Interplay of magnetism and superconductivity in CeCu2Si2 under hydrostaticpressure

We present transport measurements under hydrostatic pressure, low temperatu re and magnetic field on a single crystal of the heavy fermion superconduct or CeCu2Si2. The presumably magnetic A-phase is shown to collapse rapidly w ith pressure, and to almost disappear at 3.2 kbar. We also present measurem ents of the upper critical field H-c2(T). We find evidence for a relation b etween the A-phase and the presence of a maximum on the temperature depende nce of the H-c2. The magnetic susceptibility deduced from the analysis of t he variation of H-c2(T), taking into account the exchange interaction, show s a sharp variation at the A-phase boundary obtained from resistivity measu rements in the normal state. Our analysis shows that the sign of the exchan ge integral should be negative, thus superconductivity is enhanced by the p aramagnetic susceptibility as in the Jaccarino-Peter effect.