Charge density waves and phonon-electron coupling inZrTe3

Abstract

Charge-density-wave (CDW) order has long been interpreted as arising from a Fermi-surface instability in the parent metallic phase. While phonon-electron coupling has been suggested to influence the formation of CDW order in quasi-two-dimensional (quasi-2D) systems, the presumed dominant importance of Fermi-surface nesting remains largely unquestioned in quasi-1D systems.Here we show that phonon-electron coupling is also important for the CDW formation in a model quasi-1D system ZrTe 3 . Our joint experimental and computational study reveals that particular lattice vibrational patterns possess exceedingly strong coupling to the conduction electrons, and are directly linked to the lattice distortions associated with the CDW order. The dependence of the coupling matrix elements on electron momentum further dictates the opening of (partial) electronic gaps in the CDW phase. Since lattice distortions and electronic gaps are the defining signatures of CDW order, our result demonstrates that the conventional wisdom based on Fermisurface geometry needs to be substantially supplemented by phonon-electron coupling even in the simplest quasi-1D case. As prerequisites for the CDW formation, the highly anisotropic electronic structure and strong phonon-electron coupling in ZrTe 3 give rise to a distinct Raman scattering effect, namely, measured phonon linewidths depend on the direction of momentum transfer in the scattering process.

Distinction between pristine and disorder-perturbed charge density waves in ZrTe3

“…A pronounced resistivity anomaly can be observed at 63 ± 1 K ( Supplementary Fig. 1), a temperature that is usually referred to as the CDW ordering temperature, T CDW , in earlier literature [34][35][36][37][38][39] . The Fermi surface, contributed by four bands, comprises two sectors ( Fig.…”

“…At even higher T, the diffraction pattern becomes smeared and weak to the point of being buried under the fluorescence background. Nonetheless, a CDW-related electronic gap 34,36 and suppression of phonon-damping effects 34,38 have been observed up to higher temperatures % 140 K, indicative of persisting shortrange charge correlations and fluctuations above T CDW . Diffuse scattering signals centered around q CDW , presumably related to thermally activated soft phonons, have been observed in hard Xray scattering experiments even up to room temperature 37 .…”

“…ZrTe 3 is a quasi-one-dimensional (1D) metal belonging to the monoclinic space group P2 1 =m (see Fig. 1a), with a ¼ 5:89 Å, b ¼ 3:93 Å, c ¼ 10:09 Å, α ¼ γ ¼ 90 , and β ¼ 97:8 34,35 . A pronounced resistivity anomaly can be observed at 63 ± 1 K ( Supplementary Fig.…”

“…1a), with wave vector q CDW ¼ ð0:07a à ; 0; 0:33c à Þ. The electronic gap associated with the CDW order opens near the D-point of the BZ 36,39 , where electron-phonon coupling is strongest 34 .…”

“…Denoting pair-wise nesting as involving electronic states at momenta k and k þ qðkÞ, both of which are restricted to the Fermi surfaces and qðkÞ depends on k, the overall nesting wave vector q avg is determined by the (weighted) average of qðkÞ over k. At T ¼ T CDW , q avg (¼ q CDW ) is primarily contributed by electronic states with k close to the D-point of the BZ Fig. 1c), where strong electron-phonon coupling puts high weights in this region in the k-average for the purpose of CDW formation 34 . Indeed, the CDW electronic gap is most prominent in this region 36,39 .…”