Identification of a Nematic Pair Density Wave State in Bi₂Sr₂CaCu₂O_8+x

Pair density waves (PDW) are an intense focus of research in the field of cuprate superconductivity. Although theory suggests that intertwining the d-wave superconducting (DSC) and PDW order parameters allows a plethora of global electron-pair orders to appear, which one actually occurs in the various cuprates is unknown. Here we use scanned Josephson tunneling microscopy (SJTM) to visualize the interplay of PDW and DSC states in near optimal-doped BSCCO. Simultaneous imaging of their amplitudes reveals that the PDW and DSC are mutually attractive states. By separately imaging the two orthogonal PDWs, we discover a robust nematic PDW state. Its spatial arrangement entails Ising domains of opposite nematicity. We further demonstrate that Zn impurity sites occur predominantly within boundaries between these domains. This implies that the nematic PDW state is pinned by Zn atoms, as was recently proposed. Taken in combination, these data indicate that the PDW in BSCCO is a vestigial nematic pair density wave state.