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Crack the secrets in a new branch of physics MIT News

Thanh Nguyen has a habit of breaking down barriers. Take language, for example: Nguyen, a third-year doctoral student in nuclear science and technology (NSE), wanted to “connect with other people and cultures” for his work and social life, he says, learning Vietnamese, French, German and Russian. and is now taking an MIT course in Mandarin. But this attempt to push past obstacles really emerges in his research, where Nguyen tries to crack the secrets of a new and budding branch of physics.

“My dissertation focuses on neutron scattering on topological semi-metals, which was first discovered experimentally in 2015,” he says. “They have very special properties, but because they are so new, there is a lot that is unknown, and neutrons offer a unique perspective to study their properties on a new level of clarity.”


Topological materials do not fit nicely into conventional categories of substances found in everyday life. They first materialized in the 1980s, but only became practical in the mid-2000s with an in-depth understanding of topology, which relates itself to geometric objects whose properties remain the same even when the objects undergo extreme deformation. Scientists experimentally discovered topological materials even more recently using the tools of quantum physics.

Within this domain, topological semi-metals that share qualities of both metals and semiconductors are of particular interest to Nguyen. “They offer high levels of thermal and electrical conductivity and inherent robustness, making them very promising for applications in microelectronics, energy conversion and quantum computing,” he says.

Fascinated by the possibilities that can arise in such “unconventional physics”, Nguyen pursues two related but different areas of research: “On the one hand, I try to identify and then synthesize new, robust topological semi-metals and on the other hand, I want to discover fundamentally new physics with neutrons and further design new units. ”

On a fast track to research

Achieving these goals over the next few years may seem like a high order. But at MIT, Nguyen has used every opportunity to master the specialized techniques required to perform large-scale experiments with topological materials and achieve results. Supervised by his advisor, Mingda Li, Norman C Rasmussen Assistant Professor and Director of the Quantum Matter Group within the NSE, Nguyen was able to dive into significant research, even before setting foot on campus.

“The summer before I joined the group, Mingda sent me on a trip to the Argonne National Laboratory for a very fun experiment that used synchrotron X-ray scattering to characterize topological materials,” Nguyen recalls. “Learning the techniques fascinated me in the field and I began to see my future.”

During the first two years of graduate school, he participated in four studies and served as lead author of three journals. In a remarkable project described earlier this year in Physical review letters, Nguyen and other Quantum Matter Group scientists demonstrated through experiments performed at three national laboratories unexpected phenomena involving the way electrons move through a topological semimetal, tantalum phosphide (TaP).

“These materials resist inherent disturbances such as heat and ailments and can conduct electricity with a level of robustness,” says Nguyen. “With robust properties like this, certain materials can conduct electricity better than the best metals, and in some circumstances superconductors – which is an improvement over the current generation of materials.”

This discovery opens the door to topological quantum computation. Current quantum computing systems, where elementary computing devices are qubits that perform super-fast computations, require superconducting materials that operate only in extremely cold conditions. Fluctuations in heat can throw one of these systems out of whack.

“The properties associated with materials such as TaP could form the basis of future qubits,” says Nguyen. He envisions synthesizing TaP and other topological semimetals – a process involving the delicate cultivation of these crystalline structures – and then characterizing their structural and excitation properties using neutron and X-ray technology, which study these materials at the atomic level. This would allow him to identify and implement the right materials for specific applications.

“My goal is to create programmable artificial structured topological materials that can be used directly as a quantum computer,” says Nguyen. “With infinitely better heat management, these quantum computing systems and devices can prove to be incredibly energy efficient.”

Physics for the environment

Energy efficiency and its benefits have long affected Nguyen. A native of Montreal, Quebec, with an ability in math and physics and a concern for climate change, he devoted his final year of high school to environmental studies. “I was working on a Montreal initiative to reduce the heat islands in the city by creating more city parks,” he says. “Climate change was important to me and I wanted to make an impact.”

At McGill University, he took physics. “I was fascinated by problems in the field, but I also felt that I could eventually apply what I learned to meet my goals of protecting the environment,” he says.

In both classes and research, Nguyen immersed himself in various physical domains. He worked for two years in a high-energy physics laboratory, manufacturing detectors for neutrinos, part of a much larger collaboration that sought to verify the standard model. In the fall of his senior year at McGill, Nguyen took an interest in condensed drug research. “I really enjoyed the interplay between physics and chemistry in this area and especially enjoyed exploring superconductivity issues, which seemed to have many important uses,” he says. That spring, as he sought 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 toward his current master’s degree course. “Mingda Li proposed an interesting research plan, and although I did not know much about topological materials, I knew that they had recently been discovered and I was excited to get into the field,” he says.

Man with a plan

Nguyen has mapped out the remaining years of his doctoral program and they will prove demanding. “Topological semi-metals are difficult to work with,” he says. “We do not yet know the optimal conditions for synthesizing them, and we need to produce these crystals, which are in micrometers in scale, in quantities large enough to enable testing.”

With the right materials in hand, he hopes to develop “a qubit structure that is not as vulnerable to interference, fast forward in quantum computation, so computations that now take years may only require minutes or seconds,” he says. “Much higher calculation rates can have huge consequences for problems such as climate or health or the economy that have important consequences for society.” If his research into topological materials “benefits the planet or improves the way people live,” Nguyen says, “I would be completely happy.”

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