Surface Magnetoplasmons Research Articles

Wideband isolator based on one-way surface magnetoplasmons with ultra-high isolation

In this paper, we present a new type of isolator based on one-way surface magnetoplasmons (SMPs) at microwave frequencies, and it is the first time that an experimental prototype of isolator with wideband and ultra-high isolation is realized using SMP waveguide. The proposed model with gyromagnetic and dielectric layers is systematically analyzed to obtain the dispersion properties of all the possible modes, and a one-way SMP mode is found to have the unidirectional transmission property. In simulation and experiment with metallic waveguide loaded with yttrium–iron–garnet (YIG) ferrite, the scattering parameters and the field distributions agree well with the analysis and verify the one-way transmission property. The isolation is found to be as high as 80 dB and the typical value of insertion loss is 1 dB. Besides, the one-way transmission band can be controlled by changing the magnetic bias. From theoretical analysis and simulation, it is found that with a tiny value of 10 Oe of the magnetic bias, the relative bandwidth can be tuned to be greater than 50%. Compared with conventional isolators, this one-way SMP isolator has the advantages of ultra-high isolation, wide relative frequency band, and requires much smaller bias field, which has promising potential in non-reciprocal applications.

Unidirectional guided-wave-driven metasurfaces for arbitrary wavefront control

Metasurfaces are capable of fully reshaping the wavefronts of incident beams in desired manners. However, the requirement for external light excitation and the resonant nature of their meta-atoms, make challenging their on-chip integration. Here, we introduce the concept and design of a fresh class of metasurfaces, driven by unidirectional guided waves, capable of arbitrary wavefront control based on the unique dispersion properties of unidirectional guided waves rather than resonant meta-atoms. Upon experimentally demonstrating the feasibility of our designs in the microwave regime, we numerically validate the introduced principle through the design of several microwave meta-devices using metal-air-gyromagnetic unidirectional surface magneto-plasmons, agilely converting unidirectional guided modes into the wavefronts of 3D Bessel beams, focused waves, and controllable vortex beams. We, further, numerically demonstrate sub-diffraction focusing, which is beyond the capability of conventional metasurfaces. Our unfamiliar yet practical designs may enable full, broadband manipulation of electromagnetic waves on deep subwavelength scales.

Surface wave control via unidirectional surface magnetoplasmon waveguide arrays

Freely tailoring the wavefronts of surface waves (SWs), including surface plasmon polaritons (SPPs) and their equivalent counterparts, holds significant importance in the field of on-chip photonics. However, conventional diffraction-optics based devices often suffer from limited functionalities and low working efficiencies. Here, we present a novel concept of a unidirectional surface magnetoplasmon (USMP) waveguide array composed of carefully engineered subwavelength-spaced unidirectional waveguide slits. By utilizing the unique propagation properties of USMPs within these waveguides, the USMP waveguide array efficiently converts USMPs into SWs with predetermined wavefronts. As proof of the concept, we numerically demonstrate this new principle through the design of two microwave USMP waveguide arrays using a metal-air-YIG structure, which directly converts USMPs into SWs with the wavefronts of Bessel beam and focusing. Additionally, we extend this concept to the terahertz regime and achieve beam deflection of SWs using a metal-air-semiconductor waveguide array. These findings may inspire the development of highly miniaturized on-chip devices for integrated photonics applications.

Resonant excitation of terahertz surface magnetoplasmons by optical rectification over a rippled surface of n-type indium antimonide

We analysed the excitation of a surface magnetoplasmon wave by the mode conversion of a p-polarized laser beam over a rippled semiconductor (n-type)-free space interface. The pump surface magnetoplasmon wave exerts a ponderomotive force on the free electrons in the semiconductor, imparting a linear oscillatory velocity at the laser modulation frequency to them. This linear oscillatory velocity couples with the modulated electron density to produce a current density, which develops a resonant surface magnetoplasmon wave in the terahertz region. The amplitude of the terahertz surface magnetoplasmon wave can be tuneable with an external magnetic field and the semiconductor's temperature.

Terahertz large-area unidirectional surface magnetoplasmon and its applications

Unidirectional surface waves in nonreciprocal plasmonic platforms with nonlocal effects have been a topic of significant interest and some controversy. In this study, we present a scheme to achieve unidirectional surface magnetoplasmons (USMPs) with large modal areas at terahertz frequencies. Such large-area USMPs (LUSMPs) exist in a metal-UENZ (uniaxial-ε\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varepsilon $$\\end{document}-near-zero)-Si-InSb structure under external magnetic field, where the effect of nonlocality is included. The field of the LUSMP extends almost uniformly in the UENZ layer with a thickness of wavelength scale, thus its modal size can be represented by the UENZ-layer thickness. Due to the modal energy primarily distributed in the thick UENZ layer, the nonlocality-induced leakage of the LUSMP is significantly reduced by an order of magnitude, compared to previous USMP existing at interface between InSb and opaque isotropic medium. Due to their large modal sizes, such LUSMPs can be efficiently excited by terahertz radiations directly from free space. In addition, LUSMPs offer high degree of freedom for manipulating terahertz waves, such as energy squeezing and trapping. Based on LUSMPs, a terahertz free-space isolator is also developed. Our findings have important implications to the development of innovative plasmonic devices in terahertz regime.

Numerical design of surface magneto-plasmon sensors of Au/Co double-layer square arrayed nanopores on the continuous gold thin film

Surface magneto-plasmon (SMP) sensors have attracted continuous attention due to their field enhanced signal-to-noise ratios, sensitivities, and detection limits. Although many progresses have been achieved in the nanodots, nanorods, or nanodiscs, few studies have been conducted on films containing arrays of nanopores or nanoholes. SMP sensors based on arrays of nanopores could be much more promising for future ultrasensitive optical detectors since they can couple the SMP enhancement with Fabry–Pérot interference of nanopores for high-performance resonator sensors that can be further tuned under a magnetic field. We, thus, propose a high-performance SMP sensor based on the magneto-optical Kerr effect (MOKE) of films containing a square array of Au–Co double-layer nanopores on the Au film substrate or SMP-MOKE sensor. The local electric field around the magneto-plasmon arrays of nanopore photonic crystals can be greatly enhanced by applying an external magnetic field due to their magneto-optical activity and excitation of high-quality surface plasmon resonances. Multi-physics coupling simulations and validation by COMSOL on the structure-dependent optical properties suggest that the proposed SMP-MOKE sensor has a high sensitivity of 711 nm/Refractive Index Units (RIUs) and a figure of merit (FOM) of the order of 105 RIU−1, which is an order of magnitude greater than the best grating-type sensors, to the best of our knowledge. Our results shall facilitate the theoretical design for the future fabrication of ultra-sensitive sensors or resonators with excellent FOM and reliability for air-quality monitoring or chemical sensing, etc.

Propagation of surface magnetoplasmon polaritons in a symmetric waveguide with two-dimensional electron gas

The properties of surface magnetoplasmon polaritons (SMPPs) in a symmetric structure, composed of two semi-infinite regions of high-density two-dimensional electron gas (2DEG) separated by a thin film in Voigt configuration, are investigated. The normal and absorption dispersion relations for the transverse magnetic polarization are derived by correlating Maxwell’s equation and the boundary conditions. It is demonstrated that the features of SMPPs are greatly influenced by the external magnetic field, collision frequency of 2DEG, the dielectric constant, and the thickness of the thin film, suggesting that the locations and propagation lengths of SMPPs can be governed accordingly. It is shown that the symmetry of the physical geometry preserves the symmetry of the dispersion relations of SMPPs. Furthermore, it is discovered that as the external magnetic field increases, the penetration depth of SMPPs decreases, while their energy loss reduces, implying that plasmons can propagate for longer distances. Additionally, it is observed that SMPPs in the symmetric configuration have a longer lifetime than those in the asymmetric configuration.

Subwavelength-Scale 3D Broadband Unidirectional Waveguides Based on Surface Magnetoplasmons at Terahertz Frequencies

Unidirectional electromagnetic modes have significant potential for routing electromagnetic radiation and are highly desirable for various applications, such as isolators, splitters, and switches. In this study, we theoretically investigate surface magnetoplasmons (SMPs) in a four-layer structure consisting of a perfect magnetic conductor (PMC)–semiconductor–dielectric–metal, which exhibits complete unidirectional propagation. We extend this structure to a 3D model by decreasing the width of the PMC-semiconductor part to an appropriate value and demonstrate that the SMPs in the proposed 3D waveguide retain complete unidirectional propagation. Our findings indicate that the unidirectional SMPs are robust to backscattering caused by surface roughness and defects. Moreover, the proposed 3D waveguide can be efficiently coupled to conventional microstrip line waveguides. Our results (based on the numerical method) demonstrate that SMPs based on semiconductors offer a promising approach to creating devices with new functionalities in the terahertz regime below the diffraction limit.

A kinetic treatment of surface plasmon polaritons in the Voigt configuration

The study of microscopic effects on the dispersion of surface magnetoplasmon polaritons is important. We use the collisionless Vlasov equation and Maxwell’s equations to evaluate the dielectric tensor for evaluating the dispersion relations of surface magnetoplasmon polaritons. We treat the case in the Voigt geometry assuming a semi-infinite dielectric medium. The direction of the magnetic field is considered parallel to the surface and perpendicular to the propagation vector k. The analysis shows the influence of additional microscopic kinetic effects. Standard Drude model results are retrieved in the absence of these effects.

Electron exchange effect on surface magnetoplasmon polaritons dynamics in a graphene-plasmonic structure

By employing a two-dimensional linearized magnetoquantum hydrodynamic model and Maxwell’s equations, the electron exchange effect on the dispersion spectrum of surface magneto-plasmon polaritons (SMPPs) is studied in a perpendicular configurated graphene-plasmonic structure where a graphene sheet is directly covered by two semi-infinite dielectrics. Besides, other influences (including the graphene electron density, the dielectric constant of the dielectric medium, and the external magnetic field) on dispersion characteristics in both classical and quantum regimes of graphene surface magneto plasmon polaritons (GSMPPs) have been investigated in the presence of an electron exchange effect. Our results show that these influences greatly affect the dynamics of GSMPPs. Also, it is found that in the presence of the electron exchange effect, the propagation speed and the dispersion spectrum shift of GSMPPs in the classical regime are largely increased more than those in the case of the quantum regime. Our findings demonstrate that the electron exchange effect has a vital function in the modulation of the dynamical behavior of SMPPs in graphene-nano optical and plasmonic devices.

Excitation of second harmonic terahertz surface magnetoplasmons over a rippled surface of n-InSb

We analyzed the excitation of second harmonic (SH) terahertz (THz) surface magnetoplasmons (SMPs) over a n-type semiconductor (n-InSb)-free space interface. P-polarized laser obliquely incidents on the magnetized rippled surface of semiconductor with frequency ω and wave number k0z and k0x and exerts a ponderomotive force on free electrons of semiconductor surface and imparts second harmonic oscillatory velocity v→2ω. Second harmonic oscillatory velocity v→2ω couples with modulated electron density nq of rippled surface to produce a second harmonic nonlinear current J→2ωnl, which resonantly derives SH THz SMPs with wave number k2z=2k0z+q and frequency 2ω. SH THz SMPs amplitude increases with applied external magnetic field as well as with incident angle and gets the maximum value then decreases further increase in the applied external magnetic field and incident angle. The conversion efficiency of SH THz SMPs amplitude is achieved up to 4.2%.

Valley-dependent conductivity and dispersion relation of surface magnetoplasmons

Electron hydrodynamics attracts increasing interest in solid state physics, offering a universal long-wavelength description of collective modes in a two-dimensional system. In two-dimensional materials with broken inversion symmetry and two degenerate valleys, a perpendicular magnetic field lifts the valley degeneracy via a Zeeman effect due to the orbital magnetic moments arising from electron rotations, relevant for developing valleytronic devices. In this work, we use a two-component hydrodynamic model to investigate the valley-dependent conductivity tensor and valley-dependent dispersion relation of surface magnetoplasmons under the modulations of the perpendicular magnetic field, Berry curvature and topological orbital magnetic moment. It is shown that the valley splitting of conductivity is large and tunable in the presence of the valley Zeeman effect. Valley splitting of frequency appears on the order of terahertz, which is preferable for realizing sub-wavelength nonreciprocal magneto-optical devices in the terahertz range.

Cherenkov terahertz surface magnetoplasmons excitation by an electron beam

We developed the scheme of terahertz (THz) surface magnetoplasmons (SMPs) over n-type semiconductor by an electron beam in the presence of an external magnetic field. Electron beam bunching by SMPs generates perturbed current density and develops THz SMPs by resonant Cherenkov interaction. More beam energy is required for the generation of high-frequency THz SMPs in the presence of large applied magnetic field. Growth rate of Cherenkov THz SMPs grows with THz frequency and attains a maximum value and then falls off with THz frequency. It grows with temperature and decreases with the electron cyclotron frequency. Growth rate is directly proportional to beam density's cube root and inversely proportional to γ0b, where γ0b is relativistic factor of incident electron beam. The proposed mechanism may develop an actively tunable device for the generation of THz SMPs due to growth rate dependence on semiconductor temperature, applied magnetic field, and electron beam energy. The beam energy of 212.31–222.03 keV is used for the excitation of SMPs 0.81–2.3 THz.

Near-Infrared Unidirectional Waveguide Based on Surface Magnetoplasmons

Near-Infrared Unidirectional Waveguide Based on Surface Magnetoplasmons

The impact of magnetic field on the surface of carbon-insulator-GaAs Semiconductors which is tunable with a frequency range in the presence of surface magneto Plasmon

In this paper, group velocity and frequency wave can be tuned with an applied external magnetic field when we increase the magnetic field from 0-4 tesla the frequency range can be reduced for given semiconductor materials. The excitation of the two layers of semiconducting material propagating band structures can be explained by the oscillations of electrons in semiconductors on applying the magnetic field, we study the effects of an external magnetic field in the band structure of C-insulator-GaAs materials in presence of surface magneto plasmons concerning plasma frequency below and above the surface band structures. The surface magneto plasmon bands get excited and show the dispersion relation with frequency range. The higher dispersion band moves in faster than the lower dispersion band structure of semiconducting material. The most energy is stored in a lower surface of magneto plasmon. When we increase the magnetic field, the surface of the semiconductor moves opposite to the lower surface of the semiconductor material. Here, we use semiconducting materials instead of metals because metal cannot support a wide frequency range on the magneto-plasmonic surface providing a good tunning property and more flexibility in this mechanism, which is widely useful in telecommunications, magneto-plasmonic devices, and data processing unit. This study is widely more promising due to its wavelength confinements of electromagnetic fields on semiconducting and insulating layers. Due to nonreciprocal effects, the dispersion of frequency waves varies with different band structures and group velocity also varies with two propagating directions among semiconductor-insulator-semiconductor layers.

Excitation of terahertz surface magnetoplasmons by nonlinear mixing of laser and its second harmonic on a rippled surface of n type semiconductor

We investigated the excitation of terahertz (THz) surface magneto plasmons (SMPs) by nonlinear mixing of laser and its second harmonic on a rippled surface of n-type semiconductor-free space interface. Obliquely incident p-polarized lasers exert a nonlinear ponderomotive force on free electrons of n-type semiconductor. Nonlinear ponderomotive force induces the oscillatory velocities at frequencies \(2\omega _{1}\) and (\(\omega _{1}-\omega _{2}\)). These oscillatory velocities beat the modulated electron density \(n_{q}\) to get the charge density perturbation at (\(2\omega _{1}, 2k_{1z}+q\)) and (\(\omega _{1}-\omega _{2}, k_{1z}-k_{2z}+q\)). Perturbed charge density couples with the linear oscillatory velocities to produce a nonlinear current density, which resonantly derives THz SMPs at frequency \(\omega =2\omega _{1}-\omega _{2}\) and propagation constant \(k_{z}=2k_{1z}-k_{2z}+q\). Here, q provides the extra wave number for the phase matching condition. The efficiency of THz SMPs wave amplitude was attained up to \(9\%\) and THz SMPs wave amplitude controlled by the electron cyclotron frequency \(\omega _{ce}\) and incident angle \(\theta\).

Quantum effects on the propagation of surface magnetoplasmon polaritons in a graphene-plasmonic structure

We investigate the properties of surface magnetoplasmon polaritons (SMPPs) in a graphene-plasmonic structure which is constructed as a graphene film sandwiched with two semi-infinite dielectrics under a perpendicular configuration. By solving Maxwell equations and quantum magneto-hydrodynamic equations with considering the quantum statistical and quantum diffraction effects, we deduce the dispersion relation of graphene SMPPs (GSMPPs) in detail. We show how the graphene electron density, the external magnetic field, and the dielectric constant, affect the features of the dispersion of GSMPPs in both classical and quantum cases. We find that the quantum effects (QEs) significantly alter the properties of GSMPPs, which are entirely different from those in a classical model. We find that the propagation speed of classical GSMPPs has small increases while the propagation speed of quantum GSMPPs has fast and sharp increases along with the increases in graphene electron density. We further find that the propagation speed decreases gradually by increasing the applied magnetic field in both classical and quantum GSMPPs. Moreover, we also find that the propagation speed of classical GSMPPs has fast decreases tending to zero at large wavenumber while the propagation speed of quantum GSMPPs has slow decreases tending to infinity with increasing the dielectric constant. Our findings elucidate that QEs play a crucial role in the properties of GSMPPs and their response to different parameters.

Excitation of terahertz surface magnetoplasmons by nonlinear mixing of two lasers on a rippled surface of magnetized n-InSb

We investigated the generation of terahertz (THz) surface magnetoplasmons (SMPs) over a rippled surface of magnetized n-type semiconductor (n-InSb) by using the nonlinear mixing of two p-polarized lasers with frequencies ω1, ω2 and wave numbers k1z, k2z, respectively. Incident obliquely from free space on the semiconductor surface with ripple wave number q exerts a nonlinear ponderomotive force on the free electrons at the frequency difference, ω=ω1−ω2. Ponderomotive force induces the nonlinear current that drives resonant terahertz surface magnetoplasmons at beat frequency with suitable wave number, kz=k1z−k2z+q. The amplitude of THz SMPs increases with the increase in applied external magnetic field. It also increases with increase the incidence angle of lasers and attains a maximum, and then drops to zero with further increase in the angle of incidence.

Realization of broadband truly rainbow trapping in gradient-index metamaterials.

Unidirectionally propagating wave (UPW) such as surface magnetoplasmon (SMP) has been a research hotspot in the last decades. In the study of the UPW, metals are usually treated as perfect electric conductors (PECs). However, it was reported that the transverse resonance condition induced by the PEC wall(s) may significantly narrow up the complete one-way propagation (COWP) band. In this paper, ultra-broadband one-way waveguides are built by utilizing the epsilon-negative (ENG) metamaterial (MM) and/or the perfect magnetic conductor (PMC) boundary. In both cases, the total bandwidth of the COWP bands are efficiently enlarged by more than three times than the one in the original metal-dielectric-semiconductor-metal structure. Moreover, the one-way waveguides consisting of gradient-index metamaterial are proposed to achieve broadband truly rainbow trapping (TRT). In the full-wave simulations, clear broadband TRT without back reflection is observed in terahertz regime. Besides, giant electric field enhancement is achieved in a PMC-based one-way structure, and the amplitude of the electric field is enormously enhanced by five orders of magnitude. Our findings are beneficial for researches on broadband terahertz communication, energy harvesting and strong-field devices.

Nonreciprocal electron hydrodynamics under magnetic fields: Applications to nonreciprocal surface magnetoplasmons

Recent experiments have elucidated that novel nonequilibrium states inherent in the so-called hydrodynamic regime are realized in ultrapure metals with sufficiently strong momentum-conserving scattering. In this letter, we formulate a theory of electron hydrodynamics with broken inversion symmetry under magnetic fields and find that novel terms emerge in hydrodynamic equations which play a crucial role for the realization of the nonreciprocal responses. Specifically, we clarify that there exist a novel type of nonreciprocal collective modes dubbed nonreciprocal surface magnetoplasmons arising from an interplay between magnetic fields and the orbital magnetic moment. We reveal that these nonreciprocal collective modes indeed give rise to the nonreciprocity in magneto-optical responses such as the reflectivity. The physics discussed here will bridge the two important notions of magnetoplasmonics and nonreciprocity in electron hydrodynamic materials with inversion symmetry breaking and magnetic fields.