Modification of structural disorder by hydrostatic pressure in the superconducting cuprate YBa2 Cu3 O6.73

Compelling efforts to improve the critical temperature (Tc) 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 YBa2Cu3O6.73 (YBCO) using x-ray scattering under hydrostatic pressure (HP) up to ∼6.0GPa. We found the reinforced oxygen order of YBCO under HP, revealing an oxygen rearrangement in the Cu-O layer, which evidently shows the charge-transfer phenomenon between the CuO2 plane and Cu-O layer. Concurrently, we also observed no disorder-pinned charge-density-wave signature in CuO2 plane under HP. This indicates that the oxygen rearrangement modifies the quenched disorder state in the CuO2 plane. Using these results, we appropriately explain why pressure condition can achieve higher Tc compared with the optimal Tc under ambient pressure in YBa2Cu3O6+x. As an implication of these results, finally we have discussed that the change in disorder could make it easier for YBa2Cu3O6+x to undergo a transition to the nematic order under an external magnetic field.