Measurement of the dynamical charge susceptibility near the charge density wave transition in ErTe3 with Dipanjan Chaudhuri

A charge density wave (CDW) phase, observed in many materials with a highly anisotropic electronic structure, is characterized by a periodic modulation of valence electron density coupled with lattice distortion. The formation of a CDW ground state is closely tied to the dynamical charge susceptibility, χ(q,ω), which reveals the collective behavior of charge carriers in materials. However, χ(q, ω) near a CDW transition had never been measured at finite momentum transfer with ~meV energy resolution, despite decades of extensive studies. In this talk, I will present our results on the investigation of the canonical CDW transition in ErTe3 using momentum-resolved electron energy loss spectroscopy (M-EELS), a technique uniquely sensitive to valence band charge excitations. Unlike phonons, which soften via the Kohn anomaly, we find that the electronic excitations exhibit purely relaxational dynamics well described by a diffusive model, with the diffusivity peaking just below the ordering temperature. Additionally, we report, for the first time, a divergent behavior in the real part of χ(q, ω) in the static limit (ω → 0), a long-predicted hallmark of CDWs. Unexpectedly, this divergence occurs as T→0, with only a weak thermodynamic signature at the ordering temperature. Our study necessitates a re-examination of the traditional description of CDW formation and demonstrates the power of M-EELS as a versatile probe of charge dynamics in correlated quantum materials.

This lecture was made possible by the William C. Ferguson Fund.