Infinite Resistivity Research Articles

Disorder-Induced Superconductor-Insulator Transition

In this paper, we report the results of our theoretical investigation on the interplay of superconductivity and disorder in two-dimensional (2D) systems. The effect of disorder on superconductivity of 2D systems was found analytically using Green’s function formalism. The results of our calculation revealed that disorder induced due to randomly distributed superconducting islands enhances decoherence of Cooper pairs and suppresses superconductivity. We have also determined the critical value of disorder at which the 2D system completely loses its superconducting properties. Below this critical value of disorder, the system acts as a superconductor, a system with zero electrical resistance. Above the critical value, it acts as an insulator, a system with infinite electric resistance. This is a fascinating result because a direct transition from the state of the infinite conductivity to the opposite extreme of infinite resistivity is unexpected in the theory of condensed matter physics.

The detection of old masonry tunnels as low electrical resistivity anomalies-application to one covered stream tunnel of the Cevennes Mountain region (France)

More than 70 km of old masonry tunnels covering natural streams were recently inventoried in the Cevennes mountain region (France, département du Gard). Due to their advanced state of degradation and their shallow depth, the covered stream tunnels have been responsible for several surface collapses since 2012. The mapping of the trajectory of these tunnels therefore is of primordial importance for the risk assessment of the affected municipalities. But only few of them were mapped so far due to their difficult accessibility and their precarious stability. Consequently there is a need to identify non-destructive methods for detecting them quickly from the surface of the most preoccupying areas. Two ERT profiles using 48 electrodes and the Wenner-Schlumberger array, under dry and wet conditions, were realized at the surface of one tunnel of which the position was precisely known in order to determine the ability of the technique to detect it. Analysis of the measured apparent resistivity showed an unexpected local decrease of resistivity near the tunnel boundary. The inverse models performed without any filtering of the measured apparent resistivity did not allow detecting any anomaly that could be interpreted as the presence of the tunnel. Conversely, the inversion of a smoothed version of the apparent resistivity allows detecting a low resistivity anomaly at the tunnel position. This result was quite surprising because we rather expected a high resistivity anomaly due to the infinite resistivity of the tunnel atmosphere compared to the surroundings. According to a study recently published by Putiška et al. (2012) on this topic and to a set of forward resistivity models we conducted, this unexpected low resistivity anomaly was explained to be due to the presence of a thin conductive layer around the tunnel. The fact that this anomaly was unobserved after inversion of the unfiltered apparent resistivity was explained by the presence of a high resistivity material (probably composed of coal) beside the thin conductive layer that altered the least-squares inversion process.

Current quantization and fractal hierarchy in a driven repulsive lattice gas.

Driven lattice gases are widely regarded as the paradigm of collective phenomena out of equilibrium. While such models are usually studied with nearest-neighbor interactions, many empirical driven systems are dominated by slowly decaying interactions such as dipole-dipole and Van der Waals forces. Motivated by this gap, we study the nonequilibrium stationary state of a driven lattice gas with slow-decayed repulsive interactions at zero temperature. By numerical and analytical calculations of the particle current as a function of the density and of the driving field, we identify (i) an abrupt breakdown transition between insulating and conducting states, (ii) current quantization into discrete phases where a finite current flows with infinite differential resistivity, and (iii) a fractal hierarchy of excitations, related to the Farey sequences of number theory. We argue that the origin of these effects is the competition between scales, which also causes the counterintuitive phenomenon that crystalline states can melt by increasing the density.

Geophysical prospecting for new cave passages: Fort Stanton Cave, New Mexico, USA

Geophysical surveys have been used to predict extensions of newly discovered sections of Fort Stanton Cave, the third-longest cave in New Mexico. Because air-filled caves have almost infinite resistivity, the electrical resistivity (ER) method is a very effective tool for detection of subsurface conduits in the unsaturated zone. Resistivity profiles have been used for several years by local cavers to guide exploration in Fort Stanton Cave. However, the most recent discoveries approach the limits of the depth of investigation of the resistivity equipment used by the cavers. The National Cave and Karst Research Institute has begun conducting resistivity profiles over these deeper portions of the cave system using a SuperSting™ R-8 resistivity meter coupled with longer 112-electrode arrays. These ER tools have been very successful at identifying extensions of known passage in Fort Stanton Cave.

Determination of cavities using electrical resistivity tomography

Abstract Geophysical surveys for cavity detection are one of the most common nearsurface applications. The usage of resistivity methods is also very straightforward for the air-filled underground voids, which should have theoretically infinite resistivity in the ERT image. In the first part of the paper, we deal with the comparison of detectability of the cavity by several types of the electrode arrays, the second part discusses the effect of a thin layer around the cavity itself, by means of 2D modelling. The presence of this layer deforms the resistivity image significantly as the resistive anomaly could be turned into a conductive one, in the case when the thin layer is more conductive than the background environment. From the electrical array analysis for the model situation a dipole-dipole and combined pole-dipole shows the best results among the other involved electrical arrays.

(Invited) Atomic Layer Deposition of Superconductors

We report the use of atomic layer deposition (ALD) to synthesize thin superconducting films and multilayer superconductor-insulator (S-I) hetero-structures. ALD being applied to superconducting films opens the way for a variety of applications, including improving the performance and decreasing the cost of high energy particle accelerators, superconducting wires for energy storage, and bolometers for radiation detection. Furthermore, the atomic-scale thickness control afforded by ALD enables the study of superconductivity and associated phenomena in homogeneous layers in the ultra-thin film limit. Two-dimensional superconductivity in such films is of interest from a fundamental point of view, as a new effect has recently been discovered at ultra-low temperature in thin superconducting films made by ALD: the super-insulating transition. The discovery of a new state with apparently infinite resistivity in ultra-thin ALD films offers both a platform to explore new physics as well as the promise, on a longer term, of new opportunities for loss electronics and detectors.

Existence and stability of viscous shock profiles for 2-D isentropic MHD with infinite electrical resistivity

For the two-dimensional Navier-Stokes equations of isentropic magnetohydrodynamics (MHD) with γ-law gas equation of state, γ≤ 1, and infinite electrical resistivity, we carry out a global analysis categorizing all possible viscous shock profiles. Precisely, we show that the phase portrait of the traveling-wave ODE generically consists of either two rest points connected by a viscous Lax profile, or else four rest points, two saddles and two nodes. In the latter configuration, which rest points are connected by profiles depends on the ratio of viscosities, and can involve Lax, overcompressive, or undercompressive shock profiles. Considered as three-dimensional solutions, undercompressive shocks are Lax-type (Alfven) waves. For the monatomic and diatomic cases γ = 5/3 and γ = 7/5, with standard viscosity ratio for a nonmagnetic gas, we find numerically that the the nodes are connected by a family of overcompressive profiles bounded by Lax profiles connecting saddles to nodes, with no undercompressive shocks occurring. We carry out a systematic numerical Evans function analysis indicating that all of these two-dimensional shock profiles are linearly and nonlinearly stable, both with respect to two- and three-dimensional perturbations. For the same gas constants, but different viscosity ratios, we investigate also cases for which undercompressive shocks appear; these are seen numerically to be stable as well, both with respect to two-dimensional and (in the neutral sense of convergence to nearby Riemann solutions) three-dimensional perturbations.

Hydromagnetic instability of a resistive hollow jet

The magnetohydrodynamic (MHD) stability criterion of a resistive hollow cylinder with respect to its capillary, pressure gradient, and electromagnetic forces is established. Numerous stability criteria are obtained as limiting cases from the present relation. The capillary force is destabilizing only for certain wavelengths to axisymmetric mode and stable to all other disturbances. There are three different cases for discussing the electromagnetic force (EMF) influence on the resistive hollow jet instability. As the fluid is with finite resistivity, the EMF does not have any influence on the capillary instability of a resistive hollow jet, however, the finite resistivity has a stabilizing tendency on the MHD hollow jet. As the fluid has infinite resistivity, the EMF is (de-)stabilizing according to restrictions. As the fluid is with zero resistivity, the EMF exerts an influence giving a sort of rigidity to the conducting fluid and that influence causes the bending and twisting of the lines of force in the fluid. Consequently, for a magnetic field of high intensity the capillary destabilization could be suppressed and stability arises.PACS No.: 47.17+e

Current sharing among filaments for Bi-2223 Ag-sheathed tapes with inter-filament barrier

Current distribution in Bi-2223 multifilamentary tapes with inter-filament barrier is numerically evaluated for the application of an alternating transport current. In the case of barrier materials with an infinite resistivity, the current distribution can be determined with a lumped parameter circuit model including the inductances and resistances of all the filaments. The mutual inductance between a pair of filaments is obtained by estimating their geometric mean distance. The power-law model is also assumed to take into account the effect of resistance in each filament. The influences of the silver ratio and filament number in the tape wire on the current distribution are discussed systematically as well as the power index and frequency.

Detection and 2d modelling of cavities using pole–dipole array

The resistivity method is often used in cave prospecting. In this paper the pole–dipole array ability to detect cavities at different depths and with different water contents is investigated. The research was performed using analogical and numerical modelling. According to the results, empty caves at a depth less than four times its diameter can be easily detected. The ability of the pole–dipole array to detect water-filled caves reaches a minimum at filling percentages of 30–50%. Overburden effects research shows that low resistivity overburden reduces the resolution capability of the array. This study shows that equivalent results can be obtained by modelling the empty caves as infinite resistivity bodies or, alternatively, as very high resistivity ones. The analysis of field data acquired in the Macico Calcario Estremenho (Portugal) shows the practical importance of the pole–dipole array in cavities prospecting.

Numerical 3-D Simulation of a Cathodic Protection System for a Buried Pipe Segment Surrounded by a Load Relieving U-Shaped Vault

Abstract A three-dimensional, multi-domain boundary element method approach was used to determine the performances of a cathodic protection system applied to a buried pipeline of limited longitudinal dimension, surrounded by a U-shaped vault of infinite resistivity (insulator). A Laplace model describing the potential problem was solved in combination with nonlinear boundary conditions that hold for the polarization behavior of the coated pipeline and coating holidays. The efficiency of this cathodic protection system was examined as a function of the soil conductivity, the position of the defects, and the presence of the U-shaped vault. The objective of these simulations was the quantitative determination of the reducing effect of this structure on the protection level of the outer pipe surface, as a result of its spatial obstruction for the protective currents that originate from the far-field anode beds.

Low Frequency Fluctuations near Relaxed State of Reversed Field Pinch (RFP) in the Presence of Stationary Plasma Flow

The frequencies of the fluctuations near the relaxed state of reversed field pinch (RFP) plasma in the presence of a stationary toroidal flow are investigated using magneto-hydrodynamical (MHD) theory in the approximation of the infinite aspect ratio and finite resistivity. We treat the fluctuations as MHD waves and derive their dispersion relations at the edge plasma. It is shown that there exists a new fluctuation mode with low frequency in the presence of a stationary toroidal flow, and that with the plasma resistivity it can be unstable. The dispersion relations of the new fluctuation mode and other MHD modes of the compressible plasma are obtained. The magnitudes of the frequencies are estimated using the parameters of TPE-RX, MST and RFX devices.

On gas bubbles in industrial aluminium cells with prebaked anodes and their influence on the current distribution

The secondary current distribution in industrial aluminium cells with prebaked anodes was calculated, taking into account the gas bubbles. The input data were obtained on the basis of a physical model and data suggested in the literature. The bubbles were modelled in the following manner: (i) as very small bubbles dispersed in a homogeneous layer with higher electrical resistivity than the bulk of the electrolyte, (ii) as large bubbles modelled as discrete slabs with infinite resistivity, and (iii) as a combination of (i) and (ii). The bubble size and the number of bubbles, as well as the resistance of the homogeneous bubble layer, were varied to give an equivalent voltage drop in the range 0.1–0.4 V. Large bubbles (slabs) appeared to have a significant screening effect on the anodic current densities. The anodic current densities between slabs showed local maxima, sometimes reaching twice the value of the working current density (0.75 A cm−2). The cathodic current densities had local minima underneath the large anodic bubbles, following their position at the anode. Underneath a bubble of 6.1 cm width, the cathodic current density decreased from 0.75 to 0.23 A cm−2.

Percolation-like approach to resistivity behaviour of glassforming ionic melts

The Vogel–Fulcher equation (and percolation approach) predicts an infinite resistivity below the “ideal” glassification point T 0 (correspondingly- percolation threshold). However, the ions still preserve a noticeable mobility within the real glasses even below T 0. To model the finite resistivity in glass a resistance R max of a broken bond is introduced. The ratio of R max/ R min in real glasses is about 10 14 and 1/ R max might be identified with a probability of tunnelling process. The comparison of calculations’ result (with R max/ R min=10 7 or 10 9) with our data on CKN is encouraging.

Only Fermi Liquids Are Metals

Any singular deviation from Landau Fermi-liquid theory appears to lead, for arbitrarily small concentration of impurities coupling to a non-conserved quantity, to a vanishing density of states at the chemical potential and infinite resistivity as temperature approaches zero. Applications to copper-oxide metals including the temperature dependence of the anisotropy in resistivity, and to other cases of non Fermi-liquids are discussed.

GRADIENT ARRAY PROFILES OVER THIN RESISTIVE VEINS1

AbstractFurness, P. 1993. Gradient Array Profiles over thin resistive veins. Geophysical Prospecting41, 113–130.Gradient array geoelectric surveys are commonly used to explore for buried sheet‐like targets. It is demonstrated that under certain circumstances the responses of such features can become practically equivalent for a range of models differing considerably in resistivity and thickness. This is the dual of the familiar equivalence phenomenon associated with thin beds in geoelectric sounding operations. Hence the geoelectric response profiles over thin dipping resistive veins are conveniently studied by considering equivalent forms with vanishing thickness and infinite resistivity but with the same resistivity‐thickness product. The effects of varying the dip, depth of burial, depth extent and resistivity–thickness product of such features on the gradient array response profiles are investigated by means of a series of numerical experiments. These demonstrate several effects of significance to survey design and data interpretation.In particular it is found that while the resistivity–thickness product influences the amplitude of the response profiles it has little effect on their form. A similar behaviour is found to be exhibited by veins with extended depth extent when the dip is varied.A complete quantitative interpretation of gradient array profiles over thin dipping resistive veins is thus only possible for veins of limited depth extent. For veins with an extended depth dimension, the data is ambiguous (in a practical sense) in terms of the dip and the resistivity–thickness product. Here, the interpretation can only be expected to deduce the horizontal and vertical locations of the vein apex.

Martens-Kuin models of normal and inverse polarity filament eruptions and coronal mass ejections

An analysis is made of the Martens-Kuin filament eruption model in relation to observations of coronal mass ejections (CMEs). The field lines of this model are plotted in the vacuum or infinite resistivity approximation with two background fields. The first is the dipole background field of the model and the second is the potential streamer model of Low. The assumption is made that magnetic field evolution dominates compression or other effects which is appropriate for a low-β coronal plasma. The Martens-Kuin model predicts that, as the filament erupts, the overlying coronal magnetic field lines rise in a manner inconsistent with observations of CMEs associated with eruptive filaments. Initially, the bright arc of a CME broadens in time much more slowly than the dark cavity between it and the filament, whereas in the model they broaden at the same rate or the bright arc broadens more rapidly than the dark cavity, depending on the background field. Thus, this model and, by generalization the whole class of so-called Kuperus-Raadu configurations in which a neutral point occurs below the filament, are of questionable utility for CME modeling. An alternate case is considered in which the directions of currents in the Martens-Kuin model are reversed resulting in a so-called normal polarity configuration of the filament magnetic field. In this case, a neutral line occurs above the current-carrying filament. The background field lines now distort to support the filament and help eject it. While the vacuum field results make this configuration appear very promising, a full two- or more-dimensional MHD simulation is required to properly analyze the dynamics resulting from this configuration.

Epicardial potential mapping. Effects of conducting media on isopotential and isochrone distributions.

Epicardial excitation sequences, recovery sequences, and potential distributions are recorded from patients during surgery and from animals in the research laboratory for a variety of purposes. During such recordings, a portion of the cardiac surface is exposed to air, and the remainder of the epicardial surface variably is in contact with conductive tissue. No systematic studies document the degree to which these different conditions affect measured excitation times, potential distributions, and/or the configuration of epicardial electrograms. Epicardial potential distribution was recorded from five isolated, perfused hearts using a 64-unipolar-lead sock. Data were recorded first with the heart suspended in air and then with the heart immersed in a heated tank filled sequentially to full and half-full levels with conductive Tyrode's solution and then NaCl-sucrose solution. These solutions had resistivity less than and more than that of blood, respectively, and air was assumed to have infinite resistivity. Epicardial potentials were recorded from two hearts before removal from the chest, both with and without a latex sheet insulating the heart from the pericardial cradle. Amplitude of recorded potentials from both intact and isolated hearts was markedly higher when the heart was surrounded by an insulating medium, but locations of positive and negative regions were less affected by surrounding medium. Isochrone activation maps calculated using the minimum derivative of the QRS (intrinsic deflection) were not affected by the conductivity of media surrounding the heart. The present study provides evidence that isochrone maps recorded at surgery are not distorted by exposure of the cardiac surface to insulating air. Results suggest that epicardial isochrones recorded during cardiac surgery could be used in patients to assess the accuracy of "inverse" procedures that noninvasively compute epicardial electrograms and isochrones from body surface potentials.

Silica Glasses

Fifty years ago, who could have imagined that silicon dioxide—the material of ordinary beach sand—would become one of the most important materials of present-day optics and electronics? Yet SiO2is arguably the most crucial material component in current-generation fiber optics and metal-oxide-semiconductor (MOS) device technology. In MOS field-effect transistors (MOSFETs), SiO2serves not only as the gate insulator, but also as the “field oxide” (which isolates various components of an integrated circuit) and as the packaging material which seals the device from outside contamination. In these roles silica acts as a “perfect dielectric,” being characterized by an essentially infinite resistivity (actually ~1016Ohm · m at 300 K). The ability to form such a high quality dielectric film with a near-perfect lattice match on single-crystal silicon continues to favor silicon-based MOS technology over technologies founded on electrically superior GaAs.In the rapidly developing fiber optic arena, fused silica is still “king” due to a combination of properties, including extremely high transparency over a range of usable wavelengths (Figure 1), low material dispersion (~0 at 1.3/üm), high tensile strength (~ 150 kpsi), and high chemical durability. In addition, bulk forms of silica continue to find application in lenses, prisms, windows, and low-coefficient-of-thermal-expansion reflective optics; thin silica films are common components of the highly reflective and anti-reflective surface coatings which are laid down on reflective and transmissive optics, respectively.

The Kronig-Penney model on a fibonacci lattice

We have studied both analytically and numerically the spectral properties of the continuous Schrödinger operator with Kronig-Penney potential on a quasiperiodic linear chain. We have found infinite resistivity in the infinite chain for almost all energies, except an infinite discrete set of k-points, for which the chain is conducting. For a finite, but macroscopic chain an approximate analytic expression is given for the “proportion of the conducting points” at a given energy for practical use.