Electrical creation of all-oxide metasurfaces

New publication featured on the inside front cover of Advanced Materials

Scientists from Prof. Stuart S. P. Parkin`s group at the Max-Planck Institute of Microstructure Physics, in collaboration with Prof. Georg Woltersdorf`s group at the Martin-Luther-Universität Halle-Wittenberg, have demonstrated a groundbreaking concept: synchronized local ionic gating of a continuous oxide layer. This concept allows for the local control of electrical, magnetic, and optical properties of numerous nano-regions simultaneously, paving the way for the electrical creation of all-oxide metasurfaces. The result was featured on the inside cover of Advanced Materials on September 6, 2024.
 

Ionic gating has attracted great attention for its ability to electrically manipulate various physical phenomena, such as insulator-metal transitions, ferromagnetism, and superconductivity, via the migration of ions in or out of thin films. However, previous studies on ionic gating have largely focused on single devices, and the kinetics during ionic gating are poorly understood. Researchers in Prof. Stuart Parkin`s group at the Max-Planck Institute of Microstructure Physics have elucidate the electrokinetics during ionic gating and found that the gating response of insulating films is highly non-uniform. But, when employing a conducting underlayer, the gating response is not only very uniform but also much faster over the entire thin film surface. Exploiting this phenomenon, the researchers developed a new concept of synchronized local ionic gating through nano-patterned windows in a resist layer that is deposited on top of the thin film of interest. They show that the local ionic liquid gating of an antiferromagnetic insulating SrCoO_2.5 (brownmillerite structure) thin film results in the local phase transformation of the gated regions into ferromagnetic metallic SrCoO₃ (perovskite structure) arrays. This concept allows for the simultaneous local control of electrical, magnetic, and optical properties of numerous nano-regions. Moreover, in a collaboration with Prof. Georg Woltersdorf’s group at the Martin-Luther-Universität Halle-Wittenberg, the researchers demonstrate the anomalous reflection of light from arrays of SrCoO₃ V-antennas embedded in an insulating SrCoO_2.5 film. i.e., the electrical formation of all-oxide metasurfaces via synchronized local ionic gating.

The first author, Dr. Hyeon Han from the Max-Planck Institute of Microstructure Physics (now an assistant professor at Pohang University of Science and Technology), stated "We have revealed, for the first time, the electrokinetics during the ionic gating process by developing time and space-resolved in-situ transport/optical measurement systems. This novel concept of synchronized local ionic gating enables us to locally control diverse physical phenomena of thin films on a large scale".

The corresponding author, Prof. Stuart S. P. Parkin at the Max Planck Institute of Microstructure Physics, commented that "We have introduced a new technique that allows for the electrical creation of all-oxide metasurfaces. This approach is highly versatile and can be extended beyond oxides to other materials whose properties can be significantly altered through ionic gating. As a result, this technique holds potential for a wide range of applications, including optical/magnetic metasurfaces and superconducting devices, which can be further tuned by voltage control."

The paper entitled “All-Oxide Metasurfaces Formed by Synchronized Local Ionic Gating” by Hyeon Han, Arpit Sharma, Jiho Yoon, Zhong Wang, Chris Körner, Hakan Deniz, Ankit K. Sharma, Fan Li, Chris Sturm, Georg Woltersdorf, and Stuart S. P. Parkin can be found at: https://doi.org/10.1002/adma.202401064

Acknowledgments
This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 737109. Funding has been provided by the Alexander von Humboldt Foundation in the framework of the Alexander von Humboldt Professorship to S.S.P.P. endowed by the Federal Ministry of Education and Research.