scholarly journals SPECTRAL CORRELATIONS IN DISORDERED MESOSCOPIC METALS AND THEIR RELEVANCE FOR PERSISTENT CURRENTS

1996 ◽  
Vol 10 (28) ◽  
pp. 1397-1406 ◽  
Author(s):  
AXEL VÖLKER ◽  
PETER KOPIETZ
Keyword(s):  
Energy Levels ◽  
Three Dimensional ◽  
Average Density ◽  
Electron Interaction ◽  
Energy Window ◽  
Persistent Currents ◽  
Dependent Part ◽  
The Difference ◽  
Aharonov Bohm ◽  
Grand Canonical

We use the Lanczos method to calculate the variance σ2(E, ϕ) of the number of energy levels in an energy window of width E below the Fermi energy for noninteracting disordered electrons on a thin three-dimensional ring threaded by an Aharonov–Bohm flux ϕ. We confirm numerically that for small E the flux-dependent part of σ2(E, ϕ) is well described by the Altshuler–Shklovskii-diagram involving two Cooperons. However, in the absence of electron–electron interactions this result cannot be extrapolated to energies E where the energy-dependence of the average density of states becomes significant. We discuss consequences for persistent currents and argue that for the calculation of the difference between the canonical- and grand canonical current it is crucial to take the electron–electron interaction into account.

THE ANALOGUE OF THE AHARONOV–BOHM EFFECT FOR BOUND STATES FOR NEUTRAL PARTICLES

2011 ◽  
Vol 26 (18) ◽  
pp. 1331-1341 ◽  
Author(s):  
KNUT BAKKE ◽  
C. FURTADO
Keyword(s):  
Bound States ◽  
Neutral Particle ◽  
Energy Levels ◽  
Quantum Ring ◽  
Persistent Currents ◽  
One Dimensional ◽  
Neutral Particles ◽  
Quantum Flux ◽  
Bohm Effect ◽  
Aharonov Bohm

We study the analogue of the Aharonov–Bohm effect for bound states for a neutral particle with a permanent magnetic dipole moment interacting with an external field. We consider a neutral particle confined to moving between two coaxial cylinders and show the dependence of the energy levels on the Aharonov-Casher quantum flux. Moreover, we show that the same flux dependence of the bound states can be found when the neutral particle is confined to a one-dimensional quantum ring and a quantum dot, and we also calculate the persistent currents in each case.

scholarly journals WHY HOLES ARE NOT LIKE ELECTRONS III: HOW HOLES IN THE NORMAL STATE TURN INTO ELECTRONS IN THE SUPERCONDUCTING STATE

2009 ◽  
Vol 23 (14) ◽  
pp. 3035-3057 ◽  
Author(s):  
J. E. HIRSCH
Keyword(s):  
Single Particle ◽  
Normal State ◽  
Superconducting State ◽  
Negative Charge ◽  
Energy Levels ◽  
Particle Energy ◽  
Point Of View ◽  
Electron Interaction ◽  
Single Particle Energy ◽  
The Difference

In recent work, we discussed the difference between electrons and holes in energy band in solids from a many-particle point of view, originating in the electron–electron interaction,1 and from a single particle point of view, originating in the electron–ion interaction.2 We proposed that superconductivity in solids only occurs when the Fermi level is close to the top of a band (hole carriers), that it originates in "undressing" of carriers from both the electron–electron and the electron–ion interaction, and that as a consequence holes in the normal state behave like electrons in the superconducting state.3 However, the connection between both undressing effects was left unclear, as was left unclear how the transformation from hole behavior to electron behavior occurs. Here, we clarify these questions by showing that the same electron–electron interaction physics that promotes pairing of hole carriers and undressing of carriers from the electron–electron interaction leads to undressing of carriers from the electron–ion interaction and transforms the behavior of carriers from hole-like to electron-like. A complete reorganization of the occupation of single-particle energy levels occurs. Furthermore this phenomenon is connected with the expulsion of negative charge that we predict to occur in superconductors. These unexpected connections support the validity of our theoretical framework, the theory of hole superconductivity, to explain superconductivity in solids.

(ALMOST) EVERYTHING YOU ALWAYS WANTED TO KNOW ABOUT THE CONDUCTANCE OF MESOSCOPIC SYSTEMS

1995 ◽  
Vol 09 (07) ◽  
pp. 751-802 ◽  
Author(s):  
ALEX KAMENEV ◽  
YUVAL GEFEN
Keyword(s):  
Magnetic Flux ◽  
Electron Interaction ◽  
Level Spacing ◽  
Systematic Analysis ◽  
Multiply Connected ◽  
Statistical Ensembles ◽  
The Mean ◽  
Limiting Case ◽  
Aharonov Bohm ◽  
Grand Canonical

We present a systematic analysis of the average complex conductance of an ensemble of disordered mesoscopic conductors. It is argued that multiply connected Aharonov-Bohm rings are particularly amenable to this study, and reflect certain general features of the problem. Two ingredients are shown to be crucial in this context: (i) the ratio between the mean level spacing and the inelastic broadening of each level and (ii) the type of the statistical ensemble employed. Correspondingly, we distinguish between continuous and discrete spectrum limits and between canonical and grand canonical statistical ensembles. The conductance varies qualitatively as either of these two ingredients is changed. Analytical results for the conductance as a function of the magnetic flux, frequency and temperature are obtained in each limiting case. In particular, the sign of the d.c. (ω→0) magnetoconductance may change between the two limits. We also discuss the effect of electron-electron interaction.

THE CAPACITANCE MODEL FOR PERSISTENT CURRENTS IN MESOSCOPIC METAL RINGS

1994 ◽  
Vol 08 (19) ◽  
pp. 2593-2635 ◽  
Author(s):  
PETER KOPIETZ
Keyword(s):  
Energy Levels ◽  
Theoretical Work ◽  
Mean Free Path ◽  
Persistent Currents ◽  
Diffusive Regime ◽  
Metal Rings ◽  
Dependent Part ◽  
Recent Theoretical Work ◽  
Capacitance Model ◽  
Hartree Energy

We review recent theoretical work on persistent currents in mesoscopic normal-metal rings and present a detailed discussion the generalized capacitance model.20(a) This model provides a natural explanation for the surprisingly large experimentally observed currents in the diffusive regime. We pay particular attention to the problem of screening in a thin mesoscopic ring, and argue that screening corrections to the flux-dependent part of the Hartree energy are negligible provided the condition [Formula: see text] is satisfied. Here e2/C0 is the classical charging energy for adding one electron to the system, and [Formula: see text] is the average number of energy levels within an interval of width E c below the Fermi energy µ, where E c is the Thouless energy. This condition is equivalent with (k F l)(L⊥/L)2 ≪ 1 (where l is the elastic mean free path, L is the circumference and L⊥ is the transverse thickness of the ring), and shows that the ring geometry plays an important role. In thin rings the mesoscopic persistent current is universal in precisely the same sense as the variance of the conductance.

Defocus ramp correction in spot-scan imaging

1992 ◽  
Vol 50 (1) ◽  
pp. 130-131
Author(s):  
Kenneth H. Downing
Keyword(s):  
Computer Control ◽  
Three Dimensional ◽  
Sufficient Accuracy ◽  
Objective Lens ◽  
Electron Crystallography ◽  
Contrast Transfer Function ◽  
Tilt Axis ◽  
Specimen Height ◽  
The Difference ◽  
Envelope Functions

Three-dimensional structures of a number of samples have been determined by electron crystallography. The procedures used in this work include recording images of fairly large areas of a specimen at high tilt angles. There is then a large defocus ramp across the image, and parts of the image are far out of focus. In the regions where the defocus is large, the contrast transfer function (CTF) varies rapidly across the image, especially at high resolution. Not only is the CTF then difficult to determine with sufficient accuracy to correct properly, but the image contrast is reduced by envelope functions which tend toward a low value at high defocus.We have combined computer control of the electron microscope with spot-scan imaging in order to eliminate most of the defocus ramp and its effects in the images of tilted specimens. In recording the spot-scan image, the beam is scanned along rows that are parallel to the tilt axis, so that along each row of spots the focus is constant. Between scan rows, the objective lens current is changed to correct for the difference in specimen height from one scan to the next.

The iron content of iron superoxide dismutase: determination by anomalous scattering

1983 ◽  
Vol 218 (1210) ◽  
pp. 119-126 ◽  
Keyword(s):  
Superoxide Dismutase ◽  
Iron Content ◽  
Three Dimensional ◽  
Anomalous Scattering ◽  
Total Iron Content ◽  
Iron Site ◽  
Iron Superoxide Dismutase ◽  
Density Map ◽  
The Difference ◽  
Electron Density Map

The number of iron atoms in the dimeric iron-containing superoxide dismutase from Pseudomonas ovalis and their atomic positions have been determined directly from anomalous scattering measurements on crystals of the native enzyme. To resolve the long-standing question of the total amount of iron per molecule for this class of dismutase, the occupancy of each site was refined against the measured Bijvoet differences. The enzyme is a symmetrical dimer with one iron site in each subunit. The iron position is 9 ņ from the intersubunit interface. The total iron content of the dimer is 1.2±0.2 moles per mole of protein. This is divided between the subunits in the ratio 0.65:0.55; the difference between them is probably not significant. Since each subunit contains, on average, slightly more than half an iron atom we conclude that the normal state of this enzyme is two iron atoms per dimer but that some of the metal is lost during purification of the protein. Although the crystals are obviously a mixture of holo- and apo-enzymes, the 2.9 Å electron density map is uniformly clean, even at the iron site. We conclude that the three-dimensional structures of the iron-bound enzyme and the apoenzyme are identical.

scholarly journals The role of L/W in the solar radiation for Saharian cities

2019 ◽  
Vol 91 ◽  
pp. 05006
Author(s):  
Rami Qaoud ◽  
Alkama Djamal
Keyword(s):  
Solar Radiation ◽  
Solar Energy ◽  
Energy Levels ◽  
Direct Solar Radiation ◽  
Test Field ◽  
Natural Lighting ◽  
The Difference ◽  
The Impact ◽  
The Relationship

The urban fabric of the desert cities is based on the principle of reducing the impact of urban canyons on direct solar radiation. Here comes this research, which is based on a comparative study of the periods of direct solarisation and values of the solar energy of urban canyons via two urban fabrics that have different building densities, where the ratio between L/W is different. In order to obtain the real values of the solar energy (thermal, lighting), the test field was examined every two hours, each three consecutive days. The measurement stations are positioned by the three types of the relationship between L/W, (L≥2w, L=w, L≤0.5w). According to the results, we noticed and recorded the difference in the periods of direct solarization between the types of urban engineering canyons, reaching 6 hours a day, the difference in thermal values of air, reaching 4 °C, and the difference in periods of direct natural lighting, reaching 6 hours. It should be noted that the role of the relationship between L/W is to protect the urban canyons by reducing the impact of direct solar radiation on urban canyons, providing longer hours of shading, and reducing solar energy levels (thermal, lighting) at the urban canyons. This research is classified under the research axis (the studies of external spaces in the urban environment according to the bioclimatic approach and geographic approach). But this research aims to focus on the tracking and studying the distribution of the solar radiation - thermal radiation and lighting radiation - in different types of street canyons by comparing the study of the direct solarization periods of each type and the quantity of solar energy collected during the solarization periods.

A gravity model of the basement structure in the Santa Maria Basin, California

Geophysics ◽  
1986 ◽  
Vol 51 (5) ◽  
pp. 1127-1140 ◽  
Author(s):  
Paul M. Kieniewicz ◽  
Bruce P. Luyendyk
Keyword(s):  
Short Wavelength ◽  
Large Scale ◽  
Bouguer Anomaly ◽  
Three Dimensional ◽  
Average Density ◽  
Structure Model ◽  
Basement Structure ◽  
Santa Maria Basin ◽  
Clastic Rocks ◽  
Santa Maria

The Santa Maria Basin in southern California is a lowland bounded on the south by the Santa Ynez River fault and on the northeast by the Little Pine‐Foxen Canyon‐Santa Maria River faults. It contains Neogene sedimentary rocks which rest unconformably on a basement of Cretaceous and older clastic rocks. Analysis of over 4 000 gravity stations obtained from the Defense Mapping Agency suggests that the Bouguer anomaly contains a short‐wavelength component arising from a variable‐density contrast between the basin’s Neogene units and the Cretaceous basement. A three‐dimensional inversion of the short‐wavelength component (constrained by wells drilled to basement) yields a structure model of the basement and the average density of the overlying sediments, assuming that the basement does not contain large‐scale density variations. The density anomalies modeled in the Neogene sediments, showing higher densities in the basin troughs, can be related to diagenetic changes in the silica facies of the Monterey and Sisquoc formations. The basement structure model shows the basin as composed of parallel ridges and troughs, trending west‐northwest and bounded by steep slopes interpreted as fault scarps. The basin is bounded on the west by a north‐south trending slope which may also represent a fault scarp.

On Bose-Einstein Condensation

1954 ◽  
Vol 50 (1) ◽  
pp. 65-76 ◽  
Author(s):  
P. T. Landsberg
Keyword(s):  
Closed System ◽  
Canonical Ensemble ◽  
Energy Levels ◽  
Volume Density ◽  
Einstein Condensation ◽  
Bose Einstein Condensation ◽  
Quantum Numbers ◽  
Finite Integer ◽  
Bose Einstein ◽  
Grand Canonical

ABSTRACTThis paper contains a proof that the description of the phenomenon of Bose-Einstein condensation is the same whether (1) an open system is contemplated and treated on the basis of the grand canonical ensemble, or (2) a closed system is contemplated and treated on the basis of the canonical ensemble without recourse to the method of steepest descents, or (3) a closed system is contemplated and treated on the basis of the canonical ensemble using the method of steepest descents. Contrary to what is usually believed, it is shown that the crucial factor governing the incidence of the condensation phenomenon of a system (open or closed) having an infinity of energy levels is the density of states N(E) ∝ En for high quantum numbers, a condition for condensation being n > 0. These results are obtained on the basis of the following assumptions: (i) For large volumes V (a) all energy levels behave like V−θ, and (b) there exists a finite integer M such that it is justifiable to put for the jth energy level Ej= c V−θand to use the continuous spectrum approximation, whenever j ≥ M c θ τ are positive constants, (ii) All results are evaluated in the limit in which the volume of the gas is allowed to tend to infinity, keeping the volume density of particles a finite and non-zero constant. The present paper also serves to coordinate much of previously published work, and corrects a current misconception regarding the method of steepest descents.

Theory of ultrasonic attenuation in one and two dimensional metals

1976 ◽  
Vol 54 (14) ◽  
pp. 1454-1460 ◽  
Author(s):  
T. Tiedje ◽  
R. R. Haering
Keyword(s):  
Ultrasonic Attenuation ◽  
Three Dimensional ◽  
Electronic Systems ◽  
Two Dimensional ◽  
Temperature Dependent ◽  
One Dimensional ◽  
The Difference

The theory of ultrasonic attenuation in metals is extended so that it applies to quasi one and two dimensional electronic systems. It is shown that the attenuation in such systems differs significantly from the well-known results for three dimensional systems. The difference is particularly marked for one dimensional systems, for which the attenuation is shown to be strongly temperature dependent.

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