Ambient-pressure Dirac electron system in the quasi-two-dimensional molecular conductor α-(BETS)2I3

We investigated the precise crystal structures and electronic states of a quasi-two-dimensional molecular conductor alpha-(BETS)(2)I-3 at ambient pressure. The electronic resistivity of this molecular solid shows metal-to-insulator (MI) crossover behavior at T-MI = 50 K. Our x-ray diffraction and C-13 nuclear magnetic resonance experiments revealed that alpha-(BETS)(2)I-3 maintains the inversion symmetry below T-MI. First-principles calculations found a pair of anisotropic Dirac cones at a general k point, with the degenerate contact points at the Fermi level. The origin of the insulating state in this system is a small energy gap of similar to 2 meV opened by the spin-orbit interaction. The Z(2) topological invariants indicate that this system is a weak topological insulator. Our results suggest that alpha-(BETS)(2)I-3 is a promising material for studying the bulk Dirac electron system in two dimensions.

Automated summary

Through investigations on the crystal structures and electronic states of α-(BETS)(2)I-3, it was found that the system maintains inversion symmetry below T-MI and exhibits a metal-to-insulator transition. First-principles calculations revealed the presence of anisotropic Dirac cones and a small energy gap opened by spin-orbit interaction, suggesting that the system is a weak topological insulator.