Nanoscale self-organization of electrons is ubiquitously observed in correlated electron systems such as complex oxides of transition metals. The phenomenon of charge ordering (CO) or the formation of charge stripes, as observed for layered-structure cuprates and nickelates, is one such example. Among them, CO in manganites is closely tied to the orbital degree of freedom of 3d electrons, leading to staggered orbital ordering or the formation of orbital stripes in the layered structure. Here, we describe the phenomena of thermally induced rotation of the orbital stripes by 90( composite function) for bilayered manganite crystals with half hole doping, that is, a 1:1 ratio of Mn3+/Mn4+. The rotation of orbital stripes and the consequent CO coupled with the underlying lattice distortion were found to produce the charge-polarized state, as also shown by its optical second-harmonic generation activity.

A clear experimental explanation of the contribution of Mott and Peierls transitions to the insulator−metal transition (IMT) characteristics in vanadium dioxide (VO 2 ) is still lacking. Examining the crystal and electronic structures of epitaxial VO 2 films grown at various deposition temperatures, a Mott or a Peierls transition was observed. The VO 2 film deposited at 500 °C showed suppressed Peierls transition characteristics because of the large inplane compressive strain in the insulating phase. The VO 2 films deposited at 600 and 650 °C had a higher IMT temperature because of the relaxation of both the in-plane and out-of-plane strain, and there were abundant V 4+ states. Therefore, it was related to a collaborative Mott−Peierls transition. Finally, the VO 2 film deposited at 720 °C showed a suppressed Mott transition because of the abundance of V 3+ states in the insulating phase. Furthermore, an analysis of the electronic structure of the insulating and metallic phases using in situ X-ray photoelectron spectroscopy and X-ray absorption spectroscopy provide a complete band diagram to support the above explanation of the deposition-temperature-dependent IMT characteristics.

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