Experimental Study of Spin Fluctuations in a One-Dimensional Antiferromagnet

An experimental study of nuclear relaxation in the low-temperature antiferromagnetic regime of $N$-methyl phenazinium tetracyanoquinodimethan (NMP) (TCNQ) is presented. The data are characterized by a relatively weak temperature dependence; the extrapolated zerotemperature rate is finite and of the same magnitude as the rate at $T\gtrsim \frac{J}{k_B}$. These results are in good agreement with predictions based on the fermion representation for the spin-½ antiferromagnet in one dimension. The conventional Boson assumption, on the other hand, leads to a predicted rate off by four orders of magnitude in comparison with experiment. The experimental measurements of $T_1^{-1\mathrm{}}$ thus strongly suggest fermion-like excitations in the spin-½ one-dimensional antiferromagnet.