Abstract
We combined the group theory and data mining approach within the Organic Materials Database that leads to the prediction of stable Dirac-point nodes within the electronic band structure of three-dimensional organic crystals. We find a particular space group P212121 (#19) that is conducive to the Dirac nodes formation. We prove that nodes are a consequence of the orthorhombic crystal structure. Within the electronic band structure, two different kinds of nodes can be distinguished: 8-fold degenerate Dirac nodes protected by the crystalline symmetry and 4-fold degenerate Dirac nodes protected by band topology. Mining the Organic Materials Database, we present band structure calculations and symmetry analysis for 6 previously synthesized organic materials. In all these materials, the Dirac nodes are well separated within the energy and located near the Fermi surface, which opens up a possibility for their direct experimental observation.
Highlights
Since the crystal structure plays a crucial role for hosting Dirac nodes, attempts of identifying organic Dirac materials so far are mainly based on variations of already known Dirac materials
Within the band structure of the materials, two different kinds of nodes can be distinguished: 8-fold degenerate Dirac nodes protected by the crystalline symmetry and 4-fold degenerate tilted Dirac nodes protected by the band topology
We searched for isolated linear crossings in a neighborhood of 0.5 eV above the lowest unoccupied electronic state and below the highest occupied electronic state within the Kohn-Sham band structures stored in the Organic Materials Database (OMDB) by explicitly focusing our attention to materials with the space group P212121 (#19)
Summary
Since the crystal structure plays a crucial role for hosting Dirac nodes, attempts of identifying organic Dirac materials so far are mainly based on variations of already known Dirac materials. To achieve stable Dirac points within the electronic structure, symmetry or topological protection needs to be present. In this connection, crystals with non-symmorphic space groups have been widely discussed[18,19,20] where the key role is played by high-dimensional irreducible representations at the Brillouin zone boundary. We point out the first real material examples in the class of three-dimensional organic crystals hosting isolated Dirac nodes in the electronic structure: C6H7ClO325, C10H 10Br2Cl3NO226, C12H13NO227, C13H12N2O28, C9H10F3NO29, and C10H12BrNO30. Within the band structure of the materials, two different kinds of nodes can be distinguished: 8-fold degenerate Dirac nodes protected by the crystalline symmetry and 4-fold degenerate tilted Dirac nodes protected by the band topology
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