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.     

Scaling of the current-voltage characteristics of superconducting films in the flux creep model

On the basis of the magnetic flux creep model, taking viscous vortex motion and the spatial shape of the pinning potential into account, we have constructed a model explaining the shape of the current-voltage characteristics (CVC’s) of high-temperature superconducting films and the sign change of the curvature of these characteristics with change in temperature. The model given also allows one to explain the scaling of these curves. Fiz. Tverd. Tela (St. Petersburg) 40, 989–992 (June 1998)     

Influence of structural disorder on the current-voltage characteristic of a quasi-one-dimensional tunnel junction

The influence of the subbarrier impurity scattering of tunneling electrons on the current-voltage characteristic of a quasi-one-dimensional insulator layer with weak structural disorder (a small impurity concentration) is considered in the one-electron approximation at T=0. An expansion in powers of the impurity concentration gives the form of the current-voltage characteristic and the conditions for small mesoscopic fluctuations of the static tunneling conductance of such a layer in the cases of resonant and nonresonant tunneling. Zh. éksp. Teor. Fiz. 113, 1522–1530 (April 1998)     

Electrodynamic stabilization conditions for high-temperature superconducting composites with different types of current-voltage characteristic nonlinearity

The current instability is studied in high-temperature superconducting current-carrying elements with I–V characteristics described by power or exponential equations. Stability analysis of the macroscopic states is carried out in terms of a stationary zero-dimensional model. In linear temperature approximation criteria are derived that allow one to find the maximum allowable values of the induced current, induced electric field intensity, and overheating of the superconductor. A condition is formulated for the complete thermal stabilization of the superconducting composite with regard to the nonlinearity of its I–V characteristic. It is shown that both subcritical and supercritical stable states may arise. In the latter case, the current and electric field intensity are higher than the preset critical parameters of the superconductor. Conditions for these states depending on the properties of the matrix, superconductor’s critical current, fill factor, and nonlinearity of the I–V characteristic are discussed. The obtained results considerably augment the class of allowable states for high-temperature superconductors: it is demonstrated that there exist stable resistive conditions from which superconductors cannot pass to the normal state even if the parameters of these conditions are supercritical.     

退火时间对MgB_2超导薄膜的影响

在多晶A l2O3衬底上,以B2H6作为硼源,化学气相沉积先驱B薄膜,采用Mg扩散方法,在不同退火时间条件下制备了MgB2超导薄膜。通过电阻-温度曲线测量、X射线衍射分析和扫描电子显微镜形貌观测方法,研究了退火时间对MgB2薄膜的超导特性、晶体结构、表面形貌的影响。     

On the current-voltage characteristic of the oxide process

The transport equations that simulate the passage of the ionic current through an oxide layer under Steady-state conditions have been investigated. These equations are integrated by the method of matched asymptotic expansions. An analysis of the current-voltage characteristic of the system has revealed a region with negative differential conductivity. On this basis, it has been argued that the system is characterized by an instability of the initially uniform distribution of the electric current, which, in turn, leads to the appearance of “current filaments.” The threshold value of this instability is determined.     

Hg-based cuprate superconducting films patterned into structures for ultrafast photodetectors

We present results which describe procedures of the preparation and patterning of Hg,Re-Ba-Ca-Cu-O superconducting films suitable for coplanar structures usable as possible photodetectors and for microbridges. We compare structural and electrical properties of the final films from the point of their applicability for photodetectors. Our prepared Re-doped Hg-based films on LaAlO₃ substrate are continuous with a sufficient adhesion to the substrate and with a maximum zero resistance critical temperature T_C0 ∼ 122 K. The X-ray diffraction of all the films confirmed the Hg-1212 phase beside the minor Hg-1223 phase and intergrowth phases in some cases. In spite of epitaxial character of the final Hg-based films, the microwave and magnetic measurements suggest a possible existence of nonstoichiometric material between the grains which we register as a presence of weak links near the transition into the superconducting state. We show some electrical properties of the prepared superconducting structures, too. The prepared coplanar structures show ultrafast photoresponse signal to incident laser pulse.     

Estimation of the current-voltage characteristic of an open discharge

The simplest mathematical model for describing the processes in the electron beam generators based on an open discharge (i.e., high-voltage glow discharge with electron runaway) is considered. On the basis of the model, the discharge current-voltage characteristic is found. The resultant dependences are compared with experimental results.     

Interaction of surface acoustic waves with moving vortex structures in superconducting films

A method is proposed for describing a moving film vortex structure and its interaction with surface acoustic waves. It is shown that the moving vortex structure can amplify (generate) surface acoustic waves. In contrast to a similar effect in semiconductor films, this effect can appear when the velocity of the vortex structure is much lower than the velocity of the surface acoustic waves. A unidirectional collective mode is shown to exist in the moving vortex structure. This mode gives rise to an acoustic analogue of the diode effect that is resonant in the velocity of the vortex structure. This acoustic effect is manifested as an anomalous attenuation of the surface acoustic waves in the direction of the vortex-structure motion and as the absence of this attenuation for the propagation in the opposite direction.     

Empirical model for the current-voltage characteristic of resonant-tunneling devices

An empirical model is presented for the current-voltage characteristics of resonanttunneling (RT) devices. By using this model an analytical study of millimeter-band electronic circuits employing RT devices can be performed.     

On the current-voltage characteristic of a tunnel metal-semiconductor Schottky-Barrier contact

A possibility of a more simple and exact representation of the current-voltage (I–V) characteristic of a tunnel metal-semiconductor contact is investigated. Analysis is made on the basis of the approach proposed earlier, according to which the behaviour of the (I–V) characteristics of the Schottky-barrier contacts at low temperatures depends on the nonlinear dependence of the true (or effective for a tunnel contact) barrier height on the bias voltage. A simple equation for the (I–V) characteristic of the tunnel contact is theoretically substantiated using measurable parameters-the ideality factor n and barrier height ϕ_bm where the quantity ϕ_bn ≡ nϕ_bm plays the role of a barrier height. The calculation shows that this quantity is very close to the true barrier height of the tunnel contact (with allowance for the effect of image force) in wide current, temperature, and impurity-concentration ranges. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 18–25, March, 2006.     

Effect of normal electrons in superconductors on the current-voltage characteristic of a Josephson junction

It is established that the conductivity of normal electrons in superconductors plays a large role in the current-voltage characteristic of a Josephson junction having a high critical current density, described on the basis of a nonlocal electrodynamics. It is shown in the resistive limit that the normal-electron contribution increases the current through the Josephson junction, while in the capacitive limit it decreases the contribution of Cherenkov resonances. Fiz. Tverd. Tela (St. Petersburg) 41, 582–587 (April 1999)     

Current instability with an S -shaped current-voltage characteristic in thin films of composites based on polymers and inorganic particles

The switching and memory effects, which manifest themselves in the transition from a high-resistance state to a low-resistance state, are observed in thin films of composites based on polymers (carbazole derivatives) and silicon inorganic particles. It is established that, at small thicknesses of composite films, the resistance (with an initial value of no less than 100 MΩ) upon transition from the high-resistance state to the low-resistance state is changed by three or four orders of magnitude. This transition in the composites under investigation is accompanied by the appearance of an S-shaped current-voltage characteristic and its hysteresis. It is demonstrated that the observed effects are associated with the specific features of the thermomechanical and electrical properties of the polymer in the composite material. Original Russian Text ? é.A. Lebedev, E.L. Alexandrova, A.N. Aleshin, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 1, pp. 195–197.     

Nucleation and collapse of the superconducting phase in type-I superconducting films

The phase transition between the intermediate and normal states in type-I superconducting films is investigated using magneto-optical imaging. Magnetic hysteresis with different transition fields for collapse and nucleation of superconducting domains is found. This is accompanied by topological hysteresis characterized by the collapse of circular domains and the appearance of lamellar domains. Magnetic hysteresis is shown to arise from supercooled and superheated states. Domain-shape instability resulting from long-range magnetic interaction accounts well for topological hysteresis.     

Quantized resistances in the current-voltage characteristics of superconducting PbAgPb sandwiches

We have compared the voltage steps and the linear current branches in the current-voltage characteristic of PbAgPb sandwiches with numerical results given by a theoretical model due to Kümmel. In this model the occurrence of a potential difference between the film ends is explained by quasiparticle-induced spatial and temporal variations of the superconducting order parameters phase. In these experiments a new feature is found: Also without an external magnetic field the resistance of the current branches are proportional to a quantum number. From this we can draw important conclusions about the shape of the pair potential well and the proximity effect. Furthermore we give an explanation for the temperature dependent hysteresis of the critical current.     

Tunneling in superconducting structures

Here we review our results on the breakpoint features in the coupled system of IJJ obtained in the framework of the capacitively coupled Josephson junction model with diffusion current. A correspondence between the features in the current voltage characteristics (CVC) and the character of the charge oscillations in superconducting layers is demonstrated. Investigation of the correlations of superconducting currents in neighboring Josephson junctions and the charge correlations in neighboring superconducting layers reproduces the features in the CVC and gives a powerful method for the analysis of the CVC of coupled Josephson junctions. A new method for determination of the dissipation parameter is suggested.     

Numerical study of the current-voltage characteristic of a plasma-filled high-current diode

A numerical study is performed of a one-dimensional model of a high current plasma-filled diode, connected in a circuit with a voltage generator. Flow of the plasma from an external source into the diode anode-cathode gap through the plane of the cathode grid proves to have a definite effect on the diode current-voltage characteristic. An estimate is made of the limiting current above which formation of a cathode double layer occurs. Generation of explosive emission at a high value of current or the time derivative of current causes rapid expansion of the cathode layer due to a lack of the majority, electron current component and the presence of a phase intensified by plasma erosion. Dependence of the current-voltage characteristic on density of cathode explosive emission centers is noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 48–53, October, 1988.