Title: Impact of the charge density wave state in the electrodynamic response of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>ZrTe</mml:mi><mml:mrow><mml:mn>3</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Se</mml:mi><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math> : Optical evidence for a pseudogap phase
Abstract: The emergence of superconductivity upon progressively suppressing the long-range, charge-density-wave (CDW) order characterizes the phase diagram of several materials of interest in the on-going solid-state physics research. Se-doped ${\mathrm{ZrTe}}_{3}$ compounds provide the most recent, suitable arena in order to investigate the interplay of otherwise competing orders in layeredlike two-dimensional systems. We present an optical study of the CDW state in ${\mathrm{ZrTe}}_{3\ensuremath{-}x}{\mathrm{Se}}_{x}$ at selected Se dopings, based on the measurement of the reflectivity from the far-infrared up to the ultraviolet, as a function of temperature. We particularly focus our attention to the redistribution of the spectral weight, which images the impact of the CDW state within the optical conductivity across the phase diagram of the title compounds. The electrodynamic response is consistent with a scenario based on a long-range CDW condensate at low Se doping. Upon increasing the Se content, this then gives way to local, short-range order CDW segments. Our spectral weight analysis reveals the presence of a pseudogap phase, as fingerprint of the CDW precursor effects and thus shaping the charge dynamics of the title compounds in their normal state, preceding the onset of superconductivity.