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Joe Paddison: Uncovering hidden information in neutron scattering data with computational science

Joe Paddison a Eugene P. Wigner Fellow, studies how statistical sampling methods can be coupled with neutron scattering experiments of magnetic and other new materials to provide richer information. Image credit: Carlos Jones/Oak Ridge National Laboratory, U.S. Department of Energy.

Topic: Materials

Joe Paddison, a Eugene P. Wigner Fellow at the Department of Energy’s Oak Ridge National Laboratory, believes there’s more information to be found in neutron scattering data than scientists like himself might expect.

Paddison, who completed his PhD in inorganic chemistry through a joint project of Oxford University and Britain’s neutron source in Oxfordshire, England, says today’s new materials aren’t always available as single crystals, the ideal form for study. Instead, they may be available only as polycrystals, a form that limits the amount of information gathered from experiments.

Single crystals, like those characteristic of gemstones, are ideal because their atoms form a repeating, “periodic” arrangement in three dimensions.

When neutron scattering scientists work with polycrystals, the experimental data detected is shown in one dimension rather than three, so they get less information from their experiments.

“We can’t always make a perfect sample, but nevertheless the materials remain interesting to study,” Paddison said. “By using computational techniques, we can obtain the type of information from powders that we thought we could only get from crystals.”

Paddison’s fellowship research focuses on uncovering hidden information about how magnetic materials behave, and he says neutrons are a particularly good vehicle because they have a magnetic moment and can return very detailed information on nanometer length scales.

Paddison works in the Materials Science and Technology Division with his mentor, neutron scattering scientist Andy Christianson.

Paddison says that bulk magnets like the ones that stick on your fridge are well understood because each atom has a magnetic moment, and all the moments point in the same direction. The magnetic moments of today’s new magnetic materials form more complicated patterns, and often the patterns don’t repeat and aren’t fixed.

“One of the focuses of my work is trying to understand what kind of interactions drive that complicated behavior to create those patterns and states, and how we can extract that information with neutron scattering,” he said.

Paddison says that in addition to the “really nice experiments you can do at the Spallation Neutron Source,” another great thing about being at ORNL is that he’s “right here next to the people who make materials,” referring to the Laboratory’s broad-ranging materials research and development efforts.

“I’ll work with a lot more interesting materials here, I’m sure,” he added.

Some of the interesting new materials Paddison is studying may prove to be quantum-spin liquids. Because of their liquid-like magnetic state, quantum-spin liquids lack a conventional magnetic structure, and their magnetic moments are constantly in motion.

“The magnetic moments of quantum-spin liquids fluctuate all the time, but they’re also driven by quantum effects, so you have this entangled state driven by magnetism,” he explained.

Understanding these phenomena could lead to development of better quantum computers that incorporate quantum materials to facilitate entanglement.

Paddison credits geometry classes with inspiring his love of shapes, which led to his interest in chemistry and investigating crystalline structures, and his undergrad research experience introduced him to the joys of empirical study. His inorganic chemistry coursework taught him a lot about materials, and he thinks of himself as a physicist given the time he’s spent understanding them with neutrons. Using computational methods to extract as much information as possible from an experiment, he says, is the bit he really likes.

Like many of today’s early-career scientists, he enjoys working at the edge of multiple fields. “I guess it’s really best to do the best science you can without worrying too much about how to classify it,” Paddison reflected. “It doesn’t really matter what you call it because it’s all science.”

A Brit by birth, Paddison has bounced back and forth between the United States and home over the past few years. After receiving his PhD from Oxford University, he moved into a postdoctoral fellowship at Georgia Tech, where he focused on neutron spectroscopy. He then held a junior research fellowship in physics at the University of Cambridge before coming to Oak Ridge as a Wigner Fellow. “I like it a lot in the States, so here I am back again,” he smiled.

Paddison’s main interest outside science is music: he played guitar in a funk band growing up in Britain. “This is a really exciting place to be from that point of view,” Paddison said. “Such a range of music has come out of Tennessee and the South in general.”

Paddison cites Americana, alternative country and the blues as among his favorites, in addition to funk, which he says “is very fun to play. Maybe when things quiet down I’ll find another band over here!”

The Spallation Neutron Source is a DOE Office of Science User Facility.

UT-Battelle manages ORNL for DOE’s Office of Science. The single largest supporter of basic research in the physical sciences in the United States, the Office of Science is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.