Magnetoplasmons of the tilted-anisotropic Dirac cone material $\alpha-$(BEDT-TTF)$_2$I$_3$

TL;DR

This paper investigates the collective excitations in a layered organic material with tilted and anisotropic Dirac cones, revealing unique damping effects and tunable screening properties influenced by magnetic fields and doping.

Contribution

It provides the first analysis of magnetoplasmon modes in a material with tilted and anisotropic Dirac cones, including effects of massive carriers and doping.

Findings

Identification of two sets of magnetoplasmon modes between cyclotron resonances.

Discovery of a unique intervalley damping effect caused by cone tilt.

Demonstration of doping-controlled transition between isotropic and anisotropic screening.

Abstract

We study the collective modes of a low-energy continuum model of the quasi-two-dimensional electron liquid in a layer of the organic compound $\alpha-$(BEDT-TTF)$_2$I$_3$ in a perpendicular magnetic field. As testified by zero magnetic field transport experiments and \textit{ab initio} theory, this material hosts both massless and massive low-energy carriers, the former being described by tilted and anisotropic Dirac cones. The polarizability of these cones is anisotropic, and two sets of magnetoplasmon modes occur between any two cyclotron resonances. We show that the tilt of the cones causes a unique intervalley damping effect: the upper hybrid mode of one cone is damped by the particle-hole continuum of the other cone in generic directions. We analyse how the presence of massive carriers affects the response of the system, and demonstrate how doping can tune $\alpha-$(BEDT-TTF)$_2$I$_3$ between regimes of isotropic and anisotropic screening.