Once a Crystal Collector, Now a Crystal Scientist

Since earning his doctorate in solid-state physics through the APS Bridge Program, Brian Casas says it feels like life has come full circle.

By Liz Boatman | October 13, 2023

Brian Casas has liked crystalline solid-state materials his entire life — long before he knew that’s what they were called. As a kid, he decorated his parents’ house with rocks he found, eventually becoming an avid crystal collector.

“That’s why I started college as a chemistry major, thinking that was how I could understand materials and their properties,” he says. “But I ended up moving into physics because ultimately I wanted to understand the complex states of matter that exist within crystalline materials.”

Today, Casas, an APS Bridge Program graduate, is a senior process engineer in crystal growth at Coherent Corp., a Pennsylvania-based company that engineers materials for diverse applications. The program, established in 2012 to increase the number of underrepresented minority students who earn PhDs in physics, now has 47 partner schools across the country. Partner schools — which retain more of these students than the national average — have graduated 27 students since 2019, doubling what the data projects the graduation rate would have been without the Bridge Program.

At Coherent, Casas puts his skills to work as a crystal grower. “It's interesting — I'm in the production group,” he says. “This means I'm looking at the quality of crystals weekly, trying to identify emerging problems or concerns or deviations from what we expect, and then working backwards to find the root cause and correct it.”

Despite working in physics today, Casas didn’t take his first physics course, AP Physics, until his senior year of high school, in 2008. “It demolished me,” he says, even though he’d been a star chemistry student in his school’s accelerated science track since middle school.

Compared to chemistry, physics was “an entirely different mode of thought,” Casas says. “Suddenly there was open-ended problem solving and a mantra of ‘derive, don’t memorize.’”

He says AP Physics was so challenging that he questioned his intent to study physics in college, which had been his plan. “After I started taking that physics class, I thought, ‘no, no, no — maybe chemistry is for me.’”

In 2009, when he started college at Rutgers University in New Jersey, he initially enrolled as a chemistry student intending to specialize in chemical physics.

“When I started taking chemical physics courses at Rutgers, I was still taking Intro to Physics,” he says. Taking physics again, with a different instructor, “healed the wounds I had from my AP physics experience,” he says. He decided physics was still the best path toward a career focused on crystalline materials.

So, starting his sophomore year, he enrolled in the classes a physics major would need. But because he started his physics major “a year late,” he always felt “a little bit on the outside,” he says — unsure about his track.

As a senior, he finally took solid-state physics, the course in which majors learn to apply concepts in crystallography, quantum mechanics, and solid-state chemistry to solids and crystalline materials. “I finally really felt grounded. It gave me a good perspective on why I took this major to begin with,” says Casas. “That motivated me enough to pursue graduate school.”

Unfortunately, Casas’ graduate school applications came back as rejections, but one school suggested he look into the APS Bridge Program.

“I had never heard of [the program] before. It was actually brand new,” he says. “But when I looked into it, I could see how the program would help me bridge the gaps that I had.” He says that because he hadn’t developed many close relationships with faculty mentors during college, his grad school applications had fallen short, despite his good grades.

Casas submitted an application to the University of South Florida’s Bridge Program in applied physics and was accepted immediately. “The Bridge Program offered a lot of mentorship, a lot of interactions with faculty members,” he says.

Casas stayed at USF for two years, completing his master’s on “exotic” behavior in magnetic insulator materials. He thought hard about whether the program was the right fit for his doctoral studies. By then, he had developed a deeper interest in an area of condensed-matter physics — “so-called heavy fermions, materials that contain F electrons,” he says — that USF wasn’t able to support experimentally.

Heavy fermion compounds are intermetallic materials that tend to contain elements from the F-block on the periodic table, down at the bottom. “They start to behave as if they're thousands of times heavier than they really are,” says Casas, leading to “exotic behaviors.” He was captivated.

Casas decided the University of California, Irvine, was a better fit. In 2015, he made the difficult decision to apply to a new doctoral program and uproot his life.

At UC-Irvine, his research was focused on looking for “signatures of exotic physics” in heavy fermion insulators, he says. He focused on samarium hexaboride, which exhibits different conductivity properties based on temperature.

Casas spent two years developing a method for measuring the thermal conductivity — a material’s ability to transmit heat — of the crystals he was growing in the lab, while stretching them at extremely low temperatures. When he plotted his first set of data against the power law function predicted by theory, it “fit perfectly,” he says.”

“I'd finally ironed out the kinks. But that memory is slightly bittersweet, because two weeks later, the university shut down because of COVID,” he recalls. “All experiments had to stop.”

Eventually, Casas was able to return to the lab and collect enough data to graduate. In 2020, he landed a postdoc at the National High Magnetic Field Laboratory in Florida, where his research focused on a layered magnetic compound containing iron, germanium, and tellurium. The crystal is considered ‘exfoliable’ — the thin layers can be easily separated, creating 2D magnetic sheets, says Casas. The project leaned into his crystal growth and characterization skills. “It was a really nice culmination of all the work that I’d done up to that point,” he says.

In April 2023, Casas accepted an offer from Coherent, where he’s now working with silicon carbide — a material that’s poised to impact the future of electric vehicles and the power grid.

“Being able to use what experience I have in crystal growth towards something that has societal impact is something I couldn't have imagined years ago,” he says.

Liz Boatman is a staff writer for APS News.