Characterization of unusual orbital configuration and possible low-energy orbital excitations in CuSb2O6 single crystals

The electronic configuration of Cu (3d9) ions in low-dimensional cuprates is such that the electron hole is generally found in the eg 3d(x2-y2)-orbital instead of the 3d(3z2-r2). Remarkably, the quasi-1D Mott-insulator CuSb2O6 shows fairly regular CuO6 octahedra that seem to promote a close competition between the 3z2-r2 and x2-y2 levels that leads to a unusual orbital ordering with mixed character. This mixed character orbital ordering still lacks experimental cerification. Therefore, we propose to establish this unusual orbital ordering in CuSb2O6 by a series of momentum dependent RIXS experiments. Additionally, this unusual orbital configuration may provide new pathways for electron-phonon interaction in cuprates. Indeed, our group reported evidence by Raman scattering of low-energy electronic excitations in CuSb2O6 single crystals that strongly interact with phonons of similar energy that also lacks experimental verification by RIXS