An original interferometer-based setup for measurements of length of needle-like samples is developed, and thermal expansion of o-TaS3 crystals is studied. Below the Peierls transition the temperature hysteresis of length L is observed, the width of the hysteresis loop δL/L being up to 5 · 10 −5 . The behavior of the loop is anomalous: the length changes so that it is in front of its equilibrium value. The hysteresis loop couples with that of conductivity. The sign and the value of the length hysteresis are consistent with the strain dependence of the charge-density waves (CDW) wave vector. With lowering temperature down to 100 K the CDW elastic modulus grows achieving a value comparable with the lattice Young modulus. Our results could be helpful in consideration of different systems with intrinsic superstructures.PACS Numbers: 71.45.Lr, 65.40.De Internal degrees of freedom is a feature of a random system; in principle, they can give rise to metastable size states resulting, say, to hysteresis in thermal expansion. 1 A special class form the compounds with intrinsic superstructures.Comprising two periodicities, generally incommensurate, the compounds occupy intermediate place between genuine aperiodic and truly periodic systems. 2 In these systems, such as charge-and spindensity waves (CDW and SDW), 3 Wigner cristals, superconductors in magnetic fields, 4 structurally incommensurate crystal phases, 5 the superstructure periodicities could be varied by external fields or temperature changes. The resulting metastable configurations can be reflected back onto the elastic properties and size of the underlying lattice, 3-5 though this question is still poorly understood.Quasi 1-dimensional conductors with CDW belong to a widely studied class of materials, in which intrinsic superstructure develops through the Peierls transition 6 . When electrons condense into CDW they form a deformable medium, -an electronic crystal. Deformation of the CDW affects their main static and dynamic properties and gives rise to metastability and hysteresis.The straightforward treatment of the CDW as a spring, whose strain is just applied to the crystal at the ends or via the impurities is not valid. Moreover, in the simple one-dimensional model the strains of the CDW and the crystal do not couple at all: if initially the CDW are relaxed, any change of the crystal length would not draw the CDW away from the equilibrium, i.e. give rise to a CDW deformation, 7 as it was noticed in Refs. 8-11. Similarly, once the CDW is deformed, any change of the lattice constant, c, would neither decrease nor increase the deviation of the CDW wavelength λ from the equilibrium value, λ eq . So, within this model a CDW deformation would not give rise to a length change.At the same time, the interaction of the CDW and the lattice is clearly seen from the elastic anomalies, including a drop of the Young modulus of the lattice, 8-11 Y l , up to 4%, 10 when the CDW become depinned.Mozurkewich 8 has concluded that the lattice deformation does give rise to a de...

We propose a model of the Peierls transition (PT) taking into account amplitude fluctuations of the charge-density waves and spontaneous thermally activated suppression of the Peierls gap, akin to the phase slip process. The activation results in the exponential growth of the normal phase with increasing temperature. The model fairly describes the behavior of resistance, thermal expansion, Young modulus and specific heat both below and above the PT temperature $T_P$. The PT appears to have a unique nature: it does not comprise $T_P$ as a parameter, and at the same time it has features of the 1st order transition. The possible basis for the model is activation of non-interacting amplitude solitons perturbing large volumes around them.Comment: 5 pages, 4 figure

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An interferometer-based setup for measurements of length of needle-like samples is developed, and thermal expansion of o-TaS3 crystals is studied. Below the Peierls transition the temperature hysteresis of length L is observed, the width of the hysteresis loop $\delta L/L$ being up to $5\times 10^{-5}$. Curiously, $L(T)$ changes so that it is in front of its equilibrium value. The hysteresis loop couples with that of conductivity. With lowering T the charge-density waves' (CDW) elastic modulus grows and at 100 K becomes comparable with that of the lattice Yl. The results justify the assumption about the strain dependence of the CDW wave vector and clarify the nature of the anomalies of Yl which occur on the CDW depinning. In particular, Yl, is expected to show a strong drop in the static regime, if measured at sufficiently small sample elongation $(\delta L/L < 10^{ -5}) $.

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