Discovery of Semi-Dirac Fermions

Context: Recently, the researchers at Columbia University and Pennsylvania State University have reported finding a strange particle called a semi-Dirac fermion.

Relevance of the Topic: Prelims: Key facts about Standard Model of Particle Physics; Basic understanding of the terms- Fermions, Bosons, Quasi-particles and semi-Dirac fermion. 

What is the Standard Model of Particle Physics?

• The Standard Model of Particle Physics is scientists' current best theory to describe the most basic building blocks of the universe. It attempts to explain how the basic building blocks of matter (fundamental particles) interact, governed by fundamental forces.
• The Model describes the behaviour of:
  • Fundamental particles- Fermions (six types of quarks and six types of leptons)
  • Three fundamental forces (Strong force, Electromagnetic force & Weak force) and their four associated particles (Bosons)
  • Higgs boson (particles associated with the Higgs field. Any particle that interacts with Higgs Bosons gets mass, and particles that do not interact remain massless).
• As per the Model:
  • All the known matter is made up of fundamental particles called quarks and leptons. 
  • These particles interact with each other in accordance with rules known as the fundamental forces. 
• Limitations: Currently, the Model is incomplete and does not explain:
  • Fourth fundamental force- Gravitational force (Graviton is the force-carrying particle for gravity which has not been discovered yet)
  • Existence of dark matter and dark energy. 

Fermions and Bosons

• Fermions (Quarks + Leptons) are the fundamental particles which have half-integer spin. Fermions are the fundamental building blocks of matter. E.g., Electron, Proton.
• Boson is a name given to particles that carry fundamental forces. Each fundamental force has its own corresponding force carrier (boson). E.g., Photon
  • Strong force is carried by gluons.
  • Electromagnetic force is carried by photons.
  • W and Z bosons are responsible for the Weak force.
  • Graviton is a suggested force carrier for Gravitational force (Graviton is still not discovered)

Quest for New Particles

• Physicists explore ‘new physics’ in terms of whether it agrees or disagrees with the Standard Model (SM) of particle physics.  
• They use particle collider experiments (particularly CERN’s Large Hadron Collider) to find new fundamental particles to verify the predictions/ or challenge the Standard Model and find the missing answers. 
• The CERN supercollider smashes billions of protons head on with energy equivalent to the Big Bang (dawn of the universe).

Semi-Dirac Fermion

• Semi-Dirac fermion is a quasi-particle (a collection of particles), first theorised 16 years ago, recently spotted inside a crystal of semi-metal material called zirconium silicon sulphide (ZrSiS).
• Properties: 
  • Semi-Dirac fermion has mass when it is moving in one particular direction, but is massless when moving in another direction. 
• Experimental Set-up:
  •  ZrSiS was cooled to near absolute zero and was subjected to a magnetic field 2.7 lakh times stronger than the Earth’s magnetic field.
  • Infrared light was directed at the crystal to reveal its quantum behaviour. The experiment confirmed the presence of semi-Dirac fermions.
• Significance of finding Semi-Dirac Fermion: Understanding behaviour of semi-Dirac Fermion may lead to advances in a range of emerging technologies, like quantum computing, high-end electronics, batteries and sensors.