The phonon propagation dynamics in a phononic crystal waveguide, realized via a suspended one-dimensional membrane array with periodic air holes, is investigated as function of its geometry. The bandstructure of the phononic crystal can be engineered by modifying the characteristics of the phonon standing waves in the waveguide by varying the waveguide width and the pitch of the air holes. This enables the phonon transmission bands, the bandgaps, the velocity and the nonlinear dispersion in the phononic crystal to be controlled. Indeed the engineered bandstructure can also be tuned to sustain multiple phonon modes in a given branch which whilst being spectrally degenerate can be temporally resolved via their differing group velocities. This systematic study reveals the key geometric parameters that enable the phonon transport in phononic crystal waveguides to be fully controlled.
This study investigates the topological behavior of a continuous elastic phononic structure characterized by a 3-term Kekulé distortion. The elastic waveguide consists of a hexagonal unit cell whose geometric dimensions are intentionally perturbed according to a generalized Kekulé scheme. The resulting structure exhibits an effective Hamiltonian that resembles a quantum spin Hall system, hence suggesting that the waveguide can support helical topological edge states. Using first-principles calculations, we show the existence of nondegenerate pseudospin states and a very peculiar 6-lobe pseudos…
Nanoelectromechanical systems (NEMS), utilising localised mechanical vibrations, were pioneered for sensors, signal processors and to study macroscopic quantum mechanics. Increasingly the concept of integrating multiple mechanical elements via electrical/optical means has emerged as a challenge towards NEMS circuits. Here we develop phononic crystal waveguides (PnC WGs), using a 1-dimensional array of suspended membranes, that offer purely mechanical means to integrate isolated NEMS resonators. In the first steps to this objective, we demonstrate the PnC WG can support and guide mechanical vib…
We study a spin-phononic system where diamond defect centers are interfaced with a quasi-one-dimensional phononic crystal. We show that, a single defect center, coupled to the phonon modes of a phononic crystal waveguide near the band gap, can seed its own phononic cavity mode with an exponentially decaying envelope around the defect center's position. The spin-induced phononic cavity, with a greatly reduced and tunable mode volume, allows coherent phonon-mediated interactions between distant spins with a highly tunable range, enabling access to a variety of long-range interacting spin models.…
This study investigates the occurrence of acoustic topological edge states in a 2D phononic elastic waveguide due to a phenomenon that is the acoustic analogue of the quantum valley Hall effect. We show that a topological transition takes place between two lattices having broken space inversion symmetry due to the application of a tunable strain field. This condition leads to the formation of gapless edge states at the domain walls, as further illustrated by the analysis of the bulk-edge correspondence and of the associated topological invariants. Although time reversal symmetry is still intac…
We report direct visualization of gigahertz-frequency Lamb waves propagation in aluminum nitride phononic circuits by transmission-mode microwave impedance microscopy (TMIM). Consistent with the finite-element modeling, the acoustic eigenmodes in both a horn-shaped coupler and a sub-wavelength waveguide are revealed in the TMIM images. Using fast Fourier transform filtering, we quantitatively analyze the acoustic loss of individual Lamb modes along the waveguide and the power coupling coefficient between the waveguide and the parabolic couplers. Our work provides insightful information on the …
We analytically predict and numerically demonstrate the existence of a family of bound modes in the continuum (BICs) in bi-layered spring mass chains. A coupled array of such chains is then used to illustrate transversely bound waves propagating along a channel in a lattice. We start by considering the compact region formed by coupling two spring mass chains with defects and predict bound modes arising due to reflection symmetries in this region. Dispersion analysis of a waveguide consisting of an array of appropriately coupled bi-layered chains reveals the presence of a branch having bound mo…
Hexagonal boron nitride (h-BN), one of the hallmark van der Waals (vdW) layered crystals with an ensemble of attractive physical properties, is playing increasingly important roles in exploring two-dimensional (2D) electronics, photonics, mechanics, and emerging quantum engineering. Here, we report on the demonstration of h-BN phononic crystal waveguides with designed pass and stop bands in the radio frequency (RF) range and controllable wave propagation and transmission, by harnessing arrays of coupled h-BN nanomechanical resonators with engineerable coupling strength. Experimental measuremen…
The possibility of realizing an electrostatically induced phononic crystal is investigated numerically in an acoustic waveguide based on a graphene sheet that is suspended over periodically arrayed electrodes. The application of dc voltage to these electrodes exerts electrostatic force on the graphene and this results in the periodic formation of stress in the waveguide structure in a non-invasive way, unlike the cases with mass loading and air holes. This non-invasive scheme enables a bandgap, namely a phononic crystal, to be created in the waveguide that can be used to dynamically tune the a…
A phononic crystal formed in a suspended membrane provides full confinement of hypersonic waves and thus realizes a range of chip-scale manipulations. In this letter, we demonstrate the mode-resolved real-space characterization of the mechanical vibration properties in cavities and waveguide systems. Multiple resonant modes are independently characterized in various designed cavities, and wavelength-scale high-$Q$ resonances up to $Q=$ 4200 under atmospheric conditions are confirmed. This also reveals that the waveguide allows us to resolve single-mode wave transmission and thereby drive evane…
We demonstrate a single-mode phononic waveguide that enables robust propagation of mechanical waves. The waveguide is a highly-stressed silicon nitride membrane that supports the propagation of out-of-plane modes. In direct analogy to rectangular microwave waveguides, there exists a band of frequencies over which only the fundamental mode is allowed to propagate, while multiple modes are supported at higher frequencies. We directly image the mode profiles using optical heterodyne vibration measurement, showing good agreement with theory. In the single-mode frequency band, we show low-loss prop…
We report the design of a diamond-based honeycomb phononic network, in which a mechanical resonator couples to three distinct phononic crystal waveguides. This two-dimensional (2D) phononic network extends an earlier study on one-dimensional (1D) phononic networks with closed mechanical subsystems. With a special design for the phononic band structures of the waveguides, any two neighboring resonators in the 2D network and the waveguide between them can form a closed mechanical subsystem, which enables nearest neighbor coupling and at the same time circumvents the scaling problems inherent in …
Nanophononics has the potential for information transfer, in an analogous manner to its photonic and electronic counterparts. The adoption of phononic systems has been limited, due to difficulties associated with the generation, manipulation, and detection of phonons, especially at GHz frequencies. Existing techniques often require piezoelectric materials with an external radiofrequency excitation that are not readily integrated into existing CMOS infrastructures, while non-piezoelectric demonstrations have been inefficient. In this work, we explore the optomechanical generation of coherent ph…
We demonstrate that a phonon stopband can be synthesized from an aperiodic structure comprising a discrete set of phononic filter stages. Each element of the set has a dispersion relation that defines a complete bandgap when calculated under a Bloch boundary condition. Hence, the effective stopband width in an aperiodic phononic filter (PnF) may readily exceed that of a phononic crystal with a single lattice constant or a coherence scale. With simulations of multi-moded phononic waveguides, we discuss the effects of finite geometry and mode-converting junctions on the phonon transmission in Pn…
The ability to create, manipulate and detect non-classical states of light has been key for many recent achievements in quantum physics and for developing quantum technologies. Achieving the same level of control over phonons, the quanta of vibrations, could have a similar impact, in particular on the fields of quantum sensing and quantum information processing. Here we present a crucial step towards this level of control and realize a single-mode waveguide for individual phonons in a suspended silicon micro-structure. We use a cavity-waveguide architecture, where the cavity is used as a sourc…
Photonic structures in diamond are key to most of its application in quantum technology. Here, we demonstrate tapered nano-waveguides structured directly onto the diamond substrate hosting shallow-implanted nitrogen vacancy (NV) centers. By optimization based on simulations and precise experimental control of the geometry of these pillar-shaped nano-waveguides, we achieve a net photon flux up to ~ $1.7 \cdot 10^6 /s$. This presents the brightest monolithic bulk diamond structure based on single NV centers so far. We observe no impact on excited state lifetime and electronic spin dephasing time…
The ability to manipulate phonon waveforms in continuous media has attracted significant research interest and is crucial for practical applications ranging from biological imaging to material characterization. Although several spatial focusing techniques have been developed, these systems require sophisticated artificial structures, which limit their practical applications. This is because the spatial control of acoustic phonon waves is not as straightforward as photonics so there is a strong demand for an alternative approach. Here we demonstrate a phononic time lens in a dispersive one-dime…
We report the results of Brillouin-Mandelstam spectroscopy and Mueller matrix spectroscopic ellipsometry of the nanoscale "pillar with the hat" periodic silicon structures, revealing intriguing phononic and photonic properties. It has been theoretically shown that periodic structures with properly tuned dimensions can act simultaneously as phononic and photonic - phoxonic - crystals, strongly affecting the light-matter interactions. Acoustic phonon states can be tuned by external boundaries, either as a result of phonon confinement effects in individual nanostructures, or as a result of artifi…
We propose a platform for robust and tunable nonreciprocal phonon transport based on arrays of optomechanical microtoroids. In our approach, time-reversal symmetry is broken by the interplay of photonic spin-orbit coupling, engineered using a state-of-the-art geometrical approach, and the optomechanical interaction. We demonstrate the topologically protected nature of this system by investigating its robustness to imperfections. This type of system could find application in phonon-based information storage and signal processing devices.
Topological metamaterials have robust properties engineered from their macroscopic arrangement, rather than their microscopic constituency. They can be designed by starting from Dirac metamaterials with either symmetry-enforced or accidental degeneracy. The latter case provides greater flexibility in the design of topological switches, waveguides, and cloaking devices, because a large number of tuning parameters can be used to break the degeneracy and induce a topological phase. However, the design of a topological logic element--a switch that can be controlled by the output of a separate swit…
This letter investigates a flow-free, pseudospin-based acoustic topological insulator. Zone folding, a strategy originated from photonic crystal, is used to form double Dirac cones in phononic crystal. The lattice symmetry of the phononic crystal is broken by tuning the size of the center "atom" of the unit cell in order to open the nontrivial topological gap. Robust sound one-way propagation is demonstrated both numerically and experimentally. This study provides a flexible approach for realizing acoustic topological insulators, which are promising for applications such as noise control and w…
We report a new type of phononic crystals with topologically non-trivial bandgaps for both longitudinal and transverse polarizations, resulting in protected one-way elastic edge waves. In our design, gyroscopic inertial effects are used to break the time-reversal symmetry and realize the phononic analogue of the electronic quantum Hall effect. We investigate the response of both hexagonal and square gyroscopic lattices and observe bulk Chern number of 1 and 2, indicating that these structures support single and multi-mode edge elastic waves immune to back-scattering. These robust one-way phono…
Recent years witnessed much broader use of Brillouin inelastic light scattering spectroscopy for the investigation of phonons and magnons in novel materials, nanostructures, and devices. Driven by developments in instrumentation and the strong need for accurate knowledge of energies of elemental excitations, the Brillouin - Mandelstam spectroscopy is rapidly becoming an essential technique, complementary to the Raman inelastic light scattering spectroscopy. We provide an overview of recent progress in the Brillouin light scattering technique, focusing on the use of this photonic method for the…
Coulomb interactions play an essential role in atomically-thin materials. On one hand, they are strong and long-ranged in layered systems due to the lack of environmental screening. On the other hand, they can be efficiently tuned by means of surrounding dielectric materials. Thus all physical properties which decisively depend on the exact structure of the electronic interactions can be in principle efficiently controlled and manipulated from the outside via Coulomb engineering. Here, we show how this concept can be used to create fundamentally new plasmonic waveguides in metallic layered mat…
Multi Moire Networks in Engineered Lateral Hetero-Bilayers: Programmable Phononic Reconfiguration and Second Harmonic Generation
Indian Institute of Technology Kharagpur（印度理工学院卡拉格普尔分校）；Universidade Federal de Minas Gerais（米纳斯吉拉斯联邦大学）；Aarhus University（奥胡斯大学）；Indian Institute of Technology Goa（印度理工学院果阿分校）；Indian Institute of Science Education and Research Tirupati（蒂鲁帕蒂科学教育研究所）；KIIT Deemed to be University（KIIT认定大学）
Photonic structures with topologically nontrivial bands are usually designed by arranging simple meta-atoms, ideally, single-mode ones, in a carefully designed photonic lattice with symmetry that guarantees the emergence of topological states. Here we investigate an alternative option that does not require complex lattice geometry but instead relies on the tuning of the parameters of the individual meta-atoms to achieve the degeneracy of the modes with different symmetry. As an illustrative example, we consider a one-dimensional array of equidistant identical periodic nanophotonic waveguides s…
The quest to understand, design, and synthesize new forms of quantum matter guides much of contemporary research in condensed matter physics. One-dimensional (1D) electronic systems form the basis for some of the most interesting and exotic phases of quantum matter. The variety of experimentally-accessible ballistic 1D electronic systems is highly restricted, and furthermore these systems typically have few tuning parameters other than electric and magnetic fields. However, electron waveguides formed from two-dimensional (2D) LaAlO$_3$/SrTiO$_3$ heterointerfaces exhibit remarkable 1D propertie…
We present a methodology to perform inverse analysis on reconfigurable topological insulators for flexural waves in plate-like structures. First the unit cell topology of a phononic plate is designed, which offers two-fold degeneracy in the band structure by topology optimization. In the second step, piezoelectric patches bonded over the substrate plate are connected to an external circuit and used appropriately to break space inversion symmetry. The space inversion symmetry breaking opens a topological band gap by mimicking quantum valley Hall effect. Numerical simulations demonstrate that th…
We study the implementation of quantum state transfer protocols in phonon networks, where in analogy to optical networks, quantum information is transmitted through propagating phonons in extended mechanical resonator arrays or phonon waveguides. We describe how the problem of a non-vanishing thermal occupation of the phononic quantum channel can be overcome by implementing optomechanical multi- and continuous mode cooling schemes to create a 'cold' frequency window for transmitting quantum states. In addition, we discuss the implementation of phonon circulators and switchable phonon routers, …
In the field of phononics, periodic patterning controls vibrations and thereby the flow of heat and sound in matter. Bandgaps arising in such phononic crystals realize low-dissipation vibrational modes and enable applications towards mechanical qubits, efficient waveguides, and state-of-the-art sensing. Here, we combine phononics and two-dimensional materials and explore the possibility of manipulating phononic crystals via applied mechanical pressure. To this end, we fabricate the thinnest possible phononic crystal from monolayer graphene and simulate its vibrational properties. We find a ban…
We fabricated and characterized a single-crystal silicon phonon waveguide structure with lead zirconate titanate (PZT) piezoelectric transducers. The compressive stress in a silicon-on-insulator wafer causes a membrane waveguide to buckle, leading to the quadratic nonlinearity. The PZT transducer integrated in an on-chip configuration enables us to excite high-intensity mechanical vibration, which allows the characterization of nonlinear behavior. We observed a softening nonlinear response as a function of the drive power and demonstrated the mode shift and frequency conversion. This is the fi…
Observation of Erratic Non-Hermitian Skin Effect in Phononic Crystals
Institute of Acoustics, School of Physics Science and Engineering, Tongji University（同济大学物理科学与工程学院声学研究所）；School of Advanced Manufacturing Engineering, Nanjing University（南京大学先进制造工程学院）
We identify a broad class of phonon modes with persistent vortex fluxes at arbitrarily slow propagating velocities in periodic nano-waveguides. Such phonon vortices are associated with the split band-edges in dispersion dependencies, which can be engineered by waveguide design. Modulations introduced in such waveguides can support a pair of defect cavity phonon modes with an arbitrarily small frequency splitting. These features can find applications for sensing and nano-manipulation.
Optomechanics, nano-electromechanics, and integrated photonics have brought about a renaissance in phononic device physics and technology. Central to this advance are devices and materials that support ultra long-lived photonic and phononic excitations, providing access to novel regimes of classical and quantum dynamics based on tailorable photon-phonon coupling. Silica-based devices have been at the forefront of such innovations for their ability to support optical excitations persisting for nearly 1 billion cycles, and for their low optical nonlinearity. Remarkably, acoustic phonon modes can…
Zak phase, i.e. the Berry phase acquired during an adiabatic motion of a Bloch particle across the Brillouin zone, provides a measure of the topological invariant of Bloch bands in one-dimensional crystalline potentials. Here a photonic structure, based on engineered lattices of evanescently-coupled optical waveguides, is proposed to detect Zak phase difference of photons undergoing Bloch oscillations in topologically distinct Bloch bands of dimerized superlattices.
We have studied acoustic topological edge modes in a honeycomb phononic crystal composed of metallic nano-pillars on a LiNbO$_3$ substrate. Acoustic band calculations show that the topological surface acoustic wave (SAW) mode inhabits the edge of the honeycomb phononic crystal in spite of the hybridization with the internal acoustic modes of the substrate. Pulse-type microwave impedance microscopy realized clear visualization of the gigahertz topological edge mode between two mutually inverted topological phononic crystals. A frequency-dependent image showed that the edge mode evolves as the b…
Critical couplings in topological-insulator waveguide-resonator systems observed in elastic waves
National Laboratory of Solid State Microstructures & Department of Materials Science and Engineering, Nanjing University（南京大学固态微结构实验室与材料科学与工程系）；Jiangsu Key Laboratory of Artificial Functional Materials, Nanjing University（南京大学江苏省人工功能材料重点实验室）
Heat flow control in phononics has received significant attention recently due to its widespread applications in energy transfer, conversion and utilization. Here, we demonstrate that by applying external stress or strain we can effectively tune the thermal conductivity through changing the density of twin boundaries, which in turn offers the intriguing mechanical-controlled thermal switch and hysteresis operations. Twin boundaries perpendicular to the transport direction strongly scatter phonons. As such, the heat flow is in inverse proportional to the density of twin boundaries and hence all…
Distributing quantum entanglement on a chip is a crucial step towards realizing scalable quantum processors. Using traveling phonons - quantized guided mechanical wavepackets - as a medium to transmit quantum states is currently gaining significant attention, due to their small size and low propagation speed compared to other carriers, such as electrons or photons. Moreover, phonons are highly promising candidates to connect heterogeneous quantum systems on a chip, such as microwave and optical photons for long-distance transmission of quantum states via optical fibers. Here, we experimentally…
