Plasmonic Hot Carriers-Controlled Second Harmonic Generation in WSe2 Bilayers

Modulating second harmonic generation (SHG) by a static electrical field through either electric-field-induced SHG1-4 or charge-induced SHG5 has been well documented. Nonetheless, it is essential to develop ability to dynamically control and manipulate the nonlinear properties, preferably at high speed. Plasmonic hot carriers can be resonantly excited in metal nanoparticles and then injected into semiconductors within 10-100 fs6, 7, where they eventually decay on a comparable time scale. This allows one to rapidly manipulate all kinds of characteristics of semiconductors, including their nonlinear properties. Here we demonstrate that plasmonically generated hot electrons can be injected from plasmonic nanostructure into bilayer (2L) tungsten diselenide (WSe2), breaking the material inversion symmetry and thus inducing an SHG. With a set of pump-probe experiments we confirm that it is the dynamic separation electric field resulting from the hot carrier injection (rather than a simple optical field enhancem...