A doped graphene layer in the integer quantum Hall regime reveals a highly unusual particle-hole excitation spectrum, which is calculated from the dynamical polarizability in the random phase approximation. We find that the elementary neutral excitations in graphene in a magnetic field are unlike those of a standard two-dimensional electron gas (2DEG): in addition to the upper-hybrid mode, the particle-hole spectrum is reorganized in linear magneto-plasmons that disperse roughly parallel to $ω=v_F q$, instead of the usual horizontal (almost dispersionless) magneto-excitons. These modes could be detected in an inelastic light scattering experiment.
We report strong amplification of photo-magnetic spin precession in Co-doped YIG employing a surface plasmon excitation in a metal-dielectric magneto-plasmonic crystal. Plasmonic enhancement is accompanied by the localization of the excitation within the 300~nm-thick layer inside the transparent dielectric garnet. Experimental results are nicely reproduced by numerical simulations of the photo-magnetic excitation. Our findings demonstrate the magneto-plasmonic concept of subwavelength localization and amplification of the photo-magnetic excitation in dielectric YIG:Co and open up a path to all…
Cyclotron-resonance (CR) spectra of a gas of interacting polarons confined in a GaAs/AlAs quantum well are theoretically investigated taking into account the magneto-plasmon-phonon mixing and band nonparabolicity. Contributions of different magneto-plasmon-phonon modes to the total magneto-polaron coupling strength are investigated as a function of the electron density. It is confirmed theoretically, that the resonant magneto-polaron coupling in a high-density GaAs/AlAs quantum well occurs near the GaAs TO-phonon frequency rather than near the GaAs LO-phonon frequency. Calculated CR spectra ar…
The exchange effect and the magneto-plasmon mode dispersion are studied theoretically for an anisotropic two-dimensional electronic system in the presence of an uniform perpendicular magnetic field. Employing an effective low-energy model with anisotropic effective masses, which is relevant for a monolayer of phosphorus, the exchange effect due to the electron-electron interaction is treated within the self-consistent Hartree-Fock approximation. The magneto-plasmon mode dispersion is obtained by solving a Bethe-Salpeter equation for the electron density-density correlation function within the …
Electrons on the liquid helium surface form an extremely clean two dimensional system where different plasmon-excitations can coexist. Under a magnetic field time reversal symmetry is broken and all the bulk magneto-plasmons become gaped at frequencies below cyclotron resonance while chiral one dimensional edge magneto-plasmons appear at the system perimeter. We theoretically show that the presence of a homogeneous density gradient in the electron gas leads to the formation of a delocalized magneto-plasmon mode in the same frequency range as the lowest frequency edge-magnetoplasmon mode. We ex…
We have analytically studied plasmons in an electron system comprised of two spatially separated layers -- an infinite two-dimensional electron system (2DES) and a 2D strip. Our analysis reveals the existence of plasmon modes that are localized near and propagate along the strip. These modes are characterized by the wave vector in the direction of the strip, as well as the number of charge density nodes, N, across the strip. In the long-wavelength limit, the fundamental mode N=0 is found to have gapless linear dispersion. When the external perpendicular magnetic field is applied, this mode rem…
Auger relaxation in 2D strongly correlated electron gas can be represented as an Auger-like process for neutral magnetoplasmon excitations. The case of "dielectric" state with lack of free electrons (i.e. at integer filling $ν$) is considered. Really the Auger-like process is a coalescence of two magnetoplasmons which are converted into a single one of a different plasmon mode with zero 2D wave-vector. This event turns out to be energetically allowed for magnetoplasmons near their roton minima where the spectrum has the infinite density of states. As a result the additional possibility appears…
The spectrally resolved Terahertz photoconductivity between two separately contacted edge-channels of a two-dimensional electron gas in the quantum Hall regime is investigated. We use a not-simply-connected sample geometry which is topologically equivalent to a Corbino disc. Due to the high sensitivity of our novel sample structure, a weak resonance situated on the high energy side of the well known cyclotron resonance is revealed. The magnetic field as well as the carrier density dependence of this weak resonance, in comparison with different models suggests that the additional resonance is a…
In this Letter we study the generation of quasi-static magnetic fields by the plasmon-induced inverse Faraday effect and propose a magneto-optical waveguide structure for achieving magnetization switching at sub-ps time in a nano-confined magneto-optical structure. In particular we show that the direction of the generated quasi-static field in a magneto-optical dielectric cavity side-coupled to a metal-insulator-metal (MIM) waveguide depends sensitively on the wavelength of the surface plasmon polaritions (SPP). This phenomenon could open up a new energy-efficient ultrafast method for nano-con…
We present a microscopic theory on the observation of a beating pattern in the radiation-induced magnetoresistance oscillations at very low magnetic field. We con- sider that such a beating pattern develops as a result of the coupling between two oscillatory components: the first is a system of electron Landau states being harmon- ically driven by radiation. The second is a lattice oscillation, i.e., an acoustic phonon mode. We analyze the dependence of the beating pattern on temperature, radiation frequency and power. We conclude that the beating pattern is an evidence of the radiation-driven…
We address the problem of separating the short-distance, high-energy physics of cyclotron motion from the long- distance, low-energy physics within the Lowest Landau Level in field theoretic treatments of the Fractional Quantum Hall Effect. We illustrate our method for the case $ν=1/2$. By a sequence of field transformations we go from electrons to fermions that carry flux tubes of thickness $l_o$ (cyclotron radius) and couple to harmonic oscillators corresponding to magnetoplasmons. The fermions keep track of the low energy physics while the oscillators describe the Landau level, cyclotron cu…
A giant thermal magnetoresistance is predicted for the electromagnetic transport of heat in magneto-optical plasmonic structures. In chains of InSb-Ag nanoparticles at room temperature, we found that the resistance can be increased by almost a factor of 2 with magnetic fields of 2 T. We show that this important change results from the strong spectral dependence of localized surface waves on the magnitude of the magnetic field.
Nonlocal electrodynamics of two-dimensional anisotropic magneto-plasmons
Aeronautics Institute of Technology（航空技术学院）；University of Southern Denmark（南丹麦大学）；Universidade Federal do Ceará（塞阿拉联邦大学）；University of Antwerp（安特卫普大学）；Danish Institute for Advanced Study, University of Southern Denmark（南丹麦大学丹麦高等研究院）；Universidade do Minho（米尼奥大学）
We show that in graphene epitaxially grown on SiC the Drude absorption is transformed into a strong terahertz plasmonic peak due to natural nanoscale inhomogeneities, such as substrate terraces and wrinkles. The excitation of the plasmon modifies dramatically the magneto-optical response and in particular the Faraday rotation. This makes graphene a unique playground for plasmon-controlled magneto-optical phenomena thanks to a cyclotron mass 2 orders of magnitude smaller than in conventional plasmonic materials such as noble metals.
Collective excitations spectrum of Dirac electrons in mono and bilayer graphene in the presence of a uniform magnetic field is investigated. Analytical results for inter-Landau band plasmon spectrum within the self-consistent-field approach are obtained. SdH type oscillations that are a monotonic function of the magnetic field are observed in the plasmon spectrum of both mono- and bi-layer graphene systems. The results presented are also compared with those obtained in conventional 2DEG. The chiral nature of the quasiparticles in mono and bilayer graphene system results in the observation of $…
Magnetoplasmonics is highly promising to devise active optical elements: modulating the plasmon resonance condition with magnetic field can boost the performance of refractometric sensors and nanophotonic optical devices. Nevertheless, real life applications are hampered by the magnetoplasmonic trilemma: 1) a good plasmonic metal has sharp optical resonances but low magneto-optical response; 2) a magnetic metal has strong magneto-optical response but a very broad plasmonic resonance; 3) mixing the two components degrades the quality of both features. To overcome the trilemma, we use a differen…
The excitation of surface plasmons in magnetic nano-structures can strongly influence their magneto-optical properties. Here, we use photoemission electron microscopy to map the spatial distribution of the electric near-field on a nano-patterned magnetic surface that supports plasmon polaritons. By using different photon energies and polarization states of the incident light we reveal that the electric near-field is either concentrated in spots forming a hexagonal lattice with the same symmetry as the Ni nano-pattern or in stripes oriented along the $Γ$-K direction of the lattice and perpendic…
The plasmon frequency in standard electron gases with a parabolic single-particle dispersion is a purely classical quantity that is not sensitive to electron interactions or the equation of state. We demonstrate that this canonical result no longer holds for plasmons in three-dimensional semimetals, which can thus be used to probe many-body effects in these systems. In particular, we show that the plasmon frequency in an external magnetic field displays quantum oscillations, which is not the case for the electron gas. Using the random phase approximation, results are presented for the magnetop…
We study the properties of edge plasmons in two-component electron liquids in the presence of pseudomagnetic fields, which have opposite signs for the two different electronic populations and therefore preserve the time-reversal symmetry. The physical realizations of such systems are many. We discuss the cases of strained graphene and of electrons in proximity to a Skyrmion lattice, solving the problem with the Wiener-Hopf technique. We show (i) that two charged counter-propagating acoustic edge modes exist at the boundary and (ii) that, in the limit of large pseudomagnetic fields, each of the…
Strongly nonlinear Bernstein modes in graphene reveal plasmon-enhanced near-field magnetoabsorption
University of Regensburg（雷根斯堡大学）；Institute of High Pressure Physics of the Polish Academy of Sciences（波兰科学院高压物理研究所）；National University of Singapore（新加坡国立大学）；Faculty of Physics, Ivan Franko National University of Lviv（利沃夫伊万·弗兰科国立大学物理学院）
Graphene is a unique material to study fundamental limits of plasmonics. Apart from the ultimate single-layer thickness, its carrier concentration can be tuned by chemical doping or applying an electric field. In this manner the electrodynamic properties of graphene can be varied from highly conductive to dielectric. Graphene supports strongly confined, propagating surface plasmon-polaritons (SPPs) in a broad spectral range from terahertz to mid-infrared frequencies. It also possesses a strong magneto-optical response and thus provides complimentary architectures to conventional magneto-plasmo…
Chirality is a fundamental asymmetry phenomenon, with chiral optical elements exhibiting asymmetric response in reflection or absorption of circularly polarized light. Recent realizations of such elements include nanoplasmonic systems with broken mirror symmetry and polarization-contrasting optical absorption known as circular dichroism. An alternative route to circular dichroism is provided by spin-valley polarized excitons in atomically thin semiconductors. In the presence of magnetic fields, they exhibit an imbalanced coupling to circularly polarized photons and thus circular dichroism. Her…
Relaxation of collective plasmon inter-Landau-level excitation is determined by emission of LO-phonons or by Auger-like processes when this emission is suppressed off the magneto-phonon resonance conditions. The decay of "one-cyclotron" magneto-plasmons with wave-vectors near the roton minimum is studied under the condition of filling $ν=1$. Some features of this relaxation should be helpful for the experimental detection of the magneto-rotons in a strongly correlated 2D electron gas.
The magnetooptic and magnetic properties of hexagonal arrays of holes in optically thin iron films are presented. We analyze their dependence on the hole radius and compare the results to a continuous iron film of same thickness. We observe a large enhancement of the magnetooptic Kerr rotation with respect to that of the continuous film, at frequecies where surface plasmons excitations are expected. Additional simulations are in very good agreement with the experiment and thus confirm the effect of the surface plasmons on the Kerr rotation. The altering of the magnetic properties by the hole a…
Spatial separation of electrons and holes in graphene gives rise to existence of plasmon waves confined to the boundary region. Theory of such guided plasmon modes within hydrodynamics of electron-hole liquid is developed. For plasmon wavelengths smaller than the size of charged domains plasmon dispersion is found to be ω~ q^(1/4). Frequency, velocity and direction of propagation of guided plasmon modes can be easily controlled by external electric field. In the presence of magnetic field spectrum of additional gapless magnetoplasmon excitations is obtained. Our findings indicate that graphene…
Metallic nanostructures exhibit strong nonlinear-optical response at surface plasmon resonances, where the light-matter coupling efficiency is enhanced. An active modulation of this response can be realized by means of an external magnetic field. Here we utilize a nonlinear magneto-refractive effect in spintronic multilayer antennas to achieve a resonant 20\% modulation in second harmonic generation (SHG) in the mid-infrared. We discuss mechanisms of this modulation and show that it cannot be explained by an unequal enhancement of the electromagnetic field in the two spin states of the multila…
We study the influence of an external magnetic field on the collective electronic excitations in metallic nanoparticles. While the usual surface plasmon corresponding to the collective oscillation of the electrons with respect to the ionic background persists in the direction parallel to the magnetic field, the components in the perpendicular plane are affected by the field and give rise to two collective modes with field-dependent frequencies, the surface magnetoplasmons. We analyze the decay of these collective excitations by their coupling to particle-hole excitations and determine how thei…
Plasmons in two-dimensional electron systems with nonparabolic bands, such as graphene, feature strong dependence on electron-electron interactions. We use a many-body approach to relate plasmon dispersion at long wavelengths to Landau Fermi-liquid interactions and quasiparticle velocity. An identical renormalization is shown to arise for the magnetoplasmon resonance. For a model with N>>1 fermion species, this approach predicts a power-law dependence for plasmon frequency vs. carrier concentration, valid in a wide range of doping densities, both high and low. Gate tunability of plasmons in gr…
Resonant optical excitation was used to create a macroscopic non-equilibrium ensemble of dark excitons with unprecedentedly long lifetime in a two-dimensional (2D) electron system placed in a quantizing magnetic field. Exotic three-particle and four-particle states, plasmarons and plasmon-exciton molecules, coupled with the surrounding electrons through the collective plasma oscillations are engineered. Plasmarons and plasmon-exciton molecules are manifested as new features in the recombination spectra of non-equilibrium systems. Magnetoplasmarons and magnetotrions in a two-dimensional Hall in…
Large surface plasmon polariton assisted enhancement of the magneto-optical activity has been observed in the past, through spectral measurements of the polar Kerr rotation in Co hexagonal antidot arrays. Here, we report a strong thickness dependence, which is unexpected given that the Kerr effect is considered a surface sensitive phenomena. The maximum Kerr rotation was found to be -0.66 degrees for a 100 nm thick sample. This thickness is far above the typical optical penetration depth of a continuous Co film, demonstrating that in the presence of plasmons the critical lengthscales are drama…
At temperatures comparable to the Fermi temperature, we have measured a plasmon enhanced Coulomb drag in a GaAs/AlGaAs double quantum well electron system. This measurement provides a probe of the many-body corrections to the coupled plasmon modes, and we present a detailed comparison between experiment and theory testing the validity of local field theories. Using a perpendicular magnetic field to raise the magnetoplasmon energy we can induce a crossover to single-particle Coulomb scattering.
The magneto-optical activity, namely the polarization conversion capabilities of high-index, non-absorbing, core-shell dielectric nanospheres is theoretically analyzed. We show that, in analogy with their plasmonic counterparts, the polarization conversion in resonant dielectric particles is linked to the amount of electromagnetic field probing the magneto-optical material in the system. However, in strong contrast with plasmon nanoparticles, due to the peculiar distribution of the internal fields in resonant dielectric spheres, the magneto-optical response is fully governed by the magnetic (d…
Terahertz plasmons and magnetoplasmons propagating along electrically and chemically doped graphene p-n junctions are investigated. It is shown that such junctions support non-reciprocal magnetoplasmonic modes which get concentrated at the middle of the junction in one direction and split away from the middle of the junction in the other direction under the application of an external static magnetic field. This phenomenon follows from the combined effects of circular birefringence and carrier density non-uniformity. It can be exploited for the realization of plasmonic isolators.
We present a theoretical analysis of Dirac magneto-plasmons in topological insulator nanowires. We discuss a cylindrical geometry where Berry phase effects induce the opening of a gap at the neutrality point. By taking into account surface electron wave functions introduced in previous papers and within the random phase approximation, we provide an analytical form of the dynamic structure factor. Dispersions and spectral weights of Dirac plasmons are studied with varying the radius of the cylinder, the surface doping, and the strength of an external magnetic field. We show that, at zero surfac…
It is known that peculiar plasmons whose frequencies are purely imaginary exist in the interior of a two-dimensional electronic system described by the Drude model. We show that when an external magnetic field is applied to the system, these bulk plasmons are still non-oscillating and are isolated from the magnetoplasmons by the energy gap of the cyclotron frequency. These are mainly in a transverse magnetic mode and can combine with a transverse electronic mode locally at an edge of the system to form edge magnetoplasmons. With this observation, we reveal the intrinsic long lifetime of edge m…
We unravel the underlying near-field mechanism of the enhancement of the magneto-optical activity of bismuth-substituted yttrium iron garnet films (Bi:YIG) loaded with gold nanoparticles. The experimental results show that the embedded gold nanoparticles lead to a broadband enhancement of the magneto-optical activity with respect to the activity of the bare Bi:YIG films. Full vectorial near- and far-field simulations demonstrate that this broadband enhancement is the result of a magneto-optically enabled cross-talking of orthogonal localized plasmon resonances. Our results pave the way to the …
The particle-hole excitation spectrum for doped graphene is calculated from the dynamical polarizability. We study the zero and finite magnetic field cases and compare them to the standard two-dimensional electron gas. The effects of electron-electron interaction are included within the random phase approximation. From the obtained polarizability, we study the screening effects and the collective excitations (plasmon, magneto-excitons, upper-hybrid mode and linear magneto-plasmons). We stress the differences with the usual 2DEG.
The effect of edge modification of armchair graphene nanoribbons (AGNRs) on the collective excitations are theoretically investigated. The tight-binding method is employed in conjunction with the dielectric function. Unconventional plasmon modes and their association with the flat bands of the specially designed AGNRs are thoroughly studied. We demonstrate the robust relationship between the novel collective excitations and both the type and period of the edge modification. Additionally, we reveal that the main features displayed in the (momentum, frequency)-phase diagrams for both single-part…
We have investigated the one-way surface plasmon-polariton (SPP) at the interface of a continuous magneto-plasma material and metal. We demonstrated that TM modes inside a continuous material can be assigned non-trivial Chern numbers analogous to those of topological photonic crystals; moreover these Chern numbers can be calculated analytically. This leads to the appearance of topologically protected surface modes propagating at frequencies inside the bandgap of the magneto-plasma. Previous works considered 2D structures; here we consider the effects of 3D defects, and show that, although back…
We propose a scheme to directionally couple light into graphene plasmons by placing a graphene sheet on a magneto-optical substrate. When a magnetic field is applied parallel to the surface, the graphene plasmon dispersion relation becomes asymmetric in the forward and backward directions. It is possible to achieve unidirectional excitation of graphene plasmons with normally incident illumination by applying a grating to the substrate. The directionality can be actively controlled by electrically gating the graphene, or by varying the magnetic bias. This scheme may have applications in graphen…
We propose a mechanism to actively tune the operation of plasmonic cloaks with an external magnetic field by investigating electromagnetic scattering by a dielectric cylinder coated with a magneto-optical shell. In the long wavelength limit we show that the presence of an external magnetic field may drastically reduce the scattering cross-section at all observation angles. We demonstrate that the application of external magnetic fields can modify the operation wavelength without the need of changing material and/or geometrical parameters. We also show that applied magnetic fields can reversibl…
This Perspective surveys the state-of-the-art and future prospects of science and technology employing the nanoconfined light (nanophotonics and nanoplasmonics) in combination with magnetism. We denote this field broadly as nanoscale magnetophotonics. We include a general introduction to the field and describe the emerging magneto-optical effects in magnetoplasmonic and magnetophotonic nanostructures supporting localized and propagating plasmons. Special attention is given to magnetoplasmonic crystals with transverse magnetization and the associated nanophotonic non-reciprocal effects, and to …
We calculate the plasmon frequency and damping rate of plasma oscillations in a spin-polarized BLG system. Using the long wavelength approximation for dynamical dielectric function, we obtain an analytical expression for plasmon frequency showing that the degree of spin polarization P has negligible effect on the long wavelength plasmon frequency. Numerical calculations demonstrate that the degree of spin polarization affects slightly (strongly) plasmon frequency at small (large) wave-vectors and the maximum value of damping rate increases with increasing P. We also study the effects of carrie…
The dynamic polarization for kekulé-patterned graphene is studied within the Random Phase Approximation (RPA). It is shown how the breaking of the valley degeneracy by the lattice modulation is manifested through the dielectric spectrum, the plasmonic dispersion, the static screening and the optical conductivity. The valley-dependent splitting of the Fermi velocities due to the kekulé distortion leads to a similar splitting in the dielectric spectrum of graphene, introducing new characteristic frequencies, which are given in terms of the valley-coupling amplitude. The valley coupling also spli…
Microwave absorption spectra of a single square of two-dimensional electrons (2DES) have been investigated using an optical detection technique. Fundamental dipole and harmonic quadrupole plasmon modes have been identified and compared to those in the disk geometry. In the square-shaped 2DES, a strong interaction is discovered between the neighboring plasmon modes, whereas no such hybridization is observed in the disk-shaped geometry. We establish a rigid theoretical platform to analytically describe the magneto-optical response of confined two-dimensional systems. The developed theory provide…
Plasmons, which are collective charge oscillations, offer the potential to use optical signals in nano-scale electric circuits. Recently, plasmonics using graphene have attracted interest, particularly because of the tunable plasmon frequency through the carrier density $n$. However, the $n$ dependence of the plasmon velocity is weak ($\propto n^{1/4}$) and it is difficult to tune the frequency over orders of magnitude. Here, we demonstrate that the velocity of plasmons in graphene can be changed over two orders of magnitude by applying a magnetic field $B$ and by the presence/absence of a gat…
In order to characterize magnetic-field (B) tunable THz plasmonic detectors, spectroscopy experiments were carried out at liquid helium temperatures and high magnetic fields on devices fabricated on a high electron mobility GaAs/AlGaAs heterostructure. The samples were either gated (the gate of a meander shape) or ungated. Spectra of a photovoltage generated by THz radiation were obtained as a function of B at a fixed THz excitation from a THz laser or as a function of THz photon frequency at a fixed B with a Fourier spectrometer. In the first type of measurements, the wave vector of magnetopl…
We theoretically demonstrate that dc electron flow across the junction of two-dimensional electron systems leads to excitation of edge magnetoplasmons. The threshold current for such plasmon excitation does not depend on contact effects and approaches zero for ballistic electron systems, which makes a strong distinction from the well-known Dyakonov-Shur and Cerenkov-type instabilities. We estimate the competing plasmon energy gain from dc current and loss due to electron scattering. We show that plasmon self excitation is feasible in GaAs-based heterostructures at $T\lesssim 200$ K and magneti…
Topological materials bear gapped excitations in bulk yet protected gapless excitations at boundaries. Magnetoplasmons (MPs), as high-frequency density excitations of two-dimensional electron gas (2DEG) in a perpendicular magnetic field, embody a prototype of band topology for bosons. The time-reversal-breaking magnetic field opens a topological gap for bulk MPs up to the cyclotron frequency; topologically-protected edge magnetoplasmons (EMPs) bridge the bulk gap and propagate unidirectionally along system's boundaries. However, all the EMPs known to date adhere to physical edges where the ele…
Plasmonic Faraday rotation in nanowires manifests itself in the rotation of the spatial intensity distribution of high-order surface plasmon polariton (SPP) modes around the nanowire axis. Here we predict theoretically the giant Faraday rotation for SPP propagating on graphene-coated magneto-optically active nanowires. Upon the reversal of the external magnetic field pointing along the nanowire axis some high-order plasmonic modes may be rotated by up to ~ 100 degrees on scale of about 500 nm at mid-infrared frequencies. Tuning carrier concentration in graphene by chemical doping or gate volta…
We demonstrate plasmon-enhanced photoconduction in Au bowtie nanojunctions containing nanogaps overlaid with an amorphous Ge film. The role of plasmons in the production of nanogap photocurrent is verified by studying the unusual polarization dependence of the photoresponse. With increasing Ge thickness, the nanogap polarization of the photoresponse rotates 90 degrees, indicating a change in the dominant relevant plasmon mode, from the resonant transverse plasmon at low thicknesses to the nonresonant "lightning rod" mode at higher thicknesses. To understand the plasmon response in the presence…
