Pressure-induced crossing of the core levels in $5d$ metals

A pressure-induced interaction between core electrons, the core-level crossing (CLC) transition, has been observed in hcp Os at $P\approx 400\mathrm{GPa}$ [L. Dubrovinsky et al., Nature (London) 525, 226 (2015)]. By carrying out a systematic theoretical study for all metals of the $5d$ series (Hf, Ta, W, Re, Os, Ir, Pt, Au) we have found that the CLC transition is a general effect for this series of metals. While in Pt it occurs at $\approx 1500\mathrm{GPa}$, at a pressure substantially higher than in Os, in Ir it occurs already at 80 GPa. Moreover, we predict that in Re the CLC transition may take place already at ambient pressure. We explain the effect of the CLC and analyze the shift of the transition pressure across the series within the Thomas-Fermi model. In particular, we show that the effect has many common features with the atomic collapse in rare-earth elements.

Figure 1

Left: Electronic density of states (DOS) for $5d$ metals from Hf to Au at zero pressure. Right: DOS for $5d$ metals from Hf to Au in structures experimentally known to be stable at high pressures. For each element the pressure shown in the figure corresponds either to the pressure of the core-level crossing transition or to the highest pressure considered in this study.

Figure 2

Thomas-Fermi potentials for orbital numbers $l=1$ ($p$ electrons) and $l=3$ ($f$ electrons). Potentials are plotted for the series of $Z$ from 70 to 80. The color of the line corresponds to $Z$, as shown in the right palette.

Figure 3

Left: Band structure of iridium at ambient pressure. Right: Band structure of iridium under a pressure of 80 GPa.