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The quantum condensate of Cooper-pairs forming a superconductor wasoriginally conceived to be translationally invariant. In theory, however, pairscan exist with finite momentum $Q$ and thereby generate states with spatiallymodulating Cooper-pair density. While never observed directly in anysuperconductor, such a state has been created in ultra-cold $^{6}$Li gas. It isnow widely hypothesized that the cuprate pseudogap phase contains such a 'pairdensity wave' (PDW) state. Here we use nanometer resolution scanned Josephsontunneling microscopy (SJTM) to image Cooper-pair tunneling from a $d$-wavesuperconducting STM tip to the condensate ofBi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$. Condensate visualization capabilities aredemonstrated directly using the Cooper-pair density variations surrounding Znimpurity atoms and at the Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$crystal-supermodulation. Then, by using Fourier analysis of SJTM images, wediscover the direct signature of a Cooper-pair density modulation atwavevectors $Q_{p} \approx (0.25,0)2\pi / a_{0}$;$(0,0.25)2\pi / a_{0}$ inBi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$. The amplitude of these modulations is ~5%of the homogenous condensate density and their form factor exhibits primarily$s$/$s'$-symmetry. This phenomenology is expected within Ginzburg-Landau theorywhen a charge density wave with $d$-symmetry form factor and wave vector$Q_{c}=Q_{p}$ coexists with a homogeneous $d$-symmetry superconductor ; it isalso encompassed by several contemporary microscopic theories for the pseudogapphase.

Detection of a Cooper-Pair Density Wave in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$