Bolometric measurement of the charge-density-wave gap in TaS3

Polarized bolometric spectra were measured on orthorhombic TaS3 between 20 and 100 K. At the lowest temperature, the spectra are clearly absorption spectra, indicating that o-TaS3 has a semiconducting Peierls gap of Eg=1240 cm-1=8.1kBTc. No sharp lines indicative of midgap soliton states are observed, although a long tail may be due to weakly pinning impurity states. The spectra become more complex at higher temperatures, but indicate that the gap decreases to 1025 cm-1 at 95 K. The gap energy is close to twice the activation energy observed in transport measurements.