  Periodic driving of a quantum system can significantly alter its energy bands
and even change the band topology, opening a completely new avenue for
engineering novel quantum matter. Although important progress has been made
recently in measuring topological properties of Floquet bands in different
systems, direct experimental measurement of Floquet band dispersions and their
topology change is still demanding. Here we directly measure Floquet band
dispersions in a periodically driven spin-orbit coupled ultracold Fermi gas.
Using spin injection radio-frequency spectroscopy, we observe that the Dirac
point originating from two dimensional spin-orbit coupling can be manipulated
to emerge at the lowest or highest two dressed bands by fast modulating Raman
laser frequencies, demonstrating topological change of Floquet bands. Our work
will provide a powerful tool for understanding fundamental Floquet physics as
well as engineering exotic topological quantum matter.
