| Feb 02, 2026 |
Researchers adapted ARPES to work in magnetic fields using nanoscale alternating magnets that confine fields near a sample, letting photoelectrons travel straight.
(Nanowerk News) With an advanced technology known as angle-resolved photoemission spectroscopy (ARPES), scientists are able to map out a material’s electron energy-momentum relationship, which encodes the material’s electrical, optical, magnetic and thermal properties like an electronic DNA. But the technology has its limitations; it doesn’t work well under a magnetic field. This is a major drawback for scientists who want to study materials that are deployed under or even actuated by magnetic fields. Inspired by refrigerator magnets, a team of Yale researchers may have found a solution.
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Their study was featured recently on the cover of the The Journal of Physical Chemistry Letters (“Sub-tesla On-Chip Nanomagnetic Metamaterial Platform for Angle-Resolved Photoemission Spectroscopy”).
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| Refrigerator-magnet–inspired design reveals quantum materials under magnetic fields. (Image: Yale University)
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Quantum materials – such as unconventional superconductors or topological materials – are considered critical to advancing quantum computing, high-efficiency electronics, nuclear fusion, and other fields. But many of them need to be used in the presence of a magnetic field, or even only become activated by magnetic fields. Being able to directly study the electronic structure of these materials in magnetic fields would be a huge help in better understanding how they work.
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Typically, ARPES technology can’t measure electronic structures in a magnetic field because the magnetic field throws the photoelectrons off their natural trajectory and causes them to move in circles.
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“So it becomes almost impossible to reconstruct the electron behavior in the solid based on what our detector sees,” said Yu He, assistant professor of applied physics.” It has been a long-standing challenge to directly measure electronic structures under a magnetic field. Without it, we’re essentially blind to how the electronic states evolve under a magnetic field.”
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It turns out the solution to this long-standing scientific challenge was hiding in plain sight – stuck to the doors of millions of refrigerators. Drawing inspiration from the common refrigerator magnets found in gift shops everywhere, He and his research team came up with a solution. Instead of using one large magnet, the researchers place the sample on a substrate made of many tiny magnets of alternating polarities.
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“A fridge magnet sticks to the fridge door very strongly, but if you pull it off just a tiny bit, that attractive interaction goes away – it essentially falls off,” said Wenxin Li, first author of the paper and a Ph.D. student in He’s lab. “From afar, the magnetic field decays very quickly. But if you were to stay very close to the surface, the magnetic field is actually very strong.”
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Li explained that their system constrains the magnetic field to just a few tens of nanometers above the material.
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“And then it will essentially drop to zero beyond that,” Li said. “And the photoemitted electron will only experience the magnetic field for nanoseconds, then the magnetic field is practically gone, and the electron will just continue in a straight line.”
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This magnetic structure is akin to an industrial mainstay known as the Halbach array, and He said its introduction to quantum materials study is a serendipitous interdisciplinary adventure with many brilliant collaborators.
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“We asked ourselves, how could one make nano-scale Halbach-like arrays? Well, we had a neighbor in Becton center – the Schiffer group – that is a world leader in this. We asked ourselves, how can we figure out the actual surface magnetic field and put quantum materials onto such an array? Our colleagues at Boston College and Georgia Tech – the Ma group and the Du group – came to our rescue,” said He. “Then of course, our long-term collaborators at Rice university are indispensable to help ascertain the photoelectron trajectory through elegant analytical derivations.”
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The researchers noted that this collaborative approach was key to the breakthrough.
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“One should definitely keep an open mind in interdisciplinary research – a stone from another mountain may become your jade!” He said.
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Going forward, the researchers say their method could significantly open up research possibilities in their field.
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“Understanding the electron behavior under a magnetic field in the past has been almost impossible with ARPES,” He said. “With this development, we’re really hoping that this opens the door to direct electronic investigations of many field-induced electronic phenomena such as flatband superconductivity and magnetic vortices.”
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