Ultrafast electronic dynamics in a strongly correlated insulator SmB$_{6}$

SmB$_{6}$ is a strongly correlated Kondo insulator that forms a gap at the Fermi level due to hybridization between Sm 4f and 5d states. Such a gap can support interaction-driven excitons protected by strongly renormalized bands as discussed in inelastic neutron scattering and Raman spectroscopy studies. We excite SmB$_{6}$ with an ultrafast laser pulse, and study the resulting dynamics using time- and angle-resolved photoemission spectroscopy. We discover a coherent oscillatory response of the electronic states near the Gamma point, which we characterize as function of excitation density and temperature. We discuss possible origins for the observed mode.