High-Pressure Raman Spectroscopic and Density Functional Theory Analysis of Topological Nodal Line Semimetal PdSn4

Topological nodal line semimetal PdSn4 is investigated through high-pressure Raman spectroscopy, corroborated by first principles density functional theory (DFT) calculations. At ambient conditions, the Raman spectrum shows a broad peak structure around 130 cm-1 together with several weak peaks. DFT calculation within the Ccce orthorhombic structure identifies the 12 possible Raman active modes in this system below 140 cm-1, correlating well with the experimental observation. A comparison of the Raman spectra of RSn4 (R = Pd, Pt, and Au) showed a similar broad peak-like structure with slightly differing wavenumbers in agreement with a chemical pressure description of these systems. Indeed, phonon dispersions from DFT studies within the Ccce orthorhombic structure provided similar phonon band structures for both PdSn4 and PtSn4, and demonstrate that the orthorhombic lattice of PdSn4 to be stable to 25 GPa. In this pressure range, DFT as well as experiments showed a regular hardening of the Raman phonon modes. A careful analysis indicates the pressure dependence of the mode positions have different rate in the high- and low-pressure regions. This is an indication of a pressure-dependent isostructural phase transition in PdSn4, similar to that observed in PtSn4.