  A superconductor subject to electromagnetic irradiation in the terahertz
range can show amplitude oscillations of its order parameter. However, coupling
this so-called Higgs mode to the charge current is notoriously difficult. We
propose to achieve such a coupling in a particle-hole-asymmetric configuration
using a DC-voltage-biased normal-metal--superconductor tunnel junction. Using
the quasiclassical Green's function formalism, we demonstrate three
characteristic signatures of the Higgs mode: (i) The AC charge current exhibits
a pronounced resonant behavior and is maximal when the radiation frequency
coincides with the order parameter. (ii) The AC charge current amplitude
exhibits a characteristic nonmonotonic behavior with increasing voltage bias.
(iii) At resonance for large voltage bias, the AC current vanishes inversely
proportional to the bias. These signatures provide an electric detection scheme
for the Higgs mode.

Mesoscale and Nanoscale Physics;Superconductivity