Highly Dispersive Spin Excitations in the Chain Cuprate Li2CuO2

TL;DR

This study uses inelastic neutron scattering to reveal highly dispersive quasi-1D magnetic excitations in Li2CuO2, highlighting large ferromagnetic interactions and complex spiral behaviors near a critical point.

Contribution

First detailed neutron scattering analysis of Li2CuO2 revealing its large ferromagnetic exchange and complex dispersion relations, connecting experimental results with theoretical models.

Findings

Large ferromagnetic exchange integral J1=-228 K

Observation of anomalous quartic dispersion near zone center

Identification of spiral excitation close to a 3D FM-spiral critical point

Abstract

We present an inelastic neutron scattering investigation of Li2CuO2 detecting the long sought quasi-1D magnetic excitations with a large dispersion along the CuO2-chains studied up to 25 meV. The total dispersion is governed by a surprisingly large ferromagnetic (FM) nearest-neighbor exchange integral J1=-228 K. An anomalous quartic dispersion near the zone center and a pronounced minimum near (0,0.11,0.5) r.l.u. (corresponding to a spiral excitation with a pitch angle about 41 degree point to the vicinity of a 3D FM-spiral critical point. The leading exchange couplings are obtained applying standard linear spin-wave theory. The 2nd neighbor inter-chain interaction suppresses a spiral state and drives the FM in-chain ordering below the Ne'el temperature. The obtained exchange parameters are in agreement with the results for a realistic five-band extended Hubbard Cu 3d O 2p model and L(S)DA+U predictions.