We have now observed three distinct charge density waves in the nematic superconductor, Ba1−xSrxNi2As2 (BSNA). This pnictide material has the same structure as the 122-phase FeAs superconductors, but contains Ni instead of Fe. Paglione’s group at the University of Maryland recently observed a sixfold enhancement of superconductivity in this material due to nematic fluctuations near a quantum phase transition. Using x-ray scattering, we discovered a new charge density wave (CDW) in BSNA that is distinct from the two CDWs we reported previously.This CDW is commensurate with a period of two lattice parameters, and suggests that the anomalous superconductivity reported in this material arises from heterogeneous nucleation at domain walls in this CDW.
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