Role of Vanadium-Oxide Layer in Electronic State of Sr${}_2$VFeAsO${}_{3-\delta }$ with Oxygen Deficiency

Abstract

Iron-based superconductor Sr${}_2$VFeAsO${}_3$ is composed of alternate stacking of a superconducting FeAs layer and an insulating vanadium-oxide layer with a perovskite-type structure. Electronic orders stemming from the spin and orbital degrees of freedom of V $3d$ electrons can arise in the vanadium-oxide layer, but such orders have not been confirmed so far. Here, we systematically investigate the electronic state of Sr${}_2$VFeAsO${}_{3-\delta }$ with oxygen deficiency and demonstrate the phase diagram of Sr${}_2$VFeAsO${}_{3-\delta }$ as a function of the $c$-axis lattice parameter, which has turned out to be a suitable measure of the amount of oxygen deficiency. We found a magnetic and structural anomaly at $\sim 100$ K with a thermal hysteresis, which is manifested with the introduction of oxygen deficiency. The presence of orthorhombic distortion was revealed below the temperature at which the anomaly appears, suggestive of V orbital ordering involving the $d_{xz}$ and $d_{yz}$ orbitals. It seems that substantial fluctuations associated with the orthorhombic distortion significantly influence the electronic state of the FeAs layer. Our findings indicate that the vanadium-oxide layer plays a significant role in the electronic state of Sr${}_2$VFeAsO${}_{3-\delta }$.

10 pages, 9 figures

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