Superconductivity emerges in both $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ and $\mathrm{L}{\mathrm{a}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_{10}$ under high pressure by suppressing their density-wave (DW) transitions, but critical temperature ($T_c$) differs significantly between these two compounds. To gain deeper insights into the distinct superconducting states, it is essential to unravel the nature of the DW states at ambient pressure, a topic that remains largely unexplored. Here, using scanning tunneling microscopy/spectroscopy, we report the direct visualization of an incommensurate unidirectional charge DW (CDW) in $\mathrm{L}{\mathrm{a}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_{10}$ in real space. The density of states (DOS) is strongly depleted near $E_{\mathrm{F}}$, indicating the opening of a CDW gap of 2Δ ≈ 71 meV, which is unfavorable for the formation of superconductivity at ambient pressure. We propose that the CDW arises from Fermi surface nesting and is likely a subsidiary phase of a spin-DW. Compared with $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$, the weaker electronic correlation in $\mathrm{L}{\mathrm{a}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_{10}$ is likely one reason for the lower $T_c$.

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• Charge density waves
• Electronic structure
• Superconductivity
• Nickelates
• Single crystal materials
• Scanning tunneling microscopy
• Scanning tunneling spectroscopy