# Topological frequency conversion in Weyl semimetals

###### user

what is the main result in this paper?

**AI:**The main result in this paper is the theoretical prediction of a new working principle for optical amplification based on Weyl semimetals, through the mechanism of topological frequency conversion, which can provide a gain that exceeds the dissipative loss at suitable frequencies and intensities.

###### user

what kids of Weyl semimentals could work for this purpose?

**AI:**The text does not provide information about the specific types of Weyl semimetals that could work for this purpose.

###### user

are there specific symmetry requirements?

**AI:**The text does not mention specific symmetry requirements.

###### user

what is the power of conversion?

**AI:**The text states that "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," but it does not provide a specific value for the power of conversion.

## Authors

Frederik Nathan, Ivar Martin, Gil Refael

## 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.