Metallic condensation of Wannier-Mott impurity states in lithium-hexamethylphosphoramide glasses

1977 ◽  
Vol 55 (11) ◽  
pp. 2258-2263 ◽  
Author(s):  
Peter P. Edwards ◽  
Ron Catterall
Keyword(s):  
Tight Binding ◽  
Mott Transition ◽  
Electron Interaction ◽  
Metallic State ◽  
Binding Model ◽  
Impurity States ◽  
Coulombic Repulsion ◽  
Variational Form ◽  
Frozen Solutions ◽  
Good Agreement

A metal to non-metal (MNM) transition observed in frozen solutions of lithium in hexamethylphosphoramide (HMPA) was tentatively interpreted as a Mott transition in which localized Wannier-type impurity states were the source of electrons in the metallic state. In this paper this assertion is examined in greater detail by calculating critical densities (nc) on the basis of a scaled (variational) form of Mott's original criterion for the onset of localization in a dielectrically screened Coulomb potential, and also on the basis of the Hubbard tight-binding model. Mott's model for the transition is based upon the screening properties of a freely propagating gas of metallic electrons. In the Hubbard regime, however, the phenomenon is viewed from the tight-binding limit; the transition from localized to delocalized states occurs when the bandwidth (Δ) of a regular lattice of isolated centres exceeds the value of the intra-atomic Coulombic repulsion integral (U) associated with electron correlation.Both electron-gas (Mott) and tight-binding (Hubbard) approaches give calculated critical densities (5.6 × 1018, 3.2 × 1018 cm−3, respectively) in good agreement with the experimental value (∼3 × 1018 cm−3). These results therefore support the earlier suggestion that the MNM transition in frozen lithium-HMPA solutions is a Mott-transition associated with electron-interaction effects.

Tight-Binding Model Study of Tunneling Spectra of Monolayer Graphene-on-Substrate

2018 ◽  
Vol 17 (04) ◽  
pp. 1760027 ◽  
Author(s):  
Himanshu Sekhar Gouda ◽  
Sivabrata Sahu ◽  
G. C. Rout
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Tight Binding ◽  
Mean Field Approximation ◽  
Coulomb Energy ◽  
Electron Interaction ◽  
Model Parameters ◽  
Tight Binding Model ◽  
Binding Model ◽  
Model Study

We report here the theoretical model study of antiferromagnetic ordering in graphene. We propose a tight-binding model Hamiltonian describing electron hopping up to third-nearest neighbors in graphene. The Hamiltonian describing inequivalence of [Formula: see text] and [Formula: see text] sublattices in graphene-on-substrate is incorporated. The Hubbard-type repulsive Coulomb interaction is considered for both the sublattices with same Coulomb energy. The electron–electron interaction is considered within mean-field approximation with mean electron occupancies [Formula: see text] at [Formula: see text] sublattice and [Formula: see text] at [Formula: see text] site with [Formula: see text] and [Formula: see text] being the antiferromagnetic magnetizations at [Formula: see text] and [Formula: see text] sublattices, respectively. The total Hamiltonian is solved by Zubarev’s techniques of double time single particle Green’s functions. The magnetizations are calculated from the correlation functions corresponding to the respective Green’s functions. The temperature-dependent magnetizations are solved self-consistently taking suitable grid points for the electron momentum. Finally, the electron density of states (DOS) which is proportional to imaginary part of the electron Green’s functions is calculated and computed numerically at a given temperature varying different model parameters for the system. The conductance spectra show a gap near the Dirac point due to substrate-induced gap and magnetic gap, while the van Hove singularities split into eight peaks due to two different sublattice magnetizations and two different spin orientations of the electron in graphene-on-substrate.

Composition and Strain Dependence of the Piezoelectric Coefficients in Semiconductor Alloys

2007 ◽  
Vol 1017 ◽  
Author(s):  
T. Hammerschmidt ◽  
M. A. Migliorato ◽  
D. Powell ◽  
A. G. Cullis ◽  
G. P. Srivastava
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Piezoelectric Coefficient ◽  
Tight Binding ◽  
Tight Binding Model ◽  
Semiconductor Alloys ◽  
Binding Model ◽  
Functional Theory ◽  
Photo Current ◽  
Good Agreement

AbstractWe propose a tight-binding model for the polarization that considers direct and dipole contributions and employs microscopic quantities that can be calculated by first-principles methods, e.g. by employing Density Functional Theory (DFT). Applying our model to InxGa1-xAs alloys allows us to settle discrepancies between the values of e14 as obtained from experiments and from linear interpolations between the values of InAs and GaAs. Our calculated piezoelectric coefficient is in very good agreement with photo current measurements of InAs/GaAs(111) quantum well samples.

Effect of electron–electron interaction on polarization and dissociation of the charged oligomer after single-photon absorption

2017 ◽  
Vol 31 (32) ◽  
pp. 1750256
Author(s):  
Xiao-Xue Li ◽  
Gang Chen
Keyword(s):  
Excited State ◽  
Electric Field ◽  
Single Photon ◽  
Tight Binding ◽  
Interaction Strength ◽  
Polarization Property ◽  
Photon Absorption ◽  
Electron Interaction ◽  
Weak Electric Field ◽  
Binding Model

By using the extended Hubbard model under the Hartree–Fock approximation, we theoretically investigate the effect of electron–electron interaction on the polarization of the single-photon excited state of the charged [Formula: see text]-conjugated oligomer. In the framework of one-dimensional tight-binding model, a uniform weak electric field is applied for polarization. The results show that the polarization property will vary with the electron–electron interaction. For example, with the increase of on-site Coulomb interaction strength, the value of the induced dipole moment is decreased. Its physical origin is revealed by analyzing the wavefunction of the localized energy level. In addition, the relation between the critical electric field for the dissociation of the single-photon excited state of the charged oligomer and the electron–electron interaction strength is also discussed.

The Electron-Hole Interactions in Si Hydrogenate Nanocrystals: Tight-Binding Theory

2015 ◽  
Vol 1131 ◽  
pp. 110-116
Author(s):  
Worasak Sukkabot
Keyword(s):  
Tight Binding ◽  
Electron Hole ◽  
Binding Model ◽  
Mass Approximation ◽  
Si Nanocrystals ◽  
Interaction Scheme ◽  
Electron And Hole States ◽  
Excitonic States ◽  
Binding Configuration ◽  
Good Agreement

Theory of electronic and optical properties of excitonic states confining in Si nanocrystals is presented. The electron and hole states are numerically computed using the atomistic empirical tight-binding Hamiltonian including the spin-orbit coupling together with the first nearest-neighboring interaction. We theoretically study the electron-hole interactions in spherical silicon hydrogenated nanocrystals by incorporating coulomb and exchange interaction into the empirical tight-binding model. The comparisons of coulomb and exchange energies with empirical pseudopotential method (EPM), tight-binding method (TB), effective-mass approximation (EMA) and ab initio calculations are quantitatively realized. Finally the energies of the excitonic ground states obtained from diagonalizing the tight-binding configuration-interaction scheme are in a good agreement with other theoretical and experimental data.

A Tight-Binding Model for Optical Properties of Porous Silicon

1997 ◽  
Vol 491 ◽  
Author(s):  
M. Cruz ◽  
M. R. Beltran ◽  
C. Wang ◽  
J. Tagüeña-Martinez
Keyword(s):  
Optical Properties ◽  
Porous Silicon ◽  
Crystalline Silicon ◽  
Tight Binding ◽  
Basis Set ◽  
Extended Defects ◽  
Tight Binding Model ◽  
Binding Model ◽  
Semi Empirical ◽  
Good Agreement

ABSTRACTSemi-empirical tight-binding techniques have been extensively used during the last six decades to study local and extended defects as well as aperiodic systems. In this work we propose a tight-binding model capable of describing optical properties of disordered porous materials in a novel way. Besides discussing the details of this approach, we apply it to study porous silicon (p-Si). For this purpose, we use an sp3s* basis set and supercells, where empty columns are digged in the [001] direction in crystalline silicon (c-Si). The disorder of the pores is considered through a random perturbative potential, which relaxes the wave vector selection rule, resulting in a significant enlargement of the optically active k-zone. The dielectric function and the light absorption spectra are calculated. The results are compared with experimental data showing a good agreement.

A Tight Binding Model for The Electronic Structure of FCC and SC C60

1992 ◽  
Vol 06 (23n24) ◽  
pp. 3959-3963
Author(s):  
Nacir Tit ◽  
Vijay Kumar
Keyword(s):  
Lattice Constant ◽  
Tight Binding ◽  
Text Structure ◽  
Tight Binding Model ◽  
Energy Bands ◽  
Pairing Mechanism ◽  
Binding Model ◽  
Conduction Bands ◽  
Mechanism Of Superconductivity ◽  
Good Agreement

Ab-initio calculations1 for K3C60 indicate that the general features of the energy bands within LDA remain nearly unchanged as compared to C60. In the electronphonon pairing mechanism of superconductivity in these materials, the variation in Tc has been attributed to changes in the lattice constant2 which affects N(EF). We have therefore fitted the valence and conduction bands of the fcc C60, obtained by Troullier and Martins3 from an LDA plane wave basis calculations, with a tight binding model and studied the energy bands as a function of the lattice constant. As the overlap between orbitals on neighbouring balls is small, the band width is found to decrease by about 30% in going from K3C60 to Rb2CsC60. The density of states, thus, obtained is used to estimate variation in Tc from McMillan’s formula. These results are in good agreement with experimental data. Calculations of the energy bands are also presented for the low temperature [Formula: see text] structure.

Spin-Polarization in Ultrathin Rh Layers on Fe (001)

1993 ◽  
Vol 313 ◽  
Author(s):  
A. Chouairi ◽  
H. Dreysse ◽  
H. Nait-Laziz ◽  
C. Demangeat
Keyword(s):  
Spin Polarization ◽  
Photoelectron Spectroscopy ◽  
Tight Binding ◽  
Mean Field ◽  
Lattice Parameter ◽  
Tight Binding Model ◽  
Binding Model ◽  
Fee Structure ◽  
Self Consistent ◽  
Good Agreement

ABSTRACTThe origin of the Rh polarization at the interface with Fe is discussed within a self-consistent mean-field parameterized tight-binding model. Since experimentally it is not yet known how Rh grows on Fe (001), in this paper we consider both fee and bec growth. When Rh grows in the fee structure, it expands its lattice parameter and a polarization is present up to 3 layers, whereas in the bec case only the Rh atoms at the interface are polarized. The results obtained are compared to recent spin- and angle-resolved photoelectron spectroscopy experiments. Good agreement with experiment is obtained in the case of a fee Rh configuration.

Two-Gap Superconductivity in MgB2

2003 ◽  
Vol 17 (13) ◽  
pp. 2589-2598
Author(s):  
Angsula Ghosh
Keyword(s):  
Critical Temperature ◽  
Specific Heat ◽  
Temperature Dependence ◽  
Order Parameter ◽  
Tight Binding ◽  
Tight Binding Model ◽  
S Wave ◽  
Binding Model ◽  
Half Filling ◽  
Good Agreement

We study the superconductivity in MgB2 using a tight binding model to investigate the doping dependence of the order parameter and the critical temperature. We consider both the anisotropic and the isotropic s-wave pairing to study the coexistence of the two gaps. A good agreement between the existing experiments and our theoretical curves is observed. The temperature dependence of order parameter, specific heat and penetration depth at half filling are also demonstrated and are found to be in accord with the available experimental predictions.

scholarly journals Cobalt-based magnetic Weyl semimetals with high-thermodynamic stabilities

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Wei Luo ◽  
Yuma Nakamura ◽  
Jinseon Park ◽  
Mina Yoon
Keyword(s):  
Tight Binding ◽  
Three Dimensional ◽  
Interlayer Coupling ◽  
First Principles Calculation ◽  
Optimization Approach ◽  
Binding Model ◽  
Nodal Lines ◽  
Weyl Semimetal ◽  
Topological Quantum ◽  
First Time

AbstractRecent experiments identified Co3Sn2S2 as the first magnetic Weyl semimetal (MWSM). Using first-principles calculation with a global optimization approach, we explore the structural stabilities and topological electronic properties of cobalt (Co)-based shandite and alloys, Co3MM’X2 (M/M’ = Ge, Sn, Pb, X = S, Se, Te), and identify stable structures with different Weyl phases. Using a tight-binding model, for the first time, we reveal that the physical origin of the nodal lines of a Co-based shandite structure is the interlayer coupling between Co atoms in different Kagome layers, while the number of Weyl points and their types are mainly governed by the interaction between Co and the metal atoms, Sn, Ge, and Pb. The Co3SnPbS2 alloy exhibits two distinguished topological phases, depending on the relative positions of the Sn and Pb atoms: a three-dimensional quantum anomalous Hall metal, and a MWSM phase with anomalous Hall conductivity (~1290 Ω−1 cm−1) that is larger than that of Co2Sn2S2. Our work reveals the physical mechanism of the origination of Weyl fermions in Co-based shandite structures and proposes topological quantum states with high thermal stability.

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