Graduate School in Nonlinear Science

Sponsored by The Danish Research Agency

MIDIT                              OFD                          CATS
Modelling, Nonlinear Dynamics      Optics and Fluid Dynamics    Chaos and Turbulence Studies
and Irreversible Thermodynamics    Risø National Laboratory     Niels Bohr Institute and 
Technical University of Denmark    Building 128                 Department of Chemistry
Building 321                       P.O. Box 49                  University of Copenhagen 
DK-2800 Lyngby                     DK-4000 Roskilde             DK-2100 Copenhagen Ø
Denmark                            Denmark                      Denmark

Abstract: Measurements of the superconducting gap in CeRu₂ were performed by different methods and on samples of the different quality. Here we present a comparison of the behaviour of the superconducting gap in samples of different quality studied by point contacts. We propose a procedure for correction of the superconducting gap, D, taking into account pair-breaking effects, which result in almost equal gap values for both poly and single crystalline samples. The BCS-like behaviour of the gap 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 incorporated using the Scalsk i-Betbeder-Matibet-Weiss approach based on the Abrikosov-Gorkov theory. This all ows us to recalculate the superconducting order parameter D^a in the presence of paramagnetic impurities and the gap D^P in the pure case for polycrystalline CeRu₂ samples and for single crystals. The value of 2D^P(0)&# 187; 2 meV with 2D^P(0)/k_BT_{c »} 3.75 is found in both cases indicating that CeRu₂ is a moderately strong-coupled superconductor.