Low-energy properties of two-dimensional quantum triangular antiferromagnets: Non-perturbative renormalization group approach

TL;DR

This paper investigates the low-temperature behavior of two-dimensional quantum triangular antiferromagnets near a quantum phase transition using a non-perturbative renormalization group approach, revealing fluctuation effects and crossover phenomena.

Contribution

It introduces a non-perturbative RG analysis of quantum and thermal fluctuations in 2D triangular antiferromagnets, elucidating crossover from quantum to classical regimes and explaining experimental observations.

Findings

Identification of fluctuation-driven first order transition

Crossover from quantum $$ theory to classical nonlinear sigma model

Agreement with experimental data for NiGa$_2$S$_4$

Abstract

We explore low temperature properties of quantum triangular Heisenberg antiferromagnets in two dimension in the vicinity of the quantum phase transition at zero temperature. Using the effective field theory described by the $SO(3)\times SO(2)/SO(2)$ matrix Ginzburg-Landau-Wilson model and the non-perturbative renormalization group method, we clarify how quantum and thermal fluctuations affect long-wavelength behaviors in the parameter region where the systems exhibit a fluctuation-driven first order transition to a long-range ordered state. We show that at finite temperatures the crossover from a quantum $\phi^6$ theory to a renormalized two-dimensional classical nonlinear sigma model region appears, and in this crossover region, massless fluctuation modes with linear dispersion a la spin waves govern low-energy physics. Our results are in good agreement with the recent experimental observations for the two-dimensional triangular Heisenberg spin system, NiGa$_2$S$_4$.