Shedding light on Weyl fermions

Researchers from the Theory Department of the Max Planck Institute for Structure and Dynamics (MPSD) in Hamburg and North Carolina State University in the US have demonstrated that the long-sought magnetic Weyl semi-metallic state can be induced by ultrafast laser pulses in a three-dimensional class of magnetic materials dubbed pyrochlore iridates. Their results, which have now been published in Nature Communications, could enable high-speed magneto-optical topological switching devices for next-generation electronics.

All known elementary particles can be sorted into two categories: bosons and fermions. Bosons carry forces, like the magnetic force or gravity, while fermions are the matter particles, like electrons. Theoretically it was predicted that fermions themselves can come in three species, named after the physicists Dirac, Weyl, and Majorana.
Electrons in free space are Dirac fermions, but in solids they can change their nature. In the atomically thin carbon material graphene they become massless Dirac fermions. In other recently discovered and manufactured materials, they can also become Weyl and Majorana fermions, which makes such materials interesting for future technologies such as topological quantum computers and other novel electronic devices.
In combination with a wave of bosons, namely photons in a laser, fermions can be transformed from one type to another, as proposed by MPSD theorists in 2016 (see ref. 1) below). Now a new study led by PhD student Gabriel Topp in the Emmy Noether group of Michael Sentef suggests that electron spins can be manipulated by short light pulses to create a magnetic version of Weyl fermions from a magnetic insulator. Based on a prior study led by MPSD postdoctoral researcher Nicolas Tancogne-Déjean and Theory Director Angel Rubio (see ref. 2 below), the scientists used the idea of laser-controlled electron-electron repulsion to suppress magnetism in a pyrochlore iridate material where electron spins are positioned on a lattice of tetrahedra.

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