The newly discovered BaPt_2As_2 shows a structural distortion at around 275 K, followed by the emergence of superconductivity at lower temperatures. Here we identify the presence of charge density wave (CDW) order at room temperature and ambient pressure using single crystal x-ray diffraction, with both a superlattice and an incommensurate modulation, where there is a change of the superlattice structure below ≃ 275 K. Upon applying pressure, BaPt_2As_2 shows a rich temperature-pressure phase

more »

... agram with multiple pressure-induced transitions at high temperatures, the emergence or disappearance of which are correlated with sudden changes in the superconducting transition temperature T_c. These findings demonstrate that BaPt_2As_2 is a promising new system for studying competing interactions and the relationship between high-temperature electronic instabilities and superconductivity.