Topological surface states and weak thermal phonon anharmonicity of low-lying phonons in GeSb2Te4

Recently, solid crystalline ${\mathrm{GeSb}}_{2}{\mathrm{Te}}_{4}$ was found to host topological surface states and low lattice thermal conductivity. In this work, we conducted comprehensive investigations on the electronic structures and lattice dynamics of ${\mathrm{GeSb}}_{2}{\mathrm{Te}}_{4}$. By combining synchrotron-based and spin-resolved angle-resolved photoemission spectroscopy and first-principles calculations, we observed distinctive topological surface states with significant spin polarization near the Fermi level. Furthermore, our temperature-dependent Raman scattering measurements revealed weak changes in linewidths of low-energy optical modes, indicating the weak temperature-dependent phonon anharmonicity of those modes. This finding is further supported by our lattice thermal conductivity calculation, which explains the minor variation in lattice thermal conduction in the high-temperature region. Our study sheds light on the exotic electronic and lattice dynamics of ${\mathrm{GeSb}}_{2}{\mathrm{Te}}_{4}$, potentially leading to new insights into its technological applications.