  Recent advances in the study of nodal Weyl fermions (WFs), quasi-relativistic
massless particles, constitute a novel realm of quantum many-body phenomena.
The Coulomb interaction in such systems, having a zero density of states at the
Fermi level, is of particular interest, since in contrast to conventional
correlated metals, its long-ranged component is unscreened. Here, through
nuclear-magnetic-resonance (NMR) measurements, we unveil the exotic spin
correlations of two-dimensional WFs in an organic material, causing a divergent
increase of the Korringa ratio by a factor of 1000 upon cooling, in striking
contrast with conventional metallic behaviors. Combined with model
calculations, we show that this divergence stems from the interaction-driven
velocity renormalization that almost exclusively suppresses the zero-momentum
spin fluctuations. At low temperatures, the NMR rate shows a remarkable
increase, which is shown by numerical analyses to correspond to inter-node
excitonic fluctuations, precursor of a transition from massless to massive
quasiparticles.
