Implications of Charge Ordering in the High Tc Cuprate Superconductors in the Far-infrared Spectroscopy

TL;DR

This paper investigates the challenges in detecting charge ordering in high-Tc cuprates via far-infrared spectroscopy, revealing that previous data misinterpreted spectral features and that only a small fraction of charge carriers are itinerant, complicating the understanding of charge order's role in superconductivity.

Contribution

The study clarifies the interpretation of far-infrared reflectivity data in cuprates and highlights the limitations of current spectroscopic methods in revealing charge ordering phenomena.

Findings

Misinterpretation of reflectivity as Drude-like metallic response.

Only a small fraction (<3%) of charge carriers are itinerant.

Far-infrared spectroscopy currently insufficient to fully understand charge order.

Abstract

We addressed the issue of the absence of the far-infrared signatures pertaining to charge ordering in the published far-infrared reflectivity data of La2-xSrxCuO4 single crystals while other experimental probes unravel that charge ordering is a hallmark of the superconducting cuprates. Through direct comparison of the far-infrared data reported by various groups side by side and also with the Raman scattering data, we found that the inconsistencies stem from the failure in capturing delicate spectral features embedded in the close-to-perfect ab-plane far-infrared reflectivity of La2-xSrxCuO4 single crystals by misidentifying the reflectivity as the Drude-like metallic reflectivity. The analysis of the close-to-true reflectivity data reveals that only a small fraction (< 3 %) of the total doping-induced charge carriers (electrons) are itinerant on the electron lattice made up with the rest of the electrons (> 97 %) at all doping levels up to 16 %. We conclude that the far-infrared reflectivity study is far from being ready to construct a coherent picture of the ubiquitous charge ordering phenomenon and its relationship with the high Tc superconductivity.