Coherent acoustic phonons in PbTe quantum dots (original) (raw)
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Coherent Acoustic Phonons in a Semiconductor Quantum Dot
Physical Review Letters, 1997
Coherent acoustic phonons in PbS quantum dots are observed using femtosecond optical techniques. This is the first observation of coherent acoustic phonons in a semiconductor quantum dot; the phonons are generated through the deformation-potential coupling to the quantum-dot exciton. The acoustic modes are weakly damped, and we also find extremely weak coupling (S ϳ 0.01) to the optical modes. These conclusions have important consequences for the vibronic nature of the exciton transition in the quantum dot and its dephasing. [S0031-9007(97)04822-9]
Physical Review B, 2001
Coherent acoustic phonon oscillation is observed in PbSe quantum dots embedded in phosphate glass by femtosecond pump-and-probe. The size dependence of the oscillation is investigated. Distinct low-frequency peaks are observed in Raman spectrum for the same samples. The size-dependence of the frequencies is well explained by elastic sphere model, but the observed modes are different to each other for coherent phonon and Raman scattering. Coherent phonon measurement and Raman scattering are found to give complementary information on confined acoustic phonons in this system.
Size-dependent dynamics of coherent acoustic phonons in nanocrystal quantum dots
Physical Review B, 1999
Confined acoustic phonons in InAs nanocrystals are observed in the time domain by femtosecond pumpprobe spectroscopy. The size dependence of both frequency and damping time is investigated for InAs. The frequency of the discrete modes varies between 18 and 30 cm Ϫ1 for a nanocrystal radius ranging from 28 to 12 Å, and the dependence deviates from the expected 1/R behavior at small sizes. The damping rate is found to vary linearly with 1/R, suggesting coupling to the matrix through the particle surface as a main damping route. This is corroborated by observing faster damping for the acoustic mode in solution compared to a polymer environment. The coupling strength is found to depend on material parameters: in CdSe nanocrystals, weaker coupling is observed. The role of acoustic phonon coupling in the dephasing dynamics of semiconductor nanocrystals is discussed. ͓S0163-1829͑99͒01627-6͔
Directionality of acoustic-phonon emission in weakly confined semiconductor quantum dots
Physical Review B, 2007
The direction of propagation of acoustic phonons emitted by electron relaxation in weakly confined, parabolic quantum dots charged with one or two electrons is studied theoretically. The emission angle strongly depends on the energy of the phonon, the dominant electron-phonon scattering mechanism ͑deformation potential or piezoelectric field͒, and the orbital symmetries of the initial and final electron states. This leads to different behaviors for phonons emitted by electrons relaxing between levels of single and coupled quantum dots. Our results establish the basis to control the direction of propagation of phonon modes triggered by transitions in quantum dot systems.
Physical Review Letters, 2009
Multiple energy scales contribute to the radiative properties of colloidal quantum dots, including magnetic interactions, crystal field splitting, Pauli exclusion, and phonons. Identification of the exact physical mechanism which couples first to the dark ground state of colloidal quantum dots, inducing a significant reduction in the radiative lifetime at low temperatures, has thus been under significant debate. Here we present measurements of this phenomenon on a variety of materials as well as on colloidal heterostructures. These show unambiguously that the dominant mechanism is coupling of the ground state to a confined acoustic phonon, and that this mechanism is universal.
Exciton-Acoustic Phonon Coupling in Single CdTe Quantum Dots
physica status solidi (b), 2001
The photoluminescence spectra of individual quantum dots have been measured with high spectral and spatial resolution spectroscopy. The temperature dependence of the line broadening is analyzed for different single-confined excitons. At low temperatures, the photoluminescence spectra can be very well fitted by a Lorentzian, as expected from the lifetime broadening and the pure dephasing described by a linear phase damping. However, surprisingly, when increasing the temperature, the line shape progressively deviates from a Lorentzian and an additional broad background is observed. This non-Lorentzian line shape and its temperature dependence are theoretically modeled on the basis of lattice relaxation due to the exciton-acoustic phonon coupling.
Solid State Communications, 2000
The electron±acoustic-phonon scattering process in spherical II±VI quantum dots is discussed. The quantized acoustic modes are described in terms of Lamb's classical theory for the oscillations of a continuous sphere. The longitudinal spheroidal modes are included owing to their dominant contribution to the acoustic-phonon deformation potential (DP) scattering. We considered two mechanisms for the interaction between electrons and acoustic modes: microscopic DP, and macroscopic acoustic deformation, also called the ripple mechanism (RM). We also discuss the in¯uence of the glass matrix on the electron±phonon coupling, which is particularly important for the RM. Our calculations show that the macroscopic deformation scattering rates become dominant by more than an order of magnitude, for a small dot radius. In general, the total scattering rate depends substantially on the choice of the mechanical boundary conditions and on the acoustic properties of the glass matrix. q
Suppression of acoustic-phonon-induced electron transitions in coupled quantum dots
Physica E: Low-dimensional Systems and Nanostructures, 2005
We calculate the longitudinal-acoustic phonon scattering rate for a vertical double quantum dot (DQD) system and show that a strong modulation of the single-electron excited states lifetime can be induced by an external magnetic field. The results are obtained for typical realistic devices using a Fermi golden rule approach and a three-dimensional description of the electronic quantum states. The DQDs considered are characterized by a weak lateral confinement and the longitudinal-phonon scattering represents the dominant source of decoherence, its tunable suppression can be a valuable tool for an experimental measure of electron-states lifetimes and serve as a signature for coherent delocalization of electrons in the DQD. r