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 $[\sigma((\mathrm{D})]$ spectrum has been measured in the terahertz (THz) to vacuum-ultraviolet (VUV) region. The strong anisotropy of vibration modes appears in polarized $\sigma(\omega)$ 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.