Intimate link between charge density wave, pseudogap and superconducting energy scales in cuprates

Résumé

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 CDW order, and to compare it with the pseudogap $\Delta _{PG}$ and with the superconducting gap $\Delta _{SC}$. However, while $T _{CDW}$ is well characterized from earlier work, little is currently known about $\Delta _{CDW}$. Here, we report the extraction of $\Delta _{CDW}$ for several cuprates using electronic Raman spectroscopy. We find that on 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 reveals that these three phases have a common microscopic origin. In addition, we find that $\Delta _{CDW} \approx \Delta _{SC}$ over a substantial doping range, which suggests that CDW and superconducting phases are intimately related; for example, they may be intertwined or connected by an emergent symmetry.