The interaction of terahertz (THz) wave with condensed matter material is utilized to investigate the low-energy electronic behaviors and topological properties near its equilibrium state, for example, transport characteristics of topological semimetals. Notably, antiferromagnetic Weyl semimetal (WSM) Mn₃Sn has attracted vast attention owing to markedly anomalous effects, such as room-temperature anomalous Hall effect. Here, we investigate the thickness-dependent THz conductivity of Mn₃Sn epitaxial films by polarization-resolved THz time-domain spectroscopy, which can be attributed to the Berry curvature induced near the Weyl nodes in the momentum space. The THz longitudinal conductivities of high-quality Mn₃Sn epitaxial thin films are anisotropic along different crystal orientations with carrier localization behavior, which are well described by the Drude-Smith model. By combining first-principles calculations with a comparison between theoretical and experimental carrier concentrations, this study demonstrated that the THz conductivity of the Mn₃Sn thin film is jointly determined by intraband transitions of free carriers. These results have deepened the understanding of THz conductivity in the antiferromagnetic WSM Mn₃Sn epitaxial thin films.

Terahertz (THz) technology holds great potential across diverse applications including biosensing, security screening, and information communications, but its conventional far-field technique is diffraction-limited to submillimeter resolution. Near-field optical microscopy overcomes this barrier through a sharp metallized tip that concentrates incident THz waves into nanometric volumes, detecting the resulting scattered near-field to reveal nanoscale THz optical properties. However, owing to the large THz wavelengths, resonant surface waves arising on the tip and cantilever obscure the intrinsic near-field response. Here we combine near-field microscopy with THz time-domain spectroscopy and implement time-domain filtering with an elongated cantilever to eliminate this artifact, achieving intrinsic nanospectroscopy and nanoimaging at THz frequencies. By applying this technique, we distinguish and characterize of historical pigments of an ancient sculpture, such as vermilion and red lead, at the nanoscale. We also unravel deep-subwavelength localized resonance modes in THz optical antennas, demonstrating capabilities for THz nanophotonics. Our work advances THz nanoimaging and nanospectroscopy techniques to probe intrinsic nanoscale THz light–matter interactions.

Increasing the efficiency of thin film absorbers is critical for various applications, including photovoltaics and photodetection. Although high-performance thin film absorbers have been realized, most of them are based on interference effects, where the bandwidth is limited and strongly polarization dependent. Here, we theoretically reveal novel mechanisms for the lightweight unpolarized broadband electromagnetic absorber based on Drude–Smith ultrathin films (∼10 nm), which is particularly promising for the terahertz (THz) band. The impedance-matched condition for the theoretical maximum of free-space absorption is modified in a non-trivial way depending on the carrier localization parameter cDS. Notably, the absorption and its bandwidth deteriorate when the imaginary conductance cannot be neglected. Further results demonstrate that robust absorption is achieved under different incident angles and polarizations, which is strongly related to the complex reflection coefficients. Finally, calculations based on our previous experimental data in the THz range demonstrate the effectiveness of the above mechanisms. The results may be valuable for the development of lightweight unpolarized broadband electromagnetic absorbers.

In metamaterial analogs of electromagnetically induced transparency (EIT), near-field coupling between a radiative bright resonator and a subradiant dark resonator produces a narrow transparency window with steep dispersion. However, the direct observation and manipulation of this coupling in a single terahertz (THz) metamolecule is fundamentally challenged by the diffraction limit. Scattering-type scanning near-field optical microscope (s-SNOM) exploits strong field confinement at its tip to enable both super-resolution imaging and nanoscale modulation. Here, we utilize the s-SNOM tip as a nano-actuator to control the EIT-like response within a single metamolecule. By acquiring spatially resolved nano-spectra, we uncover a strong asymmetric response in the near-field across the dark mode resonator. We develop a coupled tri-oscillator model (CTOM) that decouples and quantifies two contributions: the inhomogeneous intrinsic bright–dark coupling and the tip-induced local field, which continuously modulate the transparency window up to full on–off switching. Our results establish the s-SNOM tip as both a quantitative nano-probe and a tuning element, opening new pathways for designing reconfigurable nanophotonic and biosensing devices.