Wave-vector-dependent electron-phonon coupling and the charge-density-wave transition inTbTe3

Abstract

We present a high-energy-resolution inelastic x-ray scattering investigation of the soft phonon mode in the charge-density-wave (CDW) system $\mathrm{TbT}{\mathrm{e}}_3$. 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 linewidths over a large part in reciprocal space adjacent to the CDW ordering vector ${\mathit{q}}_{\mathrm{CDW}}=\left(0,0,0.3\right)$. Further, ${\mathit{q}}_{\mathrm{CDW}}$ is clearly offset from the wave vector of (weak) Fermi surface nesting ${\mathit{q}}_{\mathrm{FS}}=(0,0,0.25)$, and our detailed analysis indicates that electron-phonon coupling is responsible for this shift. Hence, we can add $\mathrm{TbT}{\mathrm{e}}_3$, 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.