Orbital selective dynamics in Fe-based systems using time-resolved ARPES

Exoticity in material properties often linked to the complex interplay of spin, charge, orbital and lattice degrees of freedom that makes the study of the origin of such exoticity difficult. The outstanding issue is to disentangle parameter space and reveal the underlying physics. We propose a unique method to excite electrons of a selected symmetry without significant effect on other electrons using polarized pump light pulse in a pump-probe experiment. Using this technique, we show that the relaxation of itinerant electrons occurs faster than the local electrons; the first experimental identification of the orbital selective electron dynamics in a complex correlated system. In addition, we discover that the electrons in the energy bands responsible for magnetic order can be excited selectively without significant effect on electrons in the other energy bands. Such excitations, termed magnetic excitation, occurs at a fast time scale of 50 fs while the time scale of other electrons is about 200 fs. These results provide two important conclusions – (i) in Fe-based systems, magnetism may not be linked to the phase space occupied by other electrons and (ii) polarized pump excitation in a pump-probe experiment is a novel method to study orbital selective dynamics.