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Strain-induced transformation of charge-density waves and mechanical anomalies in the quasi one-dimensional conductors TaS_3 and K_{0.3}MoO_3

We report studies of low-field conductivity, sigma, of the orthorhombic TaS_3 samples as a function of strain, epsilon. In the Peierls state the sigma(epsilon) dependencies show hysteresis. A similar hysteresis loop is observed for K_{0.3}MoO_3. For nano-sized TaS_3 samples the sigma(epsilon) curves show step-like changes associated with the "quantization" of the wave vector, q, of the charge-density wave (CDW). The dependences clearly reveal the change of the q-vector with strain. In contrast with the traditional concept, q is found to increase with sample expansion. This means that the stretch-induced anomalies cannot be explained by the transition of the CDW to fourfold commensurability with the pristine lattice (lock-in transition). Alternatively, we suppose, that at the critical stretch a CDW with larger amplitude and modified q-vector forms. Further, the models describing metastable length states and drop of the Young modulus on CDW depinning in terms of longitudinal CDW strain, require reconsideration. Presumably, transverse effects should be taken into account.