Coherent phonons in condensed media

Dekorsy, Thomas; Cho, Gyu Cheon; Kurz, H.

doi:10.1007/bfb0084242

Cited by 139 publications

(136 citation statements)

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“…The vanishing anisotropy for n-GaAs indicates that the generation of both coherent LO and LOPC modes is dominated by TDFS, in agreement with early studies that reported on the L− mode of n-doped GaAs 6-8 . Our results confirm that ultrafast carrier separation by the built-in field in the depletion layer launches not only coherent LO phonons within the depletion layer of n-GaAs, but also coherent LOPC modes in the adjacent bulk via ultrafast drift-diffusion current 1,7 . The dominance of the TDFS generation mechanism can explain the distinct power dependence of the LO amplitude in n-GaAs [ Fig.…”

Section: A Generation Mechanism Of Lo and Lopc Modessupporting

confidence: 71%

“…In transient reflectivity measurements, a nuclear displacement Q associated with the LO phonon oscillation induces a change in reflectivity R through the refractive index n and the susceptibility χ. In a first-order approximation the change ∆R is given by 1,14 :…”

Section: Theoretical Background a Generation And Detection Of Comentioning

confidence: 99%

“…The coherent optical phonons have been observed as a periodic modulation in the THz frequency range, most conveniently by linear and non-linear optical techniques 1,2 . The generation mechanisms of the coherent phonons have been studied extensively in a variety of crystals and attributed, depending on the nature of the electron-phonon interaction, to impulsive stimulated Raman scattering (ISRS) 3,4 , displacive excitation of coherent phonons (DECP) 5 , and transient depletion field screening (TDFS) [6][7][8] .…”

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Allowed and forbidden Raman scattering mechanisms for detection of coherent LO phonon and plasmon-coupled modes in GaAs

2011

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Detection mechanisms of coherent phonons in variously doped GaAs are investigated by transient reflectivity method with photoexcitation near the E0 gap and probe near either the E0 or E1 gaps. By varying the probe light polarization angle, the coherent amplitudes of both the LO phonon and the LO phonon-plasmon coupled (LOPC) modes show evidence for an interference between their anisotropic and isotropic dielectric response components. We attribute the anisotropic and isotropic components to the reflectivity modulation by lattice and electronic polarizations via dipole-allowed and dipole-forbidden Raman scattering processes. The forbidden processes are resonantly enhanced at the E0 and E1 critical points due to the relaxation of momentum conservation and the strong built-in electric field near the surface. The relative contribution of the anisotropic and isotropic components depends on the modes (LO or LOPC) as well as the probe wavelength (E0 or E1), because of the different Raman scattering mechanisms involved. Reflectivity measurements with the near ultraviolet light, which is used to probe the E1 gap, also enable highly surface sensitive detection of ultrafast LO phonon-plasmon dynamics, which is strongly depth-dependent in the depletion layer of n-doped GaAs.

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Section: A Generation Mechanism Of Lo and Lopc Modessupporting

confidence: 71%

Section: Theoretical Background a Generation And Detection Of Comentioning

confidence: 99%

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confidence: 99%

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Allowed and forbidden Raman scattering mechanisms for detection of coherent LO phonon and plasmon-coupled modes in GaAs

2011

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“…Here, at high electric fields, field induced tunneling into above-barrier continuum states leads to a rapid dephasing of Bloch oscillations. The associated polarization change provides an additional excitation process for coherent LO phonons.1 Introduction Time-resolved investigations of resonantly coupled excitations involving phonons, such as coupled plasmon-phonon modes or phonon-polaritons, are one of the most intriguing subjects of coherent phonon spectroscopy (for a review see, e.g., [1]). …”

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confidence: 99%

“…1 Introduction Time-resolved investigations of resonantly coupled excitations involving phonons, such as coupled plasmon-phonon modes or phonon-polaritons, are one of the most intriguing subjects of coherent phonon spectroscopy (for a review see, e.g., [1]). …”

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confidence: 99%

Well‐width dependence of coupled Bloch‐phonon oscillations in biased InGaAs/InAlAs superlattices

Först

Kurz

Dekorsy

et al. 2004

phys. stat. sol. (c)

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The coupling between Bloch oscillations and longitudinal optical (LO) phonons is investigated in ternary In 0.53Ga0.47As / In0.52Al0.48As superlattices of different well widths. In femtosecond time-resolved studies, a strong increase of the coherent LO phonon amplitudes is observed when the Bloch oscillations are subsequently tuned into resonance with the different optical phonon modes of the ternary semiconductor materials. In a narrow-well superlattice where electronic minibands are energetically shifted close to the confining barrier potential, the phonon amplitudes are asymmetrically enhanced on the high-frequency edge of the resonance. Here, at high electric fields, field induced tunneling into above-barrier continuum states leads to a rapid dephasing of Bloch oscillations. The associated polarization change provides an additional excitation process for coherent LO phonons.1 Introduction Time-resolved investigations of resonantly coupled excitations involving phonons, such as coupled plasmon-phonon modes or phonon-polaritons, are one of the most intriguing subjects of coherent phonon spectroscopy (for a review see, e.g., [1]).Besides the elementary excitations involved there (plasmons, light waves), the coherent excitation of Bloch oscillations (BO's) has become possible in semiconductor superlattices by use of femtosecond laser pulses (for a review see, e.g., [2]). In general, BO's are described as the spatial oscillation of carriers in a periodic potential subject to a static electric field [3,4]. In biased superlattices, the coherent superposition of electronic Wannier-Stark (WS) states by ultrashort laser pulses leads to the formation of an electronic wave packet oscillating with a frequency ν BO = eF d/h. This frequency is determined by the externally applied electric field F , the superlattice period d, the electron charge e, and Planck's constant h.Recently, the resonant coupling between optical phonons and BO's has been demonstrated for the first time in GaAs/AlGaAs superlattices [5]. Here, we present a study on coupled Bloch-phonon oscillations in In 0.53 Ga 0.47 As / In 0.52 Al 0.48 As superlattices of different well widths but constant electronic miniband widths. A strong increase of the coherent LO phonon amplitudes is observed when the BO's are subsequently tuned into resonance with the distinct phonon modes of the ternary superlattice semiconductors by variation of the applied electric field. Furthermore, narrow superlattice wells lead to a shift of electronic minibands to higher energies in the conduction band and, thus, to an enhancement of Zener tunneling into above-barrier continuum states at high electric fields [6]. This effect results in a rapid dephasing of coherent BO's that in turn induces an incoherent polarization exciting coherent LO phonons. This contribution manifests itself as an asymmetric enhancement of the LO phonon amplitudes on the high-frequency edge of the Bloch-phonon resonance.

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