Manipulations of light–matter interaction via sub-wavelength plasmonic structures have opened up many new research opportunities in photonics from microwave to the visible spectrum, including the relatively underdeveloped but technologically important terahertz regime. Here, we have studied manipulation of terahertz transmission through a bilayer metasurface consisting of a metallic hole array and a complimentary patch array separated by an ultra-thin dielectric spacer. The terahertz transmission spectra through our studied metasurfaces exhibit characteristic resonances due to the surface plasmon induced extraordinary transmission peak. Our study reveals a counterintuitive blue shift of the transmission peak with increasing spacer thickness, which is explained by reduced Coulomb interaction between two plasmonic layers. The measured quality factor exhibits a strong dependence on the spacer thickness, and the maximum quality factor is observed for a spacer thickness of around λ/30, indicating strong electric-field confinement inside the dielectric spacer. These bilayer plasmonic structures will aid in realizing next-generation terahertz plasmonic devices such as ultrasensitive thin-film sensors, modulators, narrow-band filters, and other nonlinear components.

Interactions of Terahertz radiations with matter can lead to the realization of functional devices related to sensing, high-speed communications, non-destructive testing (NDT), spectroscopy, etc. In spite of the versatile applications that THz can offer, progress in this field is still suffering due to the dearth of suitable responsive materials. In this context, we have experimentally investigated emerging multiferroic BiFeO3 film (~ 200 nm) employing Terahertz time-domain spectroscopy (THz-TDS) under vertically applied (THz propagation in the same direction) electric fields. Our experiments reveal dynamic modulation of THz amplitude (up to about 7% within 0.2 THz to 1 THz frequency range) because of the variation in electric field from 0 kV/cm to 600 kV/cm. Further, we have captured signatures of the hysteretic nature of polarization switching in BiFeO3 film through non-contact THz-TDS technique, similar trends are observed in SS-PFM (Switching Spectroscopy Piezoresponse Force Microscope) measurements. We postulate the modulation of THz transmissions to the alignment/switching of ferroelectric polarization domains (under applied electric fields) leading to the reduced THz scattering losses (hence, reduced refractive index) experienced in the BiFeO3 film. This work indicates ample opportunities in integrating nanoscale multiferroic material systems with THz photonics in order to incorporate dynamic functionalities to realize futuristic THz devices.

Magnetotransport, the magnetic field induced electron transport phenomenon through metals and semiconductors, has proven to be a useful technique to tailor the properties of electromagnetic radiation upon interaction with suitable materials and structures. Very recently, magnetotransport has become an important tool to dynamically tailor terahertz (THz) radiation and response of different optical devices. Based on these backgrounds, optically thin, subwavelength superlattice (with alternate arrangement of four metallic films: two non-magnetic aluminum [Al] and two ferromagnetic nickel [Ni] films, having thickness of each film as 10 nm) metasurfaces are demonstrated, consisting of periodic arrays of asymmetric cut-wire pair metasurfaces, which have a unique ability to exhibit both frequency and intensity modulation at its hybridized resonances when low-intensity magnetic fields are applied. Such dynamic tuning characteristics are attributed to the combined effects of spin-dependent THz magnetotransport in superlattice films, near-field electromagnetic coupling between the resonators, and lattice mode coupling. Such THz metasurface is further employed for non-contact detection of external magnetic fields in the range of 0-30 mT, while operating at the optically thin regime. The demonstrated scheme can further be extended to realize THz magneto-spectroscopy toward devising state-of-the-art photonic and magnetic technologies.

In modern era, wireless communications at ultrafast speed are need of the hour and search for its solution through cutting edge sciences is a new perspective. To address this issue, the data rates in order of terabits per second (TBPS) could be a key step for the realization of emerging sixth generation (6G) networks utilizing terahertz (THz) frequency regime. In this context, new class of transition metal dichalcogenides (TMDs) have been introduced as potential candidates for future generation wireless THz technology. Herein, a strategy has been adopted to synthesize high-quality monolayer of molybdenum di-sulfide (MoS2) using indigenously developed atmospheric pressure chemical vapor deposition (APCVD) set-up. Further, the time-domain transmission and sheet conductivity were studied as well as a plausible mechanism of terahertz response for monolayer MoS2 has been proposed and compared with bulk MoS2. Hence, the obtained results set a stepping stone to employ the monolayer MoS2 as potential quantum materials benefitting the next generation terahertz communication devices.

The integration of active materials in terahertz (THz) metasurfaces is pivotal for the realization of functional device applications in diverse fields like sensing, imaging, communication, etc. In this context, ferroelectric materials endowed with tunable electro-optic properties have recently emerged as a novel candidate for achieving actively tuned THz metasurfaces. Here, we experimentally investigate temperature tuning of electromagnetically induced transparency (EIT) effects in a THz metasurface based on ferroelectric barium titanate (BaTiO3) thin film. We characterize tunable dielectric properties of the BTO thin film under variable temperatures (25 0C to 100 0C) at THz frequencies by utilizing THz time domain spectroscopy (THz-TDS) technique. Based on this aspect, we intelligently design a THz metasurface capable of displaying the EIT effect. THz transmissions through the metasurface sample are then probed for different applied temperatures. The EIT features undergo frequency shifts along with amplitude modulations owing to the temperature induced variations of the dielectric properties of the BTO thin film. A total red shift ~ 27 GHz in EIT resonance dip is observed experimentally as the temperature increases from 25oC to 100oC. Therefore, we demonstrate utilities of ferroelectric platform towards the development of temperature tunable EIT metasurfaces.