Paramagnetic impurities in an itinerant antiferromagnet. Theory

1969 ◽  
Vol 47 (5) ◽  
pp. 477-487 ◽  
Author(s):  
S. N. Behera ◽  
K. S. Viswanathan
Keyword(s):  
Density Of States ◽  
Energy Gap ◽  
Impurity Site ◽  
Atom Ratio ◽  
Hartree Fock ◽  
Paramagnetic Impurities ◽  
Spin Dependent Scattering ◽  
Experimental Findings ◽  
Gap Parameter ◽  
Theory And Experiment

The effects of 3-d paramagnetic impurities in an itinerant antiferromagnetic metal are investigated using the Wolff–Clogston model. The changes in the Néel temperature TN, the energy-gap parameter, and the density of states are evaluated in the Hartree–Fock approximation and in the lowest order in the impurity concentration. The results on the changes in TN are compared with the experimental findings on V, Mn, Fe, Co, Ni, Mo, and W impurities in chromium. The agreement between theory and experiment suggests that the changes in TN are essentially due to three mechanisms: (a) the effect due to changes in the electron–atom ratio, (b) the spin-dependent scattering due to paramagnetic impurities, and (c) the changes in the intra-atomic coulomb potential at the impurity site. In the case of Mo and W, the last effect explains the observed decrease in TN in Cr.

COOPER PAIRS AND TF-SCALED HIGH-TEMPERATURE SUPERCONDUCTIVITY

1991 ◽  
Vol 05 (12) ◽  
pp. 805-819 ◽  
Author(s):  
D. A. AGRELLO ◽  
V. C. AGUILERA-NAVARRO ◽  
M. DE LLANO ◽  
A. PLASTINO ◽  
CHRISTINA KELLER ◽  
...  
Keyword(s):  
High Temperature ◽  
Weak Coupling ◽  
Energy Gap ◽  
High Temperature Superconductivity ◽  
Muon Spin ◽  
High Temperature Superconductors ◽  
Strongly Coupled ◽  
Hartree Fock ◽  
Fermi Temperature ◽  
Gap Parameter

Abnormally-occupied single-fermion states, previously found to give lower total Hartree-Fock energies in numerous strongly-coupled neutral fluids, is shown to be a sufficient condition to give tighter-bound Cooper electron pairs for arbitrarily-weak coupling. Consequently, within the BCS picture where for weak-coupling the Cooper pair binding energy is simply related to the zero-temperature energy-gap parameter, which in turn is proportional to the critical temperature, T c , higher T c values which scale as the Fermi temperature are possible. This is consistent with recent muon-spin relaxation experiments on sixteen cuprate high-temperature superconductors.

SUPERCONDUCTIVITY WITH ‘η PAIRING’: GAP PARAMETER AND SINGLE PARTICLE TUNNELING

1994 ◽  
Vol 08 (03) ◽  
pp. 149-157 ◽  
Author(s):  
GRZEGORZ LITAK ◽  
TADEUSZ DOMAŃSKI
Keyword(s):  
Hubbard Model ◽  
Density Of States ◽  
Single Particle ◽  
Superconducting Gap ◽  
Hartree Fock ◽  
Quasiparticle Density ◽  
Gap Parameter

We examine the ‘η pairing’ superconductivity using the negative U Hubbard model on the bipartite lattice. The superconducting gap parameter for η pairing is compared with the equilibrium Hartree-Fock-Bogolubov solution for the half-filled system in various temperatures and strengths of interaction. The quasiparticle density of states and the single particle tunneling are investigated.

Calculations of the Electronic Structure of Vacancies in a-Si:H

1992 ◽  
Vol 291 ◽  
Author(s):  
Ariel A. Valladares ◽  
L. Enrique Sansores
Keyword(s):  
Electronic Structure ◽  
Charge Density ◽  
Density Of States ◽  
Energy Gap ◽  
Local Density ◽  
Amorphous Solids ◽  
Local Density Of States ◽  
Hydrogen Atoms ◽  
Hartree Fock ◽  
Cluster Calculations

ABSTRACTThe electronic structure of random clusters has been used in the literature as representative of the electronic structure of random solids. In this work a calculation of the local density of states (LDOS) and charge density contours for clusters of the type XSi20H28 with X an Si atom, a vacancy or 4 hydrogen atoms, has been carried out. The method used was a pseudopotential SCF Hartree-Fock and the HONDO program. It is found that the generation of a vacancy in the center of the cluster (removal of the central Si atom), introduces p-like states in the energy gap of the LDOS for the region near the center of the cluster. The saturation of the dangling bonds of the vacancy with 4 hydrogen atoms removes the states within the gap. These results are also borne out by the charge density contours, thereby reinforcing the importance of amorphous cluster calculations in the understanding of the electronic structure of amorphous solids.

ENERGY GAP DEPENDENCE ON ANION CONCENTRATION FOR GaxIn1-xAsyP1-y QUATERNARY ALLOY BY RECURSION METHOD

2004 ◽  
Vol 18 (18) ◽  
pp. 955-962
Author(s):  
MUSA EL-HASAN ◽  
REZEK ESTATIEH
Keyword(s):  
Density Of States ◽  
Energy Gap ◽  
Local Density ◽  
Tight Binding ◽  
Quaternary Alloy ◽  
Average Density ◽  
Local Density Of States ◽  
Recursion Method ◽  
Orbital Decomposition ◽  
Lattice Matched

Three terminators have been tested, square root terminator, quadreture terminator and linear terminator, it was found that the linear terminator is the best, so it was used in calculating local density of states (LDOS) and it's orbital decomposition, alloy average density of states, and energy gap for different anion concentrations for InP lattice matched alloy. The results were compared with our previous calculations of (LDOS), and results from other methods. Energy gap was compared with experimental measurements. A five orbital sp3s* per atom model was used in the tight-binding representation of the Hamiltonian.

Energy Gap in Superconductors Containing Paramagnetic Impurities

1962 ◽  
Vol 9 (7) ◽  
pp. 315-316 ◽  
Author(s):  
F. Reif ◽  
Michael A. Woolf
Keyword(s):  
Energy Gap ◽  
Paramagnetic Impurities

GAP-LABELING PROPERTIES OF THE ENERGY SPECTRUM FOR TWO-DIMENSIONAL FIBONACCI QUASILATTICES

1995 ◽  
Vol 09 (01) ◽  
pp. 55-66
Author(s):  
YOUYAN LIU ◽  
WICHIT SRITRAKOOL ◽  
XIUJUN FU
Keyword(s):  
Energy Spectrum ◽  
Density Of States ◽  
Energy Gap ◽  
Fractional Part ◽  
Numerical Results ◽  
Step Height ◽  
Integrated Density Of States ◽  
Two Dimensional

We have analytically obtained the occupation probabilities on subbands of the hierarchical energy spectrum and the step heights of the integrated density of states for two-dimensional Fibonacci quasilattices. Based on the above results, the gap-labeling properties of the energy spectrum are found, which claim that the step height is equal to {mτ}, where the braces denote the fractional part, and m is an integer that can be used to label the corresponding energy gap. Numerical results confirm these results very well.

Determination of Density of Localized States in Amorphous Silicon Alloys From the Low Field Conductance of Thin N-I-N Diodes

1985 ◽  
Vol 49 ◽  
Author(s):  
Michael Shur ◽  
Michael Hack
Keyword(s):  
Temperature Dependence ◽  
Amorphous Silicon ◽  
Bulk Density ◽  
Density Of States ◽  
Energy Gap ◽  
Localized States ◽  
New Technique ◽  
Silicon Alloys ◽  
Low Field ◽  
Density Of Localized States

AbstractWe describe a new technique to determine the bulk density of localized states in the energy gap of amorphous silicon alloys from the temperature dependence of the low field conductance of n-i-n diodes. This new technique allows us to determine the bulk density of states in the centre of a device, and is very straightforward, involving fewer assumptions than other established techniques. Varying the intrinsic layer thickness allows us to measure the,density of states within approximately 400 meV of midgap.We measured the temperature dependence of the low field conductance of an amorphous silicon alloy n-i-n diode with an intrinsic layer thjckness of 0.45 microns and deduced the density of localised states to be 3xlO16cm−3 eV−1 at approximately 0.5 eV below the bottom of the conduction band. We have also considered the high bias region (the space charge limited current regime) and proposed an interpolation formula which describes the current-voltage characteristics of these structures at all biases and agrees well with our computer simulation based on the solution of the complete system of transport equations.

scholarly journals An ab initio Hartree-Fock Investigation of Endohedral Sc@C82

1998 ◽  
Vol 53 (9) ◽  
pp. 801-805 ◽  
Author(s):  
Andrea Gruß ◽  
Michael C. Böhm ◽  
Joachim Schulte ◽  
Klaus-Peter Dinse
Keyword(s):  
Ab Initio ◽  
Minimum Energy ◽  
Fullerene Cage ◽  
Site Symmetry ◽  
Fold Axis ◽  
Hartree Fock ◽  
Endohedral Complex ◽  
Experimental Findings ◽  
Ab Initio Hf ◽  
Hf Calculations

Abstract The electronic structure of endohedral Sc@C82 with a C82 cage of C2v symmetry has been studied by ab initio Hartree-Fock (HF) calculations. The optimized position of Sc in the configuration of minimum energy is predicted to be on the two-fold axis of the fullerene cage. In the corresponding configuration Sc is above the center of a hexagon of site symmetry C2 . This structure of C2v symmetry is nearly degenerate with Cs and Ct structures with Sc slightly displaced from the center of the coordinated hexagon. The binding energy of the endohedral complex is larger than 3.55 eV. The ab initio HF data of the C2v topoisomer of the fullerene unit are compared with new experimental findings and HF results derived for the 3(C2) topoisomer of the C82 cage.

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