The normal state optical response of La2−xSrxCuO4 is found to be consistent with a simple multi–component model, based on free carriers with strong electron–phonon interaction, localized polaronic states near 0.15 eV and a mid–infrared band at 0.5 eV. Normal state reflectance and absorbance of La1.83Sr0.17CuO4 are investigated and their temperature dependence is explained. Both, the ac and dc r...

We show that the structure in ab-plane infrared spectra of the oxide superconductors can be understood in terms of the electron-phonon interaction. The minima in the optical conductivity seen in the oxygen breathing mode region translate to peaks in the frequency dependent scattering rate. The position and the width of the peaks are in reasonable agreement with structure seen in timeof-flight n...

We have observed large-amplitude coherent phonon oscillations of radial breathing modes (RBMs) in single-walled carbon nanotubes excited through the lowest-energy (E(11)) interband transitions. In contrast to the previously studied coherent phonons excited through higher-energy (E(22)) transitions, these RBMs show comparable intensities between (n-m) mod 3 = +1 and -1 nanotubes. We also find th...

Self-assembled secondary ZnO nanoparticles, recognized with the agglomeration of crystalline subcrystals, are successfully synthesized by a simple sol-gel method. TEM images display that one artificial cluster behaves in a single-crystal-like wurtzite structure because subcrystals coagulate as the same crystal orientation. Moreover, from the resonant Raman scattering, the as-grown sample exhibi...

Recent high pressure x-ray experiments show that, contrary to traditional expectations, the NaCl structure is not present in covalent semiconductors, and the diatomic b-Sn structure is absent in all compound semiconductors. We explain these systematic absences in terms of dynamical phonon instabilities of the NaCl and b-Sn crystal structures. Covalent materials in the NaCl structure become dyna...

Nonlinear probing of the fundamental lattice vibration of polar crystals is shown to reveal insight into higher-order cohesive lattice forces. With a free-electron laser tunable in the far infrared we experimentally investigate the dispersion of the second-order susceptibility due to the phonon resonance in GaAs. We observe a strong resonance enhancement of second harmonic light generation at h...

A recently developed long-wavelength continuum phenomenological model is employed to study the phonon tunneling through semiconductor heterostructures where the barrier parameters are varied gradually according to a Gaussian function. The optical modes of a Si/SixGe1Kx Gaussian superlattice are considered. Such structures allow the incident phonons to be nearly totally transmitted when the inci...

Gate-modulated low-temperature Raman spectra reveal that the electric field effect (EFE), pervasive in contemporary electronics, has marked impacts on long-wavelength optical phonons of graphene. The EFE in this two-dimensional honeycomb lattice of carbon atoms creates large density modulations of carriers with linear dispersion (known as Dirac fermions). Our EFE Raman spectra display the inter...

We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultrathin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from ~4.7 ns to 5 ps with decreasing membrane thickness from ~194 to 8 nm. The experimental resu...

We explore an analogue of optical frequency combs in driven nonlinear phononic systems, and present a mechanism for generating phononic frequency combs through nonlinear resonances. In the underlying process, a set of phonon modes is simultaneously excited by the external driving which yields frequency combs with an array of discrete and equidistant spectral lines of each nonlinearly excited ph...