Valley-selective hot electron injection from metal nanoantennas to MoS2

Abstract

A major challenge in valleytronics is to produce stable valley polarizations. Employing free electrons instead of excitons as valley-polarized carriers can provide long valley lifetimes. Using first-principles simulations, we have revealed the mechanism for the valley-selective injections of free electrons from nanoantennas to ${\mathrm{MoS}}_{2}$, through which long-lived valley polarizations can be achieved. Dynamically, electrons are injected into the $Q({Q}^{\ensuremath{'}})$ valleys instead of the most stable $K({K}^{\ensuremath{'}})$ valleys, due to the interfacial coupling. Under the ${C}_{3}$ symmetry and the time-reversal symmetry, the valley-selective electron injection is realized by the circularly polarized laser excitation, and can be tuned via the laser frequency. Because the electron injection is induced by the interfacial coupling, the valley selectivity holds as long as the interface locally has a ${C}_{3}$ symmetry. Our theoretical results pave the way for future valleytronic studies based on free carriers.