We report $^{ 133}$Cs NMR and $^{ 75}$As Nuclear Quadrupole Resonance (NQR) measurements on the normal metallic state above $T_c$ of a quasi-one-dimensional superconductor Cs$_2$Cr$_3$As$_3$ ($T_c < 1.6$~K). From the $^{ 133}$Cs NMR Knight shift $^{ 133}K$ measured at the Cs1 site, we show that the uniform spin susceptibility $\chi_{ spin}$ increases from 295~K to $\sim$ 60~K, followed by a mild suppression; $\chi_{ spin}$ then levels off below $\sim$10~K. In contrast, a vanishingly small magnitude of $^{ 133}K$ indicates that Cs2 sites contribute very little to electrical conduction and the exchange interactions between 3d electrons at Cr sites. Low frequency Cr spin dynamics, reflected on $^{ 75}$As $1/T_1T$ (the nuclear spin-lattice relaxation rate $1/T_1$ divided by temperature $T$), shows an analogous trend as $\chi_{ spin}$. Comparison with the results of $1/T_1T$ near $T_c$ with Rb$_2$Cr$_3$As$_3$ ($T_c=6.1$~K) and Rb$_2$Cr$_3$As$_3$ ($T_c=4.8$~K) establishes a systematic trend that substitution of K$^{ +}$ ions with larger alkali ions progressively suppresses Cr spin fluctuations together with $T_c$.
Categories: cond-mat.supr-con cond-mat.str-el