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

This is the authors' abstract. We don't add key points for this paper.

SrAl 4, which possesses a BaAl 4 -type tetragonal structure ( I 4/ 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 SrAl 4 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 T CDW 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 B 1 g (230.9 cm –1 ), E g 2 (302.7 cm –1 ), and A 1 g (357.4 cm –1 ), respectively. Upon compression to P C = 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 C 2/ m phase is believed to be the most plausible crystal structure of SrAl 4 above P C . In addition, the residual resistance ratio as well as magnetoresistance shows abrupt changes across P C, which further manifest the structural transition ( I 4/ mmm → C 2/ m ) of SrAl 4 under high pressure.