Martinelli Leonardo, Wohlfeld Krzysztof, Pelliciari Jonathan, Arpaia Riccardo, Brookes Nicholas B, Di Castro Daniele, Fernandez Mirian G, Kang Mingu, Krockenberger Yoshiharu, Kummer Kurt, McNally Daniel E, Paris Eugenio, Schmitt Thorsten, Yamamoto Hideki, Walters Andrew, Zhou Ke-Jin, Braicovich Lucio, Comin Riccardo, Sala Marco Moretti, Devereaux Thomas P, Daghofer Maria, Ghiringhelli Giacomo
Dipartimento di Fisica, Politecnico di Milano, piazza Leonardo da Vinci 32, I-20133 Milano, Italy.
Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Pasteura 5, PL-02093 Warsaw, Poland.
Phys Rev Lett. 2024 Feb 9;132(6):066004. doi: 10.1103/PhysRevLett.132.066004.
We have investigated the 3d orbital excitations in CaCuO_{2} (CCO), Nd_{2}CuO_{4} (NCO), and La_{2}CuO_{4} (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 d_{xy} orbital clearly disperses, 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 the orbiton from its coupling to magnons, which is associated with the orbiton hopping between nearest neighbor copper sites. Finally, we show that the exceptionally large NNN orbital superexchange can be traced back to the absence of apical oxygens suppressing the charge transfer energy.
我们使用高分辨率共振非弹性X射线散射研究了CaCuO₂（CCO）、Nd₂CuO₄（NCO）和La₂CuO₄（LCO）中的3d轨道激发。在LCO中，它们表现为局域性良好的激发，类似于其他几种铜酸盐。相反，在CCO和NCO中，dₓy轨道明显色散，表明在没有顶氧的化合物中这种激发（轨道子）具有集体特性。我们将色散的起源归因于显著的次近邻（NNN）轨道超交换。这种交换导致轨道子从与磁振子的耦合中解放出来，这与轨道子在最近邻铜位点之间的跳跃有关。最后，我们表明，异常大的NNN轨道超交换可追溯到顶氧的缺失抑制了电荷转移能量。
