Microscopic properties of the "pinwheel" kagome compound Rb_2Cu_3SnF_{12}

TL;DR

This study uses high-field NMR to investigate the microscopic magnetic properties of the Rb2Cu3SnF12 kagome compound, revealing a complex ground state with singlet-triplet mixing and an anticrossing behavior in the excitation gap.

Contribution

It provides the first detailed microscopic analysis of the pinwheel kagome compound Rb2Cu3SnF12, highlighting the role of g-tensor tilts in the observed level anticrossing.

Findings

Ground state shows strong transverse staggered spin polarization.

The excitation gap exhibits a level anticrossing with a minimum of about half its zero-field value.

Staggered g-tensor tilts are responsible for the anticrossing behavior.

Abstract

Using $^{63,65}$Cu nuclear magnetic resonance (NMR) in magnetic fields up to 30 T we study the microscopic properties of the 12-site valence-bond-solid ground state in the "pinwheel" kagome compound Rb$_2$Cu$_3$SnF$_{12}$. We find that the ground state is characterized by a strong transverse staggered spin polarization whose temperature and field dependence points to a mixing of the singlet and triplet states. This is further corroborated by the field dependence of the gap $\Delta (H)$, which has a level anticrossing with a large minimum gap value of $\approx \Delta (0)/2$, with no evidence of a phase transition down to 1.5\,K. By the exact diagonalization of small clusters, we show that the observed anticrossing is mainly due to staggered tilts of the $g$-tensors defined by the crystal structure, and reveal symmetry properties of the low-energy excitation spectrum compatible with the absence of level crossing.