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 [1,2]. To address this issue it is important to extract the energy scale ∆ CDW associated with the charge modulations, and to compare it with the pseudogap (PG) ∆ PG and the superconducting gap ∆ SC . However, while T CDW is well-characterized from earlier works [3] little has been known about ∆ CDW until now. Here, we report the extraction of ∆ CDW for several cuprates using electronic Raman spectroscopy.Crucially, we find that, upon approaching the parent Mott state by lowering p, ∆ CDW increases in a manner similar to the doping dependence of ∆ PG and ∆ 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 ∆ CDW ≈ ∆ SC over a substantial doping range, which is suggestive of an approximate emergent symmetry connecting the charge modulated phase with superconductivity [4][5][6][7][8][9].In recent years, many experiments and different techniques have established the ubiquity of CDW order in cuprates [3]. In particular, these works have determined T CDW (p), which displays a dome-like shape on the temperature-doping (T − p) phase diagram, in a fashion reminiscent of the superconducting dome T SC (p), even though the former order is present over a much narrower p-range, and mostly below optimal doping. The CDW is found to compete with superconductivity [10-16] but there are indications that the interplay between the two phenomena might be more complex than a simple competition [17,18].The energy scale ∆ CDW associated with the CDW has attracted far less experimental attention, even though this quantity is crucial to address several important ques-tions such as the following. (a) First, whether the CDW is a conventional order i.e., a phase whose existence can be understood within a scenario of weakly interacting electrons. A tell-tale signature of it would be if T CDW (p) ∝ ∆ CDW (p). On the other hand if their doping trends are different, as is famously the case of the superconducting order, it implies unconventional order, which is a consequence of strongly interacting electrons.Here we show that this is also the case of the CDW and, therefore, it is an unconventional order. (b) Second, a comparison of the magnitudes and the doping dependencies of ∆ CDW (p), ∆ SC (p) and ∆ PG (p) is important to understand the relation between these three phenomena. We show that these three energy scales have rather similar doping evolutions, implying that it is likely that they have a common origin in terms of a driving electronic interaction. Moreover, we find that the magnitude of ∆ CDW (p) and of ∆ SC (p) are comparable over a significant doping range, which is consistent with a concept that has ...

Establishing the presence and the nature of a quantum critical point in their phase diagram is a central enigma of the high-temperature superconducting cuprates. It could explain their pseudogap and strange metal phases, and ultimately their high superconducting temperatures. Yet, while solid evidences exist in several unconventional superconductors of ubiquitous critical fluctuations associated to a quantum critical point, in the cuprates they remain undetected until now. Here using symmetry-resolved electronic Raman scattering in the cuprate , we report the observation of enhanced electronic nematic fluctuations near the endpoint of the pseudogap phase. While our data hint at the possible presence of an incipient nematic quantum critical point, the doping dependence of the nematic fluctuations deviates significantly from a canonical quantum critical scenario. The observed nematic instability rather appears to be tied to the presence of a van Hove singularity in the band structure.