Magnetotransport‐Induced Non‐Contact Terahertz Detection of Weak Magnetic Fields in Optically Thin Frequency‐Agile Superlattice Metasurfaces

Abstract

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.

Magnetically Reconfigurable Toroidal Metasurfaces

“…The application of a magnetic field aligns the magnetic domains along the applied fields which reduces overall carrier scattering probabilities. [ 25,50 ] This reduction in the carrier scattering results in decreasing resistivity across the FM/NM/FM layer combinations that is reflected in the reduction of THz peak amplitudes (Figure 1e). However, the relative scattering probability of the MR structures increases as the NM spacer layer thickness increases.…”

“…[ 19 ] Therefore, active control over the dynamical response of metamaterial modes could be attained by means of external agents such as optical, external biasing, externally applied magnetic field, etc. [ 45–50 ] Among all of these methods the optical and magnetic methods are especially interesting because of their instantaneous response to tune the EM properties. [ 50,51 ] In this regard, magnetically controlled non‐radiative toroidal modes can be useful in realizing low‐loss reconfigurable metasurfaces.…”

“…[ 45–50 ] Among all of these methods the optical and magnetic methods are especially interesting because of their instantaneous response to tune the EM properties. [ 50,51 ] In this regard, magnetically controlled non‐radiative toroidal modes can be useful in realizing low‐loss reconfigurable metasurfaces. Such magnetically controlled metasurfaces can be achieved utilizing multilayers of ferromagnetic (FM) and nonmagnetic (NM) layers.…”

“…Considering such aspects, THz‐TDS based magnetotransport‐driven reconfigurable multi‐layer metasurfaces offer tremendous potentials. [ 50,56 ] Although, several studies are performed in order to actively tune the toroidal resonances utilizing light, electric field, temperatures, etc. but, in this work, we have explored magnetically reconfigurable toroidal metasurfaces in sub‐skin depth regime for low power, low loss magneto photonics.…”

Sensing Multiwall Carbon Nanotube Film Mediated by a Fano Resonant Terahertz Metasurface

“…In this context, strategically designed artificial photonic structures or widely renowned as metamaterials have emerged as an interesting framework that enables the manipulation of electromagnetic radiations. − These metamaterials alongside their two-dimensional analogue known as metasurfaces are constructed by assembling an array of artificially designed building blocks (unit cells) known as “meta-atoms”, and the optimization and layout of these artificial atoms vary per application. These structures are designed to operate in the subwavelength regime; therefore, the whole array mimics the actions of an artificially designed medium.…”