Critical Slowing Down of Triangular Lattice Spin-3/2 Heisenberg Antiferromagnet Li7RuO6 via 7Li NMR

TL;DR

This study uses 7Li NMR to investigate critical slowing down in a triangular-lattice spin-3/2 Heisenberg antiferromagnet, revealing a broad critical region and effects of spin frustration.

Contribution

First detailed NMR analysis of critical phenomena in Li7RuO6, highlighting the impact of spin frustration and Z2 vortex excitations on critical slowing down.

Findings

Critical divergence observed over a wide temperature range

Spin stiffness reduced to about 20% of spin-wave approximation

Evidence of spin frustration effects, including Z2 vortex excitations

Abstract

We report 7Li NMR studies of single crystals of triangular-lattice Heisenberg antiferromagnet Li7RuO6. Slow critical divergence with a wide critical region of |T/TN - 1|< 7 was observed in 7Li nuclear spin-lattice relaxation rate. The slowing down of staggered spin fluctuations was analyzed in a renormalized classical region of a two-dimensional triangular-lattice non-linear sigma model. A spin stiffness constant was found to reduce to about 20 % from the value in a spin-wave approximation. The effect of spin frustration, e.g., Z2 vortex excitations on the critical phenomena is suggested.