Selective nonthermal melting in phlogopite under ultrafast energy deposition

Abstract

Phlogopite is a complex magnesium-rich mineral from the dark mica group, KMg$_3$(AlSi$_3$O$_{10}$)(OH)$_2$. Its response to ultrafast excitation of its electronic system is studied using a hybrid model that combines tight-binding molecular dynamics with transport Monte Carlo and the Boltzmann equation. Simulations predict that at the deposited dose of ~0.17 eV/atom (electronic temperature $T_e$~11,000 K), the first hydrogens start to migrate in the otherwise preserved lattice, transiently turning mica into a superionic state. At the dose of ~0.4 eV/atom ($T_e$~13,000 K), Mg atoms start to diffuse like a liquid within stable sublattices of other elements, suggesting a superionic-superionic phase transition. At a dose of approximately 0.5 eV/atom ($T_e$~14,000 K), the entire atomic lattice destabilizes, disordering on picosecond timescale. It is accompanied by the formation of defect energy levels inside the bandgap. At the doses ~0.9 eV/atom ($T_e$~16,000 K), the bandgap completely collapses, turning the material metallic (electronically conducting). At even higher doses, nonthermal acceleration of atoms heats the atomic system at ultrafast timescales; K and O elements are most affected, accelerating within a few tens of femtoseconds.