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

TL;DR

This study explores how oxygen deficiency affects the electronic and magnetic properties of Sr$_2$VFeAsO$_{3-\delta}$, revealing the role of vanadium-oxide layers and orbital ordering in its phase diagram and structural anomalies.

Contribution

It demonstrates the impact of oxygen deficiency on the phase diagram and orbital ordering in Sr$_2$VFeAsO$_{3-\delta}$, highlighting the significance of vanadium-oxide layers.

Findings

Magnetic and structural anomaly at ~100 K with hysteresis.

Orthorhombic distortion below the anomaly temperature.

V orbital ordering involving d_{xz} and d_{yz} orbitals.

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$_{3-\delta}$.