Spectrally selective circular dichroism through resonant tunneling in Weyl-semimetal-based heterostacks

We demonstrate that Weyl-semimetal (WSM)/dielectric/WSM heterostacks enable spectrally selective, large circular dichroism (CD) through helicity-selective resonant tunneling. The platform consists of two finite WSM claddings symmetrically sandwiching a high-index dielectric spacer. Time-reversal-broken WSMs host pairs of Weyl nodes separated by 2b in momentum space, yielding an intrinsic anomalous Hall conductivity that splits the circular-polarization eigenchannels. When one helicity is tuned to a high-Q cavity-tunneling resonance while the opposite helicity remains detuned, the device exhibits near-unity CD and a dissymmetry factor approaching |g| → 2 at targeted wavelengths. Thickness-angle maps identify practical control knobs: the spacer thickness l₂ fixes the Fabry-Pérot order and Q-factor. The WSM thickness l₁ sets the helicity-dependent interfacial phase and loading via effective sheet admittance; and the incidence angle θ can pin resonant valleys when the gyrotropic phase dispersion compensates the Fabry-Pérot term. Electrostatic tuning of the carrier density (Fermi energy μ) reconfigures the spectra and reverses handedness. These results establish WSM heterostacks as compact, magnet-free building blocks for narrowband circular polarizers, chiral mirrors, and polarization-selective filters across the mid- to long-wave infrared.