Identification of strongly interacting organic semimetals

• Published in: Physical review. B 2020-11, Vol.102 (20), p.205134, Article 205134
• Main Authors: Geilhufe, R. Matthias, Olsthoorn, Bart
• Format: Article
• Language: English
• Subjects: Charge transfer; Conductors; Density functional theory; Machine learning; Many body interactions; Metalloids; Organic charge transfer salts; Organic crystals
• ISSN: 2469-9950; 2469-9969; 2469-9969
• DOI: 10.1103/PhysRevB.102.205134

Dirac and Weyl point- and line-node semimetals are characterized by a zero band gap with simultaneously vanishing density of states. Given a sufficient interaction strength, such materials can undergo an interaction instability, e.g., into an excitonic insulator phase. Due to generically flatbands, organic crystals represent a promising materials class in this regard. We combine machine learning, density functional theory, and effective models to identify specific example materials. Without taking into account the effect of many-body interactions, we found the organic charge transfer salts [bis(3,4-diiodo-3′,4′-ethyleneditio- tetrathiafulvalene), 2,3-dichloro-5,6-dicyanobenzoquinone, acetenitrile] [ ( EDT − TTF − I2 )2 ] ( DDQ ) ⋅ ( CH3 CN ) and 2 , 2 ′ , 5 , 5 ′ − tetraselenafulvalene – 7 , 7 , 8 , 8 − tetracyano − p − quinodimethane (TSeF-TCNQ) and a bis-1,2,3-dithiazolyl radical conductor to exhibit a semimetallic phase in our ab initio calculations. Adding the effect of strong particle-hole interactions for ( EDT − TTF − I2 )2 ( DDQ ) ⋅ ( CH3 CN ) and TSeF-TCNQ opens an excitonic gap on the order of 60 and 100 meV, which is in good agreement with previous experiments on these materials.