Non-local network-excitation in the Ising antiferromagnet on the anisotropic triangular lattice

TL;DR

This paper investigates the Ising antiferromagnet on an anisotropic triangular lattice, revealing the emergence of ferromagnetic bonds called 'good defects' that form a correlated network, with specific heat peaks indicating a soft lattice state.

Contribution

It introduces the concept of 'good defects' as ferromagnetic bonds in the anisotropic triangular lattice Ising model, highlighting their correlation and network formation, which was not previously understood.

Findings

Identification of 'good defects' as ferromagnetic bonds

Universal peak in specific heat at temperature ~ δ_J

Activation-type energy dependence with gap 2δ_J

Abstract

We study the Ising antiferromagnet on the triangular lattice which are interacting along three different directions via two $J$-bonds and one anisotropic $J'$-bond with $J' \ge J$. Although its finite temperature state has long been considered as simply disordered, we find a systematic generation of a ferromagnetic $J'$-bonds named "good defects" each carrying the energy $2\delta_J\equiv 2(J'-J)$. They exhibit an eminent correlation which is regarded as a network or a soft lattice. The specific heat shows a universal peak at $T^* \sim \delta_J$ and the corresponding energy follows the activation type of temperature-dependence with an excitation gap $2\delta_J$. Energetics and the crossover between this particular two-dimensional state and the other disordered or one-dimensional states are discussed.