Structural phase transition and superconductivity of ytterbium under high pressure

Recent advances in theory and experiment declare the rare-earth (RE) hydrogen-rich compound $\mathrm{La}{\mathrm{H}}_{10}$ is a near room-temperature superconductor under high pressure. To understand the underlying mechanism of superconductivity and explore the crucial role of lanthanides in forming the RE-based polyhydrides, we here perform a theoretical study on the structural phase transition and superconductivity of late lanthanide ytterbium (Yb) metal under high pressure up to 240 GPa. Two alternative structures, $R\overline{3}m$ and $I4/mmm$ phases, of Yb are presented. Most interestingly, the $P{6}_{3}/mmc$ phase of Yb is serendipitously discovered to be a superior superconductor with a critical temperature value of 19.5 K at 160 GPa, which is higher than other known RE elemental superconductors. The present findings establish an alternative structural phase transition sequence of Yb, which offers insights for further understanding the vital physics mechanisms of a lanthanide-based superconductor.