Collective modes in multi-Weyl semimetals.

Seongjin Ahn,Hongki Min,E H Hwang

doi:10.1038/srep34023

Seongjin Ahn, Hongki Min + Show 1 more

Open Access

https://doi.org/10.1038/srep34023

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Abstract

We investigate collective modes in three dimensional (3D) gapless multi-Weyl semimetals with anisotropic energy band dispersions (i.e., with a positive integer J). For comparison, we also consider the gapless semimetals with the isotropic band dispersions (i.e. E ~ kJ). We calculate analytically long-wavelength plasma frequencies incorporating interband transitions and chiral properties of carriers. For both the isotropic and anisotropic cases, we find that interband transitions and chirality lead to the depolarization shift of plasma frequencies. For the isotropic parabolic band dispersion the long-wavelength plasmons do not decay via Landau damping, while for the higher-order band dispersions the long-wavelength plasmons experience damping below a critical density. For systems with the anisotropic dispersion the density dependence of the long-wavelength plasma frequency along the direction of non-linear dispersion behaves like that of the isotropic linear band model, while along the direction of linear dispersion it behaves like that of the isotropic non-linear model. Plasmons along both directions remain undamped over a broad range of densities due to the chirality induced depolarization shift. Our results provide a comprehensive picture of how band dispersion and chirality affect plasmon behaviors in 3D gapless chiral systems with the arbitrary band dispersion.

Highlights

Our results provide a comprehensive picture of how band dispersion and chirality affect plasmon behaviors in 3D gapless chiral systems with the arbitrary band dispersion
In this paper we investigate theoretically electronic collective modes of 3D chiral gapless electron-hole systems and find the wave vector dependent plasmon dispersion
We find that the interband transition associated with chirality leads to the depolarization shift of plasma frequencies irrespective of band dispersion

Summary

The Isotropic Model

Before we calculate the collective modes in gapless multi-Weyl semimetals with anisotropic energy band dispersions, we first consider the gapless semimetals with the isotropic band dispersions. One interesting result is the chirality dependence of the plasmon energy, and it is important to note that in the presence of chirality, plasma frequencies are red-shifted This is due to the depolarization effect on the plasmon modes, arising from interband transitions. In this figure the boundary of interband SPE at q = 0 is 2EF. For N = 3, the plasma frequency as a function of Fermi energy exhibits a discrete jump at a critical value of EF =ħωp/2, and below the critical value the plasmon energy becomes bigger than 2EF and enters into the interband electron-hole continuum decaying via Landau damping.

Note that for

The Anisotropic Model

Summary and Conclusion

Additional Information