Distinguishing and controlling Mottness by ultrafast light

The relative energy scales of the Coulomb repulsion U and the bandwidth W determine how important electron-electron correlation is in the material properties. In the case of strong correlation, a half-filled band becomes insulating due to the strong Coulomb repulsion for double electron occupancy, leading to Mott insulator. However, when these energy scales are similar, the effect of correlation or the extent of Mottness becomes elusive, and the material is particularly sensitive to external perturbations. Finding an effective pathway to distinguish and further control the extent of Mottness is therefore important. Here we report the ultrafast electronic dynamics of a correlated material by ultrafast time- and angle-resolved photoemission spectroscopy. Distinctive dynamics in different phases is revealed, thereby providing nonequilibrium dynamical signatures and further controlling of the Mottness.