Antiferromagnetic spin fluctuations and superconductivity in NbRh$_2$B$_2$ and TaRh$_2$B$_2$ with a chiral crystal structure

Abstract

We report the 11 B nuclear magnetic resonance (NMR) measurements on non-centrosymmetric superconductors NbRh 2 B 2 (superconducting transition temperature T c = 7.8 K) and TaRh 2 B 2 (T c = 5.9 K) with a chiral crystal structure. The nuclear spin-lattice relaxation rate 1/T 1 shows no coherence peak below T c , which suggests unconventional nature of the superconductivity. In the normal state, 1/T 1 T increases with decreasing temperature T at low temperatures below T = 200 K for TaRh 2 B 2 and T = 15 K for NbRh 2 B 2 , while the Knight shift remains constant. These results suggest the presence of antiferromagnetic spin fluctuations in both compounds. The stronger spin fluctuations in TaRh 2 B 2 compared to NbRh 2 B 2 is discussed in the context of spin-orbit coupling.