Speaker
Description
The Weyl and Dirac semimetals are recently discovered topological quantum states of matter characterized by the unavoidable crossing of two non- or doubly-degenerate energy bands near the Fermi level, respectively. These crossing points (Weyl or Dirac nodes) are the source of exotic phenomena, including the realization of massless Dirac and Weyl fermions as quasiparticles in the bulk and the formation of Fermi arc states on the surfaces. I will show how the Weyl and Dirac semimetals are realized in systems with broken inversion and/or time-reversal symmetry. I shall also address the issue whether the band degeneracy can be retained when parity-time symmetry is broken, which is essential for the emergence of massless Dirac fermions as low-energy excitations in the system.
