Evolving Charge Order in a Tunable Electronic Nematic Superconducting System

Recent discoveries of charge order in the cuprates and electron nematic order in the iron-based superconductors has pointed towards the possibilities of both orderings being tied to mechanisms of high Tc superconductivity.The Ba(1-x)Sr(x)Ni2As2 system, closely related in structure to the BaFe2As2 system, has recently been shown to exhibit both types of ordering without the presence of any magnetic order. We report single crystal X-ray diffraction observations that show a unidirectional charge order with wavevector (0.27,0,0)_{tet} in BaNi2As2 decays and vanishes by x=0.65. We also show that the (0.33,0,0)_{tri} order evolves into a (0.5,0,0)_{tri}+(0,0.5,0)_{tri} charge order before vanishing at x=0.71. We also show how this charge order is seen in AC magnetic susceptibility and how it can be tuned via hydrostatic pressure. The evolution of the charge order in this system correlates well with the already reported evolutions of nematicity and superconducivity, suggesting a strong link between the three phases.