normal state the (point-contact) electron-phonon interaction function and the characteristic phonon energies of LuB12 have been determined.
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