Conductivity and Resistivity of Dirac Electrons in Single-Component Molecular Conductor [Pd(dddt)2]

Dirac electrons, which have been found in the single-component molecular conductor [Pd(dddt)(2)] under pressure, are examined by calculating the conductivity and resistivity for several pressures of P GPa, which give a nodal line semimetal or insulator. The temperature (T) dependence of the conductivity is studied using a tight-binding model with P-dependent transfer energies, where the damping energy by the impurity scattering Gamma is introduced. It is shown that the conductivity increases linearly under pressure at low T due to the Dirac cone but stays almost constant at high T. Further, at lower pressures, the conductivity is suppressed due to an unconventional gap, which is examined by calculating the resistivity. The resistivity exhibits a pseudogap-like behavior even in the case described by the Dirac cone. Such behavior originates from a novel role of the nodal line semimetal followed by a pseudogap that is different from a band gap. The present result reasonably explains the resistivity observed in the experiment.