Physicists measure quantum geometry for first time

For the first time, MIT physicists and colleagues have measured the geometry, or shape, of electrons in solids at the quantum level. Scientists have long known how to measure the energy and speed of electrons in crystalline materials, but until now the quantum geometry of these systems could only be inferred theoretically, and sometimes not at all.

This work was reported in November 25th issue of natural physics“It opens new avenues for understanding and manipulating the quantum properties of materials,” said Riccardo Comin, Class of 1947, MIT Career Development Associate Professor of Physics and leader of the work.

“We’ve basically laid out a blueprint for getting some completely new information that wasn’t available before,” said Comyn, who is also affiliated with MIT’s Materials Research Laboratory and Electronics Research Laboratory.

Mingu Kang, lead author of the Nature Physics paper and a Kaveri postdoctoral fellow at Cornell’s Atomic and Solid State Physics Laboratory, said the work could be applied to “any kind of quantum material, not just the ones we study.” ”. Kang, MIT Ph.D. 2023, conducted this work as an MIT graduate student.

Kang was also invited to write an accompanying research brief Published on November 25th natural physics.

a strange world

In the strange world of quantum physics, an electron can be described either as a point in space or as a wave shape. At the heart of the current work is a wave function This describes the latter. “You can think of it as a surface in three dimensions,” Comyn said.

There are different types of wave functions, ranging from simple to complex. Think of a ball. This is similar to a simple or trivial wave function. Now imagine a Möbius strip, the kind of structure explored by MC Escher in his art. This is analogous to complex or non-trivial wave functions. The quantum world is filled with materials made of the latter.

But until now, the quantum geometry of the wave function could only be inferred theoretically, and sometimes not at all. 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 used a method called angle resolved photoelectron spectroscopyor ARPES. Comin, Kang and some colleagues have used this technique in other studies. For example, in 2022 they report Discover the “secret sauce” Behind the bizarre properties of a new quantum material called “Kagome Metal”. This work also appears in natural physics.

In the current work, the team used ARPES to measure the quantum geometry of Kagome metal.

Close cooperation

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

The coronavirus pandemic has also had an impact. Kang, who is from South Korea, has been living in the country during the pandemic. “This facilitates collaboration with Korean theorists,” said Kang, the experimentalist.

The pandemic also presented Comyn with an unusual opportunity. He traveled to Italy to help conduct the ARPES experiment at the Italian National Laboratory Elettra Light Source. The lab was closed during the pandemic but began to reopen when Comyn arrived.

However, when Kang tested positive for COVID-19 and was unable to join him, he found himself alone. So he unintentionally conducted the experiment himself with the support of local scientists.

“As a professor, I lead the project, but the students and postdocs actually perform the work. So this is basically the last study where I really contributed to the experiment,” he said.