1 research outputs found
Collective nature of orbital excitations in layered cuprates in the absence of apical oxygens
We have investigated the 3d orbital excitations in CaCuO2 (CCO), Nd2CuO4
(NCO) and La2CuO4 (LCO) using high-resolution resonant inelastic x-ray
scattering. In LCO they behave as well-localized excitations, similarly to
several other cuprates. On the contrary, in CCO and NCO the dxy orbital clearly
disperse, pointing to a collective character of this excitation (orbiton) in
compounds without apical oxygen. We ascribe the origin of the dispersion as
stemming from a substantial next-nearest-neighbor (NNN) orbital superexchange.
Such an exchange leads to the liberation of orbiton from its coupling to
magnons, which is associated with the orbiton hopping between nearest neighbor
copper sites. We show that the exceptionally large NNN orbital superexchange
can be traced back to the absence of apical oxygens suppressing the charge
transfer energy.Comment: 18 pages, 7 figure