V. Ya. Pokrovskii

Features of the conductivity of the quasi-one-dimensional compound TiS3

The structure and transport properties of single crystal whiskers of the TiS3 quasi-one-dimensional semiconductor have been investigated. The anisotropy of the conductivity in the plane of layers (ab) has been measured as a function of the temperature. The anisotropy at 300 K is 5 and increases with a decrease in the temperature. Features on the temperature dependences of the conductivity along and across the chains are observed at 59 and 17 K. Near the same temperatures the form of the current-voltage characteristics measured along the chains is qualitatively changed. The current-voltage characteristics below 60 K exhibit nonlinearity and have a threshold form below 10 K. The results indicate possible phase transitions and the collective conduction mechanism at low temperatures.

Critical-state model for pinned charge-density waves: conditions and consequences of phase slip

Abstract In a quasi-one-dimensional conductor, phase slips can occur in pinned charge-density waves (CDWs) even under zero electric field. The conditioons for their onset and their subsequent evolution are discussed in detail. Phase slips perturb the CDW phase over the phase-coherence length, which increases exponentially with a decrease in temperature because of exponential growth of the CDW elastic modulus. At low temperatures, phase slips should evolute into static soliton-like formations (CDW dislocations). The proposed critical-state model is in agreement with our previous experiments.

Gigahertz-range synchronization at room temperature and other features of charge-density wave transport in the quasi-one-dimensional conductor NbS3

Whiskers of the quasi-one-dimensional conductor NbS3, phase II, have been synthesized. The samples show two charge-density wave (CDW) states: below 360 and below 150 K. Both CDWs show sharp threshold fields and coherent transport revealed by ac-dc coupling, i.e., Shapiro steps. The thinnest samples (cross sections below 104 nm2) exhibit Shapiro steps for frequencies at least as high as 4 GHz at room temperature. The results indicate that, for each of the CDW states, only one Nb chain per unit cell participates in the CDW transport.

Transition to 1D conduction with decreasing thickness of the crystals of TaS3 and NbSe3 quasi-1D conductors

It is found that, with decreasing thickness of the crystals of TaS3 and NbSe3 quasi-1D conductors, the dependences of the conductivity of these crystals on temperature and electric field change from the form typical of bulk samples to a nearly power law behavior typical of 1D electron systems.

Conductance anisotropy and the power-law current-voltage characteristics along and across the layers of the TiS3 quasi-one-dimensional layered semiconductor

Nonlinear conductance along the crystallographic axis c across the layered whiskers of the TiS3 quasi-one-dimensional semiconductor has been discovered. It has been shown that the current-voltage characteristics in all three directions along the a, b, and c axes obey a power law with the exponent increasing with a decrease in temperature. Possible mechanisms of the nonlinear conductance including the motion of condensed electrons, excitation and dissociation of electron-hole pairs in two-dimensional layers, and interlayer tunneling under the conditions of the Coulomb blockade with a charge spreading over the layers are considered.

Collective conduction mechanism in a quasi-one-dimensional TiS3 compound

The resistance of TiS3 single crystal whiskers has been measured as a function of temperature and electric field in the range of 4.2–340 K. At temperatures below 60 K, a strong nonlinearity of the current-voltage characteristics has been revealed. Below 10 K, the current-voltage characteristics are of the threshold type. The results are attributed to the transition of electrons to a collective state, probably, with the formation of a charge density wave.

Simulation of the control process applied to the micromechanical device with the shape memory effect

It has recently been proved that, in alloys, e.g., based on the Ti–Ni system, a shape memory effect (SME) is preserved down to the nanoscale sizes of an active alloy layer and demonstrated ultrasmall-sized and fully functional microand nanomechanical devices: actuators and nanotweezers that are fabricated via standard microelectronic technologies relying on composite materials with the SME. In the nearest future, such achievements will enable the creation of the next-generation microand nanomechanical devices whose sizes are quite comparable with those inherent to, e.g., carbon nanotubes, graphene sheets, viruses, etc. Mathematical simulation methods are used to study how the shape-memory micromechanical devices can be activated by means of resistive pulse heating. A decrease in the overall sizes of heating elements (from 1 mm to 10 μm) is demonstrated to be accompanied by the fact that the speed of operation increases sharply from 102 to 105 s–1 and, simultaneously, the energy consumption diminishes from 10–3 to 10–8 J per operation. The preliminary results of experiments whereby the control of the composite nanotweezer exhibiting the SME is perfected with the help of the automatic pulsed heating technology, as well as the prospects for creating high-speed and high-performance microrobotic systems incorporating newly developed components, are discussed.

Contribution of spontaneous phase slippage to linear and nonlinear conduction near the Peierls transition in thin samples of TaS3

In the Peierls state very thin samples of TaS3 ~cross-section area ;10 23 mm 2 ) are found to demonstrate smearing of the I-V curves near the threshold field. With approaching the Peierls transition temperature, T P , the smearing evolves into smooth growth of conductance from zero voltage interpreted by us as the contribution of fluctuations to the nonlinear conductance. We identify independently the fluctuation contribution to the linear conductance near T P . Both linear and nonlinear contributions depend on temperature with close activation energies ;(224)310 3 K and apparently reveal the same process. We reject creep of the continuous charge-density waves ~CDW’s! as the origin of this effect and show that it is spontaneous phase slippage that results in creep of the CDW. A model is proposed, accounting for both the linear and nonlinear parts of the fluctuation conduction up to T P .

Dynamic mixed state in micron-size bridges based on Bi2Sr2CaCu2Ox whiskers

Measurements of the current-voltage characteristics of micron-size bridges made of Bi2Sr2CaCu2Ox single-crystal whiskers are carried out. It is found that, at temperatures below the superconducting transition temperature, the current-voltage characteristics exhibit quasi-periodic voltage jumps with segments of constant differential resistance whose value is proportional to the jump number. For the narrowest bridges (0.5–1 ¼m), up to ten voltage jumps are observed. The result of the experiment is explained by the formation of vortex lines under the current effect.

Shapiro steps in the torsion of a quasi-one-dimensional conductor TaS3

Features have been observed in the current dependences of the torsion angle, φ(I), for samples of a quasi-one-dimensional conductor TaS3 irradiated by a high-frequency (HF) field. The features appear at the same current values as the Shapiro steps on the current-voltage characteristics, i.e., correspond to the synchronization of the motion of a charge-density wave (CDW) by the HF field. The shape of the features in the φ(I) dependences indicates a decrease in the inhomogeneous deformation of the CDW under the synchronization conditions. The investigation of torsion appears to be a highly sensitive method for determining the spatial coherence of the CDW.