Researchers have succeeded for the first time in trapping electrons in a three-dimensional crystal, an advance that has allowed them to begin playing with the quantum effects that electrons produce when they are in a state called an electronic “flat band” – and this includes superconductivity. .

An electron moving through a 3D material would interact in different ways with the lattice of its atoms, so the kinetic energy of the electron is usually defined in terms of a range or band. If the electron’s band is flat, this means that the range is zero: its energy is independent of the interaction with the lattice. To simplify, this electron has zero speed and gets stuck in a particular place.

When an electron is in the flat band, it always interacts with the electrons of the atoms around it. These interactions have too little energy to be anything but negligible when an electron is moving toward the material, but when the electron is stuck in place, they suddenly matter. And particular quantum properties become apparent, such as superconductivity and other interesting electromagnetic properties.

This rare electronic state is due to a special cubic arrangement of atoms (pictured) that resembles the Japanese art of “kagome”.

The 3D kagome network can trap electrons.

Image credit: Courtesy of researchers via MIT News

In this new work, the researchers demonstrated that it is possible to create a flat 3D band, trapping the electron in all three dimensions. They used a 3D lattice in the shape of a kagome, used in the traditional Japanese art of basket weaving. Similar 2D lattices already demonstrated flat-band electrons. So the team felt that this was a way to successfully create one in 3D.

“Now that we know we can create a flat strip from this geometry, we are very motivated to study other structures that might have new physics that could provide a platform for new technologies,” said l Study author Joseph Checkelsky, associate professor of physics at MIT, said in a statement.

By performing a chemical modification, the system was transformed into a superconductor. It is a material through which electrons flow without resistance. To make the crystal, the team synthesized pyrochlore crystals in the laboratory.

“It’s no different from how nature makes crystals,” Checkelsky explained. “We bring certain elements together – in this case calcium and nickel – melt them at very high temperatures, cool them, and the atoms will organize themselves into this kagome-like crystal configuration. “

Switching rhodium and ruthenium atoms instead of nickel creates the same geometric configuration but pushes the flat band value to zero energy (not just zero speed) – this is where superconductivity occurs.

“This presents a new paradigm for thinking about how to find new and interesting quantum materials,” added co-author physics professor Riccardo Comin. “We showed that with this special ingredient in this atomic arrangement that can trap electrons, we still find these flat bands. It’s not just luck. The challenge from now on is to optimize to deliver on the promise of flat-band materials, potentially capable of maintaining superconductivity at higher temperatures.

These crystals, or others like them, could one day be optimized to build ultra-efficient power lines, create powerful quantum computers and even faster electronic devices.

The study is published in the journal Nature.

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