Anderson-Higgs amplitude mode in Josephson junctions

The Anderson-Higgs mode in a superconductor corresponds to a collective and coherent oscillation of the order parameter amplitude. We propose to detect this mode in a tunnel Josephson junction between two singlet $s$-wave diffusive superconductors in presence of a THz external irradiation at angular frequency $\omega$. By solving the Keldysh-Usadel equations, we obtain that the current-voltage relation exhibits a series of peaks of which only a subset is enhanced by the Anderson-Higgs mode. Furthermore, at zero bias, the junction features an ac current oscillating at $2\omega$, which is resonant when $\hslash \omega$ hits the superconducting gap, thereby indicating the activation of the Anderson-Higgs mode.