MIT physicists trap electrons in a 3D crystal for the first time

MIT physicists trap electrons in a 3D crystal for the first time

3D crystal light trap

MIT physicists have managed to trap electrons in a pure crystal, marking the first achievement of a flat electron band in a 3D material. The rare electronic state is due to the special cubic arrangement of atoms (pictured) that resembles the Japanese “Kagome” art. The results provide a new way for scientists to explore rare electronic states in 3D materials. Credit: Courtesy of researchers

The results open the door to exploring superconductivity and other exotic electronic states in 3D materials.

Electrons move through a conducting material like passengers at the peak of rush hour in Manhattan. Charged particles may collide and collide with each other, but most of the time, they don’t care about other electrons as they hurtle forward, each with its own energy.

But when a material’s electrons are trapped together, they can settle into exactly the same energy state and begin to behave as a single electron. This collective, zombie-like state is what is known in physics as an electronic “flat band,” and scientists expect that when electrons are in this state they can begin to sense the quantum effects of other electrons and behave in coordinated quantum ways. Then, strange behaviors such as superconductivity and unique forms of magnetism may emerge.

3D flat band detection

Now, physicists are in with It succeeded in trapping electrons in a pure crystal. This is the first time scientists have achieved a flat electron bar in a 3D material. With some chemical manipulation, the researchers also showed they could turn the crystal into a superconductor, a material that conducts electricity without resistance.

3D crystal light trap

The rare electronic state is due to the special cubic arrangement of atoms (pictured) that resembles the Japanese “Kagome” art. Credit: Courtesy of researchers

The state of trapped electrons is possible thanks to the atomic geometry of the crystal. The crystal, created by physicists, contains an arrangement of atoms that resembles patterns woven in “kagome,” the Japanese art of basket weaving. In this specific geometry, the researchers found that instead of jumping between atoms, the electrons were caged and stabilized in the same energy range.

Potential applications and motivations for research

The researchers say this flat band state can be achieved using almost any group of atoms, as long as they are arranged in this Kagome-inspired 3D geometry. The results were published November 8 in the journal natureIt provides a new way for scientists to explore rare electronic states in 3D materials. These materials may one day be improved to enable ultra-efficient power lines, ultra-fast quantum bits, and faster and smarter electronic devices.

“Now that we know we can make a flat strip out of this geometry, we have great motivation to study other structures that might contain other novel physics that could be a platform for new technologies,” says study author Joseph Chekelski, associate professor of physics. .

MIT Checkelsky’s co-authors include graduate students Joshua Wakefield, Minguo Kang, and Paul Nieves, and postdoc Dongjin Oh, who are co-authors; graduate students Tej Lamichhane and Alan Chen; Postdoctoral researchers Xiang Fang and Frank Zhao; University student Ryan Teague; Associate Professor of Nuclear Science and Engineering Mingda Li; Associate Professor of Physics Ricardo Comin, who collaborated with Chekelski to direct the study; Together with collaborators in many other laboratories and institutions.

Setting up a 3D trap

In recent years, physicists have succeeded in trapping electrons and confirming the flat electronic band state in 2D materials. But scientists have found that electrons trapped in two dimensions can easily escape the third dimension, making it difficult to maintain flat band states in two dimensions.

In their new study, Chekelsky, Comin and their colleagues sought to create flat domains in 3D materials, so that electrons are trapped in 3D and any exotic electronic states can be maintained more stably. They had an idea that Kagome’s patterns might play a role.

In previous work, scientists observed electrons trapped in a two-dimensional lattice of atoms resembling some of Kagome’s designs. When the atoms were arranged in a pattern of interconnected triangles that shared corners, the electrons were confined within the hexagonal space between the triangles, rather than jumping across the lattice. But, as with the others, the researchers found that electrons can escape to and from the grid via the third dimension.

The team wondered: Could a three-dimensional formation of similar networks work to trap electrons? They searched for an answer in databases of physical structures, and found a particular geometric configuration of atoms, generally classified as pyrochlore – a type of mineral with a highly symmetrical atomic geometry. The three-dimensional structure of bichlor’s atoms formed a repeating pattern of cubes, with the face of each cube resembling a kagome-like grid. They found that, in theory, this geometry could effectively trap electrons within each cube.

Rocky landing

To test this hypothesis, the researchers manufactured a pyrochlor crystal in the laboratory.

“It’s no different from the way nature makes crystals,” Chekelski explains. “We put certain elements together — in this case, calcium and nickel — and melt them at very high temperatures, then cool them, and the atoms will arrange on their own in this kagome-like crystalline formation.”

They then measured the energy of the individual electrons in the crystal, to see if they actually lay in the same flat energy band. To do this, researchers typically perform photoemission experiments, where they shine light on a single piece Photon of light onto a sample, which in turn releases a single electron. The detector can then accurately measure the energy of that single electron.

Scientists have used photoemission to confirm planar band states in various 2D materials. Due to their flat, two-dimensional nature, these materials are relatively easy to measure using standard laser light. But for 3D materials, the task is more difficult.

“For this experiment, you usually need a very flat surface,” Komen explains. “But if you look at the surface of these 3D materials, they’re like the Rocky Mountains, with a very wavy landscape. Experiments on these materials are very difficult, which is part of the reason why no one has proven that they host trapped electrons.”

The team removed this hurdle by using angle-resolution photoemission spectroscopy (ARPES), a highly focused beam of light capable of targeting specific locations across a non-planar 3D surface and measuring individual electron energies at those locations.

“It’s like landing a helicopter on very small platforms, all over this rocky landscape,” Comyn says.

Using ARPES, the team measured the energies of thousands of electrons across a composite crystal sample in about half an hour. They found that the electrons in the crystal showed substantially the exact same energy, confirming the flat band state of the 3D material.

Towards superconductivity

To see if they could manipulate the coordinated electrons into an exotic electronic state, the researchers fitted the same crystal geometry, this time using rhodium and ruthenium atoms instead of nickel. On paper, the researchers calculated that this chemical exchange should convert the flat band of electrons to zero energy, a state that automatically leads to superconductivity.

In fact, they found that when they fitted a new crystal, with a slightly different set of elements, in the same kagome-like 3D geometry, the crystal’s electrons showed a flat band, this time in superconducting states.

“This provides a new paradigm for thinking about how to find new and interesting quantum materials,” Comyn says. “We’ve shown that with this special component of this atomic arrangement that can trap electrons, we always find these flat bands. It’s not just a fluke. Going forward, the challenge is to improve performance to realize the promise of flat-band materials, and perhaps to maintain superconductivity in Higher temperatures.

Reference: “3D Flat Bands in the Mineral CaNi2 Pyrochlore” by Joshua P. Wakefield, Minju Kang, Paul M. Nieves, Dongjin Oh, Xiang Fang, Ryan McTeague, S.Y. Frank Zhao, Tej N. Lamichhane, Alan Chen, Seung-Young Lee, Sodong Park, Jae-Hoon Park, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Anil Rajapitamahoney, Elio Vescovo, Jessica L. McChesney, David Graf, Joanna C. Palmstrom, Takehito Suzuki, Mingda Lee, Ricardo Comin and Joseph J. Checkelski. , November 8, 2023, nature.
doi: 10.1038/s41586-023-06640-1

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