Pair-density-wave (PDW) correlations have been proposed as an important ingredient in the complex phase diagram of high-$T_{\mathrm{c}}$ cuprates, yet bulk-sensitive experimental signatures remain scarce. Here, we report resonant x-ray scattering measurements revealing a subharmonic charge-density-wave (CDW) scattering response in Sr-doped $1/8{\text{−}\text{La}}_{1.875}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_4$ (LBCO). The subharmonic response appears at approximately half the primary CDW ordering wave vector and emerges within a physically relevant temperature regime associated with the development of in-plane superconducting correlations. Comparable subharmonic behavior is also observed in a chemically distinct La-based cuprate, ${\mathrm{La}}_{1.87}{\mathrm{Sr}}_{0.13}{\mathrm{Cu}}_{0.99}{\mathrm{Fe}}_{0.01}{\mathrm{O}}_4$ (LSCO), within the same stripe-ordered, layer-decoupled regime. Together, these observations identify a bulk-sensitive scattering signature that is consistent with PDW correlations in La-based superconducting cuprates.

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• Charge density waves
• Pair density wave
• Superconducting order parameter
• Cuprates
• High-temperature superconductors
• Resonant elastic x-ray scattering