Unusual coexistence of negative/positive charge-transfer in mixed-valence Na${}_x$Ca${}_{1-x}$Cr${}_2$O${}_4$

Abstract

We have investigated the electronic structure of Na${}_x$Ca${}_{1-x}$Cr${}_2$O${}_4$ using x-ray absorption spectroscopy together with Anderson impurity model calculations with full multiplets. We show Na${}_x$Ca${}_{1-x}$Cr${}_2$O${}_4$ taking a novel mixed-valence electronic state in which the positive charge-transfer (CT) and the negative self-doped states coexist. While CaCr${}_2$O${}_4$ (one end member) exhibits a typical CT nature with strong covalent character, Na substitution causes a self-doped state with an oxygen hole. In NaCr${}_2$O${}_4$ (the other end member), positive CT and negative self-doped states coexist with equal weight. This unusual electronic state is in sharp contrast to the conventional mixed-valence description, in which the ground state can be described by the mixture of Cr${}^{3+}$ ($3d^3$) and Cr${}^{4+}$ ($3d^2$).

arXiv comment5 pages, 5 figures

References in corpus (4)

• Ground state oxygen holes and the metal-insulator transition in the negative charge transfer rare-earth nickelates
• Charge disproportionation without charge transfer in the rare-earth nickelates as a possible mechanism for the metal-insulator transition
• Spin and charge ordering in self-doped Mott insulators
• Unusual superexchange pathways in a Ni triangular lattice of NiGa${}_2$S${}_4$ with negative charge-transfer energy

Cited by in corpus (2)

• Neutron powder diffraction study of NaMn${}_2$O${}_4$ and Li${}_{0.92}$Mn${}_2$O${}_4$: New insights on spin-charge-orbital ordering
• Revised Magnetic Structure and Tricritical Behavior of the CMR Compound NaCr${}_2$O${}_4$ Investigated with High Resolution Neutron Diffraction and ${\mu }^{+}$SR