Staggered-spin contribution to nuclear spin-lattice relaxation in two-leg antiferromagnetic spin-1/2 ladders

TL;DR

This paper investigates the nuclear spin-lattice relaxation rate in two-leg antiferromagnetic spin-1/2 ladders, revealing a crossover in temperature dependence that may explain recent experimental NMR findings in ladder cuprates.

Contribution

It identifies the staggered-spin contribution to $1/T_1$ and characterizes its temperature-dependent crossover behavior in spin-1/2 ladders.

Findings

At low temperatures, the contribution is activation-type with a gap of 2Δ.

A crossover occurs at T ≈ Δ, leading to a slow decay in relaxation rate.

The results may explain recent high-temperature NMR observations in ladder cuprates.

Abstract

We study the nuclear spin-lattice relaxation rate $1/T_1$ in the two-leg antiferromagnetic spin-1/2 Heisenberg ladder. More specifically, we consider the contribution to $1/T_1$ from the processes with momentum transfer $(\pi,\pi)$. In the limit of weak coupling between the two chains, this contribution is of activation type with gap $2\Delta$ at low temperatures ($\Delta$ is the spin gap), but crosses over to a slowly-decaying temperature dependence at the crossover temperature $T\approx\Delta$. This crossover possibly explains the recent high-temperature NMR results on ladder-containing cuprates by T. Imai et al.