Magnetoplasmons of the tilted anisotropic Dirac cone material α-(BEDT-TTF)2I3

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 ab initio theory, this material hosts both massless and massive low-energy carriers, the former being described by two 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 analyze 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.