This award (which Prof. Wu will share with Prof. Barry Bradlyn of the University of Illinois) is presented annually to a condensed matter physicist for distinguished research performed within five years of receiving a PhD.
In Prof. Wu’s case, the award is given “for novel terahertz and optical spectroscopy experiments on topological insulators and semimetals.”
https://physics.illinois.edu/people/honors-and-awards/mcmillan-award.asp