Takuma Sato, Weichao Yu, Simon Streib, Gerrit E. W. Bauer
We derive boundary conditions at the interfaces of magnetoelastic heterostructures under ferromagnetic resonance for arbitrary magnetization directions and interface shapes. We apply our formalism to magnet$\vert$nonmagnet bilayers and magnetic grains embedded in a nonmagnetic thin film, revealing a nontrivial magnetization angle dependence of acoustic phonon pumping.
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Parallel pumping of nuclear spin waves in antiferromagnetic CsMnF3 at liquid helium temperatures and magnetoelastic waves in antiferromagnetic FeBO3 at liquid nitrogen temperature in a helical resonator was studied. It was found that the absorbed microwave power is approximately equal to the irradiated power from the sample and that the main restriction mechanism of absortption in both cases is defined by the nonlinear radiation damping predicted about two decades ago. We believe that the nonlinear radiation damping is a common feature of parallel pumping technique of all normal magnetic excit…
Valley-Selective Phonon-Magnon Scattering in Magnetoelastic Superlattices
本研究利用非互易表面声波透射，在磁弹性超晶格中证明由晶格对称性和面外磁化控制的能谷选择性声子–磁振子散射，为磁场调控能谷声子输运提供途径。
We study the topological property of the magnetoelastic excitation in non-collinear antiferromagnets. As a toy model, we consider the magnon-phonon coupling in a triangular antiferromagnet with a $120^\circ$ Nèel order. We find that in the presence of out-of-plane external magnetic field, the magnon-polaron bands, which arise from hybridization of magnons and phonons, can carry Chern number, even though the individual magnon and phonon bands are topologically trivial. Large Berry curvature is induced from the anti-crossing regions between the magnon and phonon bands, which renormalizes the the…
Motivated by recent experiments, we investigate the nonreciprocal magnetoelastic interaction between the surface acoustic phonons of dielectric non-magnetic substrates and magnons of proximity nanomagnets. The magnetization dynamics exerts rotating forces at the edges of the nanomagnet that causes the nonreciprocal interaction with surface phonons due to its rotation-momentum locking. This coupling induces the nonreciprocity of the surface phonon transmission and a nearly complete phonon diode effect by several (tens of) magnetic nanowires of high (ordinary) magnetic quality. Phase-sensitive m…
Chiral phonons induced from spin dynamics via magnetoelastic anisotropy
本文提出通过键依赖磁弹耦合在无面外磁化条件下诱导手性声子，揭示晶格对称性对手性的影响，并以三角晶格铁磁体为例展示面内磁场可调的手性与拓扑，为自旋电子学和声子学应用提供新思路。
Phonon Amplification via Magnetoelastic Klein Scattering
本研究提出由非磁性与铁磁性绝缘体构成的装置，借助自旋轨道矩产生负能量磁振子，通过磁弹性Klein散射实现入射声子流放大，为结合声子与磁振子特性的纳米器件研发提供新思路。
Inertial mass of a skyrmion arising from spin-phonon interaction is computed exactly within a toy model of the magnetoelastic coupling in a ferromagnetic film. The mass scales as the square of the strength of the magnetoelastic coupling, as the square of the film thickness, and as the first power of the lateral size of the skyrmion. For nanometer skyrmions it is in the ballpark of a few electron masses but may be significantly greater in materials with large magnetostriction. These findings are expected to stand for any complex structure of spin-phonon interaction in real materials. They must …
We theoretically investigate pumping of phonons by the dynamics of a magnetic film into a non-magnetic contact. The enhanced damping due to the loss of energy and angular momentum shows interference patterns as a function of resonance frequency and magnetic film thickness that cannot be described by viscous ("Gilbert") damping. The phonon pumping depends on magnetization direction as well as geometrical and material parameters and is observable, e.g., in thin films of yttrium iron garnet on a thick dielectric substrate.
We propose a method to control surface phonon transport by weak magnetic fields based on the pumping of surface acoustic waves (SAWs) by magnetostriction. We predict that the magnetization dynamics of a nanowire on top of a dielectric films injects SAWs with opposite angular momenta into opposite directions. Two parallel nanowires form a phononic cavity that at magnetic resonances pump a unidirectional SAW current into half of the substrate.
"Pumping" of phonons by a dynamic magnetization promises to extend the range and functionality of magnonic devices. We explore the impact of phonon pumping on room-temperature ferromagnetic resonance (FMR) spectra of bilayers of thin yttrium iron garnet (YIG) films on thick gadolinium gallium garnet substrates over a wide frequency range. At low frequencies the Kittel mode hybridizes coherently with standing ultrasound waves of a bulk acoustic resonator to form magnon polarons that induce rapid oscillations of the magnetic susceptibility, as reported before. At higher frequencies, the phonon r…
Theory of polarization-dependent phonon pumping in ferromagnetic/non-magnetic bilayers
本研究建立铁磁/非磁双层结构中磁振子-声子耦合诱导偏振选择声子泵浦的理论模型，揭示磁轴与晶轴不对齐引发声子双折射、磁振子-声子杂化赋予声子磁场依赖特性，且偏振转移可由外磁场调控，定量复现了实验结果。
Magnetoelastic coupling in stripe-domain states of yttrium iron garnet
该研究针对GGG衬底上的3μm厚YIG薄膜，通过铁磁共振和有限元模拟揭示其条纹畴态中磁振子-声子弱耦合源于相位与畴符号抵消，确立磁织构可作为磁振子-声子耦合的控制参数。
Optical probing of magnons and phonons in Ni80Fe20 nanodot arrays
研究通过光学探测Ni80Fe20纳米点阵列中磁子和声子的相互作用，揭示了磁弹性效应在设计高效磁声设备中的作用。
We investigate phonon spin transport in an insulating ferromagnet-nonmagnet-ferromagnet heterostructure. We show that the magnetoelastic interaction between the spins and the phonons leads to nonlocal spin transfer between the magnets. This transfer is mediated by a local phonon spin current and accompanied by a phonon spin accumulation. The spin conductance depends nontrivially on the system size, and decays over millimeter length scales for realistic material parameters, far exceeding the decay lengths of magnonic spin currents.
We propose using a phonon pumping mechanism to transfer heat from a cold to a hot body using a propagating modulation of the medium connecting the two bodies. This phonon pump can cool nanomechanical systems without the need for active feedback. We compute the lowest temperature that this refrigerator can achieve.
Classical and quantum theory of magnonic and magnetoelastic nonlinear dynamics in continuum geometries
本文提出了一种结合经典与量子理论的磁声非线性动力学模型，用于连续几何结构，实现了磁子与声子的耦合动力学分析，并展示了其在量子化中的应用。
The spin dynamics of a single Mn atom in a laser driven CdTe quantum dot is addressed theoretically. Recent experimental results\cite{Le-Gall_PRL_2009,Goryca_PRL_2009,Le-Gall_PRB_2010}show that it is possible to induce Mn spin polarization by means of circularly polarized optical pumping. Pumping is made possible by the faster Mn spin relaxation in the presence of the exciton. Here we discuss different Mn spin relaxation mechanisms. First, Mn-phonon coupling, which is enhanced in the presence of the exciton. Second, phonon-induced hole spin relaxation combined with carrier-Mn spin flip couplin…
Orbital Pumping Incorporating Both Orbital Angular Momentum and Position
本文提出绝热轨道泵浦理论，发现振荡磁场可同时泵浦轨道角动量流和轨道角位置流，二者可产生含二次谐波的横向电压，且可由声子角动量驱动，为轨道流产生及自旋-轨道-声子耦合提供新视角。
Magnon-phonon hybrid excitations are studied theoretically in a two-dimensional antiferromagnet with an easy axis normal to the plane. We show that two magnon bands and one phonon band are intertwined by the magnetoelastic coupling through a nontrivial SU(3) topology, which can be intuitively perceived by identifying a skyrmion structure in the momentum space. We develop a continuum theory as the long-wavelength approximation to the tight-binding model, showing our results are insensitive to lattice details and generally applicable to two-dimensional antiferromagnets. The theoretical results c…
Plasmon-enhanced Raman scattering (PERS) becomes nonlinear when phonon pumping and phonon-stimulated scattering come into play. It is fundamental to the understanding of PERS and its photobleaching behavior. By quantization of the molecular vibration coherent state into phonon number states, we theoretically predict a stepwise dependence of PERS intensity on laser power. Experimental evidence is presented by measuring a monolayer of malachite green isothiocyanate molecules sandwiched in individual gold nanosphere-plane antennas, under radially polarized laser excitation of sub-microWatt powers…
Chirality-Selective Phonon Pumping by Ferroelectric Dynamics
本研究提出通过相邻铁电体的电极化进动，在普通电介质中高效产生手性选择性声子，为电控手性声子学及自旋电子功能提供了通用途径。
Geometric Phonon Energy Pumping in a Layer-Hybridized Moiré Exciton Manifold
本研究构建四态开放系统模型，通过调制WSe₂/WS₂莫尔激子流形的驱动环路，实现几何声子能量泵浦，提升了其可探测性与信噪比，验证了响应的鲁棒性。
Acoustic orbital Hall effect and orbital pumping in light-metal-ferromagnet bilayers
本文研究了Ti和Cr等轻金属中的声学轨道霍尔效应与声学轨道泵浦，发现表面声波通过声子-轨道耦合产生高效轨道电流，确立了晶格动力学驱动轨道传输的机制，为低耗散轨道电子器件开辟了新途径。
Nonlinear magnetoelastic wave dynamics and field tunable soliton excitations in hexagonal multiferroic media
研究六方多铁性介质中非线性磁弹性波动力学及电场调控的孤子激发机制。
The electron-phonon coupling in self-assembled InGaAs quantum dots is relatively weak at low light intensities, which means that the zero-phonon line in emission is strong compared to the phonon sideband. However, the coupling to acoustic phonons can be dynamically enhanced in the presence of an intense optical pulse tuned within the phonon sideband. Recent experiments have shown that this dynamic vibronic coupling can enable population inversion to be achieved when pumping with a blue-shifted laser and for rapid de-excitation of an inverted state with red detuning. In this paper we confirm th…
Modeling Magnetoelastic Wave Interactions in Magnetic Films and Heterostructures: A finite-difference approach
本文提出一种有限差分微磁学时间积分方案，自洽模拟磁弹性动力学，扩展LLG方程并处理界面不连续，通过多组示例验证了该方法在磁振子-声子相互作用研究中的有效性。
We present a theory for the coherent magnetization dynamics induced by a focused ultrafast laser beam in magnetic films, taking into account nonthermal (inverse Faraday effect) and thermal (heating) actuation. The dynamic conversion between spin waves and phonons is induced by the magnetoelastic coupling that allows efficient propagation of angular momentum. The anisotropy of the magnetoelastic coupling renders characteristic angle dependences of the magnetization propa-gation that are strikingly different for thermal and nonthermal actuation.
We analyse the influence of optically generated non-equilibrium phonons on the spin relaxation and effective spin temperature of an individual Cr atom inserted in a quantum dot. Using a three pulses pump-probe technique, we show that the spin relaxation measured in resonant optical pumping experiments strongly depends on the optical excitation conditions. We observe for an isolated Cr in the dark a heating time shorter than a few hundreds $ns$ after an initial high power non-resonant excitation pulse. A cooling time larger than a few tens of $μs$, independent on the excitation, is obtained in …
Resonantly Enhanced Phonon Transport by Magnon Pumping in a Ferromagnetic/Piezoelectric Bilayer
首次实验观测到铁磁/压电双层中磁子泵浦引起的共振增强声子输运，证实频率选择性磁子-声子耦合，为混合平台主动控制声学输运提供新机制。
We study conductance through a quantum dot under Coulomb blockade conditions in the presence of an external periodic perturbation. The stationary state is determined by the balance between the heating of the dot electrons by the perturbation and cooling. We analyze two cooling mechanisms: electron exchange with the cold contacts and emission of phonons. Together with the usual linear Ohmic heating of the dot electrons we consider possible effects of dynamic localization. The combination of the abovementioned factors may result in a drastic change of the shape of the Coulomb blockade peak with …
The magnetization dynamics induced by standing elastic waves excited in a thin ferromagnetic film is described with the aid of micromagnetic simulations taking into account the magnetoelastic coupling between spins and lattice strains. The simulations have been performed for the 2 nm thick Fe81Ga19 film dynamically strained by longitudinal and transverse standing waves with various frequencies, which span a wide range around the resonance frequency nu_res of coherent magnetization precession in unstrained Fe81Ga19 film. It is found that standing elastic waves give rise to complex local magneti…
Voltage induced magnetization dynamics of magnetic thin films is a valuable tool to study anisotropic fields, exchange couplings, magnetization damping and spin pumping mechanism. A particularly well established technique is the ferromagnetic resonance (FMR) generated by the coupling of microwave photons and magnetization eigenmodes in the GHz range. Here we review the basic concepts of the so-called acoustic ferromagnetic resonance technique (a-FMR) induced by the coupling of surface acoustic waves (SAW) and magnetization of thin films. Interestingly, additional to the benefits of the microwa…
Quantitative evaluation method for magnetoelastic coupling between surface acoustic waves and spin waves using electrical and optical measurements
本文提出一种结合电学测量与光学成像的通用方法，通过提取仅依赖材料性质的实用常数，在失谐条件下定量评估SAW与SW的磁弹耦合，克服了以往耦合强度受器件几何和磁场角度影响而难以公平比较的问题。
Spin Waves and Spin Currents in Magnon-Phonon Composite Resonator Induced by Acoustic Waves of Various Polarizations
该研究针对ZnO-YIG-GGG-YIG/Pt结构多频复合体声波谐振器，通过实验探究不同极化声波激发的自旋波与自旋流，明确了线性与参量区间下不同极化模式的激发差异及耦合机制。
We model generation and propagation of coherent acoustic phonons in piezoelectric InGaN/GaN multi-quantum wells embedded in a \textit{pin} diode structure and compute the time resolved reflectivity signal in simulated pump-probe experiments. Carriers are created in the InGaN wells by ultrafast pumping below the GaN band gap and the dynamics of the photoexcited carriers is treated in a Boltzmann equation framework. Coherent acoustic phonons are generated in the quantum well via both deformation potential electron-phonon and piezoelectric electron-phonon interaction with photogenerated carriers,…
We study nonequilibrium carriers (electrons and holes) in an intrinsic graphene at low temperatures under far- and mid-infrared (IR) radiation in a wide range of its intensities. The energy distributions of carriers are calculated using a quasiclassic kinetic equation which accounts for the energy relaxation due to acoustic phonons and the radiative generation-recombination processes associated with thermal radiation and the carrier photoexcitation by incident radiation. It is found that the nonequilibrium distributions are determined by an interplay between weak energy relaxation on acoustic …
Raman-phonon-polariton condensation in a transversely pumped cavity
本文提出利用横向泵浦拉曼方案实现可调声子-光子耦合的声子极化激元凝聚，并通过Floquet稳定性分析给出超辐射态和激光态的相图，为工程电子关联态提供新工具。
An effective field theory of damped ferromagnetic systems
本文利用in-in形式推广磁弹性有效场论，统一描述铁磁系统阻尼，推导出Gilbert与Landau-Lifshitz阻尼项，并预测声子贡献形式。
Optical dual-pulse pumping actively creates quantum-mechanical superposition of the electronic and phononic states in a bulk solid. We here made transient reflectivity measurements in an n-GaAs using a pair of relative-phase-locked femtosecond pulses and found characteristic interference fringes. This is a result of quantum-path interference peculiar to the dual-pulse excitation as indicated by theoretical calculation. Our observation reveals that the pathway of coherent phonon generation in the n-GaAs is impulsive stimulated Raman scattering at the displaced potential due to the surface-charg…
We develop the analytic theory describing the formation and evolution of entangled quantum states for a fermionic quantum emitter coupled to a quantized electromagnetic field in a nanocavity and quantized phonon or mechanical vibrational modes. The theory is applicable to a broad range of cavity quantum optomechanics problems and emerging research on plasmonic nanocavities coupled to single molecules and other quantum emitters. The optimal conditions for a tri-state entanglement are realized near the parametric resonances in a coupled system. The model includes decoherence effects due to coupl…
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