On the estimate of the spin-gap in quasi-1D Heisenberg antiferromagnets from nuclear spin-lattice relaxation

TL;DR

This paper analyzes how to accurately estimate the spin gap in quasi-1D Heisenberg antiferromagnets using nuclear spin-lattice relaxation rates, emphasizing the importance of considering triplet excitation dispersion features.

Contribution

It provides a detailed analysis of the temperature dependence of 1/T1 in gapped quasi-1D antiferromagnets, accounting for dispersion features and comparing theoretical results with experimental data.

Findings

Correct estimation of the spin gap requires considering triplet dispersion features.

The temperature dependence of 1/T1 due to two-magnon processes varies with the ratio r=J_perp/J_parallel.

Comparison with experimental data in Sr14Cu24O41 validates the theoretical approach.

Abstract

We present a careful analysis of the temperature dependence of the nuclear spin-lattice relaxation rate $1/T_1$ in gapped quasi-1D Heisenberg antiferromagnets. It is found that in order to estimate the value of the gap correctly from $1/T_1$ the peculiar features of the dispersion curve for the triplet excitations must be taken into account. The temperature dependence of $1/T_1$ due to two-magnon processes, is reported for different values of the ratio $r=J_{\perp}/J_{\parallel}$ between the superexchange constants in a 2-leg-ladder. As an illustrative example we compare our results to the experimental findings for $^{63}Cu 1/T_1$ in the dimerized chains and 2-leg-ladders contained in Sr$_{14}Cu_{24}O_{41}$