Unusual Particle Gains or Loses Mass Depending on Its Direction of Movement

Scientists have accidentally discovered a particle that has mass when moving in one direction but lacks mass when traveling in another. Known as semi-Dirac fermions, these particles with peculiar behavior were first theorized 16 years ago.

A new phenomenon observed in ZrSiS material

Researchers discovered the phenomenon in a semimetal material called ZrSiS, which consists of zirconium, silicon, and sulfur, while analyzing the properties of quasiparticles — phenomena resulting from the collective behavior of numerous particles within a solid material.

This was completely unexpected,” explained Yinming Shao, the lead author of the study. We weren’t looking for semi-Dirac fermions when we began working with this material, but we observed signals we couldn’t understand — and it turns out we made the first observation of these peculiar quasiparticles that sometimes behave as if they have mass and other times as if they don’t.”

The concept may seem impossible — how can something gain and lose mass so easily? But the explanation lies in Einstein’s famous equation, E = mc², which describes the relationship between energy (E) and mass (m), with the speed of light (c) squared as a constant.

Special relativity’s role in mass changes

According to the theory of special relativity, no object with mass can reach the speed of light, as it would require an infinite amount of energy. However, the reverse is also true: a massless particle that slows down below the speed of light gains mass.

This is precisely what happens with the observed quasiparticles. When they travel along a specific dimension within the ZrSiS crystals, they move at the speed of light and are therefore massless. However, when attempting to travel in another direction, they encounter resistance, slow down, and acquire mass.

Imagine the particle as a tiny train confined to a network of tracks, representing the material’s electronic structure, Shao explained. At certain points, the tracks intersect, and our particle train, which was moving quickly on its main track at light speed, reaches an intersection and must switch to a perpendicular track. At this moment, it encounters resistance and gains mass. Depending on the direction of its movement, the particles are either pure energy or possess mass.

Key predictions confirmed in experiments

Initially, the researchers aimed to study the quantum interactions in the material by observing how electrons responded to light. During the experiment, they found that the energy levels of the electrons followed an unexpected pattern as the strength of the magnetic field increased — a key prediction for semi-Dirac fermions.

Although this research delves into advanced physics, the team believes the discovery could lead to future applications of ZrSiS similar to those of graphene.

It’s a layered material, which means that once we figure out how to create a single layer of this compound, we could harness the power of semi-Dirac fermions and control their properties with the same precision as graphene,said Shao. The most exciting part of this experiment lies in the unexplained data, the researchers emphasized. We observed many unresolved mysteries, and we are focusing on understanding them.

Read the original article on: New Atlas

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