Physicists have captured the first-ever image of a Wigner crystal, a strange honeycomb-shaped substance inside another, made entirely of electrons.
Hungarian physicist Eugene Wegner first theorized this crystal in 1934, but it took more than eight decades for scientists to finally get a first-hand look at the “electron ice”.
The first cool image shows electrons held together in a tight repeating pattern – like the wings of a tiny blue butterfly, or the pressure of a space clover.
If the conditions are just right, some electrons inside a material will arrange themselves into a tidy honeycomb pattern — like a solid within a solid. Physicists have now directly imaged these “Wigner crystals” for the first time. https://t.co/ia1fRlJ2vI
— Scientific American (@know) October 9, 2021
Say the researchers behind the study, which was published September 29 in the journal NatureAlthough this is not the first time a Wigner crystal has reasonably been created or even studied for its properties, the visual evidence they have collected is the most corroborating evidence of the material’s existence to date.
“If you say you have an electron crystal, show me the crystal,” said study co-author Feng Wang, a physicist at the University of California.
Electrons move inside ordinary conductors such as silver or copper, or semiconductors such as silicon, so fast that they are barely able to interact with each other. But at very low temperatures, they slow to a creep, and the repulsion between negatively charged electrons begins to dominate.
The researchers trapped electrons in the gap between atom-thick layers of tungsten semiconductors — one tungsten disulfide and the other tungsten disulfide.
After applying an electric field across the gap to remove any potentially disruptive excess electrons, the researchers cooled their electron sandwich to 5 degrees above absolute zero.
Sure enough, the fast-moving electrons stopped and settled in the Wigner’s repeating structure.
Then the researchers used a device called a scanning tunneling microscope (STM) to view this new crystal. STMs work by applying a tiny voltage through a very sharp metal tip before running it directly over the material, causing electrons to jump to the surface of the material from the tip.
The rate at which electrons jump from the edge depends on what’s underneath, so the researchers can build a Braille-like image of a two-dimensional surface by measuring the current flowing into the surface at each point.
But the current provided by the STM was initially too much for the thin electronic ice, which “melts” on contact. To stop this, the researchers inserted a single-atom layer of graphene directly on top of the Wigner crystal, enabling the crystal to interact with the graphene and leave the impression that the STM could safely read it — like a camera.
By completely tracing the image printed on the graphene sheet, STM captured the first shot of the Wigner crystal, proving its existence beyond any doubt.
Now that they have definitive proof that Wigner crystals exist, scientists can use the crystals to answer deeper questions about how multiple electrons interact with each other, such as why the crystals arrange themselves in a honeycomb arrangement, and how they “melt”.
The answers will provide a rare glimpse into some of the most elusive properties of microparticles.
Source: Science Alert