Special Quantum Matter Seminar

We show that Weyl semimetals can support a unique mechanism of optical amplification, based on topological frequency conversion [from I. Martin, G. Rafael, B. Halperin, PRX 2017]. When a Weyl semimetal is irradiated by two frequencies, f1 and f2, individual electrons near Weyl points can act as topological insulators in Fock space of the two modes. As a result, they convert energy between the two modes at a quantised average rate given by the "energy transfer quantum", hf1f2. We show that known Weyl support the effect at THz frequencies. We discuss the effects of dissipation, and demonstrate that plasmons can enhance the effect, due to the small plasma frequency in Weyl semimetal.