Orbital switching from a dumbbell-shaped form to a cloverleaf shaped form in iron superconductor discovered
A group of researchers of Osaka University, The University of Tokyo, and Tohoku University has clarified that the improved electric conductivity of iron-based ladder superconductor BaFe2S3 was induced by orbital switching from one orbiter to another at the orbital-order transition temperature (𝑇*), where the clear anomaly of elastoresistance (ER) was observed.
Since iron-based superconductors were discovered in Japan in 2008, the mechanisms of superconductivity have been investigated and it was thought magnetism and orbital order of electrons was key to solving the mystery.
Electronic properties cause quantum phenomena, such as superconductivity, magnetic order (in which electrons align their spin in the same direction), and orbital order (the order in which atomic orbitals are filled is based on the potential energy of each position).
In this study, the researchers focused on low-dimensional superconductivity in Fe-ladder compound BaFe2S3, which has the strongly correlated electron interaction, shows insulating properties, and becomes superconducting at high temperature under high pressures.
Since BaFe2S3 shows the slight improvement of conductivity at -90°C, changes in the electronic state were suggested. Superconductivity occurred without significant crystal structure changes, indicating that electronic state at ambient pressure smoothly connects to the superconductivity, but the mechanisms of superconductivity was not known.
When this group conducted ER measurements by applying strain and current along various directions and distorting crystal structures in BaFe2S3, antiferromagnetic order and a weak resistivity anomaly were exhibited near 𝑇*. The observed clear anomaly of ER provides strong evidence for the existence of an electronic phase transition at 𝑇*.
There was the gradual orbital switching from leg-directed orbital order (a dumbbell-shaped form) to rung-directed orbital order (a cloverleaf shaped form) in the iron-based ladder superconductor BaFe2S3. It is thought that the electronic orbital expands through this orbital switching, thereby increasing the electric conductivity.
This study showed that it is possible to change physical properties by orbital switching, which will lead to designing devices with new functions by controlling orbital switching.
Figure 1
The article, “Dichotomy between orbital and magnetic nematic instabilities in BaFe2S3,” was published in Physical Review Research at DOI: https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.2.043293#s2.
Related links
Izawa Laboratory, Graduate School of Engineering Science (link in Japanese)
