Point-contact Andreev reflection spectroscopic study of the superconducting gap structure in LuNi 2B 2C

Abstract

We employ the point-contact Andreev reflection spectroscopy technique in LuNi 2B 2C ( T c ∼ 16.0 K ) single crystals along three different crystallographic orientations as a function of magnetic field and temperature. Our data taken on the [0 0 1] and [1 1 0] faces show gap values at ∼ 2 K of ∼ 2.4 meV , and ∼ 2.6 meV , respectively, as analyzed by the one-gap Blonder–Tinkham–Klapwijk model. Both the energy gap and the Dynes broadening parameter exhibit similar dependences on magnetic field along the two directions. Data taken as a function of temperature follow the BCS-like temperature dependence yielding 2 Δ 0 / k B T c ∼ 3.4 and ∼ 3.6 , respectively. The measured gap values in [1 0 0] direction vary from 1.6 to 2.5 meV at low temperatures and disappear at the same bulk T c .