Plasmon-phonon coupling in graphene-hyperbolic bilayer heterostructures

Polar dielectrics are important optical materials enabling the subwavelength manipulation of light in infrared due to their capability to excite phonon polaritons.In practice,it is highly desired to actively modify these hyperbolic phonon polaritons(HPPs) to optimize or tune the response of the device.In this work,we investigate the plasmonic material,a monolayer graphene,and study its hybrid structure with three kinds of hyperbolic thin films grown on SiO_2 substrate.The inter-mode hybridization and their tunability have been thoroughly clarified from both the band dispersions and the mode patterns numerically calculated through a transfer matrix method.Our results show that these hybrid multilayer structures are of strong potentials for applications in plasmonic waveguides,modulators and detectors in infrared.     

Tuning infrared absorption in hyperbolic polaritons coated silk fibril composite

Advanced textiles for thermal management give rise to many functional applications and unveil a new frontier for the study of human thermal comfort. Manipulating the coated quasi-particles between the composite components offers a platform to study the advanced thermoregulatory textiles. Here, we propose that coating the hyperbolic polariton can be an effective tool to tune infrared absorption in hexagonal boron nitride-coated silk composite. Remarkably, we achieve significant tuning of the infrared absorption efficiency of silk fibrils through the designed hexagonal boron nitride film. The underlying mechanism is related to resonance coupling between hyperbolic phonon polaritons. We find a notably high infrared absorption efficiency, nearly 3 orders larger than that without hBN coating, which can be achieved in our composite system. Our results indicate the promising future of advanced polariton-coated textiles and open a pathway to guide the artificial-intelligence design of advanced functional textiles.     

Unidirectional excitation of surface plasmon polaritons in T-shaped waveguide with nanodisk resonator

The unidirectional excitation of surface plasmon polaritons (SPPs) in a novel configuration is numerically investigated by the finite-difference time-domain method. It is found that the transmission varies periodically with the increase of distance between the nanodisk resonator and horizontal nanoslit, which can be interpreted by the interference theory. The operating wavelength of this structure can be tuned by altering the refractive index of the nanodisk resonator. This subwavelength-scale structure exhibits high transmission (～58%) due to the constructive interference of the SPP modes, and thus can find important applications on the manipulation of SPP excitation in highly integrated optical circuits.     

Far infrared measurements of bulk and surface phonons in GaAs/AlAs superlattices

We have used far-infrared oblique-incidence reflection spectroscopy to study bulk phonon polaritons, and attenuated total reflection (ATR) spectroscopy to study surface phonon polaritons, in long-period GaAs/Al_xGa_1–xAs and short-period GaAs/AlAs superlattices. Results on the former are in good agreement with an effective-medium bulk-slab model of the dielectric tensor of the superlattice; results on the latter are analysed in terms of a model that contains dielectric-tensor contributions from the confined optic phonons.     

Resonance Raman scattering of excitonic polaritons by LO and acoustic phonons in ZnTe

We have observed dispersive two-phonon Raman scattering of polaritons by LO and acoustic phonons near the lowest exciton state of ZnTe. From the Stokes shifts of these Raman lines, it has been found that the scattering process switches from an acoustic phonon followed by one LO phonon to the reversed one: a LO phonon followed by an acoustic one.     

Phonon-induced polariton superlattices

We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion.     

Resonant infrared transmission through SiC films

Resonant transmission through metallic films is observed when a periodic array of holes is drilled. This phenomenon has been attributed to surface plasmon polaritons. We study a similar system made of an array of slits in a SiC film supporting surface phonon polaritons. We find a resonant transmission in the infrared. The role of surface waves is analyzed. We find that surface waves are excited at resonance but are not a necessary condition to obtain a resonant transmission.     

Raman scattering from the upper and lower modes of surface phonon polaritons in ZnTe

The upper and lower modes of surface phonon polaritons have been observed in free-standing thin slabs (～7 μm) of single-crystal ZnTe by a conventional Raman-scattering technique at room temperature. The experimental dispersion relations were measured in various scattering angles (outside the sample) from 0.9° to 2.0° and agree with the theoretical dispersion relations. The main factors enabling us to observe the two surface modes are the appropriate selections of the material with a small attenuation factor for surface phonon polaritons and of the thickness of the sample slabs.     

孔洞缺陷对二维石墨烯/氮化硼横向异质结热传导的调控

本文采用孔洞缺陷来实现对二维石墨烯/氮化硼横向异质结热导率的调控.平衡态分子动力学(EMD)计算结果表明,界面孔洞的引入会降低二维石墨烯/氮化硼横向异质结的热导率.相较于有序的孔洞分布,无序的孔洞分布能够更有效地降低异质结的热导率,这一现象可通过声子安德森局域化来解释.孔洞缺陷的存在导致声子的频率和波失发生变化,从而使声子散射变得更加频繁,孔洞随机分布时,则导致声子波在材料中发生多次反射和散射,最终形成局域振动模式.本研究揭示了孔洞缺陷降低二维石墨烯/氮化硼横向异质结热导率的物理机制,对二维热电材料的结构设计有一定的指导意义.     

Enhanced Terahertz Phonon Polariton in Lithium Niobate Chip

Terahertz (THz) phonon polaritons, fundamental quasi-particles that couple lattice vibrations with electromagnetic fields at THz frequencies, are found in a variety of materials that offer the potential for a wide range of THz optoelectronic devices and on-chip integrated systems. However, these compact devices and on-chip systems are hampered by the absence of on-chip powerful THz phonon polariton sources. In this study, the efficient generation and amplification of THz phonon polaritons are proposed and directly visualized on a lithium niobate (LN) chip via a tilted pulsefront phase matching technique. By combining lateral pumping and phase matching schemes, two orders of magnitude are successfully attained in the interaction distance between the pump light and the LN chip, accompanied by a substantial amplification of generated THz phonon polariton. The results of this study may lead to abundant potential applications in chip scale THz photonic devices and systems based on LN materials and its integrated heterostructures.     

Graphene growth on h-BN by molecular beam epitaxy

The growth of single layer graphene nanometer size domains by solid carbon source molecular beam epitaxy on hexagonal boron nitride (h-BN) flakes is demonstrated. Formation of single-layer graphene is clearly apparent in Raman spectra which display sharp optical phonon bands. Atomic-force microscope images and Raman maps reveal that the graphene grown depends on the surface morphology of the h-BN substrates. The growth is governed by the high mobility of the carbon atoms on the h-BN surface, in a manner that is consistent with van der Waals epitaxy. The successful growth of graphene layers depends on the substrate temperature, but is independent of the incident flux of carbon atoms.     

Synthesis of Highly Stable One-Dimensional Black Phosphorus/h-BN Heterostructures:A Novel Flexible Electronic Platform

Layered black phosphorus(BP) has recently emerged as a promising semiconductor because of its tunable band gap,high carrier mobility and strongly in-plane anisotropic properties.One-dimensional(1 D) BP materials are attractive for applications in electronic and thermal devices,owing to their tailored charge and phonon transports along certain orientations.However,the fabrication of 1 D BP materials still remains elusive thus far.We herein report the successful synthesis and characterization of nanotube-like BP for the first time by a selective composite with hexagonal boron nitride(h-BN) nanotubes under high pressure and high temperature conditions.The produced 1 D BP/h-BN composites possess flexible diameter,length and thickness by adjusting the experimental synthesis parameters.Interestingly,it is important to notice that the stability of our BP sample has been significantly improved under the formation of heterostructures,which can actively promote their commercial applications.Our experimental work,together with first-principles calculations,presents a new scalable strategy of designing 1 D tube-like BP/h-BN heterostructures that are promising candidates for flexible and high efficiency electronic platform.     

采用银纳米圆盘阵列提高LED发光特性的研究

为了提高GaN基蓝光LED的发光效率,设计了在LED有源层上方引入银纳米圆盘阵列的模型。利用时域有限差分方法计算了银纳米圆盘阵列不同结构参数情况下LED有源层自发辐射率的变化情况及光提取效率值。通过对有源区的近场分布和LED远场方向性的分析,理论上解释了利用该金属纳米结构生成的表面等离激元对LED性能增强的影响,利用该模型可使得表面等离激元与有源层有效耦合,从而增强有源层的自发辐射率。此外,银纳米粒子组成的阵列结构所生成的栅格矢量可以补偿表面等离激元的波矢量,从而可将局域化表面等离激元转为辐射性表面等离激元,显著提高LED顶端光提取效率。结果表明,当银纳米圆盘颗粒满足直径为120nm,厚度为30nm时,含该结构的GaN基蓝光LED自发辐射率比普通LED增强了3.6倍。在此基础上,当其按照晶格常数为220nm的三角晶格排列时,顶端光提取效率增强为2.5倍。这些结果为实际的高性能GaN基LED的设计与优化提供了一定的参考。     

Quantum Theory of Surface Polaritons in Semi-Infinite Dielectric Systems

The interaction system of a semi-infinite diatomic dielectric and the electromagnetic field propagating parallelly to the surface is studied. The long-wave optical phonon modes of the semi-infinite dielectric are calculated including the electronic polarizability by a quantum-mechanical theory. Retardation effects are neglected. A quantum field theory method of surface polaritons is developed to calculate the operator describing the interaction between a photon and the phonon polarization fields of the semi-infinite crystal, with explicit inclusion of surface effects. The dispersion relations of the surface phonon-polaritons are derived and discussed. The results are in good agreement with those obtained by the conventional, macroscopic dielectric theory of surface polaritons and experimental ATR (attenuated total reflection) spectra. The dispersion cuwes of polariton leaking modes caused by the interaction between bulk TO mode with surface effect and photons are presented in a graphical form. The k_||-dependence of the electric field strength in each polariton branch is calculated and presented also in a graphical form. We also research the spatial dependence of the field strength in each polariton branch. It is found that these properties are influenced and modulated by the surface phonons because of the interaction between photons and the surface phonon modes of the semi-infinite dielectric system. Hence the divergent nature (diffraction effect) of light propagating along the fib& and waveguides is restrained. We present a method how to use the boundary conditions in the quantum theory, which will be discussed in detail.     

Phonon–polariton in a piezoelectric superlattice

In a series of works Zhu et al. [Phy. Rev.Lett. 90 (2003) 0532903] have investigated the possibility of acoustic polaritons in a novel superlattice system consisting of piezoelectric materials. In the present work that two excitations are pointed out are: one due to piezo polaritons and the other due to the optic phonon mode. The behavior of the photonic gaps as a function of superlattice period is investigated systematically.     

On the equilibrium spectrum of surface polaritons thermally excited by solids

The spectral energy densities of surface plasmon and phonon polaritons are calculated in case of thermodynamic equilibrium. It is demonstrated that the spectral distribution of surface polaritons in equilibrium is quite different from the Planck?s law for photons. Temperature dependence of the surface density of energy for two-dimensional fluctuations is different from the temperature dependence of volume density of energy for photons in equilibrium.     

Probing Optical Losses and Dispersion of Fully Guided Waves through Critical Evanescent Coupling

JETP Letters - Surface waves such as plasmon, exciton, or phonon polaritons as well as guided modes supported by various planar structures attract particular attention due to their capability of...     

Quantum non-demolition phonon counter with a hybrid optomechnical system

A phonon counting scheme based on the control of polaritons in an optomechanical system is proposed. This approach permits us to measure the number of phonons in a quantum non-demolition (QND) manner for arbitrary modes not limited by the frequency matching condition as in usual photon-phonon scattering detections. The performance on phonon number transfer and quantum state transfer of the counter are analyzed and simulated numerically by taking into account all relevant sources of noise.     

Far Infrared Investigation of Plasmon-LO Phonon Coupling and Surface Polaritons Modes in Donor Doped Cd1-xHgxTe and CdTe Thin Layer on GaAs Substrate

Infrared Fourier transform spectroscopy has been used to investigate phonon and plasmon modes in Cd_1-xHg_xTe and CdTe thin layer on GaAs substrate. Attenuated total reflection (ATR) spectroscopy has been used to excite surface plasmon and phonon polaritons. The plasmon-LO phonon coupling modes in samples are studied by dispersion curve calculation for various carrier concentrations. There exist three branches of coupled modes in dispersion curve. For analysis of the far infrared polarized reflectivity spectra we employ the harmonic oscillator dielectiic function model and the Drude model for free carrier response. We find that the coupling modes dependent to the concentration of free carriers. Furthermore, the experimental data have been used to calculate carrier concentration, composition parameter, mobility of carrier, thickness of layer and gap energy.     

Spin filter,spin amplifier and spin diode in graphene nanodisk

Graphene nanodisk is a graphene derivative with a closed edge. The trigonal zigzag nanodisk with size N has N-fold degenerated zero-energy states. It can be interpreted as a quantum dot with an internal degree of freedom. The ground state of nanodisk is a quasi-ferromagnet, which is a ferromagnetic-like state with a finite but very long life time. We investigate spin-filter effects in the system made of nanodisks and leads. A novel feature of the nanodisk spin filter is that its spin can be controlled by the spin current. We propose some applications for spintronics, such as spin memory, spin amplifier and spin diode. It is argued that a spin current is reinforced (rectified) by feeding it into a nanodisk spin amplifier (diode). Graphene nanodisk would be a promising candidate of future electronic and spintronic nanodevices.