Since the early 20th century, physicists have discovered numerous subatomic particles, often referred to as a "particle zoo."
Matter exhibits dual characteristics, behaving as both waves and particles.
Subatomic particles form the building blocks of the universe and everything within it.
These particles can be categorized in multiple ways to understand their properties better.
Fermions and Bosons
Subatomic particles are commonly categorized into fermions and bosons:
Fermions: Constitute matter (e.g., electrons, protons).
Bosons: Mediate the forces between matter (e.g., photons).
Fermions can be further classified into:
Dirac fermions: May or may not have mass; distinct from their antiparticles.
Majorana fermions: Serve as their own antiparticles (e.g., neutrinos are suspected to belong to this category).
Mysteries in the Particle Zoo
The subatomic "zoo" contains gaps and anomalies:
The force of gravity lacks an associated particle.
Some particles (e.g., Higgs bosons, neutrinos) are heavier than theoretical predictions.
Dark matter remains undetected despite extensive searches.
Many aspects of known particles are either incomplete or inconsistent with earlier studies.
Physicists use the Standard Model (SM) to unify and describe all known particles and their interactions.
The SM serves as a framework to explore "new physics."
Discoveries that deviate from the SM could indicate the need for a revised model.
Condensed-Matter Physics and Exotic Particles
The behavior of particles can differ based on their environment:
In condensed-matter physics, materials act as new "universes" where exotic particles emerge.
For example, two-dimensional materials host anyons, whose properties fall between those of fermions and bosons.
Recently, researchers discovered a new particle called the semi-Dirac fermion:
It exhibits mass in one direction but not in a perpendicular direction.
Its unique characteristics result from interactions with electric and magnetic forces in specific materials.
Quasiparticles and Semi-Dirac Fermions
Semi-Dirac fermions are technically quasiparticles:
Quasiparticles are clusters of particles or energy packets that behave like single particles.
For example, protons are quasiparticles made of quarks and gluons.
In materials like zirconium silicon sulphide (ZrSiS), semi-Dirac fermions exhibit distinct properties under a magnetic field.
Discovery of Semi-Dirac Fermions
Researchers identified ZrSiS as a promising material to study semi-Dirac fermions:
Earlier studies indicated unusual electronic properties in zirconium silicon selenide (ZrSiSe), a structurally similar material.
Applying a magnetic field to ZrSiS revealed unique behaviors consistent with semi-Dirac fermions.
The findings align with theoretical predictions, showcasing the potential of tabletop experiments in condensed-matter physics.
Scaling Relationships
The relationship between cyclotron energy and magnetic field strength in ZrSiS revealed a unique scaling factor of B2/3, a hallmark of semi-Dirac fermions:
Metals: Cyclotron energy increases linearly with magnetic field strength (B1).
Graphene: Cyclotron energy scales as the square root of the magnetic field (B1/2).
ZrSiS: Cyclotron energy scales as B2/3.
Significance of the Discovery
The discovery demonstrates the universality of nature's laws, which apply across both subatomic particles and condensed-matter systems.
It highlights the importance of identifying the right materials to observe exotic particles.
Expanding the Particle Zoo
Physicists use extreme conditions to study subatomic particles and understand fundamental laws:
The Large Hadron Collider at CERN recreates conditions similar to those just after the Big Bang.
ZrSiS crystals were subjected to magnetic fields 270,000 times stronger than Earth’s.
Researchers aim to further study ZrSiS to explain other unusual electronic behaviors observed during experiments.
Conclusion
The discovery of semi-Dirac fermions adds a new "animal" to the particle zoo.
Physicists now seek to understand how this new particle will reshape their understanding of the subatomic zoo and the universe.
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