Measurement of THz spectra. THz absorption spectra were measured by a FT-FIR spectrometer (JASCO: FARIS). The film samples are placed on a sample holder which is tilted against THz beam path. The tilt angle is adjusted as Brewster's angle to minimize the multireflection inside the sample, which causes fringe in the absorption spectrum. Detail of the Brewster's angle sample holder is written in elsewhere. THz absorption spectra were measured for 1-9 THz with a high-pressure mercury lamp as the light source, a wire-grid beam splitter, and a superconducting bolometer (QMC: QNbB/PTC). Each spectrum was measured with spectral resolution of 0.06 THz, accumulated for 360 scans.