Topological frequency conversion in Weyl semimetals

TL;DR

This paper predicts a novel optical amplification mechanism in Weyl semimetals utilizing topological frequency conversion, enabling energy transfer between two frequencies at quantized rates, with potential for efficient THz gap amplification.

Contribution

It introduces the concept of topological frequency conversion in Weyl semimetals as a new principle for optical amplification, supported by theoretical simulations.

Findings

Energy conversion at quantized rates proportional to Planck's constant

Feasible band structures support conversion in the THz gap at low intensities

Gain can surpass dissipative losses at frequencies above relaxation time

Abstract

We theoretically predict a new working principle for optical amplification, based on Weyl semimetals: when a Weyl semimetal is suitably irradiated at two frequencies, electrons close to the Weyl points convert energy between the frequencies through the mechanism of topological frequency conversion from [Martin et al, PRX 7 041008 (2017)]. Each electron converts energy at a quantized rate given by an integer multiple of Planck's constant multiplied by the product of the two frequencies. In simulations, we show that optimal, but feasible band structures can support topological frequency conversion in the "THz gap" at intensities down to $ 2{\rm W}/{\rm mm^2}$; the gain from the effect can exceed the dissipative loss when the frequencies are larger than the relaxation time of the system. Topological frequency conversion provides a new paradigm for optical amplification, and further extends Weyl semimetals' promise for technological applications.