After 16 years of searching, physicists have discovered a particle that possesses mass only under specific conditions.

A new study has revealed that the half-Dirac fermion, a quasi-particle that behaves as a unified entity, does indeed exist. Physicists first proposed the possibility of its existence in 2008, and a new experiment has confirmed this theory. It turns out that this quasi-particle has mass only when moving in one direction and is massless when moving in another. The findings of the study have been published in the journal Physical Review X, as reported by ScienceAlert.

While ordinary quasi-particles have the same mass regardless of their direction of motion, the half-Dirac fermion, as this research suggests, contradicts these rules. The existence of this particle was first predicted by physicists in 2008, and since then, they have been trying to detect it, finally achieving success. This new discovery is significant for quantum physics and for the industry involved in the creation of certain electronic devices.

All elementary particles are divided into two types: fermions and bosons. Fermions include quarks, electrons, protons, and neutrons, for instance. Dirac fermions were discovered by physicist Paul Dirac. These fermions, both in the form of ordinary particles and as quasi-particles, exhibit properties that manifest in opposing forms of particles and antiparticles.

The elusive half-Dirac fermion was discovered by physicists within the semi-metal ZrSiS, which was cooled to a temperature of minus 269 degrees Celsius. At such low temperatures, particles behave unusually and exhibit quantum effects. A manifestation of these effects for the half-Dirac fermion is that this quasi-particle has mass only when moving in one direction and is massless when moving in another. The presence of mass is dependent on the direction of the magnetic field lines, as physicists have determined.

Semi-metals are materials that conduct electricity like metals, but everything changes under extreme conditions. When the semi-metal was strongly cooled, the particles within it began to move in unusual ways, and the material demonstrated quantum effects that caused the particles to behave like waves.

Researchers directed infrared radiation at the semi-metal and subjected it to a magnetic field that is 900,000 times stronger than the Earth's magnetic field. As a result, scientists discovered that the strange behavior in the semi-metal corresponds exactly to the theoretical half-Dirac fermion. The study showed that these quasi-particles initially move as if they have no mass, but then, when the direction of motion is altered, mass emerges. In this case, the half-Dirac fermions represent very massive particles. So far, scientists cannot fully explain this phenomenon and intend to continue their experiments.