Origin of the stabilized simple-cubic structure in polonium: Spin-orbit interaction versus Peierls instability

Abstract

The origin of the stabilized simple-cubic (SC) structure in Po is explored by using the first-principles band calculations. We have found that the prime origin is the inherent strong spin-orbit (SO) interaction in Po, which suppresses the Peierls-type structural instability, as usually occurs in $p$-bonded systems. Based on the systematic analysis of electronic structures, charge densities, Fermi surfaces, and susceptibilities of Se, Te, and Po, we have proven that the stable crystal structure in VIA elements is determined by the competition between the SO splitting and the crystal-field splitting induced by the low-symmetry structural transition. Our study suggests that the large SO interaction would suppress the Peierls instability which is generally expected to occur in one-dimensional conductors.