Torsional Strain of TaS$_3$ Whiskers on the Charge-Density Waves Depinning

Abstract

We find that electric current $I$ exceeding the threshold value results in torsion deformation of o-TaS$_3$ samples with one contact freely suspended. The rotation angle, $\delta \phi$, of the free end achieves several degrees and exhibits hysteresis as a function of $I$. The sign of $\delta \phi$ depends on the $I$ polarity; a polar axis along the conducting chains (the {\it c}-axis) is pointed out. We associate the effect with surface shear of the charge-density waves (CDW) coupled to the crystal shear. The current-induced torsional strain could be treated in terms of enormous piezoelectric coefficients ($>10^{-4}$ cm/V) corresponding to shear. In essence, TaS$_3$ appears to be a ready torsional actuator based on the unique intrinsic property of the CDW.