Nematic order in square lattice frustrated ferromagnets

TL;DR

This paper proposes a new mechanism for the loss of ferromagnetic order in 2D quantum magnets, where two-magnon bound states condense into a nematic phase without magnetic order, supported by numerical evidence.

Contribution

It introduces a novel scenario involving Bose-Einstein condensation of two-magnon bound states leading to nematic order in square lattice ferromagnets, supported by numerical analysis.

Findings

Existence of a nematic phase with d-wave correlations

No long-range magnetic order in the nematic phase

Phase identified between ferromagnetic and antiferromagnetic states

Abstract

We present a new scenario for the breakdown of ferromagnetic order in a two-dimensional quantum magnet with competing ferromagnetic and antiferromagnetic interactions. In this, dynamical effects lead to the formation of two-magnon bound states, which undergo Bose-Einstein condensation, giving rise to bond-centered nematic order. This scenario is explored in some detail for an extended Heisenberg model on a square lattice. In particular, we present numerical evidence confirming the existence of a state with d-wave nematic correlations but no long range magnetic order, lying between the saturated ferromagnetic and collinear antiferromagnetic phases of the ferromagnetic J1-J2 model. We argue by continuity of spectra that this phase is also present in a model with 4-spin cyclic exchange.