Scientists have used radio waves to control the magnetic spin of a single atomic nucleus, achieving a result that challenges their understanding of how atomic magnetism works. The experiment, conducted at Delft University of Technology and published in Nature Communications, demonstrates that nuclear spin can be manipulated under conditions where researchers did not expect it to respond.
Unlike the relatively strong magnetism associated with electrons, nuclear magnetism is extremely weak and more isolated from its surroundings. “By far the strongest magnetism comes from the electrons,” says lead researcher Sander Otte. “But in some atoms, the nucleus also carries a spin. That spin is much weaker, but it is also much better shielded from the outside world.
To investigate magnetism at the atomic scale, Otte’s team uses a modified scanning tunneling microscope capable of directing electrical signals at individual atoms. Previous experiments primarily examined electron spin, which is easier to detect and manipulate. Nuclear spin could be observed indirectly through the hyperfine interaction, a quantum coupling between the magnetic properties of an electron and the nucleus.
In the latest experiment, lead author Hester Vennema and her colleagues applied two signals simultaneously, one targeting the electron and another targeting the nucleus. By examining their effects separately, the researchers discovered that they could flip the nuclear spin even when it was largely disentangled from the electron spin. This contradicted their expectation that the nucleus would not respond independently to the microscope’s electrical signals.
“According to our simple understanding, this should not really happen,” says Otte. “The nuclear spin should not be sensitive at all to the electrical signals from a scanning tunneling microscope.”
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