Anticrossing Effect Research Articles

Room temperature photon-magnon coupling in YIG- electric field coupled resonator system

This study presents a planar hybrid system consisting of an electric-field-coupled resonator (ELCR) and yttrium iron garnet (YIG) film, designed to investigate the interaction between photons and magnons at room temperature. This hybrid system has been designed and simulated using the commercial electromagnetic full-wave simulator CST Microwave Studio. The phenomenon of anti-crossing between the photon mode of the ELCR and the magnon modes of the YIG was observed by analyzing the |S21|-versus-frequency spectrum under varying strengths of bias magnetic fields. We present a comprehensive theoretical framework that explains the observed anti-crossing effect resulting from photon-magnon coupling (PMC) and provide estimations for the strength of PMC (Δ). Additionally, the interaction between photons and magnons was manipulated through two distinct methods: by adjusting the thickness (tYIG) of the YIG film and by positioning the YIG films along the microstripline. For the ELCR (for tYIG = 25 μm), Δ comes to 58 MHz, while changing tYIG from 2 μm to 50 μm, enabling more precise control of the Δ parameter across the span of 17 MHz to 84 MHz. Similarly, the YIG positioning at a different location along the microstripline allowed manipulation of Δ from 5 to 50 MHz. The resultant PMC can be significantly tuned by 400% to 900% in a planar-geometry ELCR-YIG hybrid system. This research offers avenues for developing innovative hybrid systems that afford greater control over the magnitude of PMC in a planar configuration, representing a promising direction for future advancements in hybrid magnonic systems.

MAGNETIC CORE APPLICATION IN A PLANAR RESONATOR WITH A YTTRIUM IRON GARNET FILM FOR ENHANCING STRONG PHOTON-MAGNON COUPLING

Subject and Purpose. This paper presents numerical simulation results on the transmission spectra of a split-ring resonator (SRR) loaded with a thin film of yttrium iron garnet (YIG). The application of a magnetic core in the SRR is proposed for increasing the photon-magnon (P-M) coupling strength. The anticrossing effect in the frequency dispersion behavior of the SRR modes and YIG film ferromagnetic resonance modes, namely SRR-YIG coupled modes, is identified. The dimensional parameters of the SRR with a magnetic core are calculated, taking care to preserve the design compactness and striving to obtain a maximum possible spin-number-normalized coupling strength for such a system. The work has been aimed at evaluating the efficiency of applying the magnetic core as a part of the planar microwave resonator to enhance the P-M coupling strength. Methods and Methodology. The transmission coefficient |S21| spectra of electromagnetic waves propagating through the planar resonator with the YIG film under the ferromagnetic resonance condition are numerically studied using the CST Studio Suite package in the frequency domain. The spatial distribution function of the magnetic field strength is calculated for the two scenarios of YIG film location: near the magnetic core (between the SRR and the feeding stripline) and inside the magnetic core (in the SRR center). Also, for each of these two scenarios, the transmission coefficient |S21| spectra of the wave propagation through the feeding stripline in the region of SRR-YIG coupled modes are simulated with and without the magnetic core. The dispersion curves of the SRR-YIG coupled modes are obtained in analytical terms. Results. It has been shown that the magnetic core application increases the P-M coupling strength 2.0 times in the scenario of YIG film location near the magnetic core (between the SRR and the feeding stripline). When the YIG film is inside the magnetic core (in the SRR center), the P-M coupling strength rises 2.3 times compared to similar cases without the magnetic core. Conclusions. The suggested magnetic core application can be used to increase the P-M coupling strength in the SRR — magnetic film resonant system, striving to develop effective microwave-to-optical converters and create efficient information exchange between quantum computers.

Theory of two-dimensional Coulomb plasmon-excitons. Excitation and relaxation processes

A theory of two-dimensional non-radiative (Coulomb) plasmon-excitons in metal and semiconductor nanolayers located nearby is presented. Electrodynamics of damped harmonic oscillators is developed for polarization waves related to Coulomb plasmons, excitons and mixed (hybrid) plasmon-excitons excited via the near field of an external oscillating dipole. For polarization fields of the collective electronic excitations in question, the equations of motion are deduced within the classical electrodynamics with the constitutive relations conditioned by quantum theory. The dispersion relations derived for the normal plasmon-exciton modes are found to reveal the anticrossing effect due to resonant energy interchange between plasmons and excitons. The time-dependent regimes of excitation and relaxation of the two-dimensional plasmon-excitons are thoroughly investigated in terms of the forced steady and concomitant transient waves. The developed analytical theory reveals practically valuable dynamical analogies of plasmon-excitons with some other kinds of mixed modes known for various objects of linear oscillations theory.

Strong coupling of localized surface plasmons and intermolecular vibration mode at terahertz frequencies

Organic molecular vibrations, typically occurring in the terahertz (THz) regime, can resonate with a metastructure. A hallmark Rabi splitting occurs when the coupling strength is sufficiently strong. In this work, we observe the strong coupling of localized surface plasmons (LSPs) and intermolecular vibration mode at THz on a metasurface spin-coated with organic molecule α-lactose monohydrate. Excited by transverse-electric THz waves, dispersive localized surface plasmons interact with nondispersive intermolecular vibrations and form two vibro-polariton modes. The angle-resolved transmission spectra of the coupled system are detected by using a terahertz time-domain spectrometer, demonstrating an anti-crossing effect with a clear Rabi splitting. By retrieving the coupling strength and Hopfield coefficients of polariton bands from the measured data, we further verify that these two bands originate from the strong coupling between LSPs and molecular vibration mode. Moreover, we show that it is possible to implement molecular concentration sensing based on this strong coupling effect. This study demonstrates a unique approach to investigate vibro-polaritons at the terahertz regime and provides a testbed for future applications of strong coupling effects in chemical detection and biosensing.

Valence subbands profile regulation in AlGaN quantum well based on k·p theory

The profiles for the valence subbands of an AlGaN-based quantum well (QW) is investigated by considering quantum confinement effect (QCE) and strain through the k · p theory. We have found that to increase the QCE and the compressive strain would rise the relative position of the heavy hole (HH) subband to the crystal field splitting hole (CH) subband in the valence band of the QW. However, although the variation trend of the relative valance subbands position is similar, the underlying mechanisms of the modulation by the QCE and strain are not the same. In addition, we have found that if the energy level between the HH and the CH subbands is close at a certain k t point, the subband anti-crossing effect of the QW will enhance their coupling level, causing dipole moments from the conduction subbands to these valence subbands transformation between each other. These results can provide important basis for the active region design of some AlGaN-based short wavelength, high carrier injection, or monolithic integration optoelectronic devices.

Relevance of Rabi splitting effect for tunable enhancement of Raman scattering in self-assembled silver – Fullerene nanocomposite films

We report on detection of plasmon-enhanced Raman scattering (PERS) in self-assembled AgxC60 nanocomposite films and on evolution of this effect with increase of the Ag concentration, x, in the interval of 2<x < 25. Optical absorption spectra show that origin of the PERS effect is closely related with dipolar plasmonic mode generated by uniform 3D-ensemble of Ag nanoparticles, which arise in the C60-based matrix during the film deposition. Careful analysis of the absorption spectra designates features of strong coupling between dipolar plasmon mode and the C60 low-energy exciton suggesting energy exchange between the arisen high- and low-energy polaritonic states. Evaluation of dispersion spectra of the polaritons revealed anti-crossing effect as a sign of the strong plasmon-exciton coupling with Rabi splitting energy of about 300 meV. In frames of the recently-reported quantum-electrodynamics model, the detected PERS effect was ascribed to abundant population of the low-energy polaritonic states caused by asymmetric transitions between the low- and high-energy polaritons. The obtained PERS-spectra display sensitivity of the C60 vibrational modes to the x-driven plasmonic field strength, which demonstrates some reduction at higher x due to charge transfer through C60 molecular junctions. The evident tunability of PERS suggests an emerging potential of the self-assembled AgxC60 films for their application in molecular electronics and molecular photochemistry.

Radio-frequency response of the optically detected level anticrossing signal in nitrogen-vacancy color centers in diamond in zero and weak magnetic fields

The response of the level anti-crossing signal to a quasi-resonant radio-frequency field, which appears in a zero magnetic field at NV color centers in diamond, is investigated. It is shown that the complex structure of this response can be explained by the Autler-Townes splitting. The possibility of controlling the parameters of the level anti-crossing signal is considered. It is shown that the slope of the central resonance recorded in this structure upon low-frequency modulation of the external magnetic field can be 2.3 times higher than the slope of the resonance recorded in the absence of an RF field. Conclusions are drawn about the nature of the level anti-crossing effect arising in zero field in NV color centers in diamond.

Asymmetry of anticrossing between atomic steps on metal and semiconductor surfaces

The interaction between intersecting vicinal and dislocation-induced atomic steps on crystal surfaces is studied experimentally on Au(111) and GaAs(001) and numerically using Monte-Carlo simulation. The interaction between intersecting steps leads to the “anticrossing” phenomenon which consists in the formation of a three-level relief configuration with the upper and lower terraces separated by a nanometer-sized bridge of intermediate height. The anticrossing effect is driven by the effective repulsion of two new combinatory steps bordering the upper and lower terraces. Two types of asymmetry between the combinatory steps are considered. In particular, the reasons for different curvature radii of the upper and lower combinatory steps are discussed, along with the issue of why dislocation-induced steps remain straight under annealing, while vicinal steps obtain clear visible ledges.

Two-dimensional Coulomb plasmon-excitons, their spectrum and near-field excitation

A theory of two-dimensional non-radiative (Coulomb) plasmon-excitons is developed for atomically thin metal and semiconductor layers located nearby. An exactly solvable model of 2D Coulomb coupled excitations is proposed, and the equations of motion for their polarization are deduced within the classical electrodynamics. The spectra of plasmon-exciton waves are investigated, and the dispersion relations are shown to display the frequency anticrossing effect near the resonance between plasmons and excitons. The dynamics of 2D polarization waves is studied for the non-radiative plasmon-excitons under time-dependent near-field excitation by an external dipole. The theory reveals principal and practically valuable dynamical analogies of plasmon-excitons with coupled oscillations in other objects of linear vibration theory, such as mechanical oscillators, resonant electric chains, etc.

Pronounced Linewidth Narrowing of Vertical Metallic Split-Ring Resonators via Strong Coupling with Metal Surface.

We theoretically study the plasmonic coupling between magnetic plasmon resonances (MPRs) and propagating surface plasmon polaritons (SPPs) in a three-dimensional (3D) metamaterial consisting of vertical Au split-ring resonators (VSRRs) array on Au substrate. By placing the VSRRs directly onto the Au substrate to remove the dielectric substrates effect, the interaction between MPRs of VSRRs and the SPP mode on the Au substrate can generate an ultranarrow-band hybrid mode with full width at half maximum (FWHM) of 2.2 nm and significantly enhanced magnetic fields, compared to that of VSRRs on dielectric substrates. Owing to the strong coupling, an anti-crossing effect similar to Rabi splitting in atomic physics is also obtained. Our proposed 3D metamaterial on a metal substrate shows high sensitivity (S = 830 nm/RIU) and figure of merit (FOM = 377), which could pave way for the label-free biomedical sensing.

Tuning electronic structure and optical properties of monolayer GeAs and GeAs2 by alloying with nitrogen and phosphorus elements

The structural, electronic and optical properties of nitrogen (N)/phosphorus (P) alloyed GeAs and GeAs2 monolayers were investigated by first-principles calculations. Our calculations show that the indirect-to-direct bandgap transition of GeAs and GeAs2 monolayers can be realized by N/P doping, owing to the doping induced valence band maximum location movement from Г→Ѕ interval to Г. The N/P doping can tune the bandgaps of GeAs and GeAs2 monolayers due to the band anti-crossing effect between extended conduction band states and localized N/P resonant states. The carrier effective mass of GeAs and GeAs2 monolayers can also be tuned by N/P doping. Notably, N/P doped GeAs and GeAs2 monolayers all have strong visible absorption (beyond 105 cm−1). Our results may be useful for the design, synthesis and applications of N/P doped GeAs and GeAs2 monolayers for future electronic and optoelectronic devices.

Кулоновские плазмон-экситоны в планарных наноструктурах металл-полупроводник

A theory of Coulomb (non-radiative) plasmons-excitons in a semiconductor with adjacent quantum well and ultrathin metal film is presented. The equations of motion are formulated for the polarization waves of surface plasmons and quasi-two-dimensional excitons with taking account of Coulomb interaction between them. Within a model of coupled harmonic oscillators, solved are the problems of Coulomb plasmon, exciton and plasmon-exciton excitations in the presence of an external dipole force. The coupling contant is calculated for plasmon-excitons, their optical spectra are investigated, and the relative contributions of plasmons and excitons to the normal modes are found. It is concluded that near the resonance between plasmon and exciton the spectrum of plasmon-exciton excitations consists of two peaks whose behavior in passing through the resonance shows the signs of anti-crossing effect (repulsion of frequencies).

Level anticrossing effect in single-level or multilevel double quantum dots: Electrical conductance, zero-frequency charge susceptibility, and Seebeck coefficient

We study electrical and thermoelectrical properties for a double quantum dot system. We consider the cases of both single-level and multilevel quantum dots whatever the way they are coupled, either in a series or in a parallel arrangement. The calculations are performed by using the nonequilibrium Green function theory. In the case of a single-level double quantum dot, the problem is exactly solvable whereas for a multilevel double quantum dot, an analytical solution is obtained in the limit of energy-independent hopping integrals. { We present a detailed discussion about} the dependences of electrical conductance, zero-frequency charge susceptibility and Seebeck coefficient on the gate voltages applied to the dots, allowing us to derive the charge stability diagram. The findings are in agreement with the experimental observations notably with the occurrence of successive sign changes of the Seebeck coefficient when varying the gate voltages. We interpret the results in terms of the bonding and antibonding states produced by the level anticrossing effect which occurs in the presence of a finite interdot coupling. We show that at equilibrium the boundary lines between the domains with different dot occupancies in the charge stability diagram, take place when the bonding and antibonding state levels are aligned with the chemical potentials in the leads. Finally the total dot occupancy is found to be considerably reduced in the case in parallel compared with the case in series, { whenever} the level energies in each dot are equal. We interpret this dip as a direct manifestation of the interference effects occurring in the presence of the two electronic transmission paths provided by each dot.

Kinetics of anticrossing between slip traces and vicinal steps on crystal surfaces

The interaction between vicinal atomic steps and slip traces – straight monatomic steps produced on a crystal surface by the emergence of dislocations – is experimentally investigated and compared to Monte-Carlo simulations. Near the point of apparent crossing between a vicinal step and a slip trace, a checkered three-level surface relief configuration is formed, with two new combinatory steps that borders the opposite highest and lowest terraces. This configuration is unstable with respect to an anticrossing effect which consists in the formation of a nanometer scale bridge that separates the regions with the highest and lowest levels and connects the opposite regions of equal level. It is shown that such an anticrossing effect is a general phenomenon observed on various crystal surfaces, from metals to semiconductors. The anticrossing kinetics was experimentally investigated on the Au(111) surface by scanning tunnelling microscopy under ultra-high vacuum. It is observed that the bridge width increases with time according to the power law with exponent β = 0.45 ± 0.01, i.e. significantly smaller than for the single-particle diffusion (β = 0.5). Monte-Carlo simulations were performed in order to clarify the involved atomic diffusion mechanisms. In particular, the competition between two microscopic mechanisms of the bridge formation is discussed, i.e., the adatom diffusion along the combinatory steps versus across the bridge from the uppermost to the lowest terrace.

Abnormal anticrossing effect in photon-magnon coupling

We report the experimental demonstration of an abnormal, opposite anti-crossing effect in a photon-magnon-coupled system that consists of an Yttrium Iron Garnet film and an inverted pattern of split-ring resonator structure (noted as ISRR) in a planar geometry. It is found that the normal shape of anti-crossing dispersion typically observed in photon-magnon coupling is changed to its opposite anti-crossing shape just by changing the position/orientation of the ISRR's split gap with respect to the microstrip line axis along which ac microwave currents are applied. Characteristic features of the opposite anti-crossing dispersion and its linewidth evolution are analyzed with the help of analytical derivations based on electromagnetic interactions. The observed opposite anti-crossing dispersion is ascribed to the compensation of both intrinsic damping and coupling-induced damping in the magnon modes. This compensation is achievable by controlling the relative strength and phase of oscillating magnetic fields generated from the ISRR's split gap and the microstrip feeding line. The position/orientation of an ISRR's split gap provides a robust means of controlling the dispersion shape of anti-crossing and its damping in a photon-magnon coupling, thereby offering more opportunity for advanced designs of microwave devices.

Kinetics of Anticrossing between Slip Traces and Vicinal Steps on Crystal Surfaces

The interaction between vicinal atomic steps and slip traces - straight monatomic steps produced on a crystal surface by the emergence of dislocations - is experimentally investigated and compared to Monte-Carlo simulations. Near the point of apparent crossing between a vicinal step and a slip trace, a checkered three-level surface relief configuration is formed, with two new combinatory steps that borders the opposite highest and lowest terraces. This configuration is unstable with respect to an anticrossing effect which consists in the formation of a nanometer scale bridge that separates the regions with the highest and lowest levels and connects the opposite regions of equal level. It is shown that such an anticrossing effect is a general phenomenon observed on various crystal surfaces, from metals to semiconductors. The anticrossing kinetics was experimentally investigated on the Au(111) surface by scanning tunneling microscopy under ultra-high vacuum. It is observed that the bridge width increases with time according to the power law with exponent β = 0.45 ± 0.01, i.e. significantly smaller than for the single-particle diffusion (β = 0.5). Monte-Carlo simulations were performed in order to clarify the involved atomic diffusion mechanisms. In particular, the competition between two microscopic mechanisms of the bridge formation is discussed, i.e., the adatom diffusion along the combinatory steps versus across the bridge from the uppermost to the lowest terrace.

Surface Plasmon Resonance Sensor Based on a Novel D-Shaped Photonic Crystal Fiber for Low Refractive Index Detection

A novel D-shaped photonic crystal fiber refractive index sensor based on surface plasmon resonance (SPR) is proposed and numerically studied. Different from the normal D-shaped structures, we here used an open-ring channel coated with gold film to excite the plamonic modes. The coupling properties and sensing performance of this structure are analyzed using finite element method. Simulation results indicate that the sensor has a sensing range from 1.20 to 1.29. When the analyte refractive index (RI) is above 1.25, the anti-crossing effect starts to appear, and the peak loss of the loss spectra remains nearly constant with increasing RI. The maximum spectral sensitivity of 11055 nm/RIU and high resolution of $9.05\times 10^{-6}$ RIU can be obtained at 1.29. For the purpose of optimizing sensing performance, the effects of the structure parameters on the resonant spectra are also studied. The excellent sensing performance makes the proposed SPR sensor a competitive candidate in low refractive index detection applications.

Robust magnon-photon coupling in a planar-geometry hybrid of inverted split-ring resonator and YIG film

We experimentally demonstrate strongly enhanced coupling between excited magnons in an Yttrium Iron Garnet (YIG) film and microwave photons in an inverted pattern of split-ring resonator (noted as ISRR). The anti-crossing effects of the ISRR’s photon mode and the YIG’s magnon modes were found from |S21|-versus-frequency measurements for different strengths and directions of externally applied magnetic fields. The spin-number-normalized coupling strength (i.e. single spin-photon coupling) {g}_{{rm{eff}}}/2pi sqrt{N} was determined to 0.194 Hz ({g}_{{rm{eff}}}/2pi = 90 MHz) at 3.7 GHz frequency. Furthermore, we found that additional fine features in the anti-crossing region originate from the excitation of different spin-wave modes (such as the magnetostatic surface and the backward-volume magnetostatic spin-waves) rather than the Kittel-type mode. These spin-wave modes, as coupled with the ISRR mode, modify the anti-crossing effect as well as their coupling strength. An equivalent circuit model very accurately reproduced the observed anti-crossing effect and its coupling strength variation with the magnetic field direction in the planar-geometry ISRR/YIG hybrid system. This work paves the way for the design of new types of high-gain magnon-photon coupling systems in planar geometry.

Anti-crossing Effect Dependence of Misalign in Ag Nanoplate Face-to-Face Dimer

Ag nanoplate dimers prepared by self-assembly method have attracted wide attentions. Due to the random effect of this method, the misaligned face-to-face dimer is a common product. The results obtained through modeling the misaligned face-to-face dimer can provide a better understanding about the influence of the misalign effect on the optical property of the dimer. Ag truncated nanoprism dimer studied using finite element method shows an anti-crossing effect with the misalign length less than the height of the truncated nanoprism in the bottom layer. As the truncated nanoprism in the upper layer replaced by a hexagonal nanoplate or nanodisk, the new dimers also show similar anti-crossing effects. This means that Ag nanoplate face-to-face dimer possesses an anti-crossing effect as a function of the misalign length. And the anti-crossing effect is scarcely influenced by the shape of the nanoplate in the upper layer. These results are promising for surface enhanced Raman spectra, surface enhanced fluorescence spectra, novel plasmon rulers, and tunable biosensors.

Coupling Between Metamolecular Modes and Lattice Diffraction Modes of Metamaterials in Terahertz Region

The coupling between plasmonic modes and lattice diffraction modes of circular split-ring resonators in terahertz (THz) region has been analyzed by changing the lattice constants. We discovered a blue shift of the individual eigenmode in short lattice constants, which is due to the longitudinal coupling of two adjacent eigenmodes from neighboring unit cells. We found an anti-crossing effect in long lattice constants for both TM and TE incidence as the lattice diffraction modes is fused with the plasmonic modes to form hybrid modes. Moreover, these hybrid modes are more sensitive to the refractive index change than the pure modes, which shows the promise to increase the sensitivity of metamaterials by coupling.