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3 distinct classes of fermions have been identified: Dirac (with mass and charge), Weyl (massless, charged), and Majorana (massless, chargeless). Dirac fermions are the stuff of ordinary matter. Majorana fermions were mathematically conjectured in 1937 but were experimentally elusive until the mid-2010s.
Also long shy were Weyl fermions. In 2015, they made an appearance in certain crystalline semimetals made of tantalum and arsenic (TaAs). Sort of. Weyl fermions were discerned via physical effects which can be inferred through the collective excitation of their quasiparticles.
A Weyl fermion can emerge as a quasiparticle in certain crystals: Weyl fermion semimetals. ~ Chinese physicist Su-Yang Xu et al
Another sort of Weyl fermion (type 2) showed up in a crystalline solid in 2017. This Weyl fermion broke Lorentz symmetry with an astonishing display of asymmetrical magnetism.
Put a normal material in a magnetic field and its resistance to electrical conduction grows. But in a solid larded with type-1 Weyl fermions, a magnetic field enhances electrical current flow.
In violating Lorentz symmetry, type-2 Weyl fermions are even stranger. In a material with these particles, a magnetic field in one direction increases conductivity; but when magnetized in another direction, electrical flow drops.
Symmetry breaking shows that our supposed ‘laws’ of Nature are nothing more than conditional codicils to something more fundamental. Nature keeps secrets.
