  Photocurrent acts as one of measurable responses of material to light, which
has proved itself to be crucial for sensing and energy harvesting. Topological
semimetals with gapless energy dispersion and abundant topological surface and
bulk states exhibit exotic photocurrent responses, such as novel quantized
circular photogalvanic effect observed in Weyl semimetals. Here we find that
for a topological nodal-line semimetal (NLSM) with nodal ring bulk states and
drumhead surface states (DSS), a significant photocurrent can be produced by an
electromagnetic (EM) wave by means of the quantum Hall effect. The Hall current
is enabled by electron transfer between Landau levels (LLs) and triggered by
both the electric field and magnetic field components of an EM wave. This Hall
current is physically connected to an unusually large quantum-Hall conductivity
of the zeroth LLs resulting from quantized DSS. These LLs are found to be
highly degenerate due to the unique band-folding effect associated with
magnetic-field-induced expansion of a unit cell. Furthermore, we observe that
the Hall current induced solely by an in-plane linearly-polarized EM wave
becomes a quantized entity which allows for possible direct measurement of the
DSS density in a topological NLSM. This work paves a way toward designing
high-magnetic-field-sensitivity detection devices for industrial and space
applications, such as the development of self-detection of
current-surge-induced overheating in electronic devices and accurate Earth's
magnetic-anomaly maps for guiding a self-navigating drone or an aircraft.
