Intimate link between Charge Density Wave, Pseudogap and Superconducting Energy Scales in Cuprates

TL;DR

This study uses electronic Raman spectroscopy to extract the charge density wave energy scale in cuprates, revealing its doping dependence and its relation to pseudogap and superconducting gaps, suggesting a common electronic origin.

Contribution

It provides the first measurement of the charge density wave energy scale in cuprates and links it to pseudogap and superconducting phases, indicating a shared electronic correlation.

Findings

$\Delta_{CDW}$ increases as doping decreases, similar to $\Delta_{PG}$ and $\Delta_{SC}$.

$\Delta_{CDW}$ is approximately equal to $\Delta_{SC}$ over a wide doping range.

Charge density wave is an unconventional order connected to superconductivity.

Abstract

The cuprate high temperature superconductors develop spontaneous charge density wave (CDW) order below a temperature $T_{CDW}$ and over a wide range of hole doping (p). An outstanding challenge in the field is to understand whether this modulated phase is related to the more exhaustively studied pseudogap and superconducting phases. To address this issue it is important to extract the energy scale $\Delta_{CDW}$ associated with the charge modulations, and to compare it with the pseudogap (PG) $\Delta_{PG}$ and the superconducting gap $\Delta_{SC}$. However, while $T_{CDW}$ is well-characterized from earlier works little has been known about $\Delta_{CDW}$ until now. Here, we report the extraction of $\Delta_{CDW}$ for several cuprates using electronic Raman spectroscopy. Crucially, we find that, upon approaching the parent Mott state by lowering $p$, $\Delta_{CDW}$ increases in a manner similar to the doping dependence of $\Delta_{PG}$ and $\Delta_{SC}$. This shows that CDW is an unconventional order, and that the above three phases are controlled by the same electronic correlations. In addition, we find that $\Delta_{CDW} \approx \Delta_{SC}$ over a substantial doping range, which is suggestive of an approximate emergent symmetry connecting the charge modulated phase with superconductivity.