A carousel turns. If you try to stop it, you feel a resistance — angular momentum. The same physical principle also applies inside crystals, at the level of individual atoms. Yet for a long time, physicists could not directly observe how angular momentum is distributed and transferred there. Now researchers have made this process visible for the first time.
More than 100 years ago, Albert Einstein and his colleague Wander Johannes de Haas made a curious observation: when the magnetization of a metal rod changes, the rod itself begins to rotate. The experiment revealed a deep connection between magnetism and rotational motion. But how angular momentum is transferred between different atomic vibrations inside a crystal remained unclear.
An international research team involving the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and Technische Universität Dresden has now succeeded in directly observing and controlling this process for the first time. The results were published in the journal Nature Physics.
Fundamental research with potential technical relevance
“I find it fascinating how physical laws are directly dictated by the symmetries of nature,” says Olga Minakova, who led the experiment. Sebastian Maehrlein from HZDR and TU Dresden emphasizes the significance of the results: “We have discovered something fundamentally new here that will hopefully find its way into textbooks.”
In the long term, the findings could help researchers better control ultrafast processes in quantum materials. Such materials are considered possible building blocks for future information and storage technologies.
Original publication:
O. Minakova, C. Paiva, M. Frenzel, M. S. Spencer, J. M. Urban, C. Ringkamp, M. Wolf, G. Mussler, D. M. Juraschek, S. F. Maehrlein: Observation of angular momentum transfer among crystal lattice modes, in Nature Physics, 2026.
