Tilted anisotropic Dirac cones in quinoid-type graphene and alpha-(BEDT-TTF)_2I_3

TL;DR

This paper explores tilted anisotropic Dirac cones in deformed graphene and organic compounds, analyzing their electronic properties, Landau levels, and potential experimental verification methods.

Contribution

It introduces a generalized Weyl Hamiltonian describing tilted anisotropic Dirac cones in these materials, highlighting the effects of next-nearest-neighbor hopping.

Findings

Tilted anisotropic Dirac cones are present in deformed graphene and alpha-(BEDT-TTF)_2I_3.

Relativistic Landau levels are formed with a renormalized Fermi velocity due to tilt.

Experimental signatures include spectroscopy and quantum Hall effect measurements.

Abstract

We investigate a generalized two-dimensional Weyl Hamiltonian, which may describe the low-energy properties of mechanically deformed graphene and of the organic compound alpha-(BEDT-TTF)_2I_3 under pressure. The associated dispersion has generically the form of tilted anisotropic Dirac cones. The tilt arises due to next-nearest-neighbor hopping when the Dirac points, where the valence band touches the conduction band, do not coincide with crystallographic high-symmetry points within the first Brillouin zone. Within a semiclassical treatment, we describe the formation of Landau levels in a strong magnetic field, the relativistic form of which is reminiscent to that of graphene, with a renormalized Fermi velocity due to the tilt of the Dirac cones. These relativistic Landau levels, experimentally accessible via spectroscopy or even a quantum Hall effect measurement, may be used as a direct experimental verification of Dirac cones in alpha-(BEDT-TTF)_2I_3.