The origin of the stabilized simple-cubic structure in Po

TL;DR

This paper investigates the origin of the simple-cubic structure in polonium, revealing that strong spin-orbit interaction suppresses typical structural instabilities and stabilizes the structure through electronic effects.

Contribution

It demonstrates that the stabilized simple-cubic structure in Po is primarily due to strong spin-orbit coupling, a novel insight into the structural stability of VIA elements.

Findings

Strong spin-orbit interaction suppresses Peierls-like instability in Po.

The stable structure results from competition between spin-orbit and crystal field splitting.

Po's cubic structure is stabilized by large spin-orbit splitting, unlike Se and Te.

Abstract

The origin of the stabilized simple-cubic (SC) structure in Po is explored by using the first principle band calculations. We have found that the prime origin is the inherent strong spin-orbit (SO) interaction in Po, which suppresses the Peierls-like 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 proved 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. The trigonal structure is stabilized in Se and Te by the larger crystal field splitting than the SO splitting, whereas in Po the SC structure is stabilized by the large SO splitting.