Anisotropic response to optical excitations in a metal/insulator heterostructure

In the framework of real-time time-dependent density functional theory (RT-TDDFT) we unravel the layer-resolved dynamics of the electronic structure of a Fe₁/(MgO)₃(001) multilayer after optical excitations. We compare short optical pulses with two polarization directions of the light and frequencies up to the band gap of bulk MgO. We observe substantial transient changes to the electronic structure, which persist after the duration of the pulse. The response at particular frequencies and polarizations of the electric field reflects the strong anisotropy of the carrier dynamics of the metal/insulator system. Time-dependent changes in the layer-resolved occupation numbers are visible in all layers even for small excitation frequencies, due to the presence of interface states close to the Fermi level. The time evolution suggests that the presence of such states and their orbital character are decisive for the propagation of optically induced excitations into and across the interface region. Furthermore, we also see a small net charge transfer away from oxygen towards the Mg sites even for MgO layers, which are not directly in contact with the metallic Fe [1].

M. E. Gruner and R. Pentcheva, Phys. Rev. B 99, 195104 (2019).