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 organic conductor -(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.

Chiral symmetry and fermion doubling in the zero-mode Landau levels of massless Dirac fermions with disorder

“…Kicked off by the experimental observation of the graphene quantum Hall effect 1,2 , fascination with massless Dirac fermions is mounting, where they appear not only in graphene but more generically in various systems such as organic metals [3][4][5] , cold atom systems in optical lattices 6 and molecular graphene 7 . Among these systems, the number of massless Dirac fermions is always even for solid state materials, which is called the "fermion doubling" 8,9 .…”

Effect of the Zero-Mode Landau Level on Interlayer Magnetoresistance in Multilayer Massless Dirac Fermion Systems

“…The carrier density depends on temperature as n = αT 2 , where α = (π 2 k 2 B /6c 2 v 2 F ) and c is the lattice constant along the direction normal to the 2D plane [6]. According to band calculations, however, the Dirac cone in this system has highly anisotropic Fermi velocity v F (φ) [7,8]. Therefore, v F = 10 7 cm/s is an average of v F (φ).…”

“…The bottom of the conduction band and the top of the valence band contact each other at two points (We call them "contact points") in the first Brillouin zone [7,8]. The Fermi energy of the electron system locates just at the contact point.…”

Local spin susceptibility in the zero-gap-semiconductor state ofα−(BEDT-TTF)2I3probed byHirose1, Kawamoto2 2010Phys. Rev. B122150View full textAdd to dashboardCite

“…16 The narrow energy gap electron system was suggested by the band calculation of this salt and the zero-gap-semiconductor ͑ZGS͒ phase in the noninsulating state is proposed. 17 The band structure of the salt has a discriminative feature. The contact points of the band dispersion are symmetrically located in k space and the shapes of the band around the contact points have a titled corn structure and an anisotropic linear dispersion structure.…”

“…The contact points of the band dispersion are symmetrically located in k space and the shapes of the band around the contact points have a titled corn structure and an anisotropic linear dispersion structure. 17 The band structure with linear dispersion is described by the Dirac electron system as similar to graphene, 1-4 inspiring many theoretical and experimental studies. [1][2][3][4][17][18][19][20] From this exotic electronic system, non-Pauli-type magnetism is expected.…”