Deep inside a crystal thinner than a human hair, physicists have caught something remarkable: a glimpse of quantum behavior that had never been seen before. Using carefully aimed laser pulses, an international team of scientists—including researchers from institutions in Italy, Switzerland, and the United States—observed what are called Jahn-Teller polarons emerging within cobalt oxide, a material already used in everything from chemical catalysts to battery electrodes.
Cobalt oxide, with the chemical formula Co₃O₄, might sound simple, but its crystal structure is anything but. Each unit cell of the material contains 56 atoms arranged in a pattern where cobalt ions exist in two different oxidation states—some carrying a +2 charge, others a +3 charge. This duality gives cobalt oxide an unusually rich electronic and magnetic structure, making it a promising candidate for spintronics, the next-generation technology expected to replace conventional electronics in many applications.
"At our institute, we had previously been modeling the physical properties of magnetite, the oldest magnetic material known to humankind," said Dr. Przemyslaw Piekarz, a professor at the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Cracow. "In terms of crystal structure, the studied cobalt oxide differs from magnetite only in that it contains cobalt atoms instead of iron atoms. We were therefore perfectly prepared for the task."
The experiments, described in the Journal of the American Chemical Society, involved a thin layer of cobalt oxide—just 27 nanometers thick—first excited by a pump laser pulse and then probed by a second laser after a controlled delay. When the team used higher-energy (blue) pump light at 3.10 eV, they observed something unexpected: the formation of Jahn-Teller polarons, quasiparticles that represent specific distortions in the crystal lattice. Lower-energy (red) light at 1.55 eV produced different behavior, with intensity oscillations but no polaron formation.
The theoretical framework that made sense of these vibrations came from the Polish team at IFJ PAN, working alongside colleagues from the University of Pavia, the Swiss Federal Institute of Technology Lausanne, the Paul Scherrer Institute, the University of Texas at Austin, MIT, and Northeastern University. Together, they confirmed that the coherent vibrations recorded in the crystal lattice were signatures of these previously unexplored polaronic states.
The discovery opens new doors for ultrafast spintronic devices, where the goal is to manipulate electron spins at unprecedented speeds. Because Jahn-Teller polarons strongly influence a material's structural, electrical, and magnetic properties simultaneously, understanding and controlling them could lead to faster, more efficient technologies down the line.