Fractional Spin Excitations in the Infinite-Layer Cuprate CaCuO2

Abstract

We use resonant inelastic x-ray scattering (RIXS) to investigate the magnetic dynamics of the infinite-layer cuprate CaCuO2. We find that close to the (1/2,0) point, the single magnon decays into a broad continuum of excitations accounting for about 80% of the total magnetic spectral weight. Polarization-resolved RIXS spectra reveal the overwhelming dominance of the spin-flip (ΔS=1) character of this continuum with respect to the ΔS=0 multimagnon contributions. Moreover, its incident-energy dependence is identical to that of the magnon, supporting a common physical origin. We propose that the continuum originates from the decay of the magnon into spinon pairs, and we relate it to the exceptionally high ring exchange Jc∼J1 of CaCuO2. In the infinite-layer cuprates, long-range and multisite hopping integrals are very important, and they amplify the 2D quantum magnetism effects in spite of the 3D antiferromagnetic Néel order.Received 12 October 2021Accepted 30 March 2022DOI:https://doi.org/10.1103/PhysRevX.12.021041Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAntiferromagnetismExchange interactionMagnonsSpinonPhysical SystemsAntiferromagnetsCharge-transfer insulatorsHigh-temperature superconductorsTechniquesResonant inelastic x-ray scatteringCondensed Matter, Materials & Applied Physics