Identification of Nuclear Relaxation Processes in a Gapped Quantum Magnet: Proton NMR in the S=1/2 Heisenberg Ladder Cu2(C5H12N2)2Cl4

TL;DR

This study uses proton NMR to investigate nuclear relaxation processes in a gapped quantum magnet, confirming the presence of a spin gap and identifying relaxation channels consistent with theoretical models.

Contribution

It provides experimental evidence of the spin gap and relaxation channels in a S=1/2 Heisenberg ladder, advancing understanding of quantum magnet relaxation mechanisms.

Findings

Presence of a spin gap supported by NMR data

Identification of two relaxation channels in gapped antiferromagnets

Agreement of experimental results with theoretical predictions

Abstract

The proton hyperfine shift K and NMR relaxation rate $1/T_1$ have been measured as a function of temperature in the S=1/2 Heisenberg antiferromagnetic ladder Cu2(C5H12N2)2Cl4. The presence of a spin gap $\Delta \simeq J_\perp-J_\parallel$ in this strongly coupled ladder ($J_\parallel < J_\perp$) is supported by the K and $1/T_1$ results. By comparing $1/T_1$ at two different proton sites, we infer the evolution of the spectral functions $S_z(q,\omega_n)$ and $S_\perp(q,\omega_n)$. When the gap is significantly reduced by the magnetic field, two different channels of nuclear relaxation, specific to gapped antiferromagnets, are identified and are in agreement with theoretical predictions.