Shear modulus of TaS3

We have measured the effective shear modulus of orthorhombic Ta${\mathrm{S}}_3$ by incorporating the sample in a torsional pendulum. In the charge-density-wave (CDW) state, the shear modulus gradually decreases by ∼20% with voltage as the CDW becomes depinned, and the internal friction increases to ∼0.01. These results suggest that interchange coupling is severely affected by CDW motion.