Strain-induced nematic response of the CDW in Sr-doped BaNi2As2*

Ba1-xSrxNi2As2 (BSNA) is a pnictide superconductor that exhibits several charge density wave (CDW) phases and a diverging nematic susceptibility observed in transport experiments under applied uniaxial strain. The nematic susceptibility was found to become strain hysteretic in the incommensurate CDW (I-CDW) phase, suggesting that nematicity and the I-CDW phase are coupled, which is surprising because the I-CDW phase does not break C4 symmetry. To explore this coupling, we performed an x-ray scattering study of the CDW phases in BSNA x=0.27 under applied uniaxial strain. We find a large nematic response in the CDW as well, detected as a breaking of the C4 symmetry induced by the applied strain field. Our results indicate that the CDW is strongly coupled to the nematic order parameter and may even be the driver of nematic phenomena in this material.