Collective excitations and screening in two-dimensional tilted nodal-line semimetals

TL;DR

This paper analytically studies the screening and collective excitations in two-dimensional tilted nodal-line semimetals, revealing isotropic polarizability despite anisotropic bands and novel features in plasmon behavior and Friedel oscillations.

Contribution

It provides the first analytical investigation of the density response and plasmon dispersion in 2D tilted nodal-line semimetals, highlighting unique screening properties and oscillation patterns.

Findings

Plasmon dispersion follows a square root dependence on wave vector.

Tilting enhances the plasmon frequency.

Static polarizability shows two singularities leading to beat patterns.

Abstract

Topological nodal-line semimetals are characterized by symmetry-protected one-dimensional band-touching lines or loops, which give rise to their peculiar Fermi surfaces at low energies. Furthermore, if time-reversal or inversion symmetry breaking tilts the bands, anisotropic Fermi surfaces hosting electron and hole carriers simultaneously can also appear. We analytically investigate the linear density-density response function of a two-dimensional tilted nodal-line semimetal in the intrinsic and doped regimes. Despite the anisotropic electronic bands, the polarizability remains isotropic in our model system. We find that the plasmon dispersion in the long wavelength limit exhibits a standard behavior that is proportional to the square root of the wave vector, characteristic of two-dimensional electron liquids. Tilting tends to enhance the plasmon frequency, and the Drude weight does not depend on the carrier density at low doping levels. In these regimes, unlike the intrinsic and highly-doped ones, the static polarizability has two distinct singularities at finite wave vectors. This results in beat patterns in the Friedel oscillations.