A series of magnon crystals appearing under ultrahigh magnetic fields in a kagom\'e antiferromagnet

TL;DR

This study reports the discovery of a series of magnon crystal states in a kagome antiferromagnet under ultrahigh magnetic fields, revealing a new form of particle physics in frustrated magnetic systems.

Contribution

It demonstrates the emergence of fractional magnetization plateaux interpreted as magnon crystallizations in a kagome antiferromagnet at ultrahigh magnetic fields.

Findings

Observation of fractional magnetization plateaux up to 160 T

Identification of magnon crystallization on kagome lattice

Revelation of a new particle physics in frustrated magnets

Abstract

Search for a new quantum state of matter emerging in a crystal is one of recent trends in condensed matter physics. For magnetic materials, geometrical frustration and high magnetic field are two key ingredients to realize it: a conventional magnetic order is possibly destroyed by competing interactions (frustration) and is replaced by an exotic state that is characterized in terms of quasiparticles, that are magnons, and the magnetic field can control the density and chemical potential of the magnons. Here we show that a synthetic copper mineral, Cd-kapellasite, comprising a kagome lattice made of corner-sharing triangles of Cu2+ ions carrying spin-1/2 exhibits an unprecedented series of fractional magnetization plateaux in ultrahigh magnetic fields up to 160 T, which may be interpreted as crystallizations of emergent magnons localized on the hexagon of the kagome lattice. Our observation reveals a novel type of particle physics realized in a highly frustrated magnet.