Establishing the fundamental magnetic interactions in the chiral skyrmionic Mott insulator Cu2OSeO3 by terahertz electron spin resonance

TL;DR

This study uses advanced terahertz ESR spectroscopy with high magnetic fields to directly measure and understand the fundamental magnetic interactions in the skyrmionic Mott insulator Cu2OSeO3, revealing its microscopic spin structure.

Contribution

It provides the first direct experimental quantification of the magnetic interactions in Cu2OSeO3 using high-field ESR, identifying the fundamental units as rigid, entangled tetrahedra.

Findings

Identification of the fundamental magnetic building blocks as tetrahedra

Direct measurement of the long-wavelength Goldstone mode

Quantification of high-energy excitation spectrum

Abstract

The recent discovery of skyrmions in Cu$_2$OSeO$_3$ has established a new platform to create and manipulate skyrmionic spin textures. We use high-field electron spin resonance (ESR) spectroscopy combining a terahertz free electron laser and pulsed magnetic fields up to 64 T to probe and quantify its microscopic spin-spin interactions. Besides providing direct access to the long-wavelength Goldstone mode, this technique probes also the high-energy part of the excitation spectrum which is inaccessible by standard low-frequency ESR. Fitting the behavior of the observed modes in magnetic field to a theoretical framework establishes experimentally that the fundamental magnetic building blocks of this skyrmionic magnet are rigid, highly entangled and weakly coupled tetrahedra.