Quantized Hall current in a topological nodal-line semimetal under electromagnetic waves

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 quantized circular photogalvanic effect observed in Weyl semimetals. Here we find that for a topological nodal-line semimetal with special 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 because of the unique band-folding effect associated with magnetic-field-induced expansion of a unit cell. We found that the Hall current generated solely by an in-plane linearly polarized EM wave is a quantized entity, regardless of its frequency and energy, which distinguishes it from the photocurrent observed thus far. This discovery opens up possibilities for Hall rectifiers and sensors, with potential industrial and space applications.