MIT Physicists Make First 'Zombie' Electron Crystal for Superconductor

In a first for science, researchers have figured out how to trap tiny electrons in a three-dimensional crystal prison, which might help them make superconductors.

The crystal was synthesized by scientists at MIT to have a special atomic arrangement that allows them to trap the electrons inside.

This entrapment of the electrons may give their crystalline prisons special properties, even enabling them to have superconductor abilities, conducting electricity with zero resistance, according to a new paper in the journal Nature.

The electrons can be trapped within the crystals due to the structure of the crystals' atoms, which are akin to Japanese "kagome" woven baskets, keeping the electrons penned inside. Electrons have been trapped within two-dimensional structures before, but this marks the first time that they have been imprisoned inside a three-dimensional crystal.

"The electrons are trapped by their environment, namely by the geometry of the atomic scaffolding that surrounds them," Riccardo Comin, an associate professor of physics at MIT and paper co-author, told Newsweek.

"When the electrons simultaneously try to hop out from this trap, they collide with each other on their way out and their quantum-mechanical trajectories are self-destroying. This effect occurs because the electrons can only escape by hopping to a neighboring atom (they cannot use the gaps) but the geometrical arrangement of the atoms makes them collide with each other destructively so that they are eventually forced to stay in the 'trap.'"

These electrons are usually very active, humming with energy and jostling each other around, but become "zombie-like" when trapped together, behaving as if they were one. Electrons enter this so-called "flat band" inside the crystal, allowing them to feel the quantum effects of other electrons and act in coordination, which may allow the crystals to behave as superconductors.

This entrapment works even better in a three-dimensional crystal trap compared to a two-dimensional one, as the electrons tend to escape out of the top.

"Now that we know we can make a flat band from this geometry, we have a big motivation to study other structures that might have other new physics that could be a platform for new technologies," Joseph Checkelsky, associate professor of physics at MIT and co-author of the study, said in a statement.

The scientists manufactured these electron-trapping crystals in the lab and measured the energy levels of the electrons stored within using light to determine that they all had the same energy levels, confirming that they had achieved a flat band state.

"It's not dissimilar to how nature makes crystals," Checkelsky said. "We put certain elements together — in this case, calcium and nickel — melt them at very high temperatures, cool them down, and the atoms on their own will arrange into this crystalline, kagome-like configuration."

The researchers hope that the flat band properties of the electrons in these crystals will help them to explore new quantum states in three-dimensional materials and therefore develop technology like superconductors, supercomputing quantum bits, and ultraefficient power lines.

"This discovery will enable us to design and create new classes of so-called quantum materials. Superconductors are the quintessential quantum materials, where electrons work collectively to realize a quantum 'choreography' that translates to various exotic phenomena not displayed by ordinary materials, including electrical current flow without dissipation (zero resistance), magnetic levitation (perfect diamagnetism, or Meissner effect), and the realization of quantum devices (through quantum interference and the Josephson effect)," Comin said. "The discovery of 3D flat bands enables a new set of design rules which will broaden and diversify the playground of quantum solids including superconductors, among others."

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