S. G. Zybtsev

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.

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.

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.

'Quantized' states of the charge-density wave in microcrystals of K 0.3 MoO 3

Quantization of electrons in solids can typically be observed in microscopic samples if the mean free path of the electrons exceeds the dimensions of the sample. A special case is a quasi one-dimensional metal, in which electrons condense into a collective state. This state, a charge-density wave (CDW), is a periodic modulation of both the lattice and electron density. Here, we demonstrate that samples of K(0.3)MoO(3), a typical CDW conductor, show jumps in conduction, regular in temperature. The jumps correspond to transitions between discrete states of the CDW and reveal the quantization of the wave vector of electrons near the Fermi vector. The effect involves both quantum and classical features of the CDW: the quantum condensate demonstrates modes, resembling those of a classical wave in a resonator. The analysis of the steps allows extremely precise studies of the CDW wave-vector variations and reveals new prospects for structural studies of electronic crystals and fine effects in their electronic states and lattice motions.

Josephson effects in YBa2Cu3O7−x grain-boundary junctions on (001) NdGaO3 bicrystal substrates

Abstract Grain-boundary YBa2Cu3O7−x Josephson junctions were fabricated on (001) NdGaO3 bicrystal substrates with a misorientation angle of 2×18.4°. Both DC and AC Josephson effects were studied in these high-Tc junctions in the range from liquid-helium up to liquid-nitrogen temperatures. The values of characteristic voltages were up to 0.34 mV at a temperature of 10 K. The I-V curves of the junctions and their response to low-intensity millimeter-wave radiation were shown to be described by the RSJ model with thermal fluctuations. Values of responsivity up to 106 V/W and a noise equivalent power as low as 10−14W/ Hz 1 2 were obtained for these junctions operating both in wideband and selective detection modes at a frequency of 78 GHz. The applicability of YBa2Cu3O7−x Josephson junctions made on NdGaO3 bicrystal substrates for detection and spectral analysis of millimeter-wave and far-infrared radiation is emphasized.

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.

Photoconduction in CDW conductors

Abstract Photoconduction study of quasi-1D conductors allows to distinguish between the single-particle and collective linear conduction, investigate the effect of screening on collective transport and obtain interesting new details of the electronic energy structure of pure and doped CDW conductors. Here we present results of photoconduction study in quasi-1D conductors o-TaS3, K0.3MoO3, and NbS3(I).

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.

Instabilities in the current-voltage characteristics of submicron BSCCO bridges

The influence of magnetic field and microwave irradiation on dynamical phase separation in submicron Bi2Sr2CaCu2O8+x bridges has been studied. Strong effect on the shape and metastable character of the step-like I-V characteristics are found. Under a weak field H < 2 Oe and low level microwave irradiation the step-like structure of the I-V characteristics smears out and disappears completely. The average frequency of switching between metastable states grows by 5 orders under increase of magnetic field by only 1 Oe. This behavior is explained in terms of the model of dynamical vortex lines.

Properties of strained TaS3 samples in the state of charge density wave and in the normal state

The uniaxial strain of quasi-one-dimensional conductor whiskers of orthorhombic TaS3 at a strain higher than εc ~ 0.8% leads to a sharp increase in the coherence of the properties of a charge density wave (CDW), which manifests itself in its motion in fields higher than threshold field Et. During uniaxial elongation, TaS3 is shown to exhibit the following unusual properties even in weak fields: Peierls transition temperature TP depends nonmonotonically on ε, one-dimensional fluctuations weaken near TP, and the coherence length of a charge density increases at T < TP. Investigations in fields higher than Et show that the ultracoherent properties of CDW exist in a wide temperature range and are retained when temperature increases up to TP. These properties of CDW make it possible to observe a sharp increase in Et near TP and an almost jumplike increase in Et at T < 90 K. The increase in Et at TP is explained by a decrease in the coherence volume of CDW because of a fluctuational suppression of the Peierls gap.