ETH Zürich Researchers Have Observed A Crystal Composed Exclusively Of Electrons

A team of researchers at ETH Zürich was able to observe a unique crystal. Scientists at ETH Zürich have announced that they have successfully observed a crystal made up completely of electrons. The crystals are known as Wigner crystals and were first theorized almost 90 years ago but were only now observed directly in a semiconductor material.

Unlike normal crystals, the crystal the team created is made up exclusively of electrons. By producing the crystal, the team has confirmed a theoretical prediction described as a type of Holy Grail in condensed matter physics. In 1934, Eugene Wigner theorized that electrons in a material could theoretically arrange themselves in regular and crystal-like patterns because of mutual electrical repulsion.

Wigner theorized this because if the energy of electrical repulsion between electrons is higher than their motional energy, the electrons arrange themselves in a way that their total energy is as small as possible. Over the decades, the prediction remained theoretical as Wigner crystals were only able to form under extreme conditions, including low temperatures and with a very small number of free electrons in the material.

In their research, the scientists overcame those obstacles by using a wafer-thin layer of semiconductor material called molybdenum diselenide, only a single atom thick. With the material a single atom thick, electrons are only able to move in a plane. The number of free electrons was varied by applying a voltage to two transparent graphene electrodes the semiconductor was sandwiched between.

The apparatus was cooled to a few degrees above absolute zero. Once the process was completed, the electron separation was calculated to be around 20 nanometers making it impossible to resolve with the microscope. The team made the regular arrangement of electrons visible using light of a particular frequency to excite excitons in a semiconductor layer. Their work led to the direct observation of Wigner crystals for the first time.