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Powerful New Measurement Technique Using Neutron Orbital Angular Momentum and Spins

20 November 2019

Using neutrons as probes, a wide variety of material properties can be investigated. An international team of researchers and engineers, among them Dr. Kirill Zhernenkov of Forschungszentrum Jülich, is now paving the way for a further powerful neutron analysis method for materials with complex and spiral structures. For the first time, these neutron experts have developed a way of simultaneously tailoring two helpful quantum properties of neutron beams.

When neutrons are collimated into particle beams, they have the capability of penetrating deep into materials without destroying them. They interact with atoms, changing their direction and velocity by doing so, and thereby revealing where certain atoms are located and how they move around. Since neutrons have a spin – or angular momentum – they are also able to react to magnetic properties in the materials being investigated.

Depending on the objective of the experiment, neutron beams must be prepared differently before they collide with samples. For instance, in studies on magnetic samples, only neutrons with a specific spin direction are used. If these scatter from magnetic moments, they alter their spin direction, which can then be measured.

The international team, working at research centres in Canada, the United States, Russia and Jülich, also used a neutron beam with a single spin direction. However, by passing the neutron beam through a carefully synchronized arrangement of triangular magnetic coils, the scientists were able to add a twist – known as orbital angular momentum – to the neutrons, making them wind like corkscrews around an imaginary centre line.

“Our method makes it possible for the first time to control the spin orientation and the angular momentum of neutrons simultaneously,” explains Dr. Kirill Zhernenkov, chief instrument scientist and researcher at the Jülich Centre for Neutron Science. “In principle, we can thus ‘tailor’ numerous fine neutron beams within the main beam. This makes new investigations possible.”

Chiral molecules, for example, can now be differentiated from each other for the first time using spiral neutron beams. These molecules behave like a mirror image of each other, and cannot be transposed over each other by simple rotation, similar to a right and a left hand. Spiral and complex magnetic structures, such as skyrmions or the interior of topological isolators, can also be studied more precisely with the help of these tailor-made neutron beams. Such materials are important candidates for computers of the future.

Original publication:

Dusan Sarenac, Connor Kapahi, Wangchun Chen, Charles W. Clark, David G. Cory, Michael G. Huber, Ivar Taminiau, Kirill Zhernenkov, Dmitry A. Pushin;
Generation and detection of spin-orbit coupled neutron beams

Proceedings of the National Academy of Sciences, October 8, 2019 116 (41) 20328-20332.

Further information:

“A twist and a spin: harnessing two quantum properties transforms a neutron beam into a powerful probe of material structure”

Article from the National Institute of Standards and Technology (NIST) from 29.10.2019