Impact of disorder in the charge-density-wave state of Pd-intercalated ErTe$_3$ revealed by the electrodynamic response

TL;DR

This study investigates how Pd-intercalation affects the charge-density-wave (CDW) states in ErTe$_3$, revealing suppression of long-range order and emergence of short-range CDW segments, with implications for understanding disorder effects and potential coexistence with superconductivity.

Contribution

It provides the first detailed optical conductivity analysis of disorder effects on in-plane CDW orders in Pd-intercalated ErTe$_3$, highlighting the evolution from long-range to short-range CDW states.

Findings

Pd-intercalation suppresses long-range CDW order

Optical response becomes less anisotropic with Pd-intercalation

Short-range CDW segments persist up to the normal state temperature

Abstract

It is a general notion that disorder, introduced by either chemical substitution or intercalation as well as by electron-irradiation, is detrimental to the realisation of long-range charge-density-wave (CDW) order. We study the disorder-induced suppression of the in-plane CDW orders in the two-dimensional Pd-intercalated ErTe$_3$ compositions, by exploring the real part of the optical conductivity with light polarised along the in-plane $a$ and $c$ axes. Our findings reveal an anisotropic charge dynamics with respect to both incommensurate unidirectional CDW phases of ErTe$_3$, 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 ErTe$_3$ tend to be progressively dwarfed by Pd-intercalation, which favours 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 $T$.