Collective modes in imbalanced nodal line semimetal

TL;DR

This paper studies collective excitations in an imbalanced nodal line semimetal with opposite spin-polarized nodal lines, revealing four bulk modes and a boundary-sensitive surface mode.

Contribution

It introduces a detailed analysis of collective modes considering spin imbalance and electron-electron interactions in nodal line semimetals, including surface state behavior.

Findings

Four bulk collective modes identified, with one gapless and three gapped.

Surface mode exists and is sensitive to boundary conditions.

Polarization operator components are calculated considering exchange interactions.

Abstract

In this work, we investigate collective modes in a nodal line semimetal with two nodal-lines that have opposite spin polarization in the presence of spin population imbalance. We find the components of polarization operator taking into account the electron-electron exchange interaction and obtain the dispersion relations of collective modes for the bulk and surface states. There exist four modes in the bulk, among which one is gapless and other three are gapped. The gapless surface mode is sensitive to the boundary conditions.