Raman scattering study of acoustical zone-center gaps in GaAs/AlAs superlattices

Jusserand, B.; Alexandre, François; Dubard, J.; Paquet, D.

doi:10.1103/physrevb.33.2897

Cited by 69 publications

(33 citation statements)

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“…The second zone center mode, in contrast, causes only a very small reflectivity bump. The large difference in reflectivity for the two modes arises from the different phases x between the light electric field and the SAWinduced modulation of the optical thickness along x [11,12]. The latter are in phase (i.e., x 0) for the third mode, thus ensuring a strong coupling to the incident light beam.…”

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Phonon-Induced Optical Superlattice

et al. 2005

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We demonstrate the formation of a dynamic optical superlattice through the modulation of a semiconductor microcavity by stimulated acoustic phonons. The high coherent phonon population produces a folded optical dispersion relation with well-defined energy gaps and renormalized energy levels, which are accessed using reflection and diffraction experiments. DOI: 10.1103/PhysRevLett.94.126805 PACS numbers: 73.21.Cd, 42.65.Es, 42.70.Qs, 77.65.Dq The notion of a superlattice, a periodic stack of layers of different materials, was originally introduced as a way of tailoring the electronic band structure of semiconductors via quantum size effects [1]. The dispersion relation of elementary excitations in superlattices is characterized by minibands within a folded mini-Brillouin zone (MBZ) defined by the artificial periodicity and separated by minigaps corresponding to regions without propagating modes. The superlattice concept was later extended to phonons [2]. Although optical superlattices in the form of Bragg mirrors have been known for a long time, their two-and threedimensional counterparts, typically referred to as photonic crystals, are presently receiving considerable attention due to the ability to induce light localization and control spontaneous emission [3,4].Elementary excitations such as phonons, plasmons, and spin waves also create, when stimulated with a welldefined wave vector, a periodic modulation of the material's optical properties. In fact, this modulation provides a primary source of information about their energy dispersion when accessed using techniques such as Raman and Brillouin spectroscopy. An interesting question is whether an elementary excitation can create a dynamic optical superlattice with a folded dispersion and energy gaps. The interaction with photons, however, is usually very weak with induced energy shifts smaller than the characteristic width of the spectral lines. This interaction becomes enhanced for photon energies in resonance with the elementary excitation (resonant scattering) or by artificially increasing their population above the equilibrium (stimulated scattering). We point out that excitations of a bosonic nature are more appropriate for optical modulation with a high excitation density in order to avoid the broadening of the spectral features due to many-body effects [5]. The previous conditions may lead to the formation of new quasiparticles, as exemplified by the different forms of polaritons.The interaction with photons can be further enhanced in low-dimensional structures. Strong optical fields in semiconductor microcavities have been shown to increase the cross section for Raman scattering by thermal vibrations by several orders of magnitude [6]. In addition, Brillouin scattering efficiencies exceeding 40% have been reported in microcavities exposed to a high, nonthermal population of coherent acoustic modes [7]. A zone folded energy dispersion with minigaps has also been predicted for cavity polaritons modulated by coherent acoustic phonons [5]. To our knowl...

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“…5. The reciprocal lattice is generated by primitive vectors k 10 and k 11 with different lengths k 10 2 = SAW and k 11 2 p k 10 , respectively. The latter leads to different Bragg angles along the 1 0 and the 1 1 directions, as shown in the measurements of the first order diffracted beam R 1 in Fig.…”

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Phonon-Induced Optical Superlattice

et al. 2005

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“…We recall that the low-frequency zone-center mode possesses the even symmetry A 1 and is, therefore, Raman allowed in the forward scattering geometry [21] whereas its higher-frequency counterpart does not scatter light because its symmetry, B 2 , is odd [12,13]. Furthermore, since the dispersion at is nearly linear, the FP modes behave as weakly-modulated plane waves.…”

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Observation of Surface-Avoiding Waves: A New Class of Extended States in Periodic Media

et al. 2006

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Coherent time-domain optical experiments on GaAs-AlAs superlattices reveal the existence of an unusually long-lived acoustic mode at ~ 0.6 THz, which couples weakly to the environment by evading the sample boundaries. Classical as well as quantum states that steer clear of surfaces are generally shown to occur in the spectrum of periodic structures, for most boundary conditions. These surface-avoiding waves are associated with frequencies outside forbidden gaps and wavevectors in the vicinity of the center and edge of the Brillouin zone. Possible consequences for surface science and resonant cavity applications are discussed.PACS numbers: 43.35.+d, 78.67.Pt, 63.20.-e -1-

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“…Graphically this means that the acoustic phonon branch is backfolded into the mini zone. Additionally, a gap in the dispersion curve opens at the edge of the mini zone, scaling with the acoustic mismatch of the materials [5]. When the acoustic mismatch is small, Eq.…”

Section: Theorymentioning

confidence: 98%

“…The maximum frequency that can be resolved is limited by the temporal width of the excitation and probing pulses. The observable range of phonon wavevectors is primarily determined by the probe light spectrum [5]. The fraction of the Brillouin zone that can be covered by this spectrum, however, depends on the sample structure.…”

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confidence: 99%