Besides superconductivity, copper-oxide high-temperature superconductors are susceptible to other types of ordering. We used scanning tunneling microscopy and resonant elastic x-ray scattering measurements to establish the formation of charge ordering in the high-temperature superconductor Bi2Sr2CaCu2O(8+x). Depending on the hole concentration, the charge ordering in this system occurs with the same period as those found in Y-based or La-based cuprates and displays the analogous competition with superconductivity. These results indicate the similarity of charge organization competing with superconductivity across different families of cuprates. We observed this charge ordering to leave a distinct electron-hole asymmetric signature (and a broad resonance centered at +20 milli-electron volts) in spectroscopic measurements, indicating that it is likely related to the organization of holes in a doped Mott insulator.

The correlations between stripe order, superconductivity, and crystal structure in La2−x Bax CuO4 single crystals have been studied by means of x-ray and neutron diffraction as well as static magnetization measurements. The derived phase diagram shows that charge stripe order (CO) coexists with bulk superconductivity in a broad range of doping around x = 1/8, although the CO order parameter falls off quickly for x = 1/8. Except for x = 0.155, the onset of CO always coincides with the transition between the orthorhombic and the tetragonal low temperature structures. The CO transition evolves from a sharp drop at low x to a more gradual transition at higher x, eventually falling below the structural phase boundary for optimum doping. With respect to the interlayer CO correlations, we find no qualitative change of the stripe stacking order as a function of doping, and in-plane and out-of-plane correlations disappear simultaneously at the transition. Similarly to the CO, the spin stripe order (SO) is also most pronounced at x = 1/8. Truly static SO sets in below the CO and coincides with the first appearance of in-plane superconducting correlations at temperatures significantly above the bulk transition to superconductivity (SC). Indications that bulk SC causes a reduction of the spin or charge stripe order could not be identified. We argue that CO is the dominant order that is compatible with SC pairing but competes with SC phase coherence. Comparing our results with data from the literature, we find good agreement if all results are plotted as a function of x ′ instead of the nominal x, where x ′ represents an estimate of the actual Ba content, extracted from the doping dependence of the structural transition between the orthorhombic phase and the tetragonal high-temperature phase.

The discovery of the pseudogap in the cuprates created significant excitement amongst physicists as it was believed to be a signature of pairing [3], in some cases well above the room temperature. In this "pre-formed pairs" scenario, the formation of pairs without quantum phase rigidity occurs below T * . These pairs condense and develop phase coherence only below T c [3]. In contrast, several recent experiments reported that the pseudogap and superconducting states are characterized by two different energy scales [4][5][6][7], pointing to a scenario, where the two compete [14][15][16]. However a number of transport, magnetic, thermodynamic and tunneling spectroscopy experiments consistently detect a signature of phase-fluctuating superconductivity above T c [17][18][19][20][21][22] leaving open the question of whether the pseudogap is caused by pair formation or not. Here we report the discovery of a spectroscopic signature of pair formation and demonstrate that in a region of the phase diagram commonly referred to as the "pseudogap", two distinct states coexist: one that persists to an intermediate temperature T pair and a second that extends up to T * . The first state is characterized by a doping independent scaling behavior and is due to pairing above T c , but significantly below T*. The second state is the "proper" pseudogap -characterized by a "checker board" pattern in STM images, the absence of pair formation, and is likely linked to Mott physics of pristine CuO 2 planes. T pair has a universal value around 130-150K even for materials with very different T c , likely setting limit on highest, attainable Tc in cuprates. The observed universal scaling behavior with respect to T pair indicates a breakdown of the classical picture of phase fluctuations in the cuprates.The traditional approach of exploring the paring origin above T c by tracking the energy scale of spectral features has not yielded convincing results so far, as these features are poorly defined above T c due to broad spectral peaks. The apparent smooth evolution of the spectral gap from the lowest temperatures up to T * [1,2,11,12] has previously been interpreted as key evidence for a common origin of the pseudgap and pairing gap. However, very detailed, high precision data (e. g. Fig. S3E in Supplementary Information), shows the gap size varies non-monotonically across T c . This behavior raises doubt about the above interpretation.A better approach is to investigate the spectral weights, which are easier to quantify and in many cases interpret. A key such measure is the density of states at the Fermi energy 2 D(E F ). In conventional, clean superconductors this weight is zero below T c , but can be finite if there are strong impurity scattering effects. In such cases D(E F ) reflects the pair breaking state. Another possibility is the case of an inhomogeneous superconductor such as cuprates [23,24], where superconducting and "normal" patches coexist in the sample, with the latter being likely due to pair breaking states states (generic de...

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Identifying the mechanism of superconductivity in the high-temperature cuprate superconductors is one of the major outstanding problems in physics. We report local measurements of the onset of superconducting pairing in the high-transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+delta using a lattice-tracking spectroscopy technique with a scanning tunneling microscope. We can determine the temperature dependence of the pairing energy gaps, the electronic excitations in the absence of pairing, and the effect of the local coupling of electrons to bosonic excitations. Our measurements reveal that the strength of pairing is determined by the unusual electronic excitations of the normal state, suggesting that strong electron-electron interactions rather than low-energy (<0.1 volts) electron-boson interactions are responsible for superconductivity in the cuprates.