Scientists have created the solid-state crystal form of electrons for the first time in the laboratory

According to foreign media reports, researchers from the Federal Institute of Technology in Zurich have created a crystal entirely composed of electrons. Although these structures have been theorized for decades, this marks the first time they have been experimentally confirmed in the laboratory. Usually, electrons behave more or less like liquids, freely flowing in matter.

But in 1934, theoretical physicist Eugene Wigner predicted that a group of electrons could crystallize into a solid form under specific conditions and form a phase now known as Wigner crystals.

To achieve this, it is necessary to find an appropriate balance between the two forces that affect electrons: their electrostatic repulsion and their kinetic energy. The latter is a more powerful effect that causes electrons to randomly bounce around, but Wigner suggests that if this effect can be sufficiently weakened, repulsion will take over and lock electrons in a unified lattice.

But it turns out that this is much more tricky than it sounds. The electron density needs to be reduced above a certain point, and they need to be trapped in a trap and cooled to almost absolute zero to reduce external influence on their motion.

Now, scientists from the Federal Institute of Technology in Zurich have met all these requirements to manufacture Wigner crystals. In order to restrict electrons, they used a single atom thick layer of molybdenum disulfide, effectively limiting the movement of electrons within a two-dimensional range. To control the number of electrons in this semiconductor, the team sandwiched the material between two graphene electrodes and applied a voltage. Finally, the entire system was cooled to near absolute zero.

Sure enough, a Wigner crystal appeared. But observing it is completely another challenge - because the distance between electrons is so small, about 20 nanometers, that even a microscope cannot see it.

Previous research attempting to manufacture Wigner crystals relied on indirect methods to detect them, such as changes in current. However, in this new study, the research team used a new method. They irradiate light onto this material at a specific frequency to excite so-called "excitons" in semiconductors, which reflect light back. If there is a Wigner crystal, then when excitons reflect light back, they should be stationary.

"A group of theoretical physicists led by Eugene Demler from Harvard University will be visiting ETH this year, and they have theoretically calculated how this effect appears in the observed exciton excitation frequency - which is exactly what we observed in the laboratory," said Ata ç Imamo, the lead author of this study ğ Lu said.

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