Abstract
We have prepared polycrystalline samples of the trimer Ir oxide BaIrO3 with face-shared Ir3O12 trimers, and have investigated the origin of the phase transition at 182 K by measuring resistivity, thermopower, magnetization and synchrotron X-ray diffraction. We propose a possible electronic model and transition mechanism, starting from a localized electron picture on the basis of the Rietveld refinement. Within this model, BaIrO3 can be basically regarded as a Mott insulator, when the Ir3O12 trimer is identified to one pseudo-atom or one lattice site. The transition can be viewed as a transition from the Mott insulator phase to a kind of charge ordered insulator phase.
Highlights
Correlated electrons are seen in a certain class of solids in which the Coulomb repulsion is too strong to hold a simple one-electron picture based on the band theory
There is a strong hybridization between the a1g levels within a trimer owing to the short intra-trimer Ir-Ir distance, and a kind of molecular orbital is expected to be formed within the trimer as shown in the right side of Figure 4a, where we denote the bonding, non-bonding and anti-bonding orbitals made of the three a1g orbitals as B, NB and AB, respectively
We propose the normal state of BaIrO3 is essentially in the Mott insulator phase, and name this “trimer Mott insulator”
Summary
Correlated electrons are seen in a certain class of solids in which the Coulomb repulsion is too strong to hold a simple one-electron picture based on the band theory They have occupied a central position in condensed matter sciences for many decades, and have attracted keen interests from vast numbers of researchers since the discovery of high-temperature superconducting copper oxides in 1986. They store a macroscopic number of degeneracy and entropy based on spin and charge degrees of freedom on each lattice site at high temperature [1,2], and release them through various phase transitions towards 0 K. The trimers are connected with each other in a corner-sharing network and construct zig-zag chains along the c axis and corrugated honeycomb lattices in the ab plane
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