Ultrafast above-transition-temperature resurrection of spin density wave driven by coherent phonon generation in BaFe

Abstract

A model incorporating the time-dependent Ginzburg-Landau theory of ultrafast cooperative interplay among charge, spin, and lattice is presented for the pnictide superconductor BaFe2As2. Under the ultrafast optical pumping, a pronounced spin-phonon coupling is found to drive the reconstruction of spin density wave (SDW) at T > Ts (Ts: SDW transition temperature) through the coherent phonon generation. First-principles electronic structure calculation confirms that the macroscopically coherent A 1g oscillation of As over a new equilibrium displacement offers a route to the antiferromagnetic SDW state. Our finding explains the recent experimental observation. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.