Anisptropic plasmons in threefold Hopf semimetals

TL;DR

This paper theoretically demonstrates that threefold Hopf semimetals exhibit anisotropic plasmons at long wavelengths due to their internal anisotropy, challenging classical expectations of isotropic plasmon behavior.

Contribution

It provides the first analytical and numerical analysis showing anisotropic plasmons in threefold Hopf semimetals, highlighting their potential for experimental observation.

Findings

Plasmons in these semimetals are anisotropic even at long wavelengths.

Anisotropy of the plasmon frequency can reach 25%.

Analytical expressions for long-wavelength plasmon frequency are derived.

Abstract

Threefold Hopf semimetals are a novel type of topological semimetals that possess an internal anisotropy characterized by a dipolar structure of the Berry curvature and an isotropic energy band structure consisting of a Dirac cone and a flat band. In this study, we theoretically investigate the impact of internal anisotropy on plasmons in threefold Hopf semimetals using random-phase approximation. In contrast to the classical intuition that isotropy of the energy band dispersion leads to isotropic plasmons in the classical regime (i.e., in the wavelength limit), we find that plasmons in threefold Hopf semimetals exhibit notable anisotropy even in the long-wavelength limit. We derive an explicit analytical form of the long-wavelength plasmon frequency, and numerically demonstrate the validity of our results in a wide range of situations. Our work reveals that the anisotropy of long-wavelength plasmons can reach 25%, making it experimentally observable.