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Bangladeshi scientist leads discovery of a novel quantum state of matter

  • Published at 10:47 am September 18th, 2018
Bangladeshi physicist M Zahid Hasan
Bangladeshi physicist of Princeton University leads an international team of researchers’ in discovering a novel quantum state of matter that can be manipulated at will with a weak magnetic field, opening up new possibilities for next-generation nanotechnologies and quantum computing. Researchers in Hasan’s lab include (from left): Jia-Xin Yin, Zahid Hasan, Songtian Sonia Zhang, Daniel Multer, Maksim Litskevich and Guoqing Chang Courtesy: Princeton University

Zahid and team’s research opens up new possibilities in nanotechnology

A Bangladeshi physicist has led an international research team in discovering a novel quantum state of matter that can be “tuned” at will and is 10 times more tunable than existing theories can explain. 

M Zahid Hasan of Princeton University in the US says his team’s discovery of this level of manipulability of quantum matter opens up enormous possibilities for next-generation nanotechnologies and quantum computing.

“We expect this is the tip of the iceberg,” he said. “There will be a new subfield of materials or physics grown out of this. … This would be a fantastic playground for nanoscale engineering.”

Hasan, a former Dhanmondi Government Boys High School and Dhaka College student, shot to fame in 2014 when he led a team of scientists which finally discovered “Weyl fermion”. 

The existence of the elusive massless particle was first predicted in 1929 by physicist Hermann Weyl, a colleague of Albert Einstein at Princeton, while pursuing an alternative theory of gravity.

Hasan and his team are calling their discovery a “novel” quantum state of matter because it is not explained by existing theories of material properties. 

“This has implications for nanotechnology research especially in developing sensors,” he said. 

The groundbreaking research – “Giant and anisotropic spin-orbit tunability in a strongly correlated kagome magnet” – appears in the current issue of the scientific journal Nature.

In the paper, Hasan said he and his colleagues found a strange quantum effect on the new type of topological magnet that can be controlled at the quantum level. 

“The key was looking not at individual particles but at the ways they interact with each other in the presence of a magnetic field,” Hasan said. 

“Some quantum particles, like humans, act differently alone than in a community. You can study all the details of the fundamentals of the particles, but there’s no way to predict the culture, or the art, or the society, that will emerge when you put them together and they start to interact strongly with each other.”

Quantum culture

To study this quantum “culture”, he and his colleagues arranged atoms on the surface of crystals in many different patterns and watched what happened. They used various materials prepared by collaborating groups in China, Taiwan and Princeton.

One particular arrangement - a six-fold honeycomb shape called a “kagome lattice” for its resemblance to a Japanese basket-weaving pattern - led to something startling. 

All the known theories of physics predicted that the electrons would adhere to the six-fold underlying pattern, but instead, the electrons hovering above their atoms decided to march to their own drummer — in a straight line, with two-fold symmetry.

“The electrons decided to reorient themselves,” Hasan said. “They ignored the lattice symmetry. They decided that to hop this way and that way, in one line, is easier than sideways. So this is the new frontier. … Electrons can ignore the lattice and form their own society.”

This behaviour was only visible when examined under a spectromicroscope in the presence of a strong magnetic field.

“The researchers were shocked to discover this two-fold arrangement,” Songtian Sonia Zhang, a graduate student in Hasan’s lab and the third co-first-author on the paper, said. 

“We had expected to find something six-fold, as in other topological materials, but we found something completely unexpected. We kept investigating and found more unexpected things. It’s interesting because the theorists didn’t predict it at all. We just found something new.”

Hasan said that although there are many things scientists can calculate based on the existing theory of quantum materials, the team’s paper is exciting because it is showing an effect that was not known. 

“The fact that we found a material with such a large effective g factor, meaning that a modest magnetic field can bring a significant effect in the system — is highly desirable. 

“This gigantic and tunable quantum effect opens up the possibilities for new types of quantum technologies and nanotechnologies.”

The discovery was made using a two-story, multi-component instrument known as a scanning tunneling spectromicroscope, operating in conjunction with a rotatable vector magnetic field capability, in Hasan’s laboratory found in the sub-basement of Jadwin Hall at Princeton. 

The spectromicroscope has a resolution of less than half the size of an atom, allowing it to scan individual atoms and detect details of their electrons while measuring the electrons’ energy and spin distribution.  

From Dhaka to Princeton

Professor M Zahid Hasan did his SSC from Dhanmondi Government Boys High School and HSC from Dhaka College, gaining outstanding results. 

He studied at the University of Texas in Austin and got his PhD from Stanford University before joining Princeton. 

Now a professor of Physics with a specific interest in the field of Quantum Condensed Matter Physics, Hasan has been working in the groundbreaking subfield of topological materials and led the discovery of topological quantum magnets a few years ago. 

His research work has featured in Physics Today, Nature News, Science News, New Scientist, Scientific American, and Physics Worlds. He was even listed in the Thomson Reuters' World's Most Influential Scientific Minds 2014.

One of the other two co-first-authors on the new paper, postdoctoral research associate Jia-Xin Yin, said he was first drawn to the project by Hasan’s interest in operating beyond the edges of known physics.

Yin said his interest was piqued when Professor Hasan announced he was searching for new phases of matter, only that the question underpinning the search was still undefined.

“He told me something very interesting,” Yin said. “He said that what we need to do is search for the question rather than the answer.”

David Hsieh, a professor of physics at the California Institute of Technology who was not involved in the research, said he was “excited” by the new discovery.

“This could indeed be evidence of a new quantum phase of matter,” he said. 

“They’ve given a few clues that something interesting may be going on, but a lot of follow-up work needs to be done, not to mention some theoretical backing to see what really is causing what they’re seeing.”

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