Weyl semimetal

[1] In these materials, electrons have a linear dispersion relation, making them a solid-state analogue of relativistic massless particles.

Due to the nontrivial topology, a Weyl semimetal is expected to demonstrate Fermi arc electron states on its surface.

[9][11] These arcs are discontinuous or disjoint segments of a two dimensional Fermi contour, which are terminated onto the projections of the Weyl fermion nodes on the surface.

On 16 July 2015 the first experimental observations of Weyl fermion semimetal and topological Fermi arcs in an inversion symmetry-breaking single crystal material tantalum arsenide (TaAs) were made.

[9] Both Weyl fermions and Fermi arc surface states were observed using direct electronic imaging using ARPES, which established its topological character for the first time.

[9] This discovery was built upon previous theoretical predictions proposed in November 2014 by a team led by Bangladeshi scientist M Zahid Hasan.

This structure lacks a horizontal mirror plane and thus inversion symmetry, which is essential to realize Weyl semimetal.

[27] A group of international researchers led by a team from Boston College discovered in 2019 that the Weyl semimetal Tantalum Arsenide delivers the largest intrinsic conversion of light to electricity of any material, more than ten times larger than previously achieved.

In 2024, an intrinsic 2D Weyl semimetal with spin-polarized Weyl cones and topological Fermi string edge states was discovered in epitaxial monolayer bismuthene by a team from University of Missouri, National Cheng Kung University, and Oak Ridge National Laboratory.

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. [ 10 ]
A detector image (top) signals the existence of Weyl fermion nodes and the Fermi arcs. [ 9 ] 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)