PSEUDOGAP PHENOMENA AND THE DENSITY WAVES IN HIGH-Tc CUPRATES

2001 ◽  
Vol 15 (32) ◽  
pp. 4161-4171 ◽  
Author(s):  
ANGSULA GHOSH
Keyword(s):  
Order Parameter ◽  
Cuprate Superconductors ◽  
Nearest Neighbor ◽  
Density Wave ◽  
Tight Binding ◽  
Spin Density Wave ◽  
Mean Field ◽  
Field Calculation ◽  
Density Waves ◽  
Binding Model

We consider the density waves as possible explanations for the pseudogap in high temperature cuprate superconductors. Both the conventional spin density wave (SDW) and the unconventional d-density waves are considered in our study using a mean-field calculation of the tight binding model including terms upto second nearest neighbor hopping (γ). The phase diagrams for the order parameter and temperature with doping in the above types of density waves are discussed. The d-SDW does not coexist with the superconducting gap when studied with doping whereas the d-charge density wave (DDW) shows a state of coexistence. The temperature dependence of the order parameter and specific heat is also demonstrated. The spectral function of the SDW is also considered for various temperatures and doping.

Symmetry Violations in Partially Oxidized One-Dimensional (1D)Transition Metal Polymers. Metal-Ligand-Metal(M-L-M) Bridged Systems

1984 ◽  
Vol 39 (9) ◽  
pp. 807-829
Author(s):  
Michael C. Böhm
Keyword(s):  
Transition Metal ◽  
Density Wave ◽  
Tight Binding ◽  
Mean Field ◽  
Valence Bond ◽  
Hole State ◽  
One Dimensional ◽  
Metal Derivatives ◽  
A Charge ◽  
Metal Ligand

The band structure of the metal-ligand-metal (M-L-M) bridged quasi one-dimensional (1D) cyclopentadienylmanganese polymer, MnCp 1, has been studied in the unoxidized state and in a partly oxidized modification with one electron removed from each second MnCp fragment. The tight-binding approach is based on a semiempirical self-consistent-field (SCF) Hartree-Fock (HF) crystal orbital (CO) model of the INDO-type (intermediate neglect of differential overlap) combined with a statistical averaging procedure which has its origin in the grand canonical ensemble. The latter approximation allows for an efficient investigation of violations of the translation symmetries in the oxidized 1D material. The oxidation process in 1 is both ligand- and metal-centered (Mn 3d-2 states). The mean-field minimum corresponds to a charge density wave (CDW) solution with inequivalent Mn sites within the employed repeat-units. The symmetry adapted solution with electronically identical 3d centers is a maximum in the variational space. The coupling of this electronic instability to geometrical deformations is also analyzed. The ligand amplitudes encountered in the hole-state wave function prevent extremely large charge separations between the 3d centers which are found in ID systems without bridging moieties (e.g. Ni(CN)2-5 chain). The symmetry reduction in oxidized 1 is compared with violations of spatial symmetries in finite transition metal derivatives and simple solids. The stabilization of the valence bond-type (VB) solution is physically rationalized (i.e. left-right correlations between the 3d centers). The computational results derived for 1 are generalized to oxidized transition metal chains with band occupancies that are simple fractions of the number of stacking units and to 1D systems that deviate from this relation. The entropy-influence for temperatures T ≠ 0 is shortly discussed (stabilization of domain or cluster structures).

scholarly journals External tuning of topological phase transitions induced by interaction driven mass renormalization

2021 ◽  
Author(s):  
Thies Jansen ◽  
Alexander Brinkman
Keyword(s):  
Phase Transition ◽  
Mean Field Theory ◽  
Tight Binding ◽  
Mean Field ◽  
Topological Phase ◽  
Binding Model ◽  
System A ◽  
Topological Phase Transition ◽  
Topological Phases Of Matter ◽  
Electron Interactions

Abstract Electron-electron interactions can be useful for realizing new nontrivial topological phases of matter. Here, we show by means of a tight-binding model and mean field theory how electron-electron interactions can lead to a topological phase transition. By externally adding or removing electrons from the system a band inversion between two bands with dierent parity is induced. This leads to a topological nontrivial phase if spin-orbit coupling is present. Besides the toy-model illustrating this mechanism, we also propose SmB6 as a possible playground for experimentally realizing a topological phase transition by external tuning.

scholarly journals MAGNETIC FIELD TUNING OF CHARGE AND SPIN ORDER IN THE CUPRATE SUPERCONDUCTORS

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3156-3163 ◽  
Author(s):  
A. POLKOVNIKOV ◽  
S. SACHDEV ◽  
M. VOJTA ◽  
E. DEMLER
Keyword(s):  
Magnetic Field ◽  
Ground State ◽  
Charge Density Wave ◽  
Cuprate Superconductors ◽  
Density Wave ◽  
Spin Density Wave ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Spin Order ◽  
New Information

Recent neutron scattering, nuclear magnetic resonance, and scanning tunneling microscopy experiments have yielded valuable new information on the interplay between charge and spin density wave order and superconductivity in the cuprate superconductors, by using a perpendicular magnetic field to tune the ground state properties. We compare the results of these experiments with the predictions of a theory which assumed that the ordinary superconductor was proximate to a quantum transition to a superconductor with co-existing spin/charge density wave order.

scholarly journals Accurate six-band nearest-neighbor tight-binding model for the π-bands of bulk graphene and graphene nanoribbons

2011 ◽  
Vol 109 (10) ◽  
pp. 104304 ◽  
Author(s):  
Timothy B. Boykin ◽  
Mathieu Luisier ◽  
Gerhard Klimeck ◽  
Xueping Jiang ◽  
Neerav Kharche ◽  
...  
Keyword(s):  
Nearest Neighbor ◽  
Graphene Nanoribbons ◽  
Tight Binding ◽  
Tight Binding Model ◽  
Binding Model

scholarly journals ON THE VERDET CONSTANT AND FARADAY ROTATION FOR GRAPHENE-LIKE MATERIALS

2013 ◽  
Vol 25 (04) ◽  
pp. 1350007 ◽  
Author(s):  
MIKKEL H. BRYNILDSEN ◽  
HORIA D. CORNEAN
Keyword(s):  
Taylor Expansion ◽  
Nearest Neighbor ◽  
Tight Binding ◽  
Transverse Component ◽  
Tight Binding Model ◽  
Binding Model ◽  
Gauge Invariant ◽  
Verdet Constant ◽  
Absolute Value ◽  
Computable Formula

We present a rigorous and rather self-contained analysis of the Verdet constant in graphene-like materials. We apply the gauge-invariant magnetic perturbation theory to a nearest-neighbor tight-binding model and obtain a relatively simple and exactly computable formula for the Verdet constant, at all temperatures and all frequencies of sufficiently large absolute value. Moreover, for the standard nearest-neighbor tight-binding model of graphene we show that the transverse component of the conductivity tensor has an asymptotic Taylor expansion in the external magnetic field where all the coefficients of even powers are zero.

Study of electron-phonon coupling and its effect on electrical resistivity in HF systems

2019 ◽  
Vol 33 (04) ◽  
pp. 1950012
Author(s):  
P. C. Baral
Keyword(s):  
Electrical Resistivity ◽  
Mean Field Theory ◽  
Tight Binding ◽  
Harmonic Approximation ◽  
Mean Field ◽  
Graphical Analysis ◽  
Kondo Lattice ◽  
Model Parameters ◽  
Binding Model ◽  
Model Hamiltonian

In this work, we report on theoretical study of the effect of electron-phonon (EP) interaction in THz frequency and temperature dependence of the electrical resistivity in heavy fermion (HF) systems. For this purpose, a model Hamiltonian is considered which consists of the Heisenberg type exchange interaction between localized moments and a tight binding model called the Kondo lattice model (KLM). The effect of EP coupling on electrical resistivity is presented by considering phonon interaction to bare f-electrons, band electrons and to the hybridization between band and f-electrons as a perturbed term. The phonon Hamiltonian in harmonic approximation is also included. The model Hamiltonian is solved by employing the mean-field theory (MFT) along with the Hubbard model of approximation. The temperature- and frequency-dependent electrical resistivity exhibits change in slopes at T[Formula: see text] as well as at T[Formula: see text]. The theoretical findings from the graphical analysis by varying the model parameters g[Formula: see text], g[Formula: see text] and g[Formula: see text] are compared to some of the experimental results in HF systems.

Tight-Binding Formalism for Ionic Fullerides and its Application to Alkali-C60 Polymers

1997 ◽  
Vol 491 ◽  
Author(s):  
Susumu Saito ◽  
Steven G. Louie ◽  
Marvin L. Cohen
Keyword(s):  
Density Wave ◽  
Tight Binding ◽  
Stable State ◽  
Coulomb Repulsion ◽  
Binding Model ◽  
Wave State ◽  
Madelung Energy ◽  
The One ◽  
Consistent Treatment ◽  
Ionic Lattice

ABSTRACTWe present a tight-binding formalism which can properly treat various ionic füllendes. In the Hamiltonian we include the intrafullerene Coulomb repulsion energy and the Madelung energy of the ionic lattice, both of which depend on the possible charge disproportion between fullerenes. This Hamiltonian requires a self-consistent treatment, but it is applicable to much larger systems than first-principles methods. Using this formalism we have studied the electronic structure of the one-dimensional A1C60 polymer. The present generalization of the tight-binding model is found to be important for ionic füllendes and a moderate-amplitude charge-density-wave state is found to be a possible stable state.

scholarly journals Superconductivity in the doped Hubbard model and its interplay with next-nearest hopping t′

Science ◽  
2019 ◽  
Vol 365 (6460) ◽  
pp. 1424-1428 ◽  
Author(s):  
Hong-Chen Jiang ◽  
Thomas P. Devereaux
Keyword(s):  
Hubbard Model ◽  
Charge Density ◽  
Spin Density ◽  
Charge Density Wave ◽  
Large Scale ◽  
Nearest Neighbor ◽  
High Temperature Superconductivity ◽  
Density Wave ◽  
Spin Density Wave ◽  
Hole Doping

The Hubbard model is widely believed to contain the essential ingredients of high-temperature superconductivity. However, proving definitively that the model supports superconductivity is challenging. Here, we report a large-scale density matrix renormalization group study of the lightly doped Hubbard model on four-leg cylinders at hole doping concentration δ = 12.5%. We reveal a delicate interplay between superconductivity and charge density wave and spin density wave orders tunable via next-nearest neighbor hopping t′. For finite t′, the ground state is consistent with a Luther-Emery liquid with power-law superconducting and charge density wave correlations associated with half-filled charge stripes. In contrast, for t′ = 0, superconducting correlations fall off exponentially, whereas charge density and spin density modulations are dominant. Our results indicate that a route to robust long-range superconductivity involves destabilizing insulating charge stripes in the doped Hubbard model.

Hybridization in Electronic States and Optical Properties of Covalent Amorphous Semiconductors

1999 ◽  
Vol 588 ◽  
Author(s):  
Yuzo Shinozuka
Keyword(s):  
Optical Properties ◽  
Spatial Correlation ◽  
Nearest Neighbor ◽  
Tight Binding ◽  
Electronic States ◽  
Amorphous Semiconductors ◽  
Transfer Energy ◽  
Binding Model ◽  
Covalent Bonds ◽  
Conduction Bands

AbstractThe electronic structure and optical properties of covalent amorphous semiconductors are theoretically studied with special attention to the s-p hybridization in electronic states and the spatial correlation in their mixing. One-dimensional tight binding model is used in which the interatomic transfer energy of an electron between nearest neighbor atoms depends linearly on their interatomic distance. All the electronic states are numerically calculated for a 150-atom system and the ensemble average is taken over 10 samples. Following results have been obtained. As the degree of randomness increases, the degree of hybridization decreases and rearrangements in the covalent bonds take place. The width of the band gap decreases but the gap remains rather long compared to a case where the spatial correlation is neglected. There appears a characteristic peak in the optical absorption spectrum, which reflects central peaks in the partial (s- or p-) density of states in the valence and conduction bands and is related to an electron localization caused by the spatial correlation.

Electronic modes in carbon nanotubes with single and double impurity sites

2017 ◽  
Vol 31 (29) ◽  
pp. 1750220
Author(s):  
P. G. Komorowski ◽  
M. G. Cottam
Keyword(s):  
Carbon Nanotubes ◽  
Nearest Neighbor ◽  
Tight Binding ◽  
Longitudinal Axis ◽  
Binding Model ◽  
Substitutional Impurity ◽  
Impurity Atoms ◽  
Spatial Configurations ◽  
Impurity Sites ◽  
Walled Carbon Nanotubes

A theoretical study of isolated and doubly-clustered impurities is presented for the electronic excitations in a carbon nanotube lattice. Using a matrix operator formalism and a tight-binding model where the interactions between atoms take place via nearest-neighbor hopping, the properties of the excitations are deduced. A geometry consisting of long, single-walled carbon nanotubes is assumed with the defects introduced in the form of substitutional impurity atoms, giving rise to the localized electronic modes of the nanotube as well as the propagating modes of the pure (host) material. The impurities are assumed to be in a low concentration, having the form of either a single, isolated defect or a small cluster of two defects close together. A tridiagonal matrix technique is employed within a Green’s function formalism to obtain the properties of the discrete modes of the system, including their frequencies and localization. The numerical examples show a dependence on the nanotube diameters and on the relative spatial configurations of the impurities. The results contrast with the previous studies of line impurities since there is no translational symmetry along the longitudinal axis of the nanotubes in the present case.

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