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

The cuprate high-temperature superconductors develop spontaneous charge density wave (CDW) order below a temperature TCDW 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 phases1,2. To address this issue, it is important to extract the energy scale ΔCDW associated with the CDW order, and to compare it with the pseudogap ΔPG and with the superconducting gap ΔSC. However, while TCDW is well characterized from earlier work3, little is currently known about ΔCDW. Here, we report the extraction of ΔCDW for several cuprates using electronic Raman spectroscopy. We find that on approaching the parent Mott state by lowering p, ΔCDW increases in a manner similar to the doping dependence of ΔPG and ΔSC. This reveals that these three phases have a common microscopic origin. In addition, we find that ΔCDW ≈ ΔSC 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 symmetry1,4–9. The authors show that the energy gap of the charge density wave is strongly linked to that of the superconducting and pseudogap in several cuprates. This indicates that the same microscopic physics may drive all three phases.