This particle has no mass... unless it moves in a specific direction 😮

A particle that changes its behavior depending on the direction it takes: in one direction, it glides effortlessly as if it weighs nothing. In the other, it seems to have weight. This might sound like something straight out of science fiction, but it's exactly what researchers have just observed for the first time. These particles, called semi-Dirac fermions, appear to defy the classical laws of physics and could revolutionize the field of materials and their technological applications.


The discovery occurred in a semimetallic material with unique properties: ZrSiS, a crystal made of zirconium, silicon, and sulfur. This material has a layered structure, comparable to graphite or the famous graphene, an ultrathin material. During a series of experiments where it was exposed to a strong magnetic field and infrared radiation, the electrons inside the crystal began to behave in a completely unexpected manner. The researchers realized they were dealing with a very peculiar particle: the semi-Dirac fermion.

Semi-Dirac fermions exhibit a strange characteristic: depending on the direction in which they move, they sometimes appear to be massless, and other times "heavy." To illustrate this phenomenon, scientists compare it to a train speeding along a high-speed track. As long as it stays in a specific direction, nothing seems able to stop it. But if it changes direction, it encounters resistance and appears to slow down, as if it has gained weight. This alternation between a "massless" and a "massive" state had never been observed in this way until now.

Yinming Shao, the lead researcher of this study, conducted these experiments with his team. Initially, their goal was simply to study the response of ZrSiS electrons when subjected to an increasing magnetic field and infrared light. But as the conditions became more extreme, unusual behavior emerged. This phenomenon led to the identification of semi-Dirac fermions, confirming a theoretical prediction made over a decade ago.

This discovery could well usher in a new era for materials science. By gaining a better understanding of these semi-Dirac fermions, scientists could design materials with exceptional properties capable of revolutionizing several technological fields. For instance, ZrSiS-inspired materials might enable the creation of electronic components that are thinner, faster, and more efficient. This includes next-generation batteries capable of storing more energy in a smaller space, or ultra-sensitive medical devices.


One of the intriguing characteristics of ZrSiS lies in its layered structure, which makes it easier to study and manipulate. By isolating ultrathin layers, as was done with graphene, researchers hope to explore the remarkable properties of semi-Dirac fermions in greater detail. This approach might allow these particles to be harnessed for groundbreaking technologies, such as more powerful quantum computers or sensors capable of detecting infinitesimal changes in their environment.

Even though this advancement marks an important milestone, many questions remain. Why do these semi-Dirac fermions behave the way they do? What other surprises might they hold for researchers? And most importantly, how can they be effectively harnessed for practical applications? These are just some of the mysteries that physicists are now striving to unravel.

The discovery of semi-Dirac fermions is yet another reminder of how materials physics is constantly evolving. This strange phenomenon, observed for the first time in ZrSiS, could fundamentally reshape our current understanding and pave the way for innovations we can scarcely imagine. The next few years will be crucial in uncovering the potential of these particles and determining how they might eventually improve everyday technologies. This scientific breakthrough, as mysterious as it is impressive, underscores that matter has yet to reveal all its secrets.