  100 % absorption in a two-dimensional electron gas (2DEG) with Dirac spectrum
is demonstrated to be obtained by controlling the interference of multiple
incident radiations, referred to as coherent perfect absorption (CPA). However,
when a 2DEG such as graphene is exposed to a magnetostatic bias, it resonantly
could absorb electromagnetic radiation by transitions of its Dirac electrons
between non-equidistant and nonlinear Landau levels. Here, the magneto-optical
terahertz (THz) CPA in graphene under the quantum Hall effect (QHE) regime at
both strong and subtesla magnetostatic bias fields is addressed. Our findings
show that an effective magneto-optical surface conductivity corresponding to
right- and left-handed circular (RHC- and LHC) polarizations could model a
magneto-tunable CPA in graphene in THz range. Significantly, graphene under QHE
regime reveals different tunable CPA properties for each circularly polarized
beams by the intensity of the applied magnetic bias. Moreover, it is observed
that different phase modulations at CPA frequencies are achieved for RHC and
LHC polarizations. Considering the maximum efficiency for a 2D absorber, our
results demonstrate the magnetostatic tuning of CPA in 2D Dirac materials for
long-wavelength sensing applications and signal processing.
