Spontaneous, Dynamical Localization of Vibrational Energy in L-Alanine

The phonon description of vibrational excitation in crystals is a result of approximating the Hamiltonian of the crystal with harmonic potentials. If this approximation is not made, the resulting eigenfunctions may no longer be infinitely extended plane waves. Instead, the system may favor the formation of solitons, shock waves, or other localized states by spontaneously breaking the translational symmetry of the crystal. Such effects are especially likely to be observed in hydrogen-bonded molecular crystals due to their strongly nonlinear lattice interactions. This dissertation describes a search for these localized modes in single crystal l-alanine. The dispersion curves, thermal conductivity, and the temperature dependent Raman spectra have been measured. A nonlinear spectroscopy lab was constructed in order to perform Coherent Anti-Stokes Raman Spectroscopy measurements. Two lattice modes that display an anomalous temperature dependence in their Raman spectra are studied using the CARS apparatus to search for k-vector nonconservation, an effect that should provide direct confirmation of spatial localization.