Magnetization process and ordering of the $S=1/2$ pyrochlore magnet in a field

TL;DR

This study investigates the magnetization behavior of the $S=1/2$ pyrochlore Heisenberg antiferromagnet in a magnetic field, revealing a robust half-magnetization plateau with broken symmetry and insights into quantum order mechanisms.

Contribution

It provides the first large-scale DMRG analysis of the $S=1/2$ pyrochlore magnet, identifying a novel half-magnetization plateau driven by quantum effects.

Findings

Identification of a robust 1/2 magnetization plateau with broken rotational symmetry.

Evidence for a finite triplet gap causing a threshold for magnetization.

Observation of a very slim 5/6 magnetization plateau possibly unstable.

Abstract

We study the $S=1/2$ pyrochlore Heisenberg antiferromagnet in a magnetic field. Using large scale density-matrix renormalization group (DMRG) calculations for clusters up to $128$ spins, we find indications for a finite triplet gap, causing a threshold field to nonzero magnetization in the magnetization curve. We obtain a robust saturation field consistent with a magnon crystal, although the corresponding $5/6$ magnetization plateau is very slim and possibly unstable. Most remarkably, there is a pronounced and apparently robust $\frac 1 2$ magnetization plateau where the groundstate breaks (real-space) rotational symmetry, exhibiting oppositely polarised spins on alternating kagome and triangular planes. Reminiscent of the kagome ice plateau of the pyrochlore Ising magnet known as spin ice, it arises via a much more subtle `quantum order by disorder' mechanism.