Coherent Optical Phonons and Parametrically Coupled Magnons Induced by Femtosecond Laser Excitation of the Gd(0001) Surface

Melnikov, Alexey; Radu, Ilie; Bovensiepen, Uwe; Krupin, O.; Starke, K.; Matthias, E.; Wolf, Martin

doi:10.1103/physrevlett.91.227403

Cited by 106 publications

(105 citation statements)

References 25 publications

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“…[13] They focused their attention into the generation mechanism of the coherent optical phonon and coupled coherent magnon. The surface coherent optical phonon was excited by a transient charge separation at the surface, which is similar proposal to the displacive excitation mechanism (DECP).…”

Section: Introductionmentioning

confidence: 99%

Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals

et al. 2005

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The femtosecond optical pump-probe technique was used to study dynamics of photoexcited electrons and coherent optical phonons in transition metals Zn and Cd as a function of temperature and excitation level. The optical response in time domain is well fitted by linear combination of a damped harmonic oscillation because of excitation of coherent E2g phonon and a subpicosecond transient response due to electron-phonon thermalization. The electron-phonon thermalization time monotonically increases with temperature, consistent with the thermomodulation scenario, where at high temperatures the system can be well explained by the two-temperature model, while below ≈ 50 K the nonthermal electron model needs to be applied. As the lattice temperature increases, the damping of the coherent E2g phonon increases, while the amplitudes of both fast electronic response and the coherent E2g phonon decrease. The temperature dependence of the damping of the E2g phonon indicates that population decay of the coherent optical phonon due to anharmonic phononphonon coupling dominates the decay process. We present a model that accounts for the observed temperature dependence of the amplitude assuming the photoinduced absorption mechanism, where the signal amplitude is proportional to the photoinduced change in the quasiparticle density. The result that the amplitude of the E2g phonon follows the temperature dependence of the amplitude of the fast electronic transient indicates that under the resonant condition both electronic and phononic responses are proportional to the change in the dielectric function.

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Section: Introductionmentioning

confidence: 99%

Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals

et al. 2005

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“…To reveal the origin of this dynamics, we note that the pump-induced oscillations are usually related to the excitation of quasiparticles [42][43][44][45][46], for instance, magnons or phonons. However, our experiments have shown that neither the phase of the oscillations changes upon switching the magnetic field, nor their frequency shifts when the magnetic field strength is changed (see Sec.…”

Section: Long Time Rangementioning

confidence: 99%

Femtosecond laser-induced optical anisotropy in a two-dimensional lattice of magnetic dots

et al. 2014

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Using pump-probe optical polarimetry we demonstrate that femtosecond laser excitation of a 2D regular lattice of magnetic nanodots effectively changes the optical anisotropy of the array. Study of the dynamics of the femtosecond laser-induced anisotropy reveals four main mechanisms occurring in the electronic, spin, and lattice subsystems. Below 1 ps, a strong Kerr-like nonlinearity causes linear birefringence, with its axis directed along the electric field of the linearly polarized femtosecond laser pump pulse. In addition, a long-living linear birefringence is also induced due to slowly relaxing excitations. Also below 1 ps, ultrafast laser-induced demagnetization of Co leads to a partial breakdown of the circular birefringence of the magnetic nanodots. On the timescale up to 300 ps, optically triggered acoustic modes of the dots drive oscillations of the linear optical birefringence. During this process, the oscillations damp while transferring their energy into acoustic modes of the substrate. On the nanosecond timescale, the signal is dominated by acoustic oscillations at the surface of the substrate.

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“…12,13,17,21,25 The observation of coherent longitudinal optical ͑LO͒ phonons in Gd was reported in Refs. 12, 13, 21, and 25.…”

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confidence: 87%

Optical excitation of a coherent transverse optical phonon in a polycrystalline Zr metal film

et al. 2007

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Optical pump-probe measurements of transient reflectivity were made on a sputtered polycrystalline thin film of hcp Zr. On top of a slow multiexponential decay, an oscillatory signal was observed with frequency varying from the initial value of f 0 = 2.24± 0.06 THz at zero time delay to a value of 2.56± 0.12 THz after 2 ps, which is similar to that of a transverse optical ͑TO͒ phonon near the ⌫ point of the Brillouin zone. From the data, the TO phonon relaxation time was determined to be 0.67 ps. The excitation of the coherent phonon was identified as being mediated by resonant coherent Raman scattering. DOI: 10.1103/PhysRevB.76.012301 PACS number͑s͒: 78.47.ϩp, 63.20.Ϫe, 78.20.Ϫe Recently, much attention has been drawn to the study of terahertz phonons in semiconductors, semimetals, and metals. The motivation for these studies arises from the need for efficient means by which to quantify the elastic properties of solids, on one hand, and to analyze the integrity of nanoscale structures, on the other. Atomic dynamics determines new phase formation in solids and the kinetics of chemical reactions. The latest advances in ultrafast laser technology have allowed the subpicosecond nonequilibrium dynamics of phonons to be investigated in the time domain. In most of these studies, acoustic modes were investigated. In such modes, neighboring atoms oscillate in phase, and so the characteristic length scale for associated nonuniformities is given by the phonon wavelength. At the same time, in crystals with two ͑or more͒ atoms in the unit cell, there also exist optical phonons. For these modes, the two basis atoms oscillate out of phase, and so by studying optical phonons, one may obtain information about interactions on the atomic length scale, even if the phonon wavelength is not small.In striking contrast to semiconductors and semimetals, 6 there have only been a few reports of the observation of coherent optical phonons by optical pump-probe measurements in metals. 12,13,17,21,25 The observation of coherent longitudinal optical ͑LO͒ phonons in Gd was reported in Refs. 12, 13, 21, and 25. Coherent transverse optical ͑TO͒ phonons in Zn and Cd were observed in Ref. 17. The samples in those studies were single crystals. At the same time, many of the metallic nanostructures that are important for applications are prepared by sputtering and so are polycrystalline. Therefore, a question arises as to whether terahertz optical phonons can be excited and detected and, hence, used for characterization of polycrystalline metallic samples. In this Brief Reports, we show that coherent TO phonons near the center of the Brillouin zone can be optically excited and detected in a sputtered polycrystalline film of Zr.Measurements were performed at room temperature with 90 fs ͑full width at half maximum͒ transform limited pulses with photon energy of 1.575± 0.005 eV from a Ti:sapphire laser with 80 MHz repetition rate. The pump and probe were focused to a 15 m spot size, had energies of 2.25 and 0.04 nJ, and were incident on the sample...

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Coherent Optical Phonons and Parametrically Coupled Magnons Induced by Femtosecond Laser Excitation of the Gd(0001) Surface

Cited by 106 publications

References 25 publications

Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals

Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals

Femtosecond laser-induced optical anisotropy in a two-dimensional lattice of magnetic dots

Optical excitation of a coherent transverse optical phonon in a polycrystalline Zr metal film

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