Investigation of the superconducting energy gap in the compound LuNi2B2C by the method of point contact spectroscopy: two-gap approximation

Abstract

It is shown that the two-gap approximation is applicable for describing the dV /dI(V ) spectra of LuNi2B2C-Ag point contacts in a wide interval of temperatures. The values and the temperature dependences of the large and the small gaps in the ab plane and in the c direction were estimated using the generalized BTK model 20 and the equations of. 21 In the BCS extrapolation the critical temperature of the small gap is 10 K in the ab plane and 14.5 K in the c direction. The absolute values of the gaps are ∆ ab 0 = 2.16 meV and ∆ c 0 = 1.94 meV . For the large gaps the critical temperature coincides with the bulk Tc, T bulk c = 16.8 K, and their absolute values are very close, being about 3 meV in both orientations. In the c direction the contributions to the conductivity from the small and the large gaps remain practically identical up to 10 ÷ 11 K. In the ab plane the contribution from the small gap is much smaller and decreases rapidly as a temperature rises.

Competition of multiband superconducting and magnetic order in ErNi 2 B 2 C observed by Andreev reflection

“…The dV /dI temperature series for these PCs are the most full, therefore they presented in Fig. 2: (Color online) Reduced position of the minima in the raw dV /dI curves for ErNi2B2C and that for LuNi2B2C from [12]. Insets: comparison of two OPs (solid line) and one-OP (dashed line) fitting of the reduced experimental dV /dI (symbols) at 1.45 K.…”

Observation of an anisotropic effect of antiferromagnetic ordering on the superconducting gap in ErNi2B2C

“…The crystals were thin (0.1 ÷ 0.2 mm) plates with the c-axis normal to the plane of the plate. The surface pretreatment was similar to that for LuNi 2 B 2 C [23,24] (either by etching in a 5% nitric acidalcohol solution or by of cleavage). The other electrode was a high-purity Ag rod or Ag wire of 0.15 mm in diameter.…”

“…This assumption is supported by the values of pair-breaking parameters γ 2 of large OP which increase with temperature. Note that the γ 2 magnitudes of larger OP calculated in the two-gap approximation within the BB model for nonmagnetic LuNi 2 B 2 C are lower and decrease (faster in the ab-plane) with temperature (see [23], Fig.9). Since spinflip scattering is absent in this compound, the parameter γ in this calculation tends to exceed the degree of the superconducting gap broadening.…”

“…The gap is distributed in the interval 1-3.35 meV (insert). The calculation in [23] Thus, the one-gap GBTK calculation results in the highest value in the S estimate. Therefore one-gap GBTK calculations [40] can be regarded as oversimplified and can be used only as a first approximation.…”

“…The technique used (detailed in [23]) is based on a selection of parameters that can ensure the smallest r.m.s. divergence between experimental and theoretical curves.…”