Superconducting gap and pair breaking in CeRu₂ studied by point contacts

The superconducting gap in a CeRu₂ single crystal is investigated by point contacts. BCS-like behavior of the gap Δ in the temperature range below T_c^* (T_c ^*<T_c, where T_c is the critical temperature) is established, indicating the presence of a gapless superconductivity region (between T_c^* and T _c). The pair-breaking effect of paramagnetic impurities, supposedly Ce ions, is taken into consideration using the Scalski-Betbeder-Matibet-Weiss approach based on Abrikosov-Gorkov theory. It allows us to recalculate the superconducting order parameter Δ^α (in the presence of paramagnetic impurities) and the gap Δ^p (in the pure case) for the single crystal and for the previously studied polycrystalline CeRu ₂. The value 2Δ^p(0)≈2 meV, with 2Δ^p(0)/k_BT_c≈3.75, is found in both cases, indicating that CeRu₂ is a "moderate" strong-coupling superconductor.