Ab-initio modeling of Al2O3 lattice instability under extreme excitation of the electronic system

Abstract

Nonthermal phase transformations induced in Al2O3 by the electronic temperatures above ∼2.5 eV is demonstrated with ab initio molecular dynamics simulations. When this temperature exceeds ∼4 eV, such a transformation occurs within ∼500 fs i.e. within the typical time-scale of relaxation of the excited electronic system in a micron-size spot of a femtosecond-laser pulse. The electronic temperature at least above 6–10 eV is required for a nonthermal melting to occur in Al2O3 within ∼50–100 fs, which is the time scale of cooling down of the electronic system in a swift heavy ion track. Because such level of the electronic temperature cannot be kept during all this time, we conclude that nonthermal melting of alumina in SHI tracks is implausible.