Superconductivity of compressed solid argon from first principles

We present first-principles calculations on the superconductivity of solid argon under high pressure. Solid argon is found to take the double hexagonal close-packed structure in pressure range from 420 to 690 GPa, where an insulator-to-metal transition occurs at around 590 GPa. The crystal structure transforms into the hexagonal close-packed structure at 690 GPa and into the face-centered cubic structure at 2300 GPa. The superconducting critical temperature is gradually increased with the successive phase transitions and reaches the maximum value of 12 K at 2600 GPa due to the enhancement of the Fermi surface nesting.

Figure 1

(a) Enthalpy comparison among the fcc, hcp, and dhcp structures at the static condition. (b) Pressure-temperature phase diagram obtained by comparison of the Gibbs free energy.

Figure 2

(a) Pressure dependence of electronic band gap for the fcc, hcp, and dhcp structures. (b) Electronic band structures of dhcp at 200 and 600 GPa.

Figure 3

Pressure dependence of $N_{\text{n}}\left({\epsilon }_{\text{F}}\right),{\omega }_{log},\lambda$, and $T_{\text{c}}$ in the fcc, hcp, and dhcp phases. The superconducting $T_{\text{c}}$ was estimated from the Allen-Dynes formula, in which ${\mu }^{*}$ is assumed to be 0.13.

Figure 4

Phonon dispersion and phonon density of states (PDOS) in the fcc phase at the pressures of 2300, 2600, and 2800 GPa.

Figure 5

(a) Fermi surface nesting function $\xi$ and (b) mode-resolved electron-phonon coupling constant for the first branch ${\lambda }_{\mathbf{q},1}$ calculated on the $K\text{−}\Gamma \text{−}L\text{−}U$ line.