Pressure-Induced Zero-Gap Semiconducting State in Organic Conductor α-(BEDT-TTF)₂I₃Salt

Abstract

We show a zero-gap semiconducting (ZGS) state in the quasi-two-dimensional\norganic conductor $\\alpha$-(BEDT-TTF)$_2$I$_3$ salt, which emerges under\nuniaxial pressure along the a-axis (the stacking axis of the BEDT-TTF\nmolecule). The ZGS state is the state in which a Dirac cone with the band\nspectrum of a linear dispersion exists around the Fermi point connecting an\nunoccupied (electron) band with an occupied (hole) band. The spectrum exhibits\na large anisotropy in velocity, which depends on the direction from the Fermi\npoint. By varying the magnitude of several transfer energies of a tight-binding\nmodel with four sites per unit cell, it is shown that the ZGS state exists in a\nwide pressure range, and is attributable to the large anisotropy of the\ntransfer energies along the stacking axis.\n