Like on a Ferris wheel, a powerful terahertz laser drives the atoms of a crystal along precise circular paths. The resulting collective oscillation of the crystal lattice was traced stroboscopically using ultrashort laser pulses; blue lines: measured data Credit: Minakova/Maehrlein/Schröder An international team of researchers, including scientists from HZDR and Fritz Haber Institute of the Max Planck Society, for the first time directly observed how angular momentum is transferred and conserved within a crystal lattice. Using intense terahertz laser pulses, the researchers were able to selectively control these processes, which unveiled a surprising effect: During the angular momentum transfer, the direction of rotation reverses—caused by the rotational symmetry of the material. The results, published in Nature Physics , provide new insights into the foundation of magnetism and open up possibilities for tailored control of quantum materials.…