Jung Ho Kim is making quantum visible at the Advanced Photon Source

Physicist Jung Ho Kim has dedicated his career to the resonant inelastic X‑ray scattering (RIXS) technique, a powerful tool for discovery. At the U.S. Department of Energy’s (DOE) Argonne National Laboratory, he uses the technique to measure miniscule changes in the particles that make up metals and other materials.

Kim works in the Advanced Photon Source (APS), a DOE Office of Science user facility.

“Ultimately, my goal is to help scientists from all over the world figure out why their material behaves the way it does,” he said.

This understanding is the first step toward innovation. The research he supports has a range of applications, from understanding superconductivity and unusual magnetism to improving battery technology and quantum computing.

“My goal is to keep pushing the capabilities of RIXS so that it remains one of the most powerful tools for scientific discovery. Whether that means improving energy resolution, reducing beam size, accelerating measurements or inventing new measurement modes, the aim is to let users see the electron, spin and orbital dynamics that tomorrow’s science will demand — today.” — Jung Ho Kim, physicist at the APS

“I’ve always been interested in understanding how things work,” Kim said. ​“That’s what drew me to physics.”

This early curiosity motivated him to focus on his studies. Growing up in South Korea in a time of social, economic and political change, Kim was a diligent student. He attended Seoul National University, where he studied physics.

His research focused on photoemission spectroscopy. This technique involves shining beams of light, such as X-rays, onto a sample in a vacuum. The light knocks out the sample’s electrons. By measuring the energies (and sometimes directions) of emitted electrons, scientists learn what energy levels electrons occupied inside the material and how they move.

“It’s like shining a light to eject swimmers from a pool and timing their exits to infer how they were swimming,” Kim said. ​“This reveals a material’s electronic landscape, which controls properties such as conductivity, magnetism and superconductivity.”

After completing his Ph.D., Kim moved to Canada for postdoctoral research at the University of Toronto and began working with RIXS.

“RIXS was a newly emerging spectroscopy tool,” he recalled. ​“I could see enormous potential for growth in this field.”

Revealing how particles move and interact

In simple terms, RIXS is a tool that lets scientists detect and study the ways groups of particles in a material move and interact.

RIXS can provide information about the lattice (how atoms vibrate). It can also reveal charge (how electric charge moves), spin (how tiny magnets behave) and orbitals (how electrons occupy different orbits). All those behaviors are linked, and information gathered via RIXS can help scientists understand why the material acts the way it does. This information is very applicable in quantum science.

Kim said, ​“At its core, RIXS studies are about exploring beautiful new states of matter that no one’s seen before.”

Like many other scientists from across the globe, he came to Argonne and the APS to do his research.

“The APS had the only hard X‑ray RIXS facility in the United States,” he said. ​“Without it, I couldn’t have done my research.”

Thomas Gog, who oversaw the RIXS beamline at that time, encouraged Kim to consider a position at the APS. Kim did not take much convincing.

Shortly after Kim joined the APS, he led a project on observing collective spin excitations with hard X-ray RIXS. His team established for the first time that X-rays can see collective spin excitations that were historically the domain of neutrons.

Teamwork, a Core Value at Argonne, accelerates the work at the APS. Because of the people and resources available to them, scientists at the APS can quickly go from idea to experiment, Kim explained.

“When a new idea pops into my head, we can usually try it out the same week, sometimes the same day,” he said. ​“If it works, we turn it into a new capability and immediately make it available to researchers from around the globe.”

Expanding the capabilities of RIXS at the APS

Kim officially joined the APS in 2008 as a postdoctoral researcher. In 2009, he became part of the beamline staff.

He now works at Sector 27, the current RIXS beamline at the APS and source of pride for Argonne. When the APS delivered its brighter X-ray beams as part of the APS Upgrade (APS-U) project, Sector 27 was the first beamline to come back online.

“We remain the leading RIXS facility in the world,” Kim said. ​“The APS-U has bolstered our leadership, making [mega-electron volt] energy resolution measurements faster and more robust.”

Kim’s responsibilities include keeping Sector 27 running smoothly. He advances RIXS techniques whenever he can.

As critical fields such as quantum mechanics continue to evolve, they present new demands for experimental techniques. Kim is eager to take on these challenges.

“My goal is to keep pushing the capabilities of RIXS so that it remains one of the most powerful tools for scientific discovery,” he said. ​“Whether that means improving energy resolution, reducing beam size, accelerating measurements or inventing new measurement modes, the aim is to let users see the electron, spin and orbital dynamics that tomorrow’s science will demand — today.”

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