Wave vector dependent electron-phonon coupling drives charge-density-wave formation in TbTe3

TL;DR

This study demonstrates that momentum-dependent electron-phonon coupling, rather than Fermi surface nesting, drives charge-density-wave formation in TbTe3, supported by high-resolution inelastic x-ray scattering and lattice dynamical calculations.

Contribution

It provides direct experimental evidence linking momentum-dependent electron-phonon coupling to CDW periodicity in TbTe3, challenging the traditional Peierls scenario.

Findings

Strong phonon softening near the CDW wave vector

Electron-phonon coupling causes the CDW wave vector offset from Fermi surface nesting

TbTe3 is characterized by momentum-dependent electron-phonon coupling in CDW formation

Abstract

We present a high energy-resolution inelastic x-ray scattering investigation of the soft phonon mode in the charge-density-wave system TbTe$_3$. We analyze our data based on lattice dynamical calculations using density-functional-perturbation-theory and find clear evidence that strongly momentum dependent electron-phonon-coupling defines the periodicity of the CDW superstructure: Our experiment reveals strong phonon softening and increased phonon line widths over a large part in reciprocal space adjacent to the CDW ordering vector $q_{CDW} = (0, 0, 0.3)$. Further, $q_{CDW}$ is clearly offset from the wave vector of (weak) Fermi surface nesting $q_{FS} = (0, 0, 0.25)$ and our detailed analysis indicates that electron-phonon-coupling is responsible for this shift. Hence, we can add TbTe$_3$, which was previously considered as a canonical CDW compound following the Peierls scenario, to the list of distinct charge-density-wave materials characterized by momentum dependent electron-phonon coupling.