  We theoretically study photocurrents in metals that break both inversion
$\mathcal{P}$ and $\mathcal{T}$ symmetries within the transparent region. We
find that the system under the ac electric fields is well described with an
effective Hamiltonian and the photocurrent is of the order of
$\mathcal{O}(\omega_J/\gamma)$ if the frequency of the induced current
$\omega_J$ and the scattering rate $\gamma$ satisfy $\omega_J/\gamma \ll 1$,
and vanishes in the limit of $\omega_J/\gamma\to 0$. On the other hand, the
effective Hamiltonian description indicates that nonvanishing photocurrent can
appear even in the transparent region if the system is thin enough compared to
the mean free path in the direction of the induced current (where $\gamma$ can
be effectively regarded as 0). Candidate materials for the such photovoltaic
effect within the transparent region include multiferroics breaking both
$\mathcal{P}$ and $\mathcal{T}$ symmetries.

Mesoscale and Nanoscale Physics;Materials Science