The temperature dependence below Tc of the lineshape of optical phonons of different symmetry as seen in Raman scattering is investigated for superconductors with anisotropic energy gaps. It is shown that the symmetry of the electron-phonon vertex produces non-trivial couplings to an anisotropic energy gap which leads to unique changes in the phonon lineshape for phonons of different symmetry. ...

We report progress towards understanding how phonon anharmonicity contributes to negative thermal expansion (NTE). Some contribution to the NTE is from "quasiharmonic" behavior, where phonon frequencies decrease as a crystal expands. A second "anharmonic" effect from phonon-phonon interactions is sometimes calculated by perturbation theory, but sometimes the anharmonic effects are too large to ...

Amorphous and crystalline phases of Ge2Sb2Te5 films are investigated by coherent phonon spectroscopy. By heating amorphous films above specific temperatures, the coherent phonon signatures exhibit pronounced changes due to the crystallization of the amorphous phase into a cubic lattice and the transition from the cubic to a hexagonal crystal structure. The phonon modes observed are identified b...

We present an analytical model for the size-dependence of thin film and nanowire thermal conductivity and compare the predictions to experimental measurements on silicon nanostructures. The model contains no fitting parameters and only requires the bulk lattice constant, bulk thermal conductivity, and an acoustic phonon speed as inputs. By including the mode-dependence of the phonon lifetimes r...

Raman spectra of rutile tin dioxide (SnO2) were measured at temperatures from 83 to 873 K. The pure anharmonicity from phonon-phonon interactions was found to be large and comparable to the quasiharmonicity. First-principles calculations of phonon dispersions were used to assess the kinematics of three-phonon and four-phonon processes. These kinematics were used to generate Raman peak widths an...

Raman spectra of rutile titanium dioxide (TiO2) were measured at temperatures from 100 to 1150 K. Each Raman mode showed unique changes with temperature. Beyond the volume-dependent quasiharmonicity, the explicit anharmonicity was large. A new method was developed to fit the thermal broadenings and shifts of Raman peaks with a full calculation of the kinematics of three-phonon and four-phonon p...

We investigate the small-particle phonon-polariton response of several microstructures that are made of silicon carbide (SiC). Phonon polaritons can be excited in a wavelength region between 10 and 12 mm. Simple structures such as elliptical cylinders support phonon polaritons at two wavelengths, which depend on the axis ratio of the particle. In particles with a more irregular shape such as re...

The dynamic form factor, S(Q, ce), of fcc 'He at high density is calculated, including the one-phonon, the two-phonon, and interference contributions, for comparison with the recent neutron-scattering measurements of Eckert et al. and of Thomlinson et al. The purpose is to test how well the standard self-consistent phonon (SCP) theory, which takes no account of short-range correlations in the a...

Mode-dependent phonon and electron transport properties in Al, Ag, and Au are predicted using density functional theory and lattice dynamics calculations. The predicted thermal conductivities, electrical conductivities, electron-phonon coupling coefficients, and electron-phonon mass enhancement parameters are in agreement with experimental measurements. At a temperature of 100 K, the phonon con...