Ferromagnetic Spin Fluctuation and Unconventional Superconductivity in Rb2Cr3As3 Revealed by As 75 NMR and NQR

We report As75 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies on the superconductor Rb2Cr3As3 with a quasi-one-dimensional crystal structure. Below T∼100K, the spin-lattice relaxation rate (1/T1) divided by temperature, 1/T1T, increases upon cooling down to Tc=4.8K, showing a Curie-Weiss-like temperature dependence. The Knight shift also increases with decreasing temperature. These results suggest ferromagnetic spin fluctuation. In the superconducting state, 1/T1 decreases rapidly below Tc without a Hebel-Slichter peak, and follows a T5 variation below T∼3K, which points to unconventional superconductivity with point nodes in the gap function.