Pressure-induced anomalous magnetism and unconventional superconductivity in CeRhIn₅: ¹¹⁵In-NQR study under pressure

We report ¹¹⁵In nuclear-quadrupole-resonance (NQR) measurements of the pressure (P)-induced superconductor CeRhIn₅ in the antiferromagnetic (AF) and superconducting (SC) states. In the AF region, the internal field H_int at the In site is substantially reduced from H_int=1.75 kOe at P=0 to 0.39 kOe at P=1.23 GPa, while the Néel temperature slightly changes with increasing P. This suggests that either the size in the ordered moment M_Q(P) or the angle θ(P) between the direction of M_Q(P) and the tetragonal c axis is extrapolated to zero at P^*=1.6±0.1 GPa at which a bulk SC transition is no longer emergent. In the SC state at P=2.1 GPa, the nuclear spin-lattice relaxation rate ¹¹⁵(1/T₁) has revealed a T³ dependence without the coherence peak just below T_c, giving evidence for the unconventional superconductivity. The dimensionality of the magnetic fluctuations in the normal state is also discussed.