Evolution of an Unconventional Superconducting State inside the Antiferromagnetic Phase of CeNiGe_3 under Pressure : A ^<73>Ge-Nuclear-Quadrupole-Resonance Study(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We report a ^<73>Ge nuclear-quadrupole-resonance (NQR) study on novel evolution of unconventional superconductivity in antiferromagnetic (AFM) CeNiGe_3. The measurements of the ^<73>Ge-NQR spectrum and the nuclear spin-lattice relaxation rate (1/T_1) have revealed that the unconventional superconductivity evolves inside a commensurate AFM phase around the pressure (P) where Neel temperature T_N exhibits its maximum at 8.5K. The superconducting transition temperature T_<SC> has been found to be enhanced with increasing T_N, before reaching the quantum critical point at which the AFM order collapses. Above T_<SC>, the AFM structure transits from an incommensurate spin-density-wave order to a commensurate AFM order at T〜2K, accompanied by a longitudinal spin-density fluctuation. With regard to heavy-fermion compounds, these novel phenomena have hitherto never been reported in the P-T phase diagram.
社団法人日本物理学会の論文
2008-10-15