Dynamics of collective modes in an unconventional charge density wave system BaNi2As2

Abstract BaNi 2 As is a non-magnetic analogue of BaFe , the parent compound prototype pnictide high-temperature superconductor, displaying superconductivity already at ambient pressure. Recent diffraction studies demonstrated existence two types periodic lattice distortions above and below triclinic phase transition, suggesting an unconventional charge-density-wave (CDW) order. The suppression CDW order upon doping results in sixfold increase superconducting transition temperature enhanced nematic fluctuations, competing with superconductivity. Here, we apply time-resolved optical spectroscopy to investigate collective dynamics . We demonstrate several amplitude modes. Their smooth evolution through structural implies commensurate evolves from unidirectional incommensurate CDW, may indeed trigger transition. Excitation density dependence reveals exceptional resilience against perturbation, implying origin underlying electronic instability.