χ(q, ω) is a fundamental quantity that reveals the collective charge dynamics of the material. Despite decades of study, χ(q, ω), near a CDW transition, had never been measured at nonzero momentum, q, with energy resolution that is relevant for these quantum phases.

A divergent behavior observed in the real part of χ’(q, ω→0) near qCDW.

Using momentum-resolved electron energy loss spectroscopy (M-EELS), a technique uniquely sensitive to valence band charge excitations, we perform the first measurements of electron dynamics across a canonical CDW transition in ErTe3. We measured the dynamic charge susceptibility, χ(q, ω), across the CDW transition in ErTe3 and showed that the collective electron dynamics is purely relaxational and the real part of χ(q, ω→0) exhibits a divergent behavior, a long-predicted hallmark of CDWs.

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