Resonance current-voltage characteristics of three-dimensional tunnel junctions with weak structural disorder

The nonlinear current-voltage characteristics of a three-dimensional tunnel junction with weak (low impurity concentration) structural disorder are obtained for temperature T=0, and a formula is derived for the magnitude of the mesoscopic fluctuations in its resonant static tunnel conductance. Zh. éksp. Teor. Fiz. 116, 1048–1057 (September 1999)     

Effect of symmetry of the electron states of HTSC on the current-voltage characteristics of SIS junctions

The current-voltage (IV) characteristics of SIS junctions are calculated in the framework of a multiband model with an anisotropic effective order parameter of HTSC. The results of calculations show that the shape of the IV characteristic and of the density of electron states changes significantly depending on the parameters of the model. A theoretical explanation is proposed for the experimentally observed s-like behavior of the IV characteristics of SIN and SIS junctions with BSCCO-type superconductors. The dependence of the superconducting peak asymmetry on the mutual arrangement of the bands is analyzed. The difference between the obtained results and the results of one-band models with the s and d symmetries of the order parameter is discussed.     

Possible influence of the quasiparticle-pair interference term on the current-voltage characteristics of oxide barrier Josephson junctions

The coefficients σ₀, σ₁ and j₁ of the current-phase relation of a planar oxide barrier Josephson junction are evaluated in the BCS theory as a function of voltage and gap energy. Since σ₁/σ₀ is ? - 1 for small voltages, and ? 1 above the gap voltage, σ₁ may have some observable consequence on the current-voltage characteristics.     

Band structure and density of States effects in co-based magnetic tunnel junctions

Utilizing Co/Al(2)O(3)/Co magnetic tunnel junctions with Co electrodes of different crystalline phases, a clear relationship between electrode crystal structure and junction transport properties is presented. For junctions with one fcc(111) textured and one polycrystalline (polyphase and polydirectional) Co electrode, a strong asymmetry is observed in the magnetotransport properties, while when both electrodes are polycrystalline the magnetotransport is essentially symmetric. These observations are successfully explained within a model based on ballistic tunneling between the calculated band structures (density of states) of fcc-Co and hcp-Co.     

Band structure characteristics for CdP2 in the tetragonal modification

We have investigated the density of states for deep local centers and special points of the M₀ type in β-CdP₂ using amplitude modulation laser spectroscopy. We used impurity absorption of laser and probe radiation for these studies. We observed deep local centers with energy levels in the forbidden gap at a depth of 0.34 (d ₁ ), 0.43 (d ₂ ), 0.86 (d ₃ ), 1.45 (a ₁ ) from the bottom of the conduction band and M₀ points at a depth of 0.46 and 1.03 eV in the conduction band, and we also confirmed the presence of M₀ points at a depth of 0.35 eV in the valence band. Ukrainian State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 64–68, April, 1998.     

Zero-field current-voltage characteristics in high-temperature superconductors

We have observed the anomalous magnetization of Bi₂Sr₂CaCu_2−xNi_xO₈ (x = 0 and 0.02) single crystals. Anisotropy decreases with iodine intercalation although it expands the space between CuO₂ layers. Iodine intercalation seems to suppress the magnetization anomaly for Ni = 1% crystals, but not for Ni = 1% substituted crystals. We have discussed these results in terms of the increase of anisotropy by Ni substitution and the dimensional crossover of flux lines. Effects of both oxygen concentration and substitution of a magnetic element for the Cu site on the anisotropy of Bi₂Sr₂CaCu₂O₈ crystals show the same tendency as the case of the YBa₂Cu₃O₇ superconductor.     

Band structure characteristics of T-square fractal phononic crystals

The T-square fractal two-dimensional phononic crystal model is presented in this article.A comprehensive study is performed for the Bragg scattering and locally resonant fractal phononic crystal.We find that the band structures of the fractal and non-fractal phononic crystals at the same filling ratio are quite different through using the finite element method.The fractal design has an important impact on the band structures of the two-dimensional phononic crystals.     

Hysteretic effects in the dc current-voltage characteristic of normal Nb/Pb tunnel junctions

High resistance normal Nb/Pb tunnel junctions have been studied. Both at 300 K and 77 K an hysteresis in the I–V characteristic has been measured: the presence of negative or positive bias voltages changes the tunneling probability. At every fixed bias current value, a voltage drift with time appears. The drift velocity increases as the voltage or the temperature increases. Moreover at 77 K anomalous low frequency oscillations arise in the junction when some positive or negative threshold voltages are exceeded.     

Resonances in the current-voltage characteristics of a dissipative Josephson junction

The I-V characteristics of a Josephson junction shunted by an Ohmic resistor shows sharp peaks when levels in neighbouring wells are crossing. We consider the shape and size of these peaks using a double-well model where the wells are given in parabolic approximation. The friction of arbitrary strength is included by the help of a bath of infinitely many degrees of freedom. 74.50.+z.     

Dynamic current-voltage characteristics of chalcogenide-glass thin-film diodes

The dynamic current-voltage characteristics are analyzed for a metal/chalcogenide glass/metal system in which the metal of one or both electrodes interacts with the glass.     

Investigation of the current-voltage characteristics of superconducting film structures

The current-voltage characteristics (CVC) of sandwich structures consisting of superconducting Pb(S) and normalconducting Ag(N) in the combination SNS, NSN and SN have been investigated with the current flow parallel to the phase boundaries. We observed step structures in the CVCs and their dependence on an external magnetic field and on the layer thickness of Pb and Ag in the temperature range between 1.5 K and 4.2 K. The experimental results are compared qualitatively with the behaviour of the CVCs calculated by Hansack and Kümmel¹⁰.     

Static current-voltage characteristics of point-contact crystal rectifiers

An investigation of the current-voltage characteristics of a point-contact rectifier, taking account of the surface states, is described. Consideration is given to the influence of the forming of the rectifier point upon the current-voltage characteristic due to the change in the charge density in the surface state, caused by the redistribution of the charges on the contact periphery and in the bulk material.     

Zero-field current-voltage characteristics in high-Tc superconductors

Zero-field current-voltage (I–V) characteristics of various high-temperature superconductor samples are analyzed in the context of the current-temperature (I−T) phase diagram. After establishing the validity and relevance of the phase diagram to these materials, the anisotropy factor is extracted from the slope ofI _c ¹ (T) (the current defined by the onset of resistance). It is concluded that studying theI−V characteristics of amples in the context of theI−T phase diagram is a simple, useful tool for comparing samples. Work supported by the Office of Naval Research.     

On the theory of sublinear current-voltage characteristics of semiconductor structures

The strong carrier accumulation in the high resistive region of semiconductor structures giving rise to field-opposed diffusion of free carriers may result in the appearance of the sublinear current-voltage dependence [V ∝ exp (Iaw)], which is extremely sensitive on external influences.     

Investigation of the current-voltage characteristics of thin-film ZnSe-ZnTe heterojunction structures

This paper investigates the current-voltage characteristics of thin-film ZnSe-ZnTe heterojunction structures grown on zinc substrates. It is shown that the maximum rectification coefficient for such systems is observed when the condition d_1,2=d₀ is satisfied. On the basis of the general equation of the current-voltage characteristics of heterojunctions taking into account the boundary conditions, equations are derived which describe the behavior of the forward and back branches of the current-voltage characteristic of the heterojunction under consideration, and an explanation is given of the divergence between the theoretical and experimental results.