Point-contact Andreev reflection spectroscopic study of the superconducting gap structure in LuNi₂B₂C

We employ the point-contact Andreev reflection spectroscopy technique in LuNi₂B₂C (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 Δ₀ / 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.