抄録
The rigid layer mode of a shear type in squaric acid has been studied at several temperatures by Brillouin and Raman scatterings under a uniaxial stress applied perpendicularly to layer planes. The temperature and uniaxial stress dependences of a transverse acoustic mode (c44) in the low temperature phase are essentially the same as those of the low frequency Ag-optic mode below Tc, which corresponds to the zone-boundary acoustic mode in the high temperature phase. This rigid layer mode is analyzed by a one dimensional model with a single force constant f1 between the nearest neighbor layers and the value of f1 is calculated to be 1.18×104 dyn/cm at room temperature. The variation of f1 with interlayer distance is also estimated.
