Phonon Flux Research Articles

Phonon Drag Contribution to Thermopower for a Heated Metal Nanoisland on a Semiconductor Substrate.

The possible contribution of phonon drag effect to the thermoelectrically sustained potential of a heated nanoisland on a semiconductor surface was estimated in a first principal consideration. We regarded electrons and phonons as interacting particles, and the interaction cross-section was derived from the basic theory of semiconductors. The solution of the equation of motion for average electrons under the simultaneous action of phonon drag and electric field gave the distributions of phonon flux, density of charge carriers and electric potential. Dimensional suppression of thermal conductance and electron-phonon interaction were accounted for but found to be less effective than expected. The developed model predicts the formation of a layer with a high density of charge carriers that is practically independent of the concentration of dopant ions. This layer can effectively intercept the phonon flow propagating from the heated nanoisland. The resulting thermoEMF can have sufficient magnitudes to explain the low-voltage electron emission capability of nanoisland films of metals and sp2-bonded carbon, previously studied by our group. The phenomenon predicted by the model can be used in thermoelectric converters with untypical parameters or in systems for local cooling.

Phonon and Magnon Jets above the Critical Current in Nanowires with Planar Domain Walls.

We show through nonequilibrium nonadiabatic electron-spin-lattice simulations that above a critical current in magnetic atomic wires with a narrow domain wall (DW), a couple of atomic spaces in width, the electron flow triggers violent stimulated emission of phonons and magnons with an almost complete conversion of the incident electron momentum flux into a phonon and magnon flux. Just below the critical levels of the current flow, the DW achieves maximal velocity of about 3×10^{4} m/s, entering a strongly nonadiabatic regime of DW propagation, followed by a breakdown at higher biases. Above this threshold, a further increase of the current with the applied bias is impossible-the electronic current suffers a heavy suppression and the DW stops. This poses a fundamental limit to the current densities attainable in atomic wires. At the same time it opens up an exciting way of generating the alternative quasiparticle currents, described above, once the requisite electronic-structure properties are met.

Parabolic mirrors collimating and focusing fluxes of thermal phonons

Manipulating heat fluxes at the nanoscale has become increasingly important in modern microelectronics. However, many methods of heat manipulations rely on complex nanofabrication. Here, we propose simple designs for collimation and focusing of thermal phonons based on parabolic mirrors that require no nanofabrication. We perform Monte Carlo simulations of a ballistic phonon transport in silicon membranes with parabolic boundaries. Our simulations demonstrate that parabolic surfaces can act as parabolic mirrors for phonons, thus collimating or focusing phonon fluxes in semiconductors. Such parabolic mirrors can create a directional flux of thermal phonons emitted from a nanoscale hot spot or focus a collimated phonon flux into a hot spot. These devices open new possibilities in the thermal management of low-temperature systems, such as quantum circuits or cryogenic particle detectors.

Phonon downconversion to suppress correlated errors in superconducting qubits

Quantum error correction can preserve quantum information in the presence of local errors, but correlated errors are fatal. For superconducting qubits, high-energy particle impacts from background radioactivity produce energetic phonons that travel throughout the substrate and create excitations above the superconducting ground state, known as quasiparticles, which can poison all qubits on the chip. We use normal metal reservoirs on the chip back side to downconvert phonons to low energies where they can no longer poison qubits. We introduce a pump-probe scheme involving controlled injection of pair-breaking phonons into the qubit chips. We examine quasiparticle poisoning on chips with and without back-side metallization and demonstrate a reduction in the flux of pair-breaking phonons by over a factor of 20. We use a Ramsey interferometer scheme to simultaneously monitor quasiparticle parity on three qubits for each chip and observe a two-order of magnitude reduction in correlated poisoning due to background radiation.

Probabilistic description for quasiparticle heat transport in one-dimensional nanostructures

Within the framework of the theory of random walks, we present an analytical study of one-dimensional ballistic flux of quasiparticles in the presence of scattering centers (SCs) such as defects or dopants. An explicit analytical expression is derived for the quasiparticle flux and the associated heat flux carried by phonons as a function of the number of SCs and the probabilities of (i) forward and backward scattering at SCs and (ii) absorption of quasiparticles by the SCs and in the conductor between SCs. The practical application of our model to one-dimensional nanostructures and to quasi-one-dimensional heat-conducting systems such as linear polycrystals is discussed. Various limiting cases are also considered. We demonstrate that our model is in excellent agreement with experimental data on the thermal conductance of Si nanowires having geometrically modified S-shaped extremities that act as SCs to the phonon flux.

Purely spatial diffusion of H atoms in solid normal- and para-hydrogen films

We present an experimental study of quantum diffusion of atomic hydrogen in solid ${\mathrm{H}}_{2}$ films at temperatures below $1\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The atoms are generated via electron impact dissociation by running a continuous rf discharge in helium gas above the ${\mathrm{H}}_{2}$ film for long (up to 30 days) times. We are able to distinguish between the diffusion of the atoms moving towards each other followed by their recombination and the pure spatial diffusion driven by the density gradient. We found that in both cases the flux of phonons generated by the discharge above the surface of molecular film is essential to observe the slow diffusive motion. We obtained rates of pure spatial diffusion of H atoms in normal-${\mathrm{H}}_{2}$ (75% ortho, 25% para) films which were two orders of magnitude faster than those obtained from the H atom recombination, the quantity used in all previous work to characterize the mobility of H atoms in solid ${\mathrm{H}}_{2}$. We investigated the influence of the film thickness and its ortho-para composition on recombination and pure spatial diffusion. For thin enough films of 0.16 $\ensuremath{\mu}\mathrm{m}$ we observed complete diffusion of the H atoms through the entire film thickness. We observed peculiar behavior of the samples with ortho-${\mathrm{H}}_{2}$ ($o\text{\ensuremath{-}}{\mathrm{H}}_{2}$) concentration below $5%$. The recombination rate in these samples was an order of magnitude faster while the rate of spatial diffusion was somewhat slower than in films containing larger $o\text{\ensuremath{-}}{\mathrm{H}}_{2}$ concentrations. The rate of production of H atoms in the low $o\text{\ensuremath{-}}{\mathrm{H}}_{2}$ samples turned out to be an order of magnitude larger. We discuss possible explanations of these somewhat contradictory observations.

Hawking radiation from acoustic black holes in relativistic heavy ion collisions

We propose a new analogue model of gravity - the evolving quark gluon plasma (QGP) produced in relativistic heavy ion collisions. This quark gluon plasma is the “most inviscid” fluid known. Such low kinematic viscosity is believed to reflect strongly correlated nature for QGP in these experiments. Hence, it may provide a good example of a quantum fluid naturally suited to studies of acoustic Hawking radiation. Due to rapid longitudinal expansion, presence of a sonic horizon is also naturally guaranteed here, though, in general, this horizon is not static. Using Ultra relativistic quantum molecular dynamics (UrQMD) simulations, we show that, under certain conditions, the longitudinal velocity of the plasma, near the sonic horizon, can become time independent for a short span during the evolution of the system. During this period, we can have a conformally static acoustic metric with a (conformal) Killing horizon coinciding with the apparent horizon. An asymptotic observer will then see a thermal flux of phonons, constituting the Hawking radiation, coming from the horizon. For the relatively low energy collision considered here, where the resulting QCD system is governed by non-relativistic hydrodynamics, we estimate the Hawking temperature to be about 4-5 MeV (with the temperature of the QCD fluid being about 135 MeV). We discuss the experimental signatures of this Hawking radiation in terms of a thermal component in the rapidity dependence of the transverse momentum distribution of detected particles. We also discuss extension to ultra-relativistic case which should lead to a higher Hawking temperature, along with the effects of dynamical horizon leading to blue/red shift of the temperature.

Phonon drag thermoelectric phenomena in mesoscopic two-dimensional conductors: Current stripes, large Nernst effect, and influence of electron-electron interaction

The interaction of electrons with a flux of ballistic phonons leads to excitation of many angular harmonics of an electron distribution function. We show that this property dramatically modifies the magnetothermoelectric phenomena in two-dimensional electron systems with boundaries. By considering classical magnetotransport of electrons in a narrow channel with partly diffusive boundary scattering, we show that the phonon flux excites a pattern of current stripes with alternating directions of propagation along the channel. The Nernst voltage due to phonon drag appears already in the classical transport regime and can be comparable with the Seebeck voltage, while the latter acquires a dependence on the magnetic field. The temperature dependence of these voltages shows an unusual behavior determined by relaxation of higher-order harmonics of the distribution function via electron-electron scattering. Our experimental studies of mesoscopic samples based on high-quality GaAs quantum wells confirm the main properties of the thermoelectric response suggested by the theory.

Nanomechanical test of quantum linearity

Spontaneous wavefunction collapse theories provide the possibility to resolve the measurement problem of quantum mechanics. However, the best experimental tests have been limited by thermal fluctuations and have operated at frequencies far below those conjectured to allow the proposed cosmological origin of collapse to be identified. Here we propose to use high-frequency nanomechanical resonators to surpass these limitations. We consider a specific implementation that uses a breathing mode of a quantum optomechanical system cooled to near its motional ground state. The scheme combines phonon counting with efficient mitigation of technical noise, including nonlinear photon conversion and photon coincidence counting. It can resolve the exquisitely small phonon fluxes required for a conclusive test of collapse models as well as testing the hypothesis of a cosmological origin of the collapse noise.

Anisotropy affects the lattice waves and phonon distributions in GaAs

The stress-strain relationship, anisotropy, heavy- and light-hole structures, and the Phillips ionicity in GaAs are theoretically investigated by Bond matrices model as well as Zener and Every anisotropies. The results show that there is a simple correspondence between anisotropy and the extreme directions of these physical properties, i.e., [0 0 1], [1 1 0] and [1 1 1] directions. Meanwhile the lattice wave propagation, phonon focusing, and phonon distributions in GaAs are also theoretically studied in detail based on lattice-dynamical method. The slowness surface of three lattice waves are the mixing of longitudinal and transverse modes. The feature is that the lattice waves, saddle Gaussian curvatures, and caustic structures are modulated by the anisotropy. The topology in phonon distribution is discussed by the presence of caustics in the anisotropic flux of phonons emanating from a localized phonon distribution. Their topological structures show the phonon distribution and the phonon focusing. The anisotropy not only affects lattice wave propagation and phonon distribution, but influences the phonon focusing.

Dynamical stabilities of photosynthesis systems: Quantum chaos approach

Abstract Bio-based materials offer new potentialities for photodetection applications due to their sensitivity, selectivity and biocompatibility. The present paper proposes an energy transfer mechanism associated with the incident light frequency. Based on the premise that the competition between the electrical current and phonon flux determines the dominant behavior, the paper reveals that the decrease in electrical current is compensated by increasing the phonon flux, and vice versa. Through simulating the internal potential difference using the metal leads, the study has focused on the difference between the electrical current and electrical potential difference. This makes it possible to determine the regions with the maximum electrical current. Furthermore, the paper investigates the efficient frequencies of the system through the fidelity, and level spacing distribution (P(s)) methods. The study indicates that the maximum efficiency is observed near the red and purple spectrum of the incident light confirmed by previous observations.

Elastic properties and lattice waves of TiAl

The elastic properties, lattice wave propagation and phonon focusing of TiAl are studied in detail based on Bond matrices model and lattice-dynamical method. The results contain remarkably complex three-dimensional variations in the phonon flux with angular distribution. The feature of elastic waves and phonon distribution is affected by the elastic anisotropy of the lattice. The correspondence between these features and contours of Gaussian curvature on the slowness surface is explored and the phonon topology is discussed about the presence of caustics in the anistropic flux of phonons emanating from a localized phonon distribution. The topology slowness surface gives insights into the mixing of longitudinal and transverse modes and gives the origin of the phonon focusing. The elastic anisotropy not only affects lattice wave propagation but also influences phonon focusing.

Detecting a phonon flux in superfluid He4 by a nanomechanical resonator

Nanoscale mechanical resonators are widely utilized to provide high sensitivity force detectors. Here we demonstrate that such high quality factor resonators immersed in superfluid \(^4\mathrm{He}\) can be excited by a modulated flux of phonons. A nanosized heater immersed in superfluid \(^4\mathrm{He}\) acts as a source of ballistic phonons in the liquid -- "phonon wind". When the modulation frequency of the phonon flux matches the resonance frequency of the mechanical resonator, the motion of the latter can be excited. This ballistic thermomechanical effect can potentially open up new types of experiments in quantum fluids.

Measurements and Simulations of Athermal Phonon Transmission from Silicon Absorbers to Aluminum Sensors

Phonon reflection and transmission at the interfaces plays a fundamental role in cryogenic particle detectors, in which the optimization of the phonon signal at the sensor (in case of phonon-mediated detectors) or the minimization of the heat transmission (when the detection occurs in the sensor itself) is of primary importance to improve sensitivity. Nevertheless, the mechanisms governing the phonon physics at the interfaces are still not completely understood. The two more successful models, the acoustic mismatch model (AMM) and diffuse mismatch model (DMM) are not able to explain all the accumulated experimental data and the measurement of the transmission coefficients between the materials remains a challenge. Here, we use measurements of the athermal phonon flux in aluminium Kinetic Inductance Detectors (KID) deposited on silicon substrates following a particle interaction to validate a Monte Carlo (MC) phonon simulation. We apply the Mattis-Bardeen theory to derive the phonon pulse energy and timing from the KID signal and compare the results with the MC for both AMM and DMM models, finding a remarkable good agreement for AMM, while diffuse reflection is clearly disfavored. For an aluminum film of 60 nm and a silicon substrate of 380~$\mu$m, we obtain transmission coefficients Si-Al in the range [0.3-0.55] and Si-Teflon in the range [0.1-0.15].

Monte Carlo simulations for phonon transport in silicon nanomaterials

In nanostructures phonon transport behaviour is distinctly different to transport in bulk materials such that materials with ultra-low thermal conductivities and enhanced thermoelectric performance can be realized. Low thermal conductivities have been achieved in nanocrystalline materials that include hierarchical sizes of inclusions and pores. Nanoporous structures present a promising set of material properties and structures which allow for ultra-low thermal conductivity - even below the amorphous limit. In this paper we outline a semi-classical Monte Carlo code for the study of phonon transport and present an investigation of the thermal conductivity in nanoporous and nanocrystalline silicon. Different disordered geometry configurations are incorporated to investigate the effects of pores and grain boundaries on the phonon flux and the thermal conductivity, including the effects of boundary roughness, pore position and pore diameter. At constant porosity, thermal conductivity reduction is maximized by having a large number of smaller diameter pores as compared to a small number of larger diameter pores. Furthermore, we show that porosity has a greater impact on thermal conductivity than the degree of boundary roughness. Our simulator is validated across multiple simulation and experimental works for both pristine silicon channels and nanoporous structures

Effect of Magnon–Magnon Drag on Spin-Wave Current in Metal/Magnetic-Insulator Structures

This paper presents the results of our investigation of the formation and interaction of two injected and thermally excited energetically distinguishable magnon fluxes and phonon flux in metal/magnetic-insulator structures and their influence on spin-wave current and drag effect. These have been studied under the conditions of the spin Seebeck effect. In the approximation of effective parameters, when the fluxes of magnons and phonons are characterized by their specific drift velocities and effective temperatures, we constructed macroscopic equations of the balance of the momenta of each of the subsystems in question. The analysis of the macroscopic equations was performed at different relationships between the drift velocities of these fluxes. The study has shown that it is possible that the basic channel of scattering of the injected magnons is the interaction with thermal magnons, and it is precisely this interaction that determines the temperature–field dependences of the spin-wave current under the conditions of spin Seebeck effect.

Phonon Flux Enhancement Factors in Crystals with Different Elastic Energy Anisotropy Types

Phonon pulse propagation in cubic crystals with different elastic energy anisotropy types is considered. A closed analytical expression is derived for the phonon flux enhancement factor. The features of its dependences on the isoenergetic surface curvature types are analyzed for all acoustic modes and anisotropy parameter values and signs.

Коэффициенты усиления потока фононов в кристаллах с различным типом анизотропии упругой энергии

AbstractPhonon pulse propagation in cubic crystals with different elastic energy anisotropy types is considered. A closed analytical expression is derived for the phonon flux enhancement factor. The features of its dependences on the isoenergetic surface curvature types are analyzed for all acoustic modes and anisotropy parameter values and signs.

Brillouin cooling in a linear waveguide

Brillouin scattering is not usually considered as a mechanism that can cause cooling of a material due to the thermodynamic dominance of Stokes scattering in most practical systems. However, it has been shown in experiments on resonators that net phonon annihilation through anti-Stokes Brillouin scattering can be enabled by means of a suitable set of optical and acoustic states. The cooling of traveling phonons in a linear waveguide, on the other hand, could lead to the exciting future prospect of manipulating unidirectional phonon fluxes and even the nonreciprocal transport of quantum information via phonons. In this work, we present an analysis of the conditions under which Brillouin cooling of phonons of both low and high group velocities may be achieved in a linear waveguide. We analyze the three-wave mixing interaction between the optical and traveling acoustic modes that participate in forward Brillouin scattering, and reveal the key regimes of operation for the process. Our calculations indicate that measurable cooling may occur in a system having phonons with spatial loss rate that is of the same order as the spatial optical loss rate. If the Brillouin gain in such a waveguide reaches the order of 105 m−1 W−1, appreciable cooling of phonon modes may be observed with modest pump power of a few mW.

Phonon Guided Biology. Architecture of Life and Conscious Perception Are Mediated by Toroidal Coupling of Phonon, Photon and Electron Information Fluxes at Discrete Eigenfrequencies.

Recently, a novel biological principle, revealing specific electromagnetic (EM) radiation frequencies that sustain life, was presented by us on the basis of an evaluation of 175 biological articles concerning beneficial effects of electromagnetic waves on the state of living cells. This concept was also based on a very similar range of frequencies emitted by a clay-mineral catalyst of RNA synthesis that may have been instrumental in the evolutionary initiation of first life, and therefore was tentatively designated as “Algorithm of Life”. The particular spectrum of frequency bands indicate that nature seems to employ discrete eigenfrequencies or standing waves that match precisely with an acoustic scale, with frequency ratios of 1:2, and closely approximated by 2:3, 3:4, 3:5, 4:5 and higher partials, allowing the discrete frequencies to be expressed in scalars. Our further studies clearly indicate now that this “life algorithm” pattern matches very well with the mathematical calculations of W. Ritz (1909) to compute eigenfrequencies of the sound induced geometric patterns. These have been earlier demonstrated through membrane vibration experiments of E. Chladni (1787), as well as several follow up studies from 1970-2013. Our findings, therefore, touch upon the science of acoustics, also since we show that the discrete frequencies could be modeled by music torus geometry. We postulate that the spectrum of EM frequencies detected, exhibit a quantum ordering effect on life cells on the basis of induction of geometric wave patterns. These constitute phonon/photon and electron wave energies, and quantum oscillations at far-infrared frequencies, that are communicated through toroidal constructive interference into scalar wave information. This idea is supported through our identification of potential intrinsic toroidal eigenfrequencies and minimal energy levels. The particular torus topology for information processing may also provide quantum error correction and protection against decoherence. Finally we propose a phonon guided organization of cells and integral brain function by three elementary processes: 1) A phonon mediated geometric organization of coherent arrangement of water molecules in cellular plasma, leading to instructive functional organization of cellular structures and metabolic processes and enabling the origination and sustainment of life processes. 2) Toroidal phonon/photon/electron coupling, protecting standing wave coherency of resonant cell components such as proteins and DNA. 3) A toroidal integration of electromagnetic and phononic fluxes of information into scalar standing waves, promoting quantum flux of informational excitons such as Ca2+- ions and electrons (polaron and polariton formation). Our brain, therefore, can be placed in a 4+1 geometry, supported by internal and external quantum states and makes use of geometrical defined information fluxes, that are converted to standing waves. The integration of these interrelated processes is considered to be instrumental in the creation of conscious perception and is proposed to be organized in a fractal, nested, 4-D toroidal geometry.