Pressure-Induced Zero-Gap Semiconducting State in Organic Conductor $\alpha$-(BEDT-TTF)$_2$I$_3$ Salt

TL;DR

This paper reports the discovery of a pressure-induced zero-gap semiconducting state with Dirac cone features in the organic conductor $ ext{α}$(BEDT-TTF)$_2$I$_3$, highlighting the role of anisotropic transfer energies.

Contribution

It demonstrates the emergence of a zero-gap semiconducting state under uniaxial pressure and links it to anisotropic transfer energies in a tight-binding model.

Findings

Zero-gap state appears under uniaxial pressure along the a-axis.

Dirac cone with linear dispersion exists around the Fermi point.

The zero-gap state persists over a wide pressure range.

Abstract

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