Structural Transition with a Sharp Change in the Electrical Resistivity and Spin-Orbit Mott Insulating State in a Rhenium Oxide, SrReO.

We report the successful synthesis, crystal structure, and electrical properties of SrReO, which contains Re with the 5d configuration. This compound is isostructural with BaReO and shows a first-order structural phase transition at ∼370 K. The low-temperature (LT) phase crystallizes in a hettotype structure of BaReO, which is different from that of the LT phase of SrWO, suggesting that the electronic state of Re plays an important role in determining the crystal structure of the LT phase. The structural transition is accompanied by a sharp change in the electrical resistivity. This is likely a metal-insulator transition, as suggested by the electronic band calculation and magnetic susceptibility. In the LT phase, the ReO octahedra are rotated in a pseudo- manner in Glazer notation, which corresponds to -type orbital ordering. Paramagnetic dipole moments were confirmed to exist in the LT phase by muon spin rotation and relaxation measurements. However, the dipole moments shrink greatly because of the strong spin-orbit coupling in the Re ions. Thus, the electronic state of the LT phase corresponds to a Mott insulating state with strong spin-orbit interactions at the Re sites.