Pressure-Driven Structural Transition in the Charge Density Wave Material SrAl₄

SrAl4, which possesses a BaAl4-type tetragonal structure (I4/mmm, No. 139), exhibits both a charge density wave (CDW) order and a topological semimetal state at ambient pressure. Here, the electronic and structural properties of SrAl4 were systematically investigated with pressure up to 49.4 GPa through electrical transport, X-ray diffraction (XRD), and Raman scattering measurements, as well as theoretical calculations. With increasing pressure, the TCDW is monotonically decreased, and the CDW state is eventually suppressed to zero temperature at ∼10 GPa based on the linear extrapolation. At ambient pressure, three Raman vibrational modes are identified, which are assigned to B1g (230.9 cm–1), Eg2 (302.7 cm–1), and A1g (357.4 cm–1), respectively. Upon compression to PC = 19.0 GPa, the original Raman modes all disappear, and simultaneously, four new peaks emerge, which indicate the occurrence of a structural transition. Combined with XRD and theoretical calculations, the C2/m phase is believed to be the most plausible crystal structure of SrAl4 above PC. In addition, the residual resistance ratio as well as magnetoresistance shows abrupt changes across PC, which further manifest the structural transition (I4/mmm → C2/m) of SrAl4 under high pressure.