Magnetic order and ballistic spin transport in a sine-Gordon spin chain

TL;DR

This study investigates magnetic order and spin transport in sine-Gordon spin chains using muon-spin spectroscopy, revealing long-range magnetic order and ballistic spin transport in one system, and spin diffusion in another, highlighting different magnetic excitations.

Contribution

The paper provides experimental evidence of magnetic ordering and distinct spin transport mechanisms in sine-Gordon spin chains, advancing understanding of their magnetic excitations.

Findings

Long-range magnetic order below 0.22 K in the studied chain.

Evidence of ballistic spin transport in one system.

Observation of spin diffusion in a related chiral spin chain.

Abstract

We report the results of muon-spin spectroscopy ($\mu^+$SR) measurements on the staggered molecular spin chain [pym-Cu(NO$_3$)$_2$(H$_2$O)$_2$] (pym = pyrimidine), a material previously described using sine-Gordon field theory. Zero-field $\mu^+$SR reveals a long range magnetically-ordered ground state below a transition temperature $T_\mathrm{N}=0.22(1)$ K. Using longitudinal-field (LF) $\mu^+$SR we investigate the dynamic response in applied magnetic fields $0< B < 500$ mT and find evidence for ballistic spin transport. Our LF $\mu^+$SR measurements on the chiral spin chain [Cu(pym)(H$_2$O)$_4$]SiF$_6 \cdot $H$_2$O instead demonstrate one-dimensional spin diffusion and the distinct spin transport in these two systems likely reflects differences in their magnetic excitations.