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Effects of the Spin-Orbit Coupling and the Superconductivity in simple-cubic alpha-Polonium

We have investigated the mechanism of stabilizing the simple-cubic (SC) structure in polonium (alpha- Po), based on the phonon dispersion calculations using the first-principles all-electron band method. We have demonstrated that the stable SC structure results from the suppression of the Peierls instability due to the strong spin-orbit coupling (SOC) in alpha-Po. Further, we have explored the possible superconductivity in alpha-Po, and predicted that it becomes a superconductor with Tc ~ 4 K. The transverse soft phonon mode at q ~ 2/3 R, which is greatly influenced by the SOC, plays an important role both in the structural stability and the superconductivity in alpha-Po. We have discussed effects of the SOC and the volume variation on the phonon dispersions and superconducting properties of alpha-Po.