Anomalous acoustic plasmons in two-dimensional over-tilted Dirac bands

TL;DR

This paper discovers two novel acoustic plasmons in 2D over-tilted Dirac materials, highlighting their unique origins, valley-dependent chirality, and tunability via material parameters.

Contribution

It reveals the existence and origin of two anomalous acoustic plasmons in 2D type-II Dirac cones, expanding understanding of plasmon behavior in tilted Dirac systems.

Findings

Two anomalous acoustic plasmons are identified in 2D type-II Dirac materials.

One plasmon arises from hybridization of anisotropic pockets; the other from band correlation enhancement.

Plasmon properties can be tuned by adjusting the gap and dielectric environment.

Abstract

The over-tilting of Dirac cones has led to various fascinating quantum phenomena. Here we find that two anomalous acoustic plasmons (AAPs) are dictated by the distinct geometry of two-dimensional (2D) type-II Dirac cones, far beyond the conventional $\sqrt{q}$ plasmon. One AAP originates from the strong hybridization of two pockets with large velocity anisotropy at one Dirac point, whereas the other is attributed to the significant enhancement of the band correlation around the open Fermi surface. Remarkably, the plasmons exhibit valley-dependent chirality along the tilting direction due to the chiral electron dispersion. Meanwhile, we discuss the tunability of plasmon dispersion and lifetime by tuning the gap and dielectric substrate. Our work provides a promising way to generate the novel plasmons in Dirac materials.