Dimensional crossover of spin chains in a transverse staggered field: an NMR study

TL;DR

This study investigates how a local transverse staggered field affects the static and dynamic properties of Heisenberg spin-1/2 chains in BaCu2Si2O7 using NMR, DMRG, and analytical methods, revealing unusual spin reorientation transitions.

Contribution

It combines experimental NMR data with numerical DMRG and analytical analysis to elucidate the effects of local transverse staggered fields on spin chain behavior in a specific compound.

Findings

Observation of divergent low-temperature transverse susceptibility.

Identification of spin reorientation transitions due to local transverse fields.

Experimental access to anisotropic magnetization contributions below ordering temperature.

Abstract

Heisenberg spin-1/2 chain materials are known to substantially alter their static and dynamic properties when experiencing an effective transverse staggered field originating from the varying local environment of the individual spins. We present a temperature-, angular- and field-dependent 29Si NMR study of the model compound BaCu2Si2O7. The experimental data are interpreted in terms of the divergent low-temperature transverse susceptibility, predicted by theory for spin chains in coexisting longitudinal and transverse staggered fields. Our analysis first employs a finite-temperature "Density Matrix Renormalization Group" (DMRG) study of the relevant one-dimensional Hamiltonian. Next we compare our numerical with the presently known analytical results. With an analysis based on crystal symmetries we show how the anisotropic contribution to the sample magnetization is experimentally accessible even below the ordering temperature, in spite of its competition with the collinear order parameter of the antiferromagnetic phase. The modification of static and dynamic properties of the system due to the presence of a local transverse staggered field (LTSF) acting on the one-dimensional spin array are argued to cause the unusual spin reorientation transitions observed in BaCu2Si2O7. On the basis of a Ginzburg-Landau type analysis, we discuss aspects of competing spin structures in the presence of magnetic order and the enhanced transverse susceptibility.