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

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 La2CuO4. 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 ∼ 2eV, beyond which there is no significant change. The behavior of zone-boundary spinwave 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.