Picosecond ultrasonic study of localized phonon surface modes in Al/Ag superlattices

Chen, Wei; Lu, Yu; Maris, Humphrey J.; Xiao, Gang

doi:10.1103/physrevb.50.14506

Cited by 80 publications

(75 citation statements)

References 19 publications

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“…1,2 Although the technique has been applied successfully to opaque multilayer structures with several layers, the case of partially transparent or transparent multilayers is less well understood because of the increased complexity of the analysis. In spite of the continuing interest shown in the application to superlattices, [5][6][7][8] only the case of a single transparent or partially transparent layer on another opaque layer has been properly analyzed to include interface motion as well as variations in the dielectric constants. [14][15][16] The exact treatment for the general case of more than one transparent or partially transparent layer presented here should therefore be extremely valuable in the field of laser picosecond acoustics for application to samples of arbitrary multilayer structure.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…Photoexcitation of such a sample by ultrashort optical pulses causes perturbations, in the guise of strain, [1][2][3][4][5][6][7][13][14][15][16] temperature, [9][10][11][12][13][23][24][25][26][27] and excited carrier distributions, [10][11][12][13][24][25][26][27][28][29] all of which are varying in both space and time. The effect of these perturbations on the dielectric constants has been extensively investigated since the advent of ultrashort-pulse lasers, thanks to the ease of monitoring the variation in the optical reflectance or transmittance with the optical pump and probe technique.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…Recently such structures with layer thicknesses in the submicrometer range have been the focus of a wide range of ultrashort time-scale experiments that probe the inhomogeneous modulation of the dielectric constant along the stacking direction induced by an incident ultrashort optical pulse. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] This modulation can be caused by, for example, the diffusion and relaxation of nonequilibrium electron and hole distributions, thermal diffusion, or coherent acoustic-phonon propagation. The main aim of these experiments is to probe such phenomena and extract quantitative information about the relevant spatiotemporally varying field.…”

Section: Introductionmentioning

confidence: 99%

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Reflection and transmission of light in multilayers perturbed by picosecond strain pulse propagation

Matsuda

Wright

2002

J. Opt. Soc. Am. B

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We derive analytical formulas for the modulation of the reflectance and transmittance of light normally incident on a multilayer thin-film structure whose refractive indices are perturbed by an ultrashort optical pulse. The formulas, expressed in compact form, should prove useful for analysis of a wide range of ultrashort timescale experiments on multilayers as well as longer time-scale photoacoustic and photothermal experiments based on optical probing. We demonstrate our method by the analysis of the modulated reflectance variation of a SiO 2 /Cr structure in which picosecond acoustic pulses have been optically excited.

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Section: Theoretical Backgroundmentioning

confidence: 99%

Section: Theoretical Backgroundmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Reflection and transmission of light in multilayers perturbed by picosecond strain pulse propagation

Matsuda

Wright

2002

J. Opt. Soc. Am. B

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“…As SL2 is positioned below SL1, the cavity with the SL2 Bragg mirror therefore includes also all layers of SL1. The studied multilayer structure possesses a number of localized phonon modes with frequencies f Ri , which fall into the stop bands of the SLs [20][21][22]. (f R2 = 28.0 GHz and f R3 = 29.5 GHz).…”

mentioning

confidence: 99%

Resonant driving of magnetization precession in a ferromagnetic layer by coherent monochromatic phonons

et al. 2015

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We realize resonant driving of the magnetization precession by monochromatic phonons in a thin ferromagnetic layer embedded into a phononic Fabry-Pérot resonator. A femtosecond laser pulse excites resonant phonon modes of the structure in the 10−40 GHz frequency range. By applying an external magnetic field, we tune the precession frequency relative to the frequency of the phonons localized in the cavity and observe an enormous increase in the amplitude of the magnetization precession when the frequencies of free magnetization precession and phonons localized in the cavity are equal. The continual miniaturization of magnetic devices down to the nanometer scale has opened new horizons in data storage [1], computing [2,3], sensing [4,5], and medical technologies [6]. Progress in nanomagnetism is stimulated by emerging technologies, where methods to control magnetic excitations on the nanometer spatial and picosecond temporal scales include optical [7,8], electrical [8], and micromechanical [9] techniques. To realize ultrafast nanomagnetism on the technological level, new physical principles to efficiently induce and control magnetic excitations are required, and this remains a challenging task. A new basic approach to this problem would be to explore nanoscale magnetic resonance phenomena-resonant driving and monitoring of magnetic excitations-which is widely used nowadays in traditional magnetism for microscopy, medicine, and spectroscopy. The typical frequencies f M of the magnetic resonances [e.g., the ferromagnetic resonance (FMR) in ferromagnetic and ferrimagnetic materials] are in the GHz and sub-THz frequency ranges. The traditional methods to scan magnetic excitations at these frequencies use microwaves, but due to the requirement of massive microwave resonators providing long wavelength radiation, they cannot provide high-speed control of magnetization locally on the nanoscale.Among various emerging techniques in nanomagnetism, the application of stress to magnetostrictive ferromagnetic layers has been shown to be an effective, low-power method for controlling magnetization: Applying in-plane stress in stationary experiments enables irreversible switching of the magnetization vector [10]; the injection of picosecond strain pulses induces free precession of the magnetization [11]; excitation of quantized elastic waves in a membrane enables driving of the magnetization at GHz phonon frequencies [12]; and surface acoustic waves can be used to control the magnetic dynamics in ferromagnetic nanostructures [13][14][15]. In the present Rapid Communication, we examine the interaction of a high-frequency (10−40 GHz) magnetic resonance in a magnetostrictive ferromagnetic film with an elastic harmonic excitation in the form of a localized phonon mode, and demonstrate how this interaction becomes significantly stronger at resonance conditions. Our device consists of a ferromagnetic layer embedded into a phonon Fabry-Pérot (FP) cavity. Such a cavity possesses quantized resonances for elastic waves (i.e., phonons) at f...

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“…3 Experimental studies with the picosecond ultrasonic technique 4 and Raman scattering have revealed the existence of localized acoustic surface modes in both semiconducting and metallic SLs. [5][6][7][8] Also the localized vibrations at the interface between a superlattice and a substrate have been investigated by DjafariRouhani and co-workers. 9,10 All these localized modes associated with the inhomogeneities that destroy the perfect periodicity of a system appear inside the band gaps of the bulk modes.…”

Section: Introductionmentioning

confidence: 99%

Acoustic-phonon cavity modes in one-dimensional multilayered elastic structures

2005

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We theoretically study "cavity" phonons, i.e., acoustic phonons localized in a foreign layer ͑a cavity layer͒ embedded in a periodic one-dimensional superlattice ͑SL͒ in the isotropic, continuum approximation. To find the eigenfrequencies of the cavity modes we develop a formulation based on the transfer matrix and Green's function methods and apply it to the case where the confined phonons propagate along the layer interfaces. These cavity phonons are predicted to exist for both the coupled longitudinal and transverse acoustic mode ͑the sagittal mode͒ and the single mode with pure transverse polarization ͑the shear-horizontal mode͒. Numerical examples are presented for periodic Al/ W multilayered structures with a Ag cavity layer and GaAs/ AlAs SLs with an Al 0.8 Ga 0.2 As layer. Finite-difference time-domain calculations for phonon packet propagation are also conducted to directly illustrate the existence of the confined cavity modes and also to confirm the validity of our formulation.

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Picosecond ultrasonic study of localized phonon surface modes in Al/Ag superlattices

Cited by 80 publications

References 19 publications

Reflection and transmission of light in multilayers perturbed by picosecond strain pulse propagation

Reflection and transmission of light in multilayers perturbed by picosecond strain pulse propagation

Resonant driving of magnetization precession in a ferromagnetic layer by coherent monochromatic phonons

Acoustic-phonon cavity modes in one-dimensional multilayered elastic structures

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