Tensor network simulation for the frustrated $J_1$-$J_2$ Ising model on the square lattice

TL;DR

This study uses tensor network methods to clarify the phase diagram of the frustrated $J_1$-$J_2$ Ising model on a square lattice, resolving controversies about the nature and extent of phase transitions.

Contribution

It provides new insights into the phase transition order and critical properties, suggesting a smaller first-order region and a continuous evolution from decoupled Ising models to tricritical behavior.

Findings

First-order transition region is smaller than previously thought.

Evidence of continuous evolution from decoupled Ising models to tricritical Ising universality.

Critical point around $g^* \,\simeq\, 0.54$ with a change in universality class.

Abstract

By using extensive tensor network calculations, we map out the phase diagram of the frustrated $J_1$-$J_2$ Ising model on the square lattice. In particular, we focus on the cases with controversy in the phase diagram, especially the stripe transition in the regime $g = |J_2/J_1|>\frac{1}{2}$, $(J_2>0,J_1<0)$. While recent studies claimed that the phase transition is of first order when $\frac{1}{2}<g<g^*$ (with the smallest $g^*$ being $0.67$), our simulations suggest that if there is such a first-order region, it is smaller than those found in earlier studies by other methods. Combining with the analysis of critical properties, we provide evidence that the classical $J_1$-$J_2$ model evolves continuously from two decoupled Ising models ($g\to\infty$ with central charge $c = 1$) to a point belonging to the tricritical Ising universality class (with $c = 0.7$) as $g$ decreases to $g^*\simeq 0.54$.