Topological Properties of τ-Type Organic Conductors with a Checkerboard Lattice

Abstract

Although the topological phases are difficult to be realized in organic molecular crystals, we demonstrate here that they can emerge in the τ-type organic layered conductors, τ-(EDO-S,S-DMEDT-TTF)_2X_{1+y} and τ-(P-S,S-DMEDT-TTF)_2X_{1+y} (X=AuBr_2, I_3, IBr_2), where EDO-S,S-DMEDT-TTF and P-S,S-DMEDT-TTF denote the planar donor molecules ethylenedioxy-S,S-dimethyl(ethylenedithio)tetrathiafulvalene and pyrazino-S,S-dimethyl(ethylenedithio)tetrathiafulvalene, respectively. The conducting layers of these conductors have a highly symmetric checkerboard structure, which can be regarded as a modified Mielke lattice. Because their electronic structure inherits that of the Mielke lattice, their conduction and valence bands exhibits the quadratic band touching. The contact point splits into a pair of Dirac cones under uniaxial strain which breaks C_4-symmetry. In τ-type conductors, we can expect rather large spin-orbit coupling (SOC) as organic conductors. We show that the SOC in this case opens a topologically nontrivial gap at the band contact point, and the helical edge states exist in the gap. The actual τ-type conductors could be regarded as heavily-doped topological insulators, which could exhibit finite spin Hall effect.

24 pages, 6 figures

References in corpus (10)

• Topological Insulators with Inversion Symmetry
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Cited by in corpus (6)

• Molecular Quantum Materials: Electronic Phases and Charge Dynamics in Two-Dimensional Organic Solids
• Interaction-driven quantum anomalous Hall insulator in Dirac semimetal
• Tight-Binding Model and Electronic Property of Dirac Nodal Line in Single-Component Molecular Conductor [Pt(dmdt)${}_2$]
• Chirality-2 fermion induced anti-Klein tunneling in 2D checkerboard lattice
• Higher-Order Topology in Monolayer FeSe
• Possible Spin-Density Wave on Fermi Arc of Edge State in Single-Component Molecular Conductors [Pt(dmdt)${}_2$] and [Ni(dmdt)${}_2$]