Impact of disorder in the charge density wave state of Pd-intercalated ErTe3 revealed by the electrodynamic response

It is a general notion that disorder, introduced by either chemical substitution or intercalation as well as by electron irradiation, is detrimental to the realization of long-range charge density wave (CDW) order. We study the disorder-induced suppression of in-plane CDW orders in two-dimensional Pd-intercalated ErTe3 compositions by exploring the real part of the optical conductivity with light polarized along the in-plane a and c axes. Our findings reveal an anisotropic charge dynamics with respect to both incommensurate unidirectional CDW phases of ErTe3, occurring within the ac plane. The anisotropic optical response gets substantially washed out with Pd intercalation, hand in hand with the suppression of both CDW orders. The spectral weight analysis, though, advances the scenario, for which the CDW phases evolve from a (partially) depleted Fermi surface already above their critical onset temperatures. We therefore argue that the long-range CDW orders of ErTe3 tend to be progressively dwarfed by Pd intercalation, which favors the presence of short-range CDW segments for both crystallographic directions persisting in a broad temperature (T ) interval up to the normal state, and being suggestive of precursor effects of the CDW orders as well as possibly coexisting with superconductivity at low T.