Terahertz Quantum Physics in 2D Materials

Classical terahertz magneto-spectroscopy of conducting systems is primarily governed by cyclotron resonance. This technique not only provides valuable information about charge carriers but, in several cases, also allows one to reconstruct the band structure of two-dimensional materials (Figure).

Quantum corrections to the optical spectra manifest themselves in several ways. For instance, optical analogs of microwave-induced resistance oscillations can be observed, and a dynamic counterpart of the Shubnikov–de Haas oscillations emerges.

In strong magnetic fields, quantum effects dominate the optical response, giving rise to phenomena such as quantized Faraday rotation. This effect is particularly pronounced in magnetically doped two-dimensional topological insulators, where experiments have directly revealed a quantized rotation angle corresponding to the fine-structure constant, α ≈ 1/137, which can be observed already in zero magnetic field.