Transient superionic state in ultrafast-irradiated post-transition metal oxides
Matter under irradiation may enter unusual transient states, outside of its equilibrium phase diagram. One of such states is a superionic-like state, in which one sublattice of a compound liquifies, whereas another one remains solid. Here, we study theoretically post-transition metal oxides under ultrafast excitation of its electronic system, identifying which compounds produce such a superionic state. It is shown that oxides with sufficiently sparce metallic sublattices (e.g. corundum structure) generally form transient superionic states via nonthermal phase transition. More closely packed lattices (such as the zinc-blend structure in ZnO and CdO) do not exhibit superionicity. Tl and Pb oxides only enter thermally-produced superionic states (induced by the atomic heating via electron-phonon coupling), but not nonthermal ones. Sn and Bi oxides demonstrate states that cannot be clearly classified, in which oxygen subsystem diffuses significantly more and faster than the metallic one, but the metallic one is not stable as it would be in a truly superionic state.