Exotic superconducting phase in CeCu2Si2 close to antiferromagnetism:: A Cu-NQR study under hydrostatic pressure -: art. no. 140501

We report Cu nuclear-quadrupole-resonance results under pressure (P) on a homogeneous CeCu2Si2 (T-c = 0.65 K) that revealed critical magnetic fluctuations at the border to an antiferromagnetic (AF) phase. This exotic superconducting (SC) phase evolves into the typical heavy-fermion SC phase at minute pressures exceeding P(c)similar to0.2 GPa. The nuclear spin-lattice relaxation data in a P range 0.85 - 2.58 GPa are shown to be accountable by the spin-fluctuation theory based on the nearly AF Ferni-liquid model. In 0 less than or equal toP0.2 GPa, by contrast, we conclude that the exotic SC phase manifests itself under the unconventional normal state where AF waves propagate over a long range without any trace of AF order and thereby the heavy-fermion state breaks up.