Spin Density Wave versus Fractional Magnetization Plateau in a Triangular Antiferromagnet

TL;DR

This paper demonstrates a non-classical incommensurate spin-density wave state in a quantum frustrated antiferromagnetic insulator, revealing a transition to a magnetization plateau with a unique SDW-UUD phase locking.

Contribution

It provides the first experimental realization of the SDW-UUD transition in a triangular quantum magnet, highlighting the role of competing anisotropies and frustration.

Findings

Observation of incommensurate SDW state in Cs$_2$CoBr$_4$

Identification of a broad 1/3 magnetization plateau

First experimental evidence of SDW-UUD transition in triangular magnets

Abstract

We report an excellent realization of the highly non-classical incommensurate spin-density wave (SDW) state in the quantum frustrated antiferromagnetic insulator Cs$_2$CoBr$_4$. In contrast to the well-known Ising spin chain case, here the SDW is stabilized by virtue of competing planar in-chain anisotropies and frustrated interchain exchange. Adjacent to the SDW phase is a broad $m = 1/3$ magnetization plateau that can be seen as a commensurate locking of the SDW state into the up-up-down (UUD) spin structure. This represents the first example of long-sought SDW-UUD transition in triangular-type quantum magnets.