Weizmann Institute of Science: QTM ‘can also be turned into a very powerful microscope’

Researchers at Weizmann Institute of Science in Rehovot, Israel, have created a new scanning probe microscope that can develop quantum materials and search the “fundamental quantum nature of their electrons.” The researchers reported their findings in the journal Nature, according to the Weizmann Wonder Wander.

“The quantum twisting microscope” demonstrated “a conceptually new type of scanning probe microscope — the quantum twisting microscope (QTM) — capable of performing local interference experiments at its tip,” the article’s abstract said. “The QTM opens the way for new classes of experiments on quantum materials.”

The study was led by Shahal Ilani from Weizmann's Condensed Matter Physics Department, PhD student Dan Yudilevich and collaborators, plus Dr. Rainer Stöhr and Dr. Andrej Denisenko from the University of Stuttgart, Germany.

In developing the quantum twisting microscope, researchers made use of the property that says that an electron is both a particle and a wave and therefore can exist "in many places at the same time."

“The QTM involves the ‘twisting,’ or rotating, of two atomically thin layers of material with respect to one another,” the Weizmann Wonder Wander said. “In recent years, such twisting has become a major source of discoveries.”

The twist angle is critical for controlling the electrons’ behavior, even as it’s the most difficult to control in experiments. Twisting two layers to a new angle requires the “long and tedious” process of “building a new ‘sandwich’ from scratch.”

“Our original motivation was to solve this problem by building a machine that could continuously twist any two materials with respect to one another, readily producing an infinite range of novel materials,” team leader Shahal Ilani of Weizmann’s Condensed Matter Physics Department said, according to Weizmann Wonder Wander. “However, while building this machine, we discovered that it can also be turned into a very powerful microscope, capable of seeing quantum electronic waves in ways that were unimaginable before.”

The QTM relies on the principle of quantum tunneling, wherein electrons can traverse through barriers, behaving as waves rather than discrete particles. By replacing the sharp tip of a conventional scanning tunneling microscope with a flat layer of a quantum material, such as graphene, the QTM allows electrons to tunnel across a two-dimensional interface at multiple locations simultaneously. This quantum interference phenomenon provides a unique opportunity to observe quantum electrons with great precision.

“To see a quantum electron, we have to be gentle,” Ilani told Weizmann Wonder Wander. “If we don’t ask it the rude question, ‘Where are you?’ but instead provide it with multiple routes to cross into our detector without us knowing where it actually crossed, we allow it to preserve its fragile wave-like nature.”

The twisting therefore allows the QTM to map how the electronic wave function depends on momentum, similarly to the way lateral translations of the tip enable the mapping of its dependence on position. Merely knowing at which angles electrons cross the interface supplies the researchers with a great deal of information about the probed material. In this manner they can learn about the collective organization of electrons within the sample, their speed, energy distribution, patterns of interference and even the interactions of different waves with one another.

“Our microscope will give scientists a new kind of ‘lens’ for observing and measuring the properties of quantum materials,” Jiewen Xiao, another lead author, told Weizmann Wonder Wander.

The QTM's capabilities open up new possibilities for studying quantum materials with unprecedented accuracy and depth. By providing researchers with an entirely new "lens" for observing and measuring the properties of quantum materials, the QTM is expected to drive groundbreaking discoveries in various scientific fields.

The Weizmann team has already applied the QTM to study several key quantum materials at room temperature, and they are preparing for new experiments “at temperatures of a few kelvins, where some of the most exciting quantum mechanical effects are known to take place.”

“Peering so deeply into the quantum world can help reveal fundamental truths about nature. In the future, it might also have a tremendous effect on emerging technologies,” according to Weizmann Wonder Wander. “The QTM will provide researchers with access to an unprecedented spectrum of new quantum interfaces, as well as new ‘eyes’ for discovering quantum phenomena within them.”