Exotic superconducting phase inCeCu2Si2close to antiferromagnetism: A Cu-NQR study under hydrostatic pressure

We report Cu nuclear-quadrupole-resonance results under pressure (P) on a homogeneous ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ ${(T}_{\mathrm{c}}=0.65\mathrm{}$ 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 $P_{\mathrm{c}}\sim 0.2$ 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 Fermi-liquid model. In $0<~P<\mathrm{}{P}_{\mathrm{c}}\sim 0.2$ 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.