Effect of strain-induced orbital splitting on the magnetic excitations in undoped cuprates

TL;DR

This study explores how strain-induced orbital splitting affects magnetic excitations in undoped cuprates, revealing that increased orbital splitting hardens spin-wave energy up to a certain threshold, explained via a two-orbital model.

Contribution

It introduces a two-orbital model to explain strain-dependent magnetic excitations in cuprates, highlighting the role of orbital splitting and hybridization effects.

Findings

Spin-wave energy increases with orbital splitting under compressive strain.

Hardening of spin-wave energy saturates at orbital splitting of about 2 eV.

Hybridization between orbitals influences magnetic excitation behavior.

Abstract

We investigate the magnetic excitations in view of the recent reports suggesting that the spin-wave energy may exhibit a significant dependence on the in-plane strain of a thin film of La$_2$CuO$_4$. The nature of dependence, as we find, can be explained naturally within a two-orbital model based on the $d_{x^2-y^2}$ and $d_{3z^2-r^2}$ orbitals. In particular, as the orbital-splitting energy between the $d_{x^2-y^2}$ and $d_{3z^2-r^2}$ orbitals increases with compressive strain, the zone-boundary spin-wave energy hardens. However, the hardening persists only until the orbital splitting reaches $\sim$ 2eV, beyond which there is no significant change. The behavior of zone-boundary spin-wave energy is explained in terms of the extent of hybridization between one of the exchange-split $d_{x^2-y^2}$ band which is nearly half filled and the $d_{3z^2-r^2}$ band. The role of second-order antiferromagnetic superexchange process involving the inter-orbital hopping is also discussed.