DATE2025.07.30 #Press Releases

First Discovery of New Electronic States in Functional Oxides

-Clues to the Development of High Performance Electronics Materials for the Future

Summary

A research group of graduate students Yuichi Seki (2nd year, Master course), Kodai Inagaki (2nd year, Master course), Takahito Takeda (3rd year, PhD course), Professor Masaaki Tanaka and Associate Professor Masaki Kobayashi at the Graduate School of Engineering, The University of Tokyo, and NTT Corporation (Head Office: Chiyoda-ku, Tokyo; President: Akira Shimada)  in collaboration with Professor Emeritus Atsushi Fujimori, School of Science, The University of Tokyo and Yuiharu Takeda and Shin-ichi Fujimori of the Japan Atomic Energy Agency, have studied a strontium ruthenium oxide, SrRuO ₃ [a compound consisting of Sr (strontium), Ru (ruthenium), and O (oxygen)], a metal with ferromagnetic properties, by means of photoelectron spectroscopy using synchrotron radiation, and revealed that the electronic orbitals of oxygen atoms have different electronic states from those of cation Ru due to strong electronic correlation. Functional oxides, which are made from transition metal atoms as cations and oxygen atoms as anions, are a treasure house of various physical properties such as magnetism, dielectricity, and superconductivity, and have been vigorously studied as next-generation electronic materials from both basic and applied science perspectives. The physical properties of functional oxides are determined by the behavior of electrons at the Fermi energy, and it has been generally believed that the electronic orbitals of the transition metals and the oxygen are strongly hybridized and have similar electronic states. The present result has not been predicted by conventional oxide research or the standard model, and provides an important guideline for the design of functional oxides and devices using these oxides in the future.

This result was published in the online in the American journal Physical Review Letters on July 25, 2025 (US east coast time).

Conducting electrons in each electron orbital in the functional oxide SrRuO_3: The interaction (electron correlation) between electrons in the Ru 4d-O2p hybrid orbital of SrRuO₃ depends on the electron orbital: the electron correlation is weak in the Ru 4d orbital (red four-leaf type orbital) and electrons in this orbital (red) mainly contribute to electrical conduction (red dashed arrow). On the other hand, in the O 2p orbital (blue dumbbell shaped orbital), electrons (blue) are localized in the O 2p orbital due to strong electron correlation and barely contribute to electrical conduction (they move between through electron scattering (blue dashed arrows)).

Related Links

Graduate School of Engineering, The UTokyo, NTT Corporation, Japan Atomic Energy Agency

Journals

Journal name	Physical Review Letters
Title of paper	Correlated Ligand Electrons in the Transition-Metal Oxide SrRuO3