Significance
Modern theoretical methods solve a long-standing mystery of cuprate high-temperature superconductivity, identifying crucial quantities that optimize the transition temperature. Superconducting cuprates have very different transition temperatures, and even if the optimal value of the superconducting transition temperature is obtained for a given parent compound by varying doping, there is no correlation between optimal doping and transition temperature. Instead, it has been found experimentally that the optimal transition temperature is controlled by oxygen hole content or by the size of the charge-transfer gap. Our calculations show that these two quantities are correlated and that together with covalency they lead to an effective superexchange interaction between copper atoms that ultimately controls the optimal superconducting order parameter.
The onset of the pseudogap in high-T c superconducting cuprates (HTSC) is marked by the T * line in the doping-temperature phase diagram, which ends at a point p * at zero temperature within the superconducting dome. There is no general consensus on how the pseudogap manifests itself within the superconducting phase. We use cluster dynamical mean field theory on a three-band Hubbard model for the HTSC to study the superconducting phase at T = 0 K, obtained when doping the correlated insulator, for two different sets of band parameters and for several values of U. We observe a first-order transition within the superconducting phase, which we believe, marks the onset of the pseudogap. Further, we also observe that the d-wave node vanishes within the superconducting phase at low values of hole doping, lower than that at which the first-order transition occurs. Various aspects of the results and their implications are discussed.
We use cluster dynamical mean field theory (CDMFT) on the one-band Hubbard model for the high-T c superconducting cuprates to study the charge-density-wave phase and its competition with superconductivity at T = 0. The d-wave charge-density-wave order, which appears as a d-wave bond-density-wave order within the one-band Hubbard model, arises purely out of local correlation effects and also leads to a swave pair-density-wave in the presence of d-wave superconductivity. The d-wave bond-density-wave order is observed to be weakened in presence of superconductivity, as has been seen earlier in experiments, and additionally demonstrates strikingly different behaviors on varying U in the normal and the superconducting states. In the normal state, the d-wave bond-density-wave order tends to decrease to zero as U → ∞ suggesting that it is mediated by magnetic interactions.
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