Experimental evidence on high-Tc cuprates reveals ubiquitous charge density wave (CDW) modulations 1-10 , which coexist with superconductivity. Although the CDW had been predicted by theory 11-13 , important questions remain about the extent to which the CDW influences lattice and charge degrees of freedom and its characteristics as functions of doping and temperature. These questions are intimately connected to the origin of the CDW and its relation to the mysterious cuprate pseudogap 10,14 . Here, we use ultrahigh resolution resonant inelastic x-ray scattering (RIXS) to reveal new CDW character in underdoped Bi 2 Sr 2 CaCu 2 O 8+δ . At low temperature, we observe dispersive excitations from an incommensurate CDW that induces anomalously enhanced phonon intensity, unseen using other techniques. Near the pseudogap temperature T*, the CDW persists, but the associated excitations significantly weaken and the CDW wavevector shifts, becoming nearly commensurate with a periodicity of four lattice constants. The dispersive CDW excitations, phonon anomaly, and temperature dependent commensuration provide a comprehensive momentum space picture of complex CDW behavior and point to a closer relationship with the pseudogap state.With sufficient energy resolution, RIXS can be an ideal probe for revealing the CDW excitations in cuprates. By tuning the incident photon energy to the Cu L 3 -edge ( Fig. 1a), the resonant absorption and emission processes can leave the system in excited final states, which couple to a variety of excitations arising from orbital, spin, charge, and lattice degrees of freedom 15 . Thus, information of these elementary excitations in energy and momentum space can be deduced from analyzing the RIXS spectra as functions of the energy loss and the momentum transfer of the photons (Fig. 1a). This is highlighted

The discovery of high-temperature superconductivity in the copper oxides in 1986 triggered a huge amount of innovative scientific inquiry. In the almost three decades since, much has been learned about the novel forms of quantum matter that are exhibited in these strongly correlated electron systems. A qualitative understanding of the nature of the superconducting state itself has been achieved. However, unresolved issues include the astonishing complexity of the phase diagram, the unprecedented prominence of various forms of collective fluctuations, and the simplicity and insensitivity to material details of the 'normal' state at elevated temperatures.

Coupling between electrons and phonons (lattice vibrations) drives the formation of the electron pairs responsible for conventional superconductivity 1 . The lack of direct evidence for electron-phonon coupling in the electron dynamics of the high transition temperature superconductors has driven an intensive search for an alternative mechanism. A coupling of an electron with a phonon would result in an abrupt change of its velocity and scattering rate near the phonon energy. Here we use angle resolved photoemission spectroscopy to probe electron dynamicsvelocity and scattering rate-for three different families of copper oxide superconductors. We see in all of these materials an abrupt change of electron velocity at 50-80meV, which we cannot explain by any known process other than to invoke coupling with the phonons associated with the movement of the oxygen atoms. This suggests that electron-phonon coupling strongly influences the electron dynamics in the high-temperature superconductors, and must therefore be included in any microscopic theory of superconductivity. We investigated the electronic quasiparticle dispersions in three different families of hole-doped cuprates, Bi 2 Sr 2 CaCu 2 O 8 (Bi2212) and Pb doped Pb-Bi2212, Pb-doped Bi 2 Sr 2 CuO 6 (Pb-Bi2201) and La 2-x Sr x CuO 4 (LSCO). Except for the Bi2201 (overdoped, T c =7K) data and that in Fig. 3b, recorded at the beam-line 5.4 of the Stanford Synchrotron Radiation Laboratory (SSRL), all the data were recorded at the Advanced Light Source (ALS), as detailed elsewhere 2 . The top panels of figure 1 report the momentum distribution curve (MDC) derived dispersions along the (0, 0)-(π, π) direction for LSCO (panel a) and Bi2212 (panel b) superconducting state and for Pb-Bi2201 normal state (panel c) vs the rescaled momentum, k ' , defined by normalizing to one the momentum k relative to the Fermi momentum k F , (k-k F ), at the binding energy E=170meV. A "kink" in the dispersion around 50-80meV, highlighted by thick arrows in the figure, is the many-body effect of

Removing electrons from the CuO 2 plane of cuprates alters the electronic correlations sufficiently to produce high-temperature superconductivity. Associated with these changes are spectral-weight transfers from the high-energy states of the insulator to low energies. In theory, these should be detectable as an imbalance between the tunneling rate for electron injection and extraction—a tunneling asymmetry. We introduce atomic-resolution tunneling-asymmetry imaging, finding virtually identical phenomena in two lightly hole-doped cuprates: Ca 1.88 Na 0.12 CuO 2 Cl 2 and Bi 2 Sr 2 Dy 0.2 Ca 0.8 Cu 2 O 8+δ . Intense spatial variations in tunneling asymmetry occur primarily at the planar oxygen sites; their spatial arrangement forms a Cu-O-Cu bond-centered electronic pattern without long-range order but with 4 a 0 -wide unidirectional electronic domains dispersed throughout ( a 0 : the Cu-O-Cu distance). The emerging picture is then of a partial hole localization within an intrinsic electronic glass evolving, at higher hole densities, into complete delocalization and highest-temperature superconductivity.