Energy Scale of the Charge Density Wave in Cuprate Superconductors ^†

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 [1]. To address this issue, it is important to extract the energy scale Δ_CDW associated with the CDW order, and to compare it with the pseudogap (PG) Δ_PG and with the superconducting gap Δ_SC. However, while T_CDW is well-characterized from earlier work, little is known about Δ_CDW until now. Here, we report the extraction of ΔCDW for several cuprates using electronic Raman spectroscopy [2]. Crucially, we find that upon approaching the $\stackrel{\approx }{\mathrm{parent}}$ Mott state by lowering p, Δ_CDW increases in a manner similar to the doping dependence of Δ_PG and Δ_SC [2]. This indicates that the above three phases have a common microscopic origin [2]. In addition, we find that Δ_CDW and Δ_SC have the same magnitude over a substantial doping range, which suggests that CDW and superconducting phases are intimately related [2], as reported for example by fractionalized pair density wave [3].