I. G. Gorlova

Vortex motion and kosterlitz-thouless transition in superconducting single crystals Bi2Sr2CaCu2Ox

Abstract Hall voltages VH in a resistive superconducting state and in a normal state are shown to have opposite signs. This is accounted for by a flux vortex motion. Current-voltage characteristics V∝Ia(T) near the transition with a characteristic Nelson-Kosterlitz jump in a(T) at T = Tc present the evidence for a Kosterlitz-Thouless (KT) transition, which may be explained by flux vortex unbinding inside the superconducting planes.

Growth and study of single-phase 2212 BSCCO whiskers of submicron cross-sectional area

Abstract The growth of perfect single-phase (2212) superconducting BSCCO whiskers with cross-sectional area S as small as 0.1 μm 2 is described. Submicron cross section whiskers are shown to have perfect crystalline structure, some of them being free of dislocations. The critical current density of the whiskers J c , is shown to increase as S decreases 2 achieving 5 × 10 5 A/cm 2 for S = 0.15 μm 2 . The temperature dependence of resistivity ϱ( T ) of submicron whiskers in contrast to bulk-like single crystals exhibits a prominent deviation Δϱ down from linear temperature dependence ϱ N up to T ≈ 200 K. Δϱ is shown to be proportional to s −1 Δϱ / ϱ N S −1 exp(− T / T 0 ), T 0 =40 K K. The origin of Δϱ due to one-dimensional (1D) superconducting fluctuations is discussed.

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.

Magnetoresistance of a layered high-Tc superconductor below the Berezinskii-Kosterlitz-Thouless transition

Abstract The mechanism of the resistivity of a weakly coupled layered supecocoductor below the Berezinskii-Kosterlitz-Thouless (BKT)_ transition temperature T BKT in a magnetic field perpendicular to the layers is studied experimentally and theoretically. The resistance of Bi 2 Sr 2 CaCu 2 O x single crystals at temperatures 70–90 K in a magnetic field H T T BKT in a field H larger than 10–30 Oe the resistance is characterized by the thermoactivated behaviour down to some characteristic temperature T ∗ (H) , below which power-law I − V curves V ∝ I aH( T )+1 were observed. We account for these results by the creation of 2D-vortices due to the breaking of Abrikosov vortex lines by thermal fluctuations and transport current. Calculated dependences of the power index a H on the temperature and magnetic field agree with the experimental ones. The observed T ∗ (H) dependence is described by the condition that the mean thermal fluctuations of the positions of the 2D-vortices forming flux lines are of the order of a mean distance between flux lines.

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.

Peculiarities of carrier scattering at the boundary of a normal metal and a quasi-one-dimensional conductor with a charge-density wave

Nonlinear effects at the interface between a normal metal and the quasi-one-dimensional conductor with a charge-density wave K0.3MoO3 are investigated experimentally. It is found that the scattering of the normal carriers with energy E less than the Peierls gap Δp gives rise to an excess resistance of the N-CDW boundary. The character of the scattering is similar to Andreev reflection. In contrast to superconductors, however, the sign of the charge of the reflected particle does not change.

The current-voltage characteristics of single-crystal whiskers of 2:2:1:2 BiSCCO

Abstract The current-voltage characteristics of a single-crystal whisker of the 2:2:1:2 phase of bismuth strontium calcium copper oxide have been measured over a wide range of temperatures and magnetic fields. In low magnetic fields there are indications of a phase transition. In higher magnetic fields the current-voltage characteristics obey powerful scaling relationships. In large fields and low currents we find that the dissipation has a number of the characteristics of the thermally activated flux creep (TAFC) model of Kim and Anderson, in particular the temperature and magnetic field dependences of the barrier height obey the typical behaviour for that class of model. However, the flux-bundle parameters must be taken as temperature dependent. At high fields and high currents the observed behaviour differs very significantly from the TAFC prediction.

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.

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.