Competing pair density wave and uniform d-wave superconductivity in phase-separated 214 cuprates at the 1/8 anomaly

Compelling evidence exists for electronic phase separation in cuprate high-Tc superconductors, emerging near 1/8 hole doping. At these dopings and low temperatures, intertwined charge and spin stripes coexist with more uniformly doped regions in the two-dimensional (2D) copper-oxide planes. Each region is capable of developing superconducting pairing, either as a pair density wave (PDW) within the stripes or as a uniform d-wave condensate (d-SC) in the more homogeneous regions. Using neutron scattering on single crystals of La1.875−yNdySr0.125CuO4, we demonstrate that the onset temperatures for spin stripe order (TN) and superconductivity (Tc) merge as the average ordered moment vanishes in LSCO (y=0), whereas Nd doping stabilizes static stripe order and suppresses Tc. Because the spin stripes possess the same in-plane periodicity (8a) as the PDW and establish the framework within which the PDW resides, the stabilization of spin stripe order enhances PDW correlations. Thus, the competition between d-wave pairing in the uniform regions and PDW pairing in the stripe-ordered regions can be controlled by the Nd concentration in La1.875−yNdySr0.125CuO4, allowing the superconducting Tc to vary by nearly an order of magnitude at a fixed 1/8-hole doping.