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Thanh Nguyen has a habit of breaking down barriers. Take languages for example: Nguyen, a third-year graduate student in nuclear science and engineering (NSE), wanted to “connect with other people and cultures” for his work and social life, he says, so he learned Vietnamese. , French, German and Russian, and is now taking an MIT course in Mandarin. But this drive to overcome obstacles really comes to the fore in his research, where Nguyen is trying to unravel the secrets of a thriving new branch of physics.
“My thesis focuses on neutron scattering on topological semimetals, only discovered experimentally in 2015,” he says. “They have very special properties, but because they are so new, there is much unknown and the neutrons offer a unique perspective to probe their properties to a new level of clarity.”
Topological materials do not perfectly fit the conventional categories of substances found in everyday life. They were first materialized in the 1980s, but only became practical in the mid-2000s with an in-depth understanding of topology, which deals with geometric objects whose properties remain the same even when objects undergo extreme deformation. Researchers have experimentally discovered topological materials even more recently, using the tools of quantum physics.
Within this domain, topological semimetals, which share the qualities of metals and semiconductors, are of particular interest to Nguyen. “They offer high levels of thermal and electrical conductivity and inherent robustness, which makes them very promising for applications in microelectronics, energy conversions and quantum computing,” he says.
Intrigued by the possibilities that could emerge from such “unconventional physics”, Nguyen is pursuing two related but distinct areas of research: “On the one hand, I am trying to identify and then synthesize new and robust topological semimetals, and on the other, I want to detect new fundamental physics with neutrons and further designing new devices “.
On a fast search track
Achieving these goals in the coming years may seem like a tall order. But at MIT, Nguyen took every opportunity to master the specialized techniques needed to conduct large-scale experiments with topological materials and get results. Led by his advisor, Mingda Li, assistant professor Norman C Rasmussen and director of the Quantum Matter Group within NSE, Nguyen was able to immerse himself in meaningful research even before setting foot on campus.
“Last summer, before I joined the group, Mingda sent me on a trip to Argonne National Laboratory for a very fun experiment that used synchrotron X-ray scattering to characterize topological materials,” recalls Nguyen. “Learning the techniques fascinated me in the field and I began to see my future.”
During his first two years of graduate school, he participated in four studies, serving as the lead author on three journal articles. In a noteworthy project, described earlier this year in Physical Review Letters, Nguyen and other researchers from the Quantum Matter Group demonstrated, through experiments conducted in three national laboratories, unexpected phenomena involving the way electrons interact. they move through a topological semimetal, tantalum phosphide (TaP).
“These materials inherently resist perturbations like heat and noise and can conduct electricity with a degree of robustness,” says Nguyen. “With robust properties like this, some materials can conduct electricity better than the best metals and in some circumstances superconductors, which is an improvement over current generation materials.”
This discovery opens the door to topological quantum computing. Current quantum computing systems, in which the elementary units of computation are qubits that perform superfast computations, require superconducting materials that only function in extremely cold conditions. Fluctuations in heat can take one of these systems out of action.
“Properties inherent in materials such as TaP could form the basis of future qubits,” says Nguyen. Imagine synthesizing TaP and other topological semimetals – a process involving the delicate cultivation of these crystal structures – and then characterizing their structural and excitational properties with the help of neutron beam and X-ray technology, which probe these materials at the level atomic. This would allow them to identify and distribute the right materials for specific applications.
“My goal is to create programmable artificial structured topological materials, which can be applied directly like a quantum computer,” says Nguyen. “With infinitely better heat management, these quantum computing systems and devices could prove to be incredibly energy efficient.”
Physics for the environment
Energy efficiency and its benefits have long worried Nguyen. Born in Montreal, Quebec, with an aptitude for math and physics and a concern for climate change, he devoted his senior year of high school to environmental studies. “I worked on a Montreal initiative to reduce heat islands in cities by creating more urban parks,” he says. “Climate change was important to me and I wanted to have an impact.”
At McGill University, he majored in physics. “I was fascinated by the problems on the ground, but I also felt I could apply what I learned to achieve my environmental goals,” he says.
In both classrooms and research, Nguyen immersed himself in several domains of physics. He worked for two years in a high-energy physics laboratory making neutrino detectors, part of a much larger collaboration trying to verify the Standard Model. In the fall of his senior year at McGill, Nguyen’s interest gravitated towards studying condensed matter. “I really enjoyed the interplay between physics and chemistry in this area, and I particularly enjoyed exploring issues related to superconductivity, which seemed to have many important applications,” he says. That spring, looking to add useful skills to his research repertoire, he worked at Ontario’s Chalk River Laboratories, where he learned to characterize materials using neutron spectroscopes and other tools.
These academic and practical experiences served to propel Nguyen towards his current undergraduate course. “Mingda Li came up with an interesting research plan, and although I didn’t know much about the topological materials, I knew they had recently been discovered and I was excited to enter the field,” he says.
Man with a plan
Nguyen has mapped out the remaining years of his doctoral program and they will prove challenging. “It’s difficult to work with topological semimetals,” he says. “We don’t yet know the optimal conditions for synthesizing them and we need to produce these crystals, which are micrometers to scale, in quantities large enough to allow testing.”
With the right materials in hand, he hopes to develop “a qubit structure that isn’t as vulnerable to perturbations, rapidly advancing the field of quantum computing so that computations now taking years could only take a few minutes or seconds,” he says. . “Significantly faster computation speeds could have huge impacts on issues like climate, health or finance that have major ramifications for society.” If his research on topological materials “benefits the planet or improves the way people live,” says Nguyen, “I’d be totally happy.”
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