Chinese scientists discover new type of fermion: Nature

Chinese scientists have discovered a new type of fermion that opens up a way of exploring the interplay between unconventional fermions in condensed-matter systems.

The research team was led by scientists with the Institute of Physics of the Chinese Academy of Sciences (CAS), whose findings were published in the online version of the academic journal "Nature Communications" on Monday.

In quantum field theory, Lorentz invariance leads to three types of fermion -- Dirac, Weyl and Majorana. The existence of Dirac and Weyl fermions in condensed-matter systems has been confirmed experimentally, and that of Majorana fermions is supported by various experiments.

In condensed-matter systems, however, fermions in crystals are "constrained by the symmetries of the crystal space groups rather than by Lorentz invariance," giving rise to the possibility of finding other types of fermionic excitation that have no counterparts in high-energy physics.

The CAS scientists used a technique to observe the distribution of electrons, called angle-resolved photoemission spectroscopy, which demonstrated the existence of a "triply degenerate point in the electronic structure of crystalline molybdenum phosphide," -- a brand new discovery in field of fermion research.

They have also observed pairs of Weyl points in the bulk electronic structure of the crystal that coexist with the three-component fermions.