Experimental Study of Spin Fluctuations in a One-Dimensional Antiferromagnet

Abstract

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 $T\ensuremath{\gtrsim}\frac{J}{{k}_{B}}$. These results are in good agreement with predictions based on the fermion representation for the spin-\textonehalf{} 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 ${T}_{1}^{\ensuremath{-}1}$ thus strongly suggest fermion-like excitations in the spin-\textonehalf{} one-dimensional antiferromagnet.