One-dimensional Phonon Research Articles

Defect-Band Splitting of a One-Dimensional Phononic Crystal with Double Defects for Bending-Wave Excitation

Extensive prior research has delved into the localization of elastic wave energy through defect modes within phononic crystals (PnCs). The amalgamation of defective PnCs with piezoelectric materials has opened new avenues for conceptual innovations catering to energy harvesters, wave filters, and ultrasonic receivers. A recent departure from this conventional paradigm involves designing an ultrasonic actuator that excites elastic waves. However, previous efforts have mostly focused on single-defect scenarios for bending-wave excitation. To push the boundaries, this research takes a step forward by extending PnC design to include double piezoelectric defects. This advancement allows ultrasonic actuators to effectively operate across multiple frequencies. An analytical model originally developed for a single-defect situation via Euler–Bernoulli beam theory is adapted to fit within the framework of a double-defect set-up, predicting wave-excitation performance. Furthermore, a comprehensive study is executed to analyze how changes in input voltage configurations impact the output responses. The ultimate goal is to create ultrasonic transducers that could have practical applications in nondestructive testing for monitoring structural health and in ultrasonic imaging for medical purposes.

Phonon transmission through a nonlocal metamaterial slab

Previous theory and experiment has shown that introducing strong (nonlocal) beyond-nearest-neighbor interactions in addition to (local) nearest-neighbor interactions into rationally designed periodic lattices called metamaterials can lead to unusual wave dispersion relations of the lowest band. For roton-like dispersions, this especially includes the possibility of multiple solutions for the wavenumber at a given frequency. Here, we study the one-dimensional frequency-dependent acoustical phonon transmission of a slab of such nonlocal metamaterial in a local surrounding. In addition to the usual Fabry-Perot resonances, we find a series of bound states in the continuum. In their vicinity, sharp Fano-type transmission resonances occur, with sharp zero-transmission minima next to sharp transmission maxima. Our theoretical discussion starts with a discrete mass-and-spring model. We compare these results with solutions of a generalized wave equation for heterogeneous nonlocal effective media. We validate our findings by numerical calculations on three-dimensional metamaterial microstructures for one-dimensional acoustical wave propagation.

Curvature-Induced One-Dimensional Phonon Polaritons at Edges of Folded Boron Nitride Sheets.

Generation and manipulation of phonon polaritons are of paramount importance for understanding the interaction between an electromagnetic field and dielectric materials and furthering their application in mid-infrared optical communication. However, the formation of tunable one-dimensional phonon polaritons has been rarely realized in van der Waals layered structures. Here we report the discovery of curvature-induced phonon polaritons localized at the crease of folded hexagonal boron nitrides (h-BNs) with a few atomic layers using monochromated electron energy-loss spectroscopy. Compared to bulk regions, the creased-localized signals undergo an abnormal blue-shift of 1.4 meV. First-principles calculations reveal that the energy shift arises from the optical phonon hardening in the curled region. Interestingly, the curvature-induced phonon polariton can also be controllably achieved via an electron-beam etching approach. This work opens an avenue of tailoring local electromagnetic response and creating unique phonon polariton modes in van der Waals layered materials for diverse applications.

Nonequilibrium scalar field dynamics starting from Fock states: Absence of thermalization in one-dimensional phonons coupled to fermions

We propose a new method to study non-equilibrium dynamics of scalar fields starting from non-Gaussian initial conditions using Keldysh field theory. We use it to study dynamics of phonons coupled to non-interacting bosonic and fermionic baths, starting from initial Fock states. We find that in one dimension long wavelength phonons coupled to fermionic baths do not thermalize both at low and high bath-temperatures. At low temperature, constraints from energy-momentum conservation lead to a narrow bandwidth of particle-hole excitations and the phonons effectively do not see this bath. On the other hand, the strong band-edge divergence of the particle-hole density of states leads to an undamped polariton-like mode of the dressed phonons above the band edge of the particle-hole excitations. These undamped modes contribute to the lack of thermalization of long wavelength phonons at high temperatures. In higher dimensions, these constraints and the divergence of density of states are weakened and lead to thermalization at all wavelengths.

Design of a Thickness Sensor Based on a One-Dimensional Phononic Crystal

Nowadays, sensor technology has attracted great interest in various domains. In this ‎work, we have analyzed a one dimensional phononic crystal made by the stack of N bilayers of ‎‎(LiNbO3/SiO2). The sensor design consists of a one dimensional phononic crystal structure with a ‎defect layer inserted in the middle. Using the Transfer Matrix Method (TMM), the transmission ‎spectrums of acoustic waves are calculated and plotted. In this work, we are interested in the ‎resonance peak that is transmitted inside the phononic band gap. The results obtained show clearly that the resonant frequency of the measured ‎transmission peak is very sensitive to the layer defect properties. This proves that such structure offers a new platform for sensing ‎applications.

Carbon Nanotube Devices for Quantum Technology.

Carbon nanotubes, quintessentially one-dimensional quantum objects, possess a variety of electrical, optical, and mechanical properties that are suited for developing devices that operate on quantum mechanical principles. The states of one-dimensional electrons, excitons, and phonons in carbon nanotubes with exceptionally large quantization energies are promising for high-operating-temperature quantum devices. Here, we discuss recent progress in the development of carbon-nanotube-based devices for quantum technology, i.e., quantum mechanical strategies for revolutionizing computation, sensing, and communication. We cover fundamental properties of carbon nanotubes, their growth and purification methods, and methodologies for assembling them into architectures of ordered nanotubes that manifest macroscopic quantum properties. Most importantly, recent developments and proposals for quantum information processing devices based on individual and assembled nanotubes are reviewed.

Elastic stiffening induces one-dimensional phonons in thin Ta2Se3 nanowires

Compared to extensive studies of thermal transport in two-dimensional materials, very limited attention has been paid to the corresponding phenomenon in quasi-one-dimensional van der Waals crystals. Here, we show that Ta2Se3 can be easily exfoliated into thin nanowires, indicating strong anisotropy in the bonding strength within the basal plane. Systematic thermal property measurements disclose signatures of one-dimensional phonons as the nanowire hydraulic diameter reduces below 19.2 nm with linearly escalating thermal conductivity as temperature increases and size dependence inconsistent with the classical size effect. We further show that these unusual transport properties are induced by elastic stiffening occurring for wires of <30 nm diameter.

From nanowires to super heat conductors

Thermal transport through various nanowires has attracted extensive attention in the past two decades. Nanowires provide an excellent platform to dissect phonon transport physics because one can change the wire size to impose systematically varying boundary conditions that can help to distinguish the contributions of various scattering mechanisms. Moreover, novel confinement phenomena beyond the classical size effect promise opportunities to achieve highly desirable properties. Based on a summary of research progresses in nanowire thermal properties, we discuss more intriguing observations due to the classical size effect, coupling between mechanical and thermal properties, and divergent thermal conductivity as a result of conversion from three-dimensional to one-dimensional phonon transport, showcasing the superdiffusive thermal transport phenomenon. We hope that these discussions could provide a new perspective on further exploring thermal transport in nanowires, which may eventually lead to breakthroughs such as achieving thermal conductivity values higher than that of any known materials.

Theory of Transport in Ferroelectric Capacitors.

The spontaneous order of electric and magnetic dipoles in ferroelectrics and ferromagnets even at high temperatures is both fascinating and useful. Transport of magnetism in the form of spin currents is vigorously studied in spintronics, but the polarization current of the ferroelectric order has escaped attention. We therefore present a time-dependent diffusion theory for heat and polarization transport in a planar ferroelectric capacitor with parameters derived from a one-dimensional phonon model. We predict steady-state Seebeck and transient Peltier effects that await experimental discovery.

Observation of superdiffusive phonon transport in aligned atomic chains.

Fascinating phenomena can occur as charge and/or energy carriers are confined in one dimension1-4. One such example is the divergent thermal conductivity (κ) of one-dimensional lattices, even in the presence of anharmonic interatomic interactions-a direct consequence of the Fermi-Pasta-Ulam-Tsingou paradox proposed in 19555. This length dependence of κ, also known as superdiffusive phonon transport, presents a classical anomaly of continued interest6-9. So far the concept has remained purely theoretical, because isolated single atomic chains of sufficient length have been experimentally unattainable. Here we report on the observation of a length-dependent κ extending over 42.5 µm at room temperature for ultrathin van der Waals crystal NbSe3 nanowires. We found that κ follows a 1/3 power law with wire length, which provides experimental evidence pointing towards superdiffusive phonon transport. Contrary to the classical size effect due to phonon-boundary scattering, the observed κ shows a 25-fold enhancement as the characteristic size of the nanowires decreases from 26 to 6.8 nm while displaying a normal-superdiffusive transition. Our analysis indicates that these intriguing observations stem from the transport of one-dimensional phonons excited as a result of elastic stiffening with a fivefold enhancement of Young's modulus. The persistent divergent trend of the observed thermal conductivity with sample length reveals a real possibility of creating novel van der Waals crystal-based thermal superconductors with κ values higher than those of any known materials.

Charge and Thermoelectric Transport in Polymer-Sorted Semiconducting Single-Walled Carbon Nanotube Networks.

Understanding the charge transport mechanisms in chirality-selected single-walled carbon nanotube (SWCNT) networks and the influence of network parameters is essential for further advances of their optoelectronic and thermoelectric applications. Here, we report on charge density and temperature-dependent field-effect mobility and on-chip field-effect-modulated Seebeck coefficient measurements of polymer-sorted monochiral small-diameter (6,5) (0.76 nm) and mixed large-diameter SWCNT (1.17-1.55 nm) networks (plasma torch nanotubes, RN) with different network densities and length distributions. All untreated networks display balanced ambipolar transport and electron-hole symmetric Seebeck coefficients. We show that charge and thermoelectric transport in SWCNT networks can be modeled by the Boltzmann transport formalism, incorporating transport in heterogeneous media and fluctuation-induced tunneling. Considering the diameter-dependent one-dimensional density of states (DoS) of the SWCNTs composing the network, we can simulate the charge density and temperature-dependent Seebeck coefficients. Our simulations suggest that scattering in these networks cannot be described as simple one-dimensional acoustic and optical phonon scattering as for single SWCNTs. Instead the relaxation time is inversely proportional to energy (τ ∝ (E - EC)s, s = -1, EC being the energy of the first van Hove singularity), presumably pointing toward the more two-dimensional character of scattering events and the necessity to include scattering at the SWCNT junctions. Finally, our observation of higher power factors in trap-free, 1,2,4,5-tetrakis(tetramethylguanidino)benzene-treated (6,5) networks than in the RN networks emphasizes the importance of chirality selection to tune the width of the DoS. To benefit from both higher intrinsic mobilities and a large thermally accessible DoS, we propose trap-free, narrow DoS distribution, large-diameter SWCNT networks for both electronic and thermoelectric applications.

An antiferromagnet as a tunable single-phase elastic hyperbolic medium with spatial dispersion

For a plane and quasi-plane SH-type bulk wave incident from the outside onto a system of equidistant antiferromagnetic dielectric layers, the inclusion of the spatial dispersion in the antiferromagnet as a hyperbolic magnetoacoustic medium induces a number of resonant refractive anomalies: the effects of total reflection (transmission) and the formation of discrete localized magnon-phonon states against the continuous spectrum, the amplification of the angular Schoch effect, and in the case of a one-dimensional resonant magnetic phonon crystal, the acoustic superradiance effect.

High-Efficiency Elastic Wave Rectifier in One-Dimensional Linear Magnetoelastic Phononic Crystal Slabs by an External Magnetostatic Field

Reciprocity is a fundamental property of wave propagation in linear time-invariant media. However, it is substantially harder to break reciprocity for elastic waves in a linear elastic system with the help of a magnetostatic field, since elastic waves are spinless in nature. Here, we realize nonreciprocal elastic waves in one-dimensional linear magnetoelastic phononic crystal slabs by an external magnetostatic field. The asymmetric dispersion of spin waves, which is induced by the simultaneous breaking of the time-reversal and spatial-inversion symmetries, results in an efficient elastic wave diode effect in a periodic system due to magnetoelastic interactions. Remarkably, a bidirectional nonreciprocity of elastic waves is achieved based on the folding-back effect of the periodic structure. Our proposed scheme opens up avenues for the design of nonreciprocal devices, such as on-chip tunable diodes, rectifiers, and topological insulators.

Nanoscale Quantum Thermal Conductance at Water Interface: Green's Function Approach Based on One-Dimensional Phonon Model.

We have derived the fundamental formula of phonon transport in water for the evaluation of quantum thermal conductance by using a one-dimensional phonon model based on the nonequilibrium Green’s function method. In our model, phonons are excited as quantum waves from the left or right reservoir and propagate from left to right of HO layer or vice versa. We have assumed these reservoirs as being of periodic structures, whereas we can also model the HO sandwiched between these reservoirs as having aperiodic structures of liquid containing N water molecules. We have extracted the dispersion curves from the experimental absorption spectra of the OH stretching and intermolecular modes of water molecules, and calculated phonon transmission function and quantum thermal conductance. In addition, we have simplified the formulation of the transmission function by employing a case of one water molecule (N=1). From this calculation, we have obtained the characteristic that the transmission probability is almost unity at the frequency bands of acoustic and optical modes, and the transmission probability vanishes by the phonon attenuation reflecting the quantum tunnel effect outside the bands of these two modes. The classical limit of the thermal conductance calculated by our formula agreed with the literature value (order of W/K) in high temperature regime (>300 K). The present approach is powerful enough to be applicable to molecular systems containing proteins as well, and to evaluate their thermal conductive characteristics.

Anisotropic surface phonon dispersion of a deuterium-terminated Si(110)-(1 × 1) surface studied by high-resolution electron-energy-loss spectroscopy and first-principles calculations: Isotope effect

The surface phonon dispersion of a deuterium-terminated Si(110)-(1 × 1) surface [D:Si(110)-(1 × 1)] is investigated by using high-resolution electron-energy-loss spectroscopy (HREELS) and first-principles calculations based on the density functional theory (DFT) with the local density approximation (LDA). The characteristics of D:Si(110)-(1 × 1) are unique compared to those of H:Si(110)-(1 × 1) (Matsushita et al., 2015) in terms of the resolved vibrational modes. By the HREELS, one-dimensional surface phonons consisting of D–Si stretching vibrations are observed above the bulk-phonon band energy edge of 64.5 meV. Ten modes are observed below this value, classified as surface, surface resonant, and bulk phonons according to the calculated energy dispersion as well as the depth profile of spectral density and displacement vectors. In particular, five D–Si bending modes are observed out of the seven theoretically predicted modes. The bending modes are strongly coupled with the displacements across the D and five Si layers. The DFT-LDA surface phonon dispersion is in good agreement with the experimental results except a few frequency/dispersion mismatches, as the structure optimized by DFT-LDA mismatches with the previous scanning tunneling microscopy (STM) results (Matsushita et al., 2015). D:Si(110)-(1 × 1) elucidates the nature of covalently bonded phonons and their characteristics both experimentally and theoretically.

Low temperature heat capacity study of Zn, Cd and Mn based coordination compounds synthesized using phenanthroline and halogenated benzoic acid

Four Zn, Cd and Mn based 1,10-phenanthroline and halogenated benzoic acid coordination compounds, formulated as Zn2II(H2O)3(phen)(SO4)·H2O (1, phen = 1,10-phenanthroline), ZnII(phen)(L2)2(H2O) (2, L2 = 2-chloro-4-fluorobenzoic acid), MnIV(phen)(L1)4 (3, L1 = 2-Chloro-4,5-difluorobenzoic acid) and CdII(phen)2(NO3)2 (4), were successfully synthesized and structurally characterized. The low temperature heat capacities of these four compounds were further investigated using a Physical Property Measurement System calorimetric method. The experimental heat capacities were fitted to a series of theoretical and empirical heat capacity models, and the corresponding thermodynamic functions were calculated in the temperature range from (0 to 300) K based on these models and fitting parameters. The low temperature fits indicated that compound 1 can be modeled using only lattice heat capacity contribution, compound 3 modeled using lattice and A-2 term or Schottky heat capacity contributions, and compound 2 and 4 modeled using contributions from lattice, vacancies and one-dimensional phonons with a finite energy onset or gap.

Topological Interface States of Shear Horizontal Guided Wave in One‐Dimensional Phononic Quasicrystal Slabs

In this Letter, the topological interface states of shear horizontal guided wave are investigated in a one‐dimension (1D) phononic quasicrystal system. It has been found that multiple interface modes can occur at the interface of two Fibonacci sequences slabs. The occurrence of the interface states is determined by the condition that the sum of the left and right surface impedances of the interface is equal to zero. Most significantly, as the generation number of the Fibonacci sequence increases, more interface states will come into being at the interface of the quasi‐periodic slabs, which is caused by the accumulation of the detuning. This study of the topological interface states in phononic quasicrystals will greatly enrich the knowledge on the topology and broaden its application scopes.

Bandgap Structures of SH-Wave in a One-Dimensional Phononic Crystal with Viscoelastic Interfaces

Phononic crystal is an artificial periodic structure with the ability to regulate and control the wave propagation of particular frequencies and has been widely used in many applications. The adhesive layer bonding different constituents in the periodic structure of phononic crystals is usually a viscoelastic material, which has frequency-dependent material properties. In this paper, an analytical model based on the transfer matrix method is developed to study the bandgap structures of SH-wave (a shear wave with the propagation direction normal to the motion plane) in a one-dimensional phononic crystal consisting of two different elastic constituents bonded by the viscoelastic adhesive layer. The results show that the viscosity of the adhesive layer has a significant influence on the bandgap structure at the region of high frequency. The effects of various material parameters of the viscoelastic adhesive layer such as the relaxation time, the final-state modulus and the initial-state modulus are systematically studied. These results are very helpful in the practical design of phononic crystals involving the viscoelastic adhesive layers.

Exploiting One-Dimensional Exciton-Phonon Coupling for Tunable and Efficient Single-Photon Generation with a Carbon Nanotube.

Condensed-matter emitters offer enriched cavity quantum electrodynamical effects due to the coupling to external degrees of freedom. In the case of carbon nanotubes, a very peculiar coupling between localized excitons and the one-dimensional acoustic phonon modes can be achieved, which gives rise to pronounced phonon wings in the luminescence spectrum. By coupling an individual nanotube to a tunable optical microcavity, we show that this peculiar exciton-phonon coupling is a valuable resource to enlarge the tuning range of the single-photon source while keeping an excellent exciton-photon coupling efficiency and spectral purity. Using the unique flexibility of our scanning fiber cavity, we are able to measure the efficiency spectrum of the very same nanotube in the Purcell regime for several mode volumes. Whereas this efficiency spectrum looks very much like the free-space luminescence spectrum when the Purcell factor is small (large mode volume), we show that the deformation of this spectrum at lower mode volumes can be traced back to the strength of the exciton-photon coupling. It shows an enhanced efficiency on the red wing that arises from the asymmetry of the incoherent energy exchange processes between the exciton and the cavity. This allows us to obtain a tuning range up to several hundred times the spectral width of the source.

An efficient two-step Monte Carlo method for heat conduction in nanostructures

Research on the heat conduction in nanostructures has drawn much attention due to their potential applications in thermoelectric devices. Although the phonon tracing Monte Carlo (MC) technique, where the trajectories of individual phonons are simulated independently, has been extensively used for simulating the heat conduction in nanomaterials, it cannot efficiently simulate the phonon transport in the large area periodic nanostructures yet, due to the demand of absorbing boundaries. In the present work, we develop a two-step phonon tracing MC method to solve this problem. At the first step, the initial phonon transmittance and the phonon emission distributions at the internal virtual boundary are obtained by simulating phonon transport in the initial simulation unit that is directly in contact with the phonon bath. At the second step, the internal phonon transmittance is calculated for the internal simulation units according to the internal boundary phonon emission distributions. Since the whole structure can be simplified as a one-dimensional phonon transport system, the total phonon transmittance can be readily calculated via the combination of initial and internal phonon transmittances, and the effective thermal conductivity is then derived. Furthermore, for verification, we calculate the effective thermal conductivities of three typical nanostructures, that is, the cross-plane and in-plane nanofilms and the periodic nanoporous structures, by using the theoretical models, the standard and the two-step MC simulations, respectively. The two-step MC method well predicts the results calculated by the standard MC simulations and the theoretical models. More importantly, the computation time of the two-step MC simulation is at least one order of magnitude less than that of the standard MC simulation, while its under-prediction can be less than 10% even 5%.