Exciton Bose condensation : the ground state of an electron-hole gas - II. Spin states, screening and band structure effects

In the paper a theoretical study the both the quantized energies of excitonic states and their wave functions in grapheneand in materials with "Mexican hat" band structure dispersion as well as in zinc-blende GaN is presented. An integral twodimensionalSchrÃ¶dinger equation of the electron-hole pairing for a particles with electron-hole symmetry of reflection isexactly solved. The solutions of SchrÃ¶dinger equation in momentum space in studied materials by projection the twodimensionalspace of momentum on the three-dimensional sphere are found exactly. We analytically solve an integral twodimensionalSchrÃ¶dinger equation of the electron-hole pairing for particles with electron-hole symmetry of reflection. Instudied materials the electron-hole pairing leads to the exciton insulator states. Quantized spectral series and lightabsorption rates of the excitonic states which distribute in valence cone are found exactly. If the electron and hole areseparated, their energy is higher than if they are paired. The particle-hole symmetry of Dirac equation of layered materialsallows perfect pairing between electron Fermi sphere and hole Fermi sphere in the valence cone and conduction cone andhence driving the Cooper instability. The solutions of Coulomb problem of electron-hole pair does not depend from a widthof band gap of graphene. It means the absolute compliance with the cyclic geometry of diagrams at justification of theequation of motion for a microscopic dipole of graphene where >1 s r . The absorption spectrums for the zinc-blendeGaN/(Al,Ga)N quantum well as well as for the zinc-blende bulk GaN are presented. Comparison with availableexperimental data shows good agreement.

Download Full-text

Magnetic Ground State and Electronic Structure Calculations of PbMnO3 Using DFT

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.895.420 ◽

2014 ◽

Vol 895 ◽

pp. 420-423 ◽

Cited By ~ 4

Author(s):

Sathya Sheela Subramanian ◽

Baskaran Natesan

Keyword(s):

Electronic Structure ◽

Band Structure ◽

Fermi Level ◽

Ground State ◽

Density Functional ◽

Electronic Structure Calculations ◽

Magnetic Ground State ◽

Electronic Band ◽

Structure Calculations ◽

Centrosymmetric Structure

Structural optimization, magnetic ground state and electronic structure calculations of tetragonal PbMnO3have been carried out using local density approximation (LDA) implementations of density functional theory (DFT). Structural optimizations were done on tetragonal P4mm (non-centrosymmetric) and P4/mmm (centrosymmetric) structures using experimental lattice parameters and our results indicate that P4mm is more stable than P4/mmm. In order to determine the stable magnetic ground state of PbMnO3, total energies for different magnetic configurations such as nonmagnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) were computed for both P4mm and P4/mmm structures. The total energy results reveal that the FM non-centrosymmetric structure is found to be the most stable magnetic ground state. The electronic band structure, density of states (DOS) and the electron localization function (ELF) were calculated for the stable FM structure. ELF revealed the distorted non-centrosymmetric structure. The band structure and DOS for the majority spins of FM PbMnO3showed no band gap at the Fermi level. However, a gap opens up at the Fermi level in minority spin channel suggesting that it could be a half-metal and a potential spintronic candidate.

Download Full-text

MO-Theoretical Studies on a Model Complex for Deoxymyoglobin

Zeitschrift für Naturforschung A ◽

10.1515/zna-1998-0905 ◽

1998 ◽

Vol 53 (9) ◽

pp. 755-765

Author(s):

Christian Kollma ◽

Sighart F. Fischer ◽

Michael C. Böhm

Keyword(s):

High Spin ◽

Ground State ◽

High Spin State ◽

Open Shell ◽

Spin States ◽

Hartree Fock ◽

Intermediate Spin ◽

Model Complex ◽

Out Of Plane ◽

Overlap Method

AbstractThe origin of the displacement of the Fe atom in deoxymyoglobin with respect to the porphyrin plane in the high-spin state is examined by a qualitative molecular orbital (MO) analysis on the extended Hückel level. We find that attachment of a fifth ligand (imidazole in our model complex) to Fe(II)porphyrin favors the out-of-plane shift due to a strengthening of the bonding interaction between Fe and the nitrogen of the imidazole ligand. This results in a high-spin (5 = 2) ground state with Fe shifted out-of-plane for the five-coordinate complex instead of an intermediate spin ground state (5 = 1) with Fe lying in the plane for four-coordinate Fe(II)porphyrin. The relative energies of the different spin states as a function of the distance between Fe and the porphyrin plane are evaluated using an ROHF (restricted open shell Hartree-Fock) version of an INDO (intermediate neglect of differential overlap) method. We observe a level crossing between high-spin and intermediate spin states whereas the low-spin (5 = 0) state remains always higher in energy.

Download Full-text

A new three-phase heterocrystal catalysts and their superior treatment efficiency for tetracycline

Functional Materials Letters ◽

10.1142/s1793604717500151 ◽

2016 ◽

Vol 10 (03) ◽

pp. 1750015

Author(s):

Feng-Rui Wang ◽

Hui-Ping Sun ◽

Yan Wang ◽

Jin-Ku Liu ◽

Yi Fang ◽

...

Keyword(s):

Catalytic Activity ◽

Band Structure ◽

Antibiotic Residues ◽

Treatment Efficiency ◽

Electron Hole ◽

Three Phase ◽

Catalytic Material ◽

Water Based ◽

The Stability ◽

Functional Components

An easy recyclable and interesting Ag3PO4@Pt@TiO2 (APTP) three-phase heterocrystal chains were self-assembled by the cohesive action and chemical construction of polyvinylpyrrolidone (PVP). We found that a new electron–hole transmission path has been built via the rematch of the band structure of Ag3PO4, Pt and TiO2 which extends the light absorption and promoted the electron–hole separation to treat the antibiotic residues in the water. Based on the thorough investigations, a new catalytic material was provided for antibiotics degradation. The catalytic activity of APTP toward the degradation of tetracycline solution was enhanced by 166.67% and the stability increased remarkably compared with pure Ag3PO4 through the integration of different functional components.

Download Full-text

Exciton-polaron Rydberg states in monolayer MoSe2 and WSe2

Nature Communications ◽

10.1038/s41467-021-26304-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Erfu Liu ◽

Jeremiah van Baren ◽

Zhengguang Lu ◽

Takashi Taniguchi ◽

Kenji Watanabe ◽

...

Keyword(s):

Boron Nitride ◽

Excited States ◽

Ground State ◽

Transition Metal Dichalcogenides ◽

Rydberg States ◽

Energy Shift ◽

Many Body ◽

Electron Hole ◽

Metal Dichalcogenides ◽

Excitonic States

AbstractExciton polaron is a hypothetical many-body quasiparticle that involves an exciton dressed with a polarized electron-hole cloud in the Fermi sea. It has been evoked to explain the excitonic spectra of charged monolayer transition metal dichalcogenides, but the studies were limited to the ground state. Here we measure the reflection and photoluminescence of monolayer MoSe2 and WSe2 gating devices encapsulated by boron nitride. We observe gate-tunable exciton polarons associated with the 1 s–3 s exciton Rydberg states. The ground and excited exciton polarons exhibit comparable energy redshift (15~30 meV) from their respective bare excitons. The robust excited states contradict the trion picture because the trions are expected to dissociate in the excited states. When the Fermi sea expands, we observe increasingly severe suppression and steep energy shift from low to high exciton-polaron Rydberg states. Their gate-dependent energy shifts go beyond the trion description but match our exciton-polaron theory. Our experiment and theory demonstrate the exciton-polaron nature of both the ground and excited excitonic states in charged monolayer MoSe2 and WSe2.

Download Full-text