Physicists measure quantum geometry for the first time

For the first time, MIT physicists have measured the geometry, or shape, of electrons in a solid at the quantum level. Scientists have long known how to measure the energy and velocity of electrons in crystalline materials, but until now the quantum geometry of those systems could only be deduced theoretically, or in some cases not at all. Sometimes I couldn’t do it.

The research, reported in the Nov. 25 issue of the journal Nature Physics, “opens new avenues for understanding and manipulating the quantum properties of materials,” said MIT’s 1947 graduate career development associate professor of physics. said Riccardo Comin, professor and leader of the study.

“We’ve basically developed a blueprint for getting completely new information that wasn’t available before,” says Comin, who is also affiliated with the MIT Materials Laboratory and Electronics Laboratory.

Mingu Kang, lead author of the Nature Physics paper and a Kavli postdoctoral fellow at Cornell University’s Atomic and Solid State Physics Laboratory, said the research was “not just for the quantum materials we worked with, but for all kinds of He said that it could be applied to “quantum materials.” Kang, MIT Ph.D. 2023, MIT graduate student.

Kang was also invited to write an accompanying research paper about the study, including its implications, in the November 25 issue of the journal Nature Physics.

strange world

In the strange world of quantum physics, electrons can be both points in space and wave-like shapes. At the heart of the current research is a fundamental object known as a wave function that describes the latter. “You can think of it like a surface in three-dimensional space,” Comin says.

There are many types of wave functions, ranging from simple to complex. Consider a ball. This is similar to a simple or trivial wave function. Now imagine a Möbius strip, the kind of structure that MC Escher explored in his art. This is similar to a complex or non-trivial wave function. And the quantum world is filled with matter composed of the latter.

However, until now, the quantum geometry of the wave function could only be deduced theoretically, or in some cases not at all. And this property is becoming increasingly important as physicists discover more and more quantum materials with potential applications in everything from quantum computers to advanced electronic and magnetic devices.

The MIT team solved this problem using a technique called angle-resolved photoelectron spectroscopy (ARPES). Comin, Kang, and some of the same colleagues had used this technique in other studies. For example, in 2022 they reported that they had discovered the “secret sauce” behind the exotic properties of a new quantum material known as Kagome Metal. This research was also published in the journal Nature Physics.

In the current study, the team applied ARPES to measure the quantum geometry of Kagome metal.

close collaboration

Kang emphasizes that the new ability to measure the quantum geometry of materials “comes from close collaboration between theorists and experimentalists.”

The coronavirus pandemic also had an impact. Kang, who is originally from South Korea, was based in the country during the pandemic. “This made it easier to collaborate with Korean theorists,” says experimentalist Kang.

The pandemic also presented Kamin with an unusual opportunity. He traveled to Italy to help run the ARPES experiment at Italy’s national laboratory, the Italian Light Source Elettra. The lab had been closed during the pandemic, but had begun to reopen when Kamin arrived.

But when Kang tested positive for the coronavirus and was unable to join them, he found himself alone. So he inadvertently conducted an experiment on himself with the help of a local scientist.

“As a professor, I lead the project, but it’s the students and postdocs who actually perform the work. So this is basically the last piece of research where I actually contributed to the experiment itself,” he said. Masu.