Weyl semimetal
（重定向自Weyl fermion）
![A schematic of the Weyl semimetal state, which include the Weyl nodes and the Fermi arcs. The Weyl nodes are momentum space monopoles and anti-monopoles. The sketch is adapted from Ref.[5]](/Images/godic/202502/20/Weyl_Balents5709.png")
![A detector image (top) signals the existence of Weyl fermion nodes and the Fermi arcs.[8] The plus and minus signs note the particle's chirality. A schematic (bottom) shows the way Weyl fermions inside a crystal can be thought as monopole and antimonopole in momentum space. (Image art by Su-Yang Xu and M. Zahid Hasan)](/Images/godic/202502/20/CartoonvWeyl5709.jpg")
Weyl fermions are massless chiral fermions that play an important role in quantum field theory and the standard model. They may be thought of as a building block for fermions in quantum field theory, and were predicted from a solution to the Dirac equation derived by Hermann Weyl. For example, one-half of a charged Dirac fermion of a definite chirality is a Weyl fermion. They have not been observed as a fundamental particle in nature. Weyl fermions may be realized as emergent quasiparticles in a low-energy condensed matter system.