The discovery of charge- and spin-density-wave (CDW/SDW) orders in superconducting cuprates has altered our perspective on the nature of high-temperature superconductivity (SC). However, it has proven difficult to fully elucidate the relationship between the density wave orders and SC. Here, using resonant soft X-ray scattering, we study the archetypal cuprate La 2- x Sr x CuO 4 (LSCO) over a broad doping range. We reveal the existence of two types of CDW orders in LSCO, namely CDW stripe order and CDW short-range order (SRO). While the CDW-SRO is suppressed by SC, it is partially transformed into the CDW stripe order with developing SDW stripe order near the superconducting T c . These findings indicate that the stripe orders and SC are inhomogeneously distributed in the superconducting CuO 2 planes of LSCO. This further suggests a new perspective on the putative pair-density-wave order that coexists with SC, SDW, and CDW orders.

Compelling efforts to improve the critical temperature (T c ) of superconductors have been made through high-pressure application. Understanding the underlying mechanism behind such improvements is critically important, however, much remains unclear. Here we studied ortho-III YBa 2 Cu 3 O 6.73 (YBCO) using x-ray scattering under hydrostatic-pressure (HP) up to ~6.0 GPa. We found the reinforced oxygen order (OO) of YBCO under HP, revealing an oxygen rearrangement in the Cu-O layer, which evidently shows the charge transfer phenomenon between the CuO 2 plane and Cu-O layer. Concurrently, we also observed no disorder-pinned charge density wave (CDW) signature in CuO 2 plane under HP. This indicates that the oxygen rearrangement modifies the quenched disorder state in the CuO 2 plane.Using these results, we appropriately explain why pressure-condition can achieve higher T c compared with the optimal T c under ambient pressure in YBa 2 Cu 3 O 6+x . As an implication of these results, finally, we have discussed that the change in disorder could make it easier for YBa 2 Cu 3 O 6+x to undergo a transition to the nematic order under an external magnetic field.

One of the central questions in the cuprate research is the nature of the normal state that develops into high-temperature superconductivity (HTSC). In the normal state of hole-doped cuprates, the existence of a charge density wave (CDW) is expected to shed light on the mechanism of HTSC. With evidence emerging for CDW order in the electron-doped cuprates, the CDW is thought to be a universal phenomenon in high-T c cuprates. However, the CDW phenomena in electron-doped cuprates are quite different than those in hole-doped cuprates. Here, we study the nature of the putative CDW in an electron-doped cuprate through direct comparisons between as-grown and postannealed Nd 1.86 Ce 0.14 CuO 4 (NCCO) single crystals using Cu L 3 -edge resonant soft x-ray scattering (RSXS) and angle-resolved photoemission spectroscopy (ARPES). The RSXS result reveals that the nonsuperconducting NCCO shows the same reflections at the wave vector (∼1=4, 0, l) as the reported superconducting NCCO. This superconductivity-insensitive signal is quite different from the CDW reflection in hole-doped cuprates. Moreover, the ARPES result suggests that the fermiology cannot account for such wave vectors. These results call into question the universality of the CDW phenomenon in the cuprates.