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A Possible Massless Dirac Electron in Molecular Two-Orbital Model

Kazuyuki Miyahara, Masahisa Tsuchiizu, and Akito Kobayashi, JPS Conf. Proc. 3, 017011 (2014).

A possible massless Dirac electron is found in a simple molecular two-orbital model for quasi-one or two dimensional molecular conductors. This model consists of two π-orbitals with opposite symmetry (bonding and anti-bonding) on a molecule in aunit cell. Using symmetry of π-orbitals, a massless Dirac electron can be provided by crossing points of two lines where coefficients for σy or σz components vanish in the momentum space. Varying anisotropy on the intra- and inter-chain hopping drives emergence of a pair of massless Dirac electrons at the time reversal symmetry point. In addition, the emergence of additional two pairs of massless Dirac electrons is found at incommensurate momenta.