Modification of structural disorder by hydrostatic pressure in the superconducting cuprate YBa2Cu3O6.73

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 ${\mathrm{YBa}}₂{\mathrm{Cu}}₃{\mathrm{O}}_6.73$ (YBCO) using x-ray scattering under hydrostatic pressure (HP) up to $\ensuremath{\sim}6.0\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. 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 $\mathrm{Cu}{\mathrm{O}}₂$ plane and Cu-O layer. Concurrently, we also observed no disorder-pinned charge-density-wave signature in $\mathrm{Cu}{\mathrm{O}}₂$ plane under HP. This indicates that the oxygen rearrangement modifies the quenched disorder state in the $\mathrm{Cu}{\mathrm{O}}₂$ 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 ${\mathrm{YBa}}₂{\mathrm{Cu}}₃{\mathrm{O}}_6+x$. As an implication of these results, finally we have discussed that the change in disorder could make it easier for ${\mathrm{YBa}}₂{\mathrm{Cu}}₃{\mathrm{O}}_6+x$ to undergo a transition to the nematic order under an external magnetic field.