Fig. 2: Causal structure in energy-momentum space and its applications.
From: Causal structure of interacting Weyl fermions in condensed matter systems
a In analogy with the theory of relativity, we define the region in energy-momentum space within/outside the Weyl cone as the energy-like/momentum-like region. b In the left panel, two Weyl nodes are energy-like in the reduced BZ. In the right panel, including interaction, the system undergoes a semimetal-insulator phase transition. c In the left panel, two Weyl nodes are momentum-like in the reduced BZ. In the right panel, including interaction, the system remains in a semimetal phase. a–c The red/blue structures represent the conduction/valence dispersion cones. The black dashed lines in (b, c) represent the position of Fermi energy. d Schematic picture of critical length KC in the reduced BZ. δk and δE represent the momentum and energy differences, respectively, between two Weyl nodes after band-folding without the CDW (δ = 0). e Band structure of (TaSe4)2I from the tight-binding model. A pair of Weyl nodes, W1 and W2, cross the Fermi energy. f The DFT band structure of Mo3Al2C shows two bands (represented by the red curves) with a pair of Weyl nodes, W− and W+ (highlighted in the blue circles), crossing the Fermi level along the Γ-M direction.
