For more than a century, Electrons continue to surprise the scientific community with their elusive and fascinating behavior. Normally, electrons orbit around atomic nuclei due to the attraction of protons. However, in the absence of protons, electrons tend to repel and disperse as much as possible. This is evident in the universe, where these tiny particles, known for their erratic movement around atoms, abound.
Repulsion between electrons generates order similar to that of attraction
Still, in the 1930s, theoretical physicist Eugene Wigner proposed a revolutionary theory. He suggested that, Under conditions of extremely low temperatures and densities, the repulsion between electrons could be organized in such a way that they formed a regular lattice structure. This phenomenon would give rise to a peculiar form of matter known as a Wigner crystal, composed of electrons in a crystalline lattice, united not by attraction but by their mutual repulsion.
Now, After almost ninety years of eluding direct detection, a team of physicists at Princeton University has managed to visualize this elusive Wigner crystal for the first time., “the strange form of matter that constitutes one of the most important quantum phases,” according to a statement from the institution. The results of this research have been published in the journal Nature.
“The Wigner crystal is one of the most fascinating quantum phases of matter ever predicted. and the subject of numerous studies that claim to have found, at best, indirect evidence of its formation,” explained Al Yazdani, a physicist at Princeton University. “Visualizing this crystal allows us not only to observe its formation, confirming many of its properties, but we can also study it in ways that could not be done in the past,” he added.
Electron density equilibrium point
The Wigner crystal is characterized by a particular balance in electron density. If the density is too low, the electrons tend to repel and scatter; If it is too high, electrons accumulate, forming an electron-liquid state, reports ScienceAlert.
To directly observe the formation of this crystal, The team used a scanning tunneling microscope (STM) and pristine graphene samples. The samples were cooled to extremely low temperatures and a magnetic field was applied to establish a two-dimensional electron gas system within the graphene layers. By adjusting the electron density, the researchers observed how the electrons spontaneously organized into an ordered lattice structure.
Indirect evidence of the Wigner crystal
These experiments have provided direct evidence for the existence of the Wigner crystal., something that previous indirect evidence had failed to demonstrate conclusively. Previous experiments, dating back to the 1970s at Bell Laboratories in New Jersey, had detected crystalline behavior when electrons were sprayed onto helium, but they did not fully conform to the laws of quantum physics.
Thus, this research demonstrates that a true Wigner crystal follows the laws of quantum physics, where bound electrons do not behave as discrete particles, but as an individual wave, rather than the classical physical laws familiar from the everyday world.
Thus, This study marked a milestone by using a device based on quantum tunneling, allowing the atomic and subatomic worlds to be visualized with unprecedented clarity. The precision of the samples and the technology used confirmed that there were no atomic imperfections in the atomic lattice of graphene.
“Our group has been able to produce samples of unprecedented cleanliness that have made this work possible,” Yazdani said. “With our microscope we can confirm that the samples do not present any atomic imperfections in the atomic lattice of graphene or foreign atoms on its surface in regions with hundreds of thousands of atoms,” he added.
“Zero point motion” of electrons
This study not only confirmed the absence of atomic imperfections in the graphene samples, but also made it possible to observe the “zero point motion” of electrons.
One of the fundamental principles of quantum mechanics is that subatomic particles, such as electrons, do not have a fixed position, but are described by a probability curve that covers several possible locations. This phenomenon is known as the “zero point motion” of electrons, so called because it occurs without the need for high energies. This movement produces a kind of blur in the location of the electrons within the crystal when they are observed.
The group of researchers managed to quantify this dithering effect, and Yazdani stated: “We discovered that this quantum behavior extends its reach to a third of the distance between the electrons, thus making the Wigner crystal a unique type of quantum crystal.”
Princeton University and the team led by Yazdani continue to analyze the Wigner crystal, studying its fusion process and their possible transition to other exotic liquid phases of electrons interacting in a magnetic field, hoping to image these phases with the same clarity with which they have visualized the Wigner crystal.
Felipe Espinosa Wang with information from Princeton University, Interesting Engineering and Science Alert.