Spiral versus modulated collinear phases in the quantum ANNNH model

TL;DR

This study explores the magnetic phases of quantum Heisenberg antiferromagnets with frustration, revealing an incommensurate spiral phase in 2D and 3D, and ruling out a proposed collinear phase due to higher energy.

Contribution

It provides the first detailed analysis of spiral and collinear phases in the quantum ANNNH model, highlighting quantum fluctuations' effects on phase boundaries.

Findings

Incommensurate spiral phase exists at T=0 in 2D and extends to finite T in 3D.

Crossover between Néel and spiral order occurs at higher frustration than classical predictions.

The proposed modulated collinear phase has higher energy and is not realized in the model.

Abstract

Motivated by the discovery of spiral and modulated collinear phases in several magnetic materials, we investigate the magnetic properties of Heisenberg spin S=1/2 antiferromagnets in 2 and 3 dimensions, with frustration arising from 2nd-neighbor couplings in one axial direction (the ANNNH model). Our results clearly demonstrate the presence of an incommensurate spiral phase at T=0 in 2 dimensions, extending to finite temperatures in 3 dimensions. The crossover between N\'eel and spiral order occurs at a value of the frustration parameter considerably above the classical value 0.25, a sign of substantial quantum fluctuations. We also investigate a possible modulated collinear phase with a wavelength of 4 lattice spacings, and find that it has substantially higher energy and hence is not realized in the model.