Broadband Search for Axion Dark Matter via Shift Current

We propose a novel method to detect axion dark matter based on a topological phenomenon known as the shift current. We exploit the second-order nonlinearity of the shift current by applying a strong oscillating electric field. This field enhances the axion-induced shift current signal and downconverts its frequency to a more accessible range. The non-dissipative nature of the shift current allows us to achieve broadband detection via difference frequency generation. We demonstrate, using Type-I Weyl semimetal TaAs property, the possibility of probing the parameter space of the QCD axion in the mass range of $\mathcal{O}(10)$ - $\mathcal{O}(100) \ \rm meV$ corresponding to the photon coupling of $g_{a\gamma\gamma}\simeq$ $\mathcal{O}(10^{-12})$ - $\mathcal{O}(10^{-11})~\text{GeV}^{-1}$, respectively.