Physicists have captured molecular "electronic ice" for the first time.

Researchers struggled for a long time to capture images of molecular electronic ice, as the methods employed tended to destroy the subject of study. The same team that demonstrated the existence of an electronic crystal devised a way to modify the scanning electron microscope, successfully obtaining the first images of the Wigner molecule.

2024-11-11 10:00:21https://naked-science.ru/article/physics/molecular-e-ice-picture

Electrons typically move through materials so quickly that they do not form bonds with anything. In the 1930s, physicist Eugene Wigner predicted that electrons could be brought to a stationary state at low densities and temperatures, forming "electron ice," also known as the Wigner crystal.

In 2021, research teams led by Feng Wang and Michael Crommie in Berkeley, USA, demonstrated the existence of such electronic crystals. Now, the same scientists have captured images of a new quantum phase of solid electronic matter—the molecular Wigner crystal. The results of their scientific work have been published in the journal Science.

Ordinary Wigner crystals form honeycomb structures with an ordered arrangement of electrons. In molecular Wigner crystals, highly ordered structures are created from artificial "molecules," each consisting of two or more electrons.

For many years, scientists have attempted to obtain direct images of the molecular Wigner crystal. This proved to be a challenging task because the molecular electron ice would disintegrate when attempts were made to capture it. The tip of the scanning tunneling microscope (STM), which is used to obtain the desired images, dismantled the electronic configuration of the material.

In the new study, researchers from the Lawrence Berkeley National Laboratory addressed this issue. They developed a method that minimizes the electric field generated by the STM tip. With this modification, the researchers were able to capture the delicate electronic structure of the molecular Wigner crystal.

For their experiments, the scientists developed a nanomaterial called "twisted tungsten disulfide (tWS₂) moiré superlattice." First, they created a bilayer of tungsten disulfide (WS₂) with layers stacked at a rotation angle of 58 degrees. They then placed it on a 49-nanometer thick hexagonal boron nitride (hBN) and a graphite gate.

Using their STM technique, the physicists discovered that doping the tWS₂ superlattice with electrons fills each 10-nanometer-wide cell with only two or three electrons. As a result, these filled cells formed a mass of moiré-type electronic molecules throughout the superlattice, leading to the formation of the molecular Wigner crystal.

"Low temperatures, combined with the energy potential created by the tWS₂ superlattice, locally trap the electrons," Wang explained.

Moving forward, Wang, Crommie, and their team plan to apply their STM technique for a deeper exploration of this new quantum phase and to investigate potential applications it may unveil.