Phason modes in spin-density wave in the presence of long-range Coulomb interaction

TL;DR

This paper investigates how long-range Coulomb interactions influence phason modes in spin-density waves, revealing a new low-frequency optical mode that could be detected via electron energy loss spectroscopy.

Contribution

It demonstrates the emergence of a low-frequency optical mode in SDW due to Coulomb interactions and pinning effects, expanding understanding of collective excitations in such systems.

Findings

In the absence of pinning, the phason is absorbed by the plasmon via the Anderson-Higgs mechanism.

A new optical mode appears at frequencies below twice the SDW gap when pinning or tilting occurs.

The low-frequency mode has small optical weight but may be observable with EELS.

Abstract

We study the effect of long-range Coulomb interaction on the phason in spin-density wave (SDW) within mean field theory. In the longitudinal limit and in the absence of SDW pinning the phason is completely absorbed by the plasmon due to the Anderson-Higgs mechanism. In the presence of SDW pinning or when the wave vector {\bf q} is tilted from the chain direction, though the plasmon still almost exhausts the optical sum rule, another optical mode appears at $\omega < 2\Delta(T)$, with small optical weight. This low frequency mode below the SDW gap may be accessible to electron energy loss spectroscopy (EELS).