Discovery of a Cooper-pair density wave state in a transition-metal dichalcogenide

Pair density wave (PDW) states are defined by a spatially modulating superconductive order-parameter. To search for such in transition metal dichalcogenides (TMD) we use high-speed atomic-resolution scanned Josephson-tunneling microscopy (SJTM). We detect PDW state whose electron-pair and energy-gap modulate at the wavevectors of preexisting charge (CDW) state. The couples linearly to both s-wave superconductor CDW, exhibits commensurate domains with discommensuration phase-slips boundaries, conforming those lattice-locked CDW. Nevertheless, find global $\delta\Phi \sim \pm2\pi/3$ phase difference between CDW states, possibly owing Cooper-pair wavefunction orbital content. Our findings presage pervasive physics many other TMDs that sustain superconducting states.