Electrons move through conductive materials like travelers during rush hour in Manhattan. The charged particles can bump and collide with each other but mostly don’t pay attention to other electrons as they zip around at high speeds, each with their own energy.

But when electrons in a material are trapped together, they can all reach exactly the same energy state and start behaving like one big electron. This collective state, similar to a zombie, is called an “electron band” by physicists.

Scientists predict that when electrons are in this state, they can start feeling the quantum effects of other electrons and act in a coordinated, quantum way. Then exotic behaviors could emerge like superconductivity and unique forms of magnetism.

Now, physicists at MIT have successfully trapped electrons in a pure crystal for the first time. This is the first time scientists have created an electron band in a 3D material.

With some chemical manipulations, the researchers also showed they could turn the crystal into a superconductor, a material that conducts electricity with zero resistance.

The trapped state of the electrons is possible thanks to the atomic geometry of the crystal. The crystal the physicists synthesized has an arrangement of atoms that looks like the woven patterns of “kagome,” the Japanese art of basket weaving.

In this specific geometry, the researchers discovered that instead of hopping between atoms, electrons would “cage” themselves and settle into the same energy band.

To trap electrons in three dimensions, the team looked for a material with the right 3D atomic pattern. They found that a crystal structure called pyrochlore, which forms a repeating pattern of interlocking cubes with kagome-like faces, could theoretically cage electrons within each cube.

The researchers synthesized a pyrochlore crystal and used a technique called angle-resolved photoemission spectroscopy to precisely measure thousands of individual electron energies across the complex 3D surface. They found the electrons all had exactly the same energy, confirming the 3D electron band state.

By tweaking the crystal’s chemical makeup, the team nudged the electron band to zero energy, causing superconductivity. This shows the incredible potential of materials with the special electron-trapping geometry.

Scientists now have a new way to explore exotic quantum states in 3D—which could optimize technologies like more efficient power lines, quantum computers, and faster devices. The results provide hope that superconductivity may someday be achieved at higher temperatures useful for applications.

So in summary, physicists have created an electron “zombie state” by cunningly arranging atoms in 3D crystals. Their success paves the way for materials with exciting quantum properties and technologies of the future.


Sources

Jennifer Chu, Physicists trap electrons in a 3D crystal for the first time (Massachusetts Institute of Technology) | Wakefield, J.P., Kang, M., Neves, P.M. et al. Three-dimensional flat bands in pyrochlore metal CaNi2. Nature 623, 301–306 (2023). doi.org/10.1038/s41586-023-06640-1


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