MIT physicists and their colleagues have measured the shape and morphology of electrons in solids at the quantum level for the first time. Scientists have long known how to measure the energy and velocity of electrons in crystalline materials, but until now the quantum geometry of such systems could only be inferred theoretically, and sometimes not at all.
The research, reported in the Nov. 25 issue of Nature Physics , “opens new avenues for understanding and controlling the quantum properties of matter,” said Ricardo Kamin, MIT’s Class of 1947 Career Development Associate Professor of Physics and leader of the study.
“We’ve basically developed a design to capture entirely new information that was previously impossible to capture,” said Comyn, who is also with MIT’s Materials Research Laboratory and Electronics Laboratory.
The research could be applied to “all kinds of quantum materials, not just the ones we study,” said Ming Kang (Class of ’23), first author of the Nature Physics paper , who conducted the research as a graduate student at MIT and is now a Kavli postdoctoral fellow at Cornell University’s Laboratory of Atomic and Solid State Physics.
Kang has also been invited to contribute an accompanying research abstract about this work and its implications to the November 25 issue of Nature Physics .
Strange World
In the strange world of quantum physics, electrons can be described as both points in space and wave-like shapes. The focus of this study is a fundamental object called a wave function, which describes their shape as follows: “You can think of it as a surface in three-dimensional space,” Kamin says.
There are many different kinds of wave functions, from simple to complex. Think of a ball; that’s similar to a simple wave function. Now imagine a Möbius strip, a type of structure explored by MC Escher in his work; that’s similar to a complex, or non-trivial, wave function. And the quantum world is filled with matter made of the latter.
But so far, the quantum geometry of the wave function has only been derived theoretically, or sometimes not at all — and this property is becoming increasingly important as physicists discover more and more quantum materials that could have applications in everything from quantum computers to advanced electronic and magnetic devices.
The MIT team tackled the problem using a technique called angle-resolved photoemission spectroscopy (ARPES). Comin, Kang, and several colleagues have used the technique in other studies as well. For example, in 2022, they reported discovering the “secret” behind the strange properties of a new quantum material called kagome metals. That work was also published in the journal Nature Physics . In the current study, the research team applied ARPES to measure the quantum structure of kagome metals.
Close cooperation
Kang emphasizes that the new ability to measure the quantum geometry of matter “arrives from close collaboration between theorists and experimentalists.”
The COVID-19 pandemic has also had an impact. Kang, a South Korean national, has been based in the country during the pandemic. “This makes it easier to collaborate with Korean theorists,” said Kang, the experimentalist.
The pandemic presented a unique opportunity for Kamin. He went to Italy to help run the ARPES experiment at the national laboratory, the Italian Light Source Elettra. The lab had been closed during the pandemic but was starting to reopen when Kamin arrived. But he was left on his own when Kang tested positive for COVID-19 and couldn’t go with him. So he unwittingly ran the experiment himself, with the help of local scientists. “As a professor I direct the project, but it’s the students and postdocs who actually do the work. So this is basically the last study where I actually contributed to the experiment itself,” he said with a smile.
In addition to Kang and Comin, other authors of the Nature Physics paper are Sunje Kim of Seoul National University (Kim was co-first author with Kang); Paul M. Neves, graduate student in the Department of Physics at MIT; Linda Ye of Stanford University; Junseo Jung of Seoul National University; Denny Puntel of the University of Trieste; Federico Mazzola of the National Research Council of Venice and Ca’ Foscari University; Shiang Fang of Google DeepMind; Chris Joswiak, Aaron Bostwick, and Eli Rotenberg of Lawrence Berkeley National Laboratory; Jun Fuji and Ivana Vobornik of the National Research Council; Jae-Hoon Park of Max Planck POSTECH/Korea Research Initiative and Pohang University of Science and Technology; Joseph G. Czechelsky, associate professor of physics at MIT; and Beom Jong Yang of Seoul National University, who co-led the research project with Comin.
This research was funded by the U.S. Air Force Office of Scientific Research, the U.S. National Science Foundation, the Gordon and Betty Moore Foundation, the National Research Foundation of Korea, the Samsung Science and Technology Foundation, the U.S. Army Research Office, the U.S. Department of Energy Office of Science, the Heisingh-Simons Physics Research Program, Tsinghua University Education Foundation, Italy’s NFFA-MUR Progetti Internazionali, the Samsung Cultural Foundation, and the Kavli Institute at Cornell University.
