scholarly journals A semi exact solution for a metallic phase in a Holstein-Hubbard chain at half filling with Gaussian anharmonic phonons

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Debika Debnath ◽  
M. Zahid Malik ◽  
Ashok Chatterjee
Keyword(s):  
Correlation Energy ◽  
Intermediate Phase ◽  
Entanglement Entropy ◽  
Metallic Phase ◽  
Spin Moment ◽  
Coulomb Correlation ◽  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Unitary Transformations ◽  
Half Filling

AbstractThe nature of phase transition from an antiferromagnetic SDW polaronic Mott insulator to the paramagnetic bipolaronic CDW Peierls insulator is studied for the half-filled Holstein-Hubbard model in one dimension in the presence of Gaussian phonon anharmonicity. A number of unitary transformations performed in succession on the Hamiltonian followed by a general many-phonon averaging leads to an effective electronic Hamiltonian which is then treated exactly by using the Bethe-Ansatz technique of Lieb and Wu to determine the energy of the ground state of the system. Next using the Mott–Hubbard metallicity condition, local spin-moment calculation, and the concept of quantum entanglement entropy and double occupancy, it is shown that in a plane spanned by the electron–phonon coupling coefficient and onsite Coulomb correlation energy, there exists a window in which the SDW and CDW phases are separated by an intermediate phase that is metallic.

VAN HOVE SINGULARITIES AND HIGH-Tc SUPERCONDUCTIVITY: A REVIEW

1991 ◽  
Vol 05 (12) ◽  
pp. 2037-2071 ◽  
Author(s):  
R. S. MARKIEWICZ
Keyword(s):  
Electronic System ◽  
Structural Instability ◽  
Hole Doping ◽  
Phonon Coupling ◽  
Van Hove Singularity ◽  
Strong Electron ◽  
High Tc ◽  
Electron Phonon Coupling ◽  
Half Filling ◽  
Fluctuation Effects

This review describes a Fermi liquid picture of high-T c superconductivity. A density-of-states (dos) peak associated with the CuO 2-plane van Hove singularity causes a peak in T c as a function of hole doping. Strong correlation effects drive a Mott transition at half filling. For intermediate doping, the electronic system is unstable against phase separation, with one phase near the insulating state, the other near the T c peak. The large dos leads to competition between superconductivity and structural instability, in analogy with the A15 compounds. The superconductivity appears to be driven by strong electron-phonon coupling, enhanced by fluctuation effects.

Effects of band structure and electron–phonon coupling on charge density waves

2013 ◽  
Vol 91 (6) ◽  
pp. 487-489 ◽  
Author(s):  
Jason W. Sadowski ◽  
K. Tanaka ◽  
Yuki Nagai
Keyword(s):  
Band Structure ◽  
Fermi Surface ◽  
Hubbard Model ◽  
Charge Density ◽  
Charge Density Waves ◽  
Phonon Coupling ◽  
Density Waves ◽  
Electron Phonon Coupling ◽  
Half Filling ◽  
Attractive Hubbard Model

We examine the effects of band structure and electron–phonon interactions on charge density waves (CDW) in terms of the extended attractive Hubbard model at half filling. It is shown that van Hove singularities well below the Fermi surface can lead to a substantial energy gain by electron–phonon coupling and result in the formation of CDW.

scholarly journals Superconductivity in Diamond-like BC3 Phase

2010 ◽  
Vol 2 (2) ◽  
pp. 203-213 ◽  
Author(s):  
M. M. Ali ◽  
A.K.M. A. Islam ◽  
M. Aftabuzzaman ◽  
F. Parvin
Keyword(s):  
Band Structure ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Density Functional Method ◽  
Metallic Phase ◽  
Tetragonal Symmetry ◽  
Phonon Coupling ◽  
Generalized Gradient ◽  
Electronic Band ◽  
Electron Phonon Coupling

Two possible phases of superhard material BC3 originating from the cubic diamond structure are investigated by ab initio pseudopotential density functional method using generalized gradient approximation (GGA). We calculate their elastic constants, electronic band structure, and density of states (DOS). Full phonon frequencies, electron-phonon coupling constant and possible superconducting Tc of the metallic phase with tetragonal symmetry (t-BC3, space group P-42m) have for the first time been investigated at 5 and 10 GPa. The calculated electron-phonon coupling (0.67) and the logarithmically-averaged frequency (862 cm-1) show superconductivity for the undoped t-BC3 with Tc = 20 K at 5 GPa, which decreases to 17.5 K at 10 GPa. Keywords: Superhard BC3; Band structure; Phonon spectra; Superconductivity. © 2010 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.DOI: 10.3329/jsr.v2i2.2638               J. Sci. Res. 2 (2), 203-213 (2010)     

scholarly journals ELECTRON-PHONON COUPLING CLOSE TO A METAL-INSULATOR TRANSITION IN ONE DIMENSION

1996 ◽  
Vol 10 (12) ◽  
pp. 1439-1451 ◽  
Author(s):  
MICHELE FABRIZIO ◽  
CLAUDIO CASTELLANI ◽  
CARLO DI CASTRO
Keyword(s):  
Electronic System ◽  
Insulator Transition ◽  
Dimensional System ◽  
Phonon Coupling ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
One Dimensional ◽  
Electron Phonon Coupling ◽  
Short Range Repulsion ◽  
Half Filling

We consider a one-dimensional system of electrons interacting via a short-range repulsion and coupled to phonons close to the metal-insulator transition at half-filling. We argue that the metal-insulator transition can be described as a standard one-dimensional incommensurate to commensurate transition, even if the electronic system is coupled to the lattice distortion. By making use of known results for this transition, we prove that low-momentum phonons, with the inclusion of the 4kF (≃2π near half-filling) scattering, do not play any relevant role close to the metal-insulator transition, unless their coupling to the electrons is large in comparison with the other energy scales present in the problem. In other words the effective strength of the low-momentum transferred electron-phonon coupling does not increase close to the metal-insulator transition, even though the effective velocity of the mobile carriers is strongly diminished.

scholarly journals PHASE DIAGRAM FOR A LUTTINGER LIQUID COUPLED TO PHONONS IN ONE DIMENSION

1995 ◽  
Vol 09 (04n05) ◽  
pp. 495-533 ◽  
Author(s):  
THIERRY MARTIN ◽  
DANIEL LOSS
Keyword(s):  
Phase Diagram ◽  
Filling Factor ◽  
Density Wave ◽  
Luttinger Liquid ◽  
Metallic Phase ◽  
Dimensional System ◽  
Phonon Coupling ◽  
Small Momentum Transfer ◽  
Electron Phonon Coupling ◽  
Interacting Electrons

We consider a one-dimensional system consisting of electrons with short-ranged repulsive interactions and coupled to small-momentum transfer acoustic phonons. The interacting electrons are bosonized and described in terms of a Luttinger liquid which allows us to calculate exactly the one- and two-electron Green function. For non-interacting electrons, the coupling to phonons alone induces a singularity at the Fermi surface which is analogous to that encountered for electrons with an instantaneous attractive interaction. The exponents which determine the presence of singlet/triplet superconducting pairing fluctuations, and spin/charge density wave fluctuations are strongly affected by the presence of the Wentzel-Bardeen singularity, resulting in the favoring of superconducting fluctuations. For the Hubbard model the equivalent of a phase diagram is established, as a function of: the electron-phonon coupling, the electron filling factor, and the on-site repulsion between electrons. The Wentzel-Bardeen singularity can be reached for arbitrary values of the electron-phonon coupling constant by varying the filling factor. This provides an effective mechanism to push the system from the antiferromagnetic into the metallic phase, and finally into the superconducting phase as the electron filling factor is increased towards half-filling.

Observation of Core Phonon in Electron–Phonon Coupling in Au25 Nanoclusters

2021 ◽  
Vol 12 (6) ◽  
pp. 1690-1695
Author(s):  
Zhongyu Liu ◽  
Yingwei Li ◽  
Wonyong Shin ◽  
Rongchao Jin
Keyword(s):  
Phonon Coupling ◽  
Electron Phonon Coupling

scholarly journals Electron-phonon coupling in the magnetic Weyl semimetal ZrCo2Sn

2021 ◽  
Vol 103 (2) ◽  
Author(s):  
I.Yu. Sklyadneva ◽  
R. Heid ◽  
P. M. Echenique ◽  
E. V. Chulkov
Keyword(s):  
Phonon Coupling ◽  
Weyl Semimetal ◽  
Electron Phonon Coupling

scholarly journals Dielectric screening in perovskite photovoltaics

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Rui Su ◽  
Zhaojian Xu ◽  
Jiang Wu ◽  
Deying Luo ◽  
Qin Hu ◽  
...  
Keyword(s):  
Open Circuit Voltage ◽  
Low Voltage ◽  
Power Conversion ◽  
Surface Recombination ◽  
Open Circuit ◽  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Dielectric Screening ◽  
Perovskite Photovoltaic ◽  
Reduced Surface

AbstractThe performance of perovskite photovoltaics is fundamentally impeded by the presence of undesirable defects that contribute to non-radiative losses within the devices. Although mitigating these losses has been extensively reported by numerous passivation strategies, a detailed understanding of loss origins within the devices remains elusive. Here, we demonstrate that the defect capturing probability estimated by the capture cross-section is decreased by varying the dielectric response, producing the dielectric screening effect in the perovskite. The resulting perovskites also show reduced surface recombination and a weaker electron-phonon coupling. All of these boost the power conversion efficiency to 22.3% for an inverted perovskite photovoltaic device with a high open-circuit voltage of 1.25 V and a low voltage deficit of 0.37 V (a bandgap ~1.62 eV). Our results provide not only an in-depth understanding of the carrier capture processes in perovskites, but also a promising pathway for realizing highly efficient devices via dielectric regulation.

scholarly journals Structural phase transition and superconductivity hierarchy in 1T-TaS2 under pressure up to 100 GPa

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Qing Dong ◽  
Quanjun Li ◽  
Shujia Li ◽  
Xuhan Shi ◽  
Shifeng Niu ◽  
...  
Keyword(s):  
Structural Phase ◽  
Transition Metal Dichalcogenides ◽  
Phonon Coupling ◽  
Structural Phase Transitions ◽  
Strong Electron ◽  
Electron Phonon Coupling ◽  
Increasing Trend ◽  
Metal Dichalcogenides ◽  
Dome Shape ◽  
Enhanced Superconductivity

AbstractThe adoption of high pressure not only reinforces the comprehension of the structure and exotic electronic states of transition metal dichalcogenides (TMDs) but also promotes the discovery of intriguing phenomena. Here, 1T-TaS2 was investigated up to 100 GPa, and re-enhanced superconductivity was found with structural phase transitions. The discovered I4/mmm TaS2 presents strong electron–phonon coupling, revealing a good superconductivity of the nonlayered structure. The P–T phase diagram shows a dome shape centered at ~20 GPa, which is attributed to the distortion of the 1T structure. Accompanied by the transition to nonlayered structure above 44.5 GPa, the superconducting critical temperature shows an increasing trend and reaches ~7 K at the highest studied pressure, presenting superior superconductivity compared to the original layered structure. It is unexpected that the pressure-induced re-enhanced superconductivity was observed in TMDs, and the transition from a superconductor with complicated electron-pairing mechanism to a phonon-mediated superconductor would expand the field of pressure-modified superconductivity.

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