Hybridization Bandgap Research Articles

Breggovskie rezonansy v mul'tiferroidnom kristalle s dvoynoy nelineynost'yu

The influence of double (electrical and magnetic) nonlinearity on the Bragg resonances of the hybrid electromagnetic-spin waves in a multiferroic crystal has been theoretically and experimentally revealed. The multiferroic crystal consists of an yttrium iron garnet layer with a periodic system of grooves on the surface and a ferroelectric strontium–barium titanate layer. A dispersion relation for the hybrid waves is obtained, and the mechanism of formation of main and hybrid band gaps, namely, suppression bands, is revealed. It is shown that taking into account the magnetic nonlinearity leads to frequency rearrangement of both band gaps and taking into account the electrical nonlinearity leads to frequency rearrangement of only the hybrid band gap. In the general case, the effects of the electrical and magnetic nonlinearities on the hybrid band gap can be compensated.

A 6.435-nW, 26.2-ppm/°C hybrid bandgap reference with stacked ΔVGS compensation in sub-threshold region

This paper illustrates a methodology to design an ultra-low power hybrid bandgap reference (HBR) with high accuracy to counteract the effect of temperature using single BJT and MOSFETs working in subthreshold region. Based on compensated VBE and ΔVth, the study provides a new insight into compensation of complementary-to-absolute-temperature (CTAT) voltage with a nano-watt proportional-to-absolute-temperature (PTAT) voltage generator with reduced threshold voltage-induced process variation. Designed in a 180 nm CMOS process, the circuit has a measured temperature coefficient of 26.2 ppm/°C with a wide temperature range of −40 °C∼125 °C and an overall variation coefficient of 0.234% among 9 chips with an active area of 0.0264 mm2. The experimental result shows that the proposed HBR circuit can operate with a supply voltage down to 1.1 V and a full frequency PSRR of better than −35 dB while the power consumption is only 6.435 nW.

Finite-amplitude nonlinear waves in inertial amplification metamaterials: Theoretical and numerical analyses

The motivation of this study is to understand the unique characteristics of finite-amplitude elastic wave propagation in an inertial amplification (IA) system coupled with a Duffing resonator and leverage the unique opportunities offered by the IA mechanism and nonlinearities to achieve the modulation of elastic waves. Based on the assumption of the perturbation method, the effective range of the wave amplitude was investigated, which is usually ignored. Meanwhile, the obvious phenomenon of bandgap transition (between the single resonance bandgap and hybrid bandgap) is observed with varying IA levels. In particular, we demonstrated a new phenomenon of negative wave propagation and an obvious standing-wave mode in this system. Here, an analytical investigation of the amplitude-dependent and IA-dependent nonlinear dispersion is conducted based on the perturbation approach. Numerical simulations using the time-domain finite element method and Gaussian pulse excitation were performed to validate the nonlinear dispersion and negative motion of the wave packet. The research results can be used to tune wave propagation in metamaterials and provide ideas for the design of metamaterials, which can be used in practical circumstances for different energy transfer needs.

Broadband solar‐driven water evaporator based on organic hybrid bandgap and bio‐mimetic interfaces

AbstractOwing to the lightweight, flexibility, and molecular diversity, organic photothermal materials are considered promising solar absorbent materials for water‐evaporating purification. Herein, we utilize the blend of two organic conjugated photothermal materials, PM6 and Y6, with broadband solar absorption from 350 to 1000 nm and high‐efficiency photothermal properties to fabricate a Janus water evaporator on cellulose paper. Similar to the asymmetric wetting behavior on the lotus leaf, the evaporator shows efficient water adhesion on the bottom surface and water repellency on the top surface for a desirable self‐floating capability and salt resistance. With a mass of only 0.5 mg per 3.14 cm2, the PM6:Y6 blend‐based water evaporator achieves 88.9% of solar thermal conversion efficiency (η) and 1.52 kg m−2 h−1 of solar water evaporation rate (m) under 1.0 kW m−2 solar irradiation. These properties are almost the best performance among purely organic water evaporators especially with such a premise of material saving. The concentrations of primary ions are significantly decreased by 4–6 orders after desalination, accompanied by excellent performance for wastewater treatment. This evaporator realizes a m of 1.21 kg m−2 h−1, a η of 75.7%, and a voltage of 61 mV under one sun irradiation by assembling with a thermoelectric equipment. This study demonstrates that the blending of PM6 and Y6 achieves photothermal synergism, which improves the photothermal property and water evaporation rate, providing a valuable prospect for their application in water purification and thermoelectric power generation.image

Theoretical analysis of guided waves propagation in periodic piezoelectric plates with shunting circuits

The tunable manipulation of guided waves in plates brings out great potential applications in engineering practices, and the electromechanical coupling effects of piezoelectric material with shunting circuits have exhibited powerful tunability and flexibility for guided wave propagation. In this paper, a theoretical model is established to analyze the guided wave propagation in one-dimensional periodic piezoelectric plate constructed from a periodic array of anisotropic piezoelectric materials under periodic electrical boundary conditions. The extended Stroh formalism incorporating with the plane wave expansion method is developed to transform the wave motion equations of the periodic piezoelectric plate into a linear eigenvalue system, and a more concise and elegant solution of generalized displacement and generalized stress can be derived. There are various dispersion relations in terms of the altering electrical boundary conditions to be acquired, if the thin electrodes with shunting circuits are attached periodically to both surfaces of the piezoelectric plate. Analytical results show that the coupling of the local electric resonant mode and propagating elastic wave modes can induce hybridization bandgaps, and the bandgaps of Lamb waves and SH waves in the piezoelectric plate can be tuned by designing appropriate material polarization orientations and shunting circuits. In addition, the Bragg bandgaps can also be influenced by the external circuits. Results indicate that the proposed theoretical model can effectively analyze the performances of guided waves in periodic piezoelectric plate and provide useful theoretical guidance for designing smart wave control devices.

Hybrid Bragg-locally resonant bandgap behaviors of a new class of motional two-dimensional meta-structure

Bragg scattering and local resonance are two fundamental mechanisms for bandgap (BG) formation of phononic crystals (PCs) and acoustic metamaterials (AMs). In this paper, a new class of motional two-dimensional (2D) hybrid Bragg-locally resonant (LR) meta-pipe model is developed, and the BG interaction behaviors of such a meta-structure are explored. The pipe is axially composed of alternate materials, and is periodically encircled with dual-layer rings, which are used to simultaneously trigger Bragg scattering and local resonance. Meanwhile, the pipe conducts an axially spinning motion, and a steady fluid flows inside the pipe. Compared to static periodic structures, the orthogonal traveling waves due to spin bring about a 2D meta-structure, and the spinning local resonators yield an additional centrifugal effect on the pipe. The results reveal the formation of hybrid Bragg-LR BGs in such a motional meta-structure, and further demonstrate their complicated evolutions with the location, number and geometry of the local resonators as well as the pipe material. The impacts of motional properties on the hybrid BGs are discussed, and they are compared with the behavior of Euler-Bernoulli model. This study provides a more in-depth interpretation for the interaction of Bragg and LR BGs, which is especially beneficial to the vibration and noise reduction of rotors and fluid-transporting devices.

Band gap enhancement and vibration reduction of functionally graded sandwich metastructure beam

A novel functionally graded (FG) sandwich metastructure beam is proposed for broadband vibration reduction based on the band gaps of Bragg scattering and local resonance. The coupling band gap performance of FG sandwich metastructure beam is used to improve vibration reduction in the low and medium frequency ranges. An analytical model for vibration transmission and band structure of the FG sandwich metastructure beam is developed. The calculation accuracy of present analytical model is verified by using finite element method (FEM). Theoretical results demonstrate that the hybrid band gap in the low and medium frequency ranges will be generated by coupling the Bragg scattering and locally resonant band gaps, and the bandwidth and location of the hybrid band gap can be enhanced and tuned by adjusting the MFC piezoelectric shunting circuit parameters. It also shows that the starting and stopping frequencies of the hybrid band gap can be flexibly designed by the height ratio and constituent gradient of FG sandwich beam. The results in the study provide a new approach to the design of broadband vibration reduction for the composite sandwich structures.

Simulation of dynamically tunable broadband and polarization-insensitive electromagnetically induced transparency in Dirac semimetal

The structure proposed in this paper is composed of an outer circular ring resonator (CRR) and four L-shaped resonators (LSRs) in the middle. The destructive interference between bright modes produces a broadband electromagnetically induced transparency (EIT) with a maximum transmission efficiency of 97.6% in both vertical polarization directions. The field distributions and the three-level Λ-type system clarify the physical mechanism of the coupling process between bright modes. The calculated transmission spectrum based on the two-particle model is consistent with the simulated transmission spectrum, which proves the correctness of the results. By introducing hybridization bandgap (HBG) to the structure, the bandwidth of EIT-like effect expands. This structure has a fourfold (C4) rotational symmetry; thus, it is insensitive to the polarization angle. In addition, the transparency window undergoes a redshift as the Fermi energy of Dirac semimetal decreases. Meanwhile, the group delay is also controlled. Due to the wide bandwidth, a large delay bandwidth product (DBP) is obtained. Our work provides a new method for the production of slow-light devices and broadband filters.

Larger hybridization bandgaps and topological phase transitions in the Sb-based topological insulator superlattices

With the aim of achieving a higher hybridization bandgap in the quantum spin Hall insulating heterostructures, we study topologically novel InAs/GaxIn1−xSb superlattices with inverted bandstructure. By tuning the strain and material composition of each layer in a precise manner, enhancement of the hybridization is achieved. The theoretically calculated hybridized bandgap reaches it's highest value ∼ 79 meV, which is one of the highest reported value so far. We also show that the bilayer superlattice shows a topological phase transition from the trivial insulating to the quantum spin Hall insulating to the semimetallic phase. These phases can be tuned by varying the InAs layer thickness. All the heterostructures showing large hybridization bandgaps are potential candidates for the realization of quantum spin Hall insulating states at the room temperature.

Transition from metal to semiconductor by semi-hydrogenation of borophene

Borophene has triggered a surge of interest due to its outstanding properties including mechanical flexibility, polymorphism, and optoelectrical anisotropy. Very recently, a novel semi-hydrogenated borophene, called ${\ensuremath{\alpha}}^{\ensuremath{'}}$-4H, was synthesized in large-scale freestanding samples, exhibiting excellent air-stability and semiconducting nature. Herein, using the density functional theory (DFT) and many-body perturbation theory (MBPT), we investigate the electronic and excitonic optical properties of ${\ensuremath{\alpha}}^{\ensuremath{'}}$-4H borophene. The DFT results reveal that hydrogenation breaks the mirror symmetry and increases the buckling height of pure ${\ensuremath{\alpha}}^{\ensuremath{'}}$ borophene, which results in an orbital hybridization and indirect band gap of 1.49 eV in ${\ensuremath{\alpha}}^{\ensuremath{'}}$-4H borophene. Moreover, the optical spectrum achieved from solving the Bethe-Salpeter equation (i.e., $\mathrm{GW}+\mathrm{BSE}$) shows an optical band gap of 2.40 eV, which corresponds to a strongly bound and stable bright exciton with a binding energy of 1.18 eV. The mean value of absorption within the visible area is 1.68 (1.13)$\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{4pt}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}$ for $E\ensuremath{\parallel}x$ ($E\ensuremath{\parallel}y$) polarization, which shows a linear dichroism for visible light. The effective mass and Bohr radius of the ground-state exciton are 0.78 ${m}_{0}$ and 2.03 \AA{}, respectively, which demonstrates the characteristics of Frenkel exciton. The excitonic states are robust against tension up to 10%, under which the monolayer is dynamically stable. We also study the bilayer ${\ensuremath{\alpha}}^{\ensuremath{'}}$-4H borophene with different stackings. For the weak van der Waals interactions between the layers, the bilayer preserves most of the structural and electronic properties of the monolayer. Our study exposes the underlying physics behind the structural, electronic, and optical properties of ${\ensuremath{\alpha}}^{\ensuremath{'}}$-4H borophene and suggests it as a very promising candidate for flexible optoelectronic applications.

Hybrid Bandgaps in Mass-coupled Bragg Atomic Chains: Generation and Switching

In this work, without introducing mass-in-mass units or inertial amplification mechanisms, we show that two Bragg atomic chains can form an acoustic metamaterial that possesses different types of bandgaps other than Bragg ones, including local resonance and inertial amplification-like bandgaps. Specifically, by coupling masses of one monatomic chain to the same masses of a diatomic or triatomic chain, hybrid bandgaps can be generated and further be switched through the adjustment of the structural parameters. To provide a tuning guidance for the hybrid bandgaps, we derived an analytical transition parameter (p-value) for the mass-coupled monatomic/diatomic chain and analytical discriminants for the mass-coupled monatomic/triatomic chain. In our proposed mass-coupled monatomic/triatomic chain system, each set of analytical discriminants determines a hybrid bandgap state and a detailed examination reveals 14 different bandgap states. In addition to bandgap switching, the analytical p-value and discriminants can also be used as a guide for designing the coupled-chain acoustic metamaterials. The relations between the mass-coupled monatomic/triatomic chain system and a three-degree-of-freedom (DOF) inertial amplification system further indicate that the band structure of the former is equivalent to that of the latter through coupling masses by negative dynamic stiffness springs.

Subwavelength Metawaveguide Filters and Metaports

This paper proposes an alternative technique for the design of miniaturized waveguide filters based on locally resonant metamaterials (LRMs). We implement ultrasmall metamaterial filters (metafilters) by exploiting a subwavelength (sub-\ensuremath{\lambda}) guiding mechanism in evanescent hollow waveguides, which are loaded by small resonators. In particular, we use composite pin-pipe waveguides (CPPWs) built from a hollow metallic pipe loaded by a set of resonant pins, which are spaced by deep-subwavelength distances. We demonstrate that, in such structures, multiple resonant scattering nucleates a sub-\ensuremath{\lambda} mode with a customizable bandwidth below the induced hybridization band gap (HBG) of the LRM. The sub-\ensuremath{\lambda} guided mode and the HBG, respectively, induce pass and rejection bands in a finite-length CPPW, creating a filter, the main properties of which are largely decoupled from the specific arrangement of the resonant inclusions. To guarantee compatibility with existing technologies, we propose a subwavelength method to match the small CPPW filters to standard waveguide interfaces, which we call a metaport. Finally, we build and test a family of low- and high-order ultracompact aluminum CPPW filters in the X and $K_{u}$ bands (10--18 GHz). Our measurements demonstrate the customizability of the bandwidth and the robustness of the passband against geometrical scaling. The three-dimensional printed prototypes, which are 1 order of magnitude smaller and lighter than traditional filters and are also compatible with standard waveguide interfaces, may find applications in future satellite systems and 5G infrastructures.

Inducing topology in a wire medium based metamaterial [Invited

We review our attempt to tackle topological photonics based on an experimental platform operating in the microwave frequency range. The latter is based on a resonant metamaterial consisting in a dense collection of finite-length resonant metallic wires, known as the wire medium. Inside, the wave propagation is accurately described by a polariton, which exhibits subwavelength propagating modes as well as a hybridization bandgap. Thanks to a relevant design of the relative lengths of the wires and/or on their spatial positioning, we explore different aspects of topology applied to wave propagation.

Broadband electromagnetically induced transparency in metamaterials based on hybridization bandgap

We present a broadband electromagnetically induced transparency-like (EIT-like) effect in a microwave waveguide system by employing a bright meta-atom side-coupled to a linear chain of dark meta-atoms with a hybridization bandgap (HBG). We find that such a configuration can generate a wideband EIT response of up to 145 MHz, covering 23.7% of the central frequency. We also show that the EIT bandwidth can even extend to 211 MHz by further broadening the HBG while keeping the device volume unchanged. We emphasize that the EIT-like meta-molecules are subwavelength structures with only about one tenth of the operating wavelength. Our findings will be beneficial for realizing compact broadband slow light components in communication systems.

Artificial resonant crystals for hydroelastic waves

Engineering the propagation of water waves is a crucial challenge for potential applications at oceanic scale. Despite their apparent complexity, they do not fundamentally differ from any other kind of physical wave. Similar to recent approaches in optics or acoustics, we propose to artificially manufacture materials at the sub-wavelength scale to modify the propagation characteristics at will. We demonstrate that hydroelastic waves allow for the straightforward control of the medium properties, as well as the quantitative measurement of the full wave field. We investigate propagation in hydroelastic metamaterials made from periodic arrays of tunable resonators. We fully characterize the band structures of such materials, revealing the coexistence of Bragg and hybridization bandgaps. We also introduce a theoretical approach to model this complex system and predict its band structure. These unprecedented experimental and theoretical results reveal the possibility to efficiently control water waves at the laboratory scale.

Seismic metasurfaces on porous layered media: Surface resonators and fluid-solid interaction effects on the propagation of Rayleigh waves

Seismic surface wave mitigation using metamaterials is a growing research field propelled by intrinsic theoretical value and possible application prospects. Up to date, the complexity of site conditions found in engineering practice, which can include layered stratigraphy and variable water table level, has been discarded in the development of analytical frameworks to favor the derivation of simple, yet effective, closed-form dispersion laws. This work provides a further step towards the analytical study of “seismic metasurfaces” in real site conditions considering the propagation of Rayleigh waves through a layered porous substrate equipped with local resonators. To this aim, we combine classical elasticity theory, Biot’s poroelasticity and an effective medium approach to describe the metasurface dynamics and its coupling with the poroelastic substrate. The developed framework naturally includes simpler configurations like seismic metasurfaces atop homogeneous dry or saturated soils. Apart from known phenomena like wave-resonance hybridization and surface wave band gaps, we predict the existence of an extended frequency range where surface waves are attenuated due to energy leakage in the form of slow pressure waves, as a result of the fluid-solid interaction. Besides, we demonstrate that the surface wave band gap and the related surface-to-shear wave conversion is robust to variations in the water table level. Conversely, when the dry and saturated layers have different material parameters, for example, due to different porosity ratios, the surface-to-shear wave conversion can be accompanied by the excitation of higher-order surface modes, which remain channeled below the metasurface. These analytical findings, augmented and confirmed by numerical simulations, evidence the importance of accounting for fluid-solid interaction in the dynamics of seismic metasurfaces.

Optical and magnetic excitations in the underscreened quasiquartet Kondo lattice

The underscreened Kondo lattice consisting of a single twofold degenerate conduction band and a CEF split 4f-electron quasi-quartet has non-conventional quasiparticle dispersions obtained from the constrained mean-field theory. An additional genuinely heavy band is found in the main hybridization band gap of the upper and lower hybridzed bands whose heavy effective mass is controlled by the CEF splitting. Its presence should profoundly influence the dynamical optical and magnetic response functions. In the former, the onset of the optical conductivity is not the main hybridisation energy but the much lower Kondo energy scale which appears in the direct transitions to the additional heavy band. The dynamical magnetic response is also strongly modified by the in-gap heavy band which can lead to unconventional resonant excitations that may be interpreted as coherent CEF-Kondo lattice magnetic exciton bands. Their instability at low temperature signifies the onset of induced excitonic magnetism in the underscreened Kondo lattice.

Slow light engineering in resonant photonic crystal line-defect waveguides.

Slow light plays an outstanding role in a wide variety of optical applications, from quantum information to optical processing. While slow optical guiding in photonic crystal waveguides is typically based on Bragg band gaps occurring in non-resonant photonic crystals, here we explore the possibility to leverage the hybridization photonic band gaps of resonant photonic crystals to induce a different form of slow light guiding. We study a line-defect waveguide in a periodic structure composed of high-permittivity resonant dielectric objects and exploit the different guiding mechanisms associated with the hybridization band gap to induce slow light in the resonant phase of the crystal. We demonstrate quantitatively that this method can, in principle, produce high group indices over large bandwidths with potential values of group-index bandwidth products up to 0.67.

Hybridization bandgap induced by an electrical resonance in piezoelectric metamaterial plates

We demonstrate numerically and experimentally the opening of a locally resonant bandgap in an active phononic crystal (PC) made of a homogeneous piezoelectric plate covered by a 1D periodic array of thin electrodes connected to inductive shunts. The application of periodic electrical boundary conditions (EBCs) enables an at will tailoring of the dispersion properties of the PC plate, thus leading to a control of the dispersion of the propagating guided elastic waves in the plate. Depending on the nature of the EBCs, several bandgaps open up, the most important being a Hybridization Bandgap (HBG) in the subwavelength regime. The PC behaves as a locally resonant metamaterial. The HBG originates from the interaction of propagating elastic waves (Lamb modes) with an electrical resonant mode whose dispersion can be effectively described through an equivalent transmission line model.

Acoustic double negativity induced by position correlations within a disordered set of monopolar resonators

Using a Multiple Scattering Theory algorithm, we investigate numerically the transmission of ultrasonic waves through a disordered locally resonant metamaterial containing only monopolar resonators. By comparing the cases of a perfectly random medium with its pair correlated counterpart, we show that the introduction of short range correlation can substantially impact the effective parameters of the sample. We report, notably, the opening of an acoustic transparency window in the region of the hybridization band gap. Interestingly, the transparency window is found to be associated with negative values of both effective compressibility and density. Despite this feature being unexpected for a disordered medium of monopolar resonators, we show that it can be fully described analytically and that it gives rise to negative refraction of waves.