Giant Thermal Effect of Vibration Modes of Single-Crystalline Alanine

Amino acids are the most basic molecules of living bodies. We have fabricated L-alanine single crystals that has the simplest molecular structure among amino acids with chirality. The temperature dependence of the polarized optical conductivity [σ(ω)] spectrum has been measured in the terahertz (THz) to vacuum-ultraviolet (VUV) region. The strong anisotropy of vibration modes appears in polarized σ(ω) spectra because of the strong anisotropic crystal structure. Furthermore, many peaks show extremely strong temperature dependence. Their giant thermal effect can be explained by using a temperature-dependent anharmonic potential model.