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Cuprate superconductors are known to harbor charge order in part of their phase diagram. Curiously, the order has a two-dimensional (2D) character at zero magnetic field, whereas a 3D order appears at high fields. Kim et al. now show that in a yttrium-based cuprate, a 3D charge order can be induced even at zero magnetic field. The authors compressed the material along one direction and measured a large inelastic x-ray scattering signal that was consistent with the formation of a 3D order. The measurements suggest that the induced order is associated with an optical lattice mode in the material.Science, this issue p. 1040Cuprates exhibit antiferromagnetic, charge density wave (CDW), and high-temperature superconducting ground states that can be tuned by means of doping and external magnetic fields. However, disorder generated by these tuning methods complicates the interpretation of such experiments. Here, we report a high-resolution inelastic x-ray scattering study of the high-temperature superconductor YBa2Cu3O6.67 under uniaxial stress, and we show that a three-dimensional long-range-ordered CDW state can be induced through pressure along the a axis, in the absence of magnetic fields. A pronounced softening of an optical phonon mode is associated with the CDW transition. The amplitude of the CDW is suppressed below the superconducting transition temperature, indicating competition with superconductivity. The results provide insights into the normal-state properties of cuprates and illustrate the potential of uniaxial-pressure control of competing orders in quantum materials.
