Probing free-carrier and exciton dynamics in a bulk semiconductor with two-dimensional electronic spectroscopy

We employ partially collinear two-dimensional electronic spectroscopy to disentangle precisely the ultrafast dynamics of excitons and free carriers in gallium selenide. Femtosecond temporal and meV energy resolution in the visible spectral region allows us to observe ultrafast bleaching at the exciton resonance with a relaxation time of 112 fs that corresponds to the thermal dissociation of excitons at room temperature, and is orders of magnitude faster than carrier relaxation in the bulk crystal. Our method is applicable to other functional materials, two-dimensional systems, and nanostructures.