Observation of Floquet-Bloch States on the Surface of a Topological Insulator

Abstract

Topological Replicas When a periodic perturbation couples strongly to electrons in a solid, replicas of the original electronic levels are predicted to develop at certain energies—the so-called Floquet-Bloch states. Such conditions can be achieved by shining light on a solid, but the effect is challenging to observe. Wang et al. (p. 453 ) used time- and angle-resolved photoemission spectroscopy to photoexcite Bi 2 Se 3 and observe its dispersion at various delay times. The replicas were seen at expected energy shifts, along with the gaps predicted to occur at the new energy-level crossings caused by the appearance of the replicas. Because Bi 2 Se 3 is a topological insulator, the breaking of the time-reversal symmetry caused by circularly polarized light resulted in the appearance of an energy gap at the Dirac point, indicating an interesting route toward manipulating electronic states in such materials.