Quantized optical Hall current in topological nodal-line semimetal

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 optical Hall effect. The optical 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 optical 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 optical 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.