Wide-range-tunable Dirac-cone band structure in a chiral-time-symmetric non-Hermitian system

In this study, we have analyzed the electronic band structure and optical properties of AA-stacked bilayer graphene and its 2D analogues and compared the results with single layers. The calculations have been done using Density Functional Theory with Generalized Gradient Approximation as exchange correlation potential as in CASTEP. The study on electronic band structure shows the splitting of valence and conduction bands. A band gap of 0.342eV in graphene and an infinitesimally small gap in other 2D materials are generated. Similar to a single layer, AA-stacked bilayer materials also exhibit excellent optical properties throughout the optical region from infrared to ultraviolet. Optical properties are studied along both parallel (||) and perpendicular ( ) polarization directions. The complex dielectric function (ε) and the complex refractive index (N) are calculated. The calculated values of ε and N enable us to analyze optical absorption, reflectivity, conductivity, and the electron loss function. Inferences from the study of optical properties are presented. In general the optical properties are found to be enhanced compared to its corresponding single layer. The further study brings out greater inferences towards their direct application in the optical industry through a wide range of the optical spectrum.

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An ab-initio study on structural, elastic, electronic, bonding, thermal, and optical properties of topological Weyl semimetal TaX (X = P, As)

Scientific Reports ◽

10.1038/s41598-021-85074-z ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

M. I. Naher ◽

S. H. Naqib

Keyword(s):

Optical Properties ◽

Band Structure ◽

Fermi Level ◽

Density Of States ◽

Electronic Band Structure ◽

Optical Parameters ◽

Electronic Density ◽

Electronic Band ◽

Wide Range ◽

Weyl Semimetals

AbstractIn recent days, study of topological Weyl semimetals have become an active branch of physics and materials science because they led to realization of the Weyl fermions and exhibited protected Fermi arc surface states. Therefore, topological Weyl semimetals TaX (X = P, As) are important electronic systems to investigate both from the point of view of fundamental physics and potential applications. In this work, we have studied the structural, elastic, mechanical, electronic, bonding, acoustic, thermal and optical properties of TaX (X = P, As) in detail via first-principles method using the density functional theory. A comprehensive study of elastic constants and moduli shows that both TaP and TaAs possesses low to medium level of elastic anisotropy (depending on the measure), reasonably good machinability, mixed bonding characteristics with ionic and covalent contributions, brittle nature and relatively high Vickers hardness with a low Debye temperature and melting temperature. The minimum thermal conductivities and anisotropies of TaX (X = P, As) are calculated. Bond population analysis supports the bonding nature as predicted by the elastic parameters. The bulk electronic band structure calculations reveal clear semi-metallic features with quasi-linear energy dispersions in certain sections of the Brillouin zone near the Fermi level. A pseudogap in the electronic energy density of states at the Fermi level separating the bonding and the antibonding states indicates significant electronic stability of tetragonal TaX (X = P, As).The reflectivity spectra show almost non-selective behavior over a wide range of photon energy encompassing visible to mid-ultraviolet regions. High reflectivity over wide spectral range makes TaX suitable as reflecting coating. TaX (X = P, As) are very efficient absorber of ultraviolet radiation. Both the compounds are moderately optically anisotropic owing to the anisotropic nature of the electronic band structure. The refractive indices are very high in the infrared to visible range. All the energy dependent optical parameters show metallic features and are in complete accord with the underlying bulk electronic density of states calculations.

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Microplasma Band Structure Engineering in Graphene Quantum Dots for Sensitive and Wide-Range pH Sensing

ACS Applied Materials & Interfaces ◽

10.1021/acsami.1c18440 ◽

2021 ◽

Author(s):

Darwin Kurniawan ◽

Bai Amutha Anjali ◽

Owen Setiawan ◽

Kostya Ken Ostrikov ◽

Yongchul G. Chung ◽

...

Keyword(s):

Quantum Dots ◽

Band Structure ◽

Graphene Quantum Dots ◽

Ph Sensing ◽

Wide Range ◽

Structure Engineering

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Evolution of Dirac Cone in Disclinated Graphene

REVIEWS ON ADVANCED MATERIALS SCIENCE ◽

10.1515/rams-2018-0057 ◽

2018 ◽

Vol 57 (2) ◽

pp. 137-142 ◽

Cited By ~ 3

Author(s):

M.A. Rozhkov ◽

A.L. Kolesnikova ◽

I. Hussainova ◽

M.A. Kaliteevskii ◽

T.S. Orlova ◽

...

Keyword(s):

Molecular Dynamics ◽

Density Functional Theory ◽

Band Structure ◽

Density Functional ◽

Md Simulation ◽

Dirac Cone ◽

Electronic Band ◽

Functional Theory ◽

Periodic Distribution ◽

Electronic Band Structures

Abstract Graphene crystals, containing arrays of disclination defects, are modeled and their energies are calculated using molecular dynamics (MD) simulation technique. Two cases are analyzed in details: (i) pseudo-graphenes, which contain the alternating sign disclination ensembles and (ii) graphene with periodic distribution of disclination quadrupoles. Electronic band structures of disclinated graphene crystals are calculated in the framework of density functional theory (DFT) approach. The evolution of the Dirac cone and magnitude of band gap in the band structure reveal a dependence on the density of disclination quadrupoles and alternating sign disclinations. The electronic properties of graphene with disclination ensembles are discussed.

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Mirror symmetry origin of Dirac cone formation in rectangular two-dimensional materials

Physical Chemistry Chemical Physics ◽

10.1039/d0cp00244e ◽

2020 ◽

Vol 22 (12) ◽

pp. 6619-6625 ◽

Cited By ~ 1

Author(s):

Xuming Qin ◽

Yi Liu ◽

Gui Yang ◽

Dongqiu Zhao

Keyword(s):

Band Structure ◽

Mirror Symmetry ◽

Density Functional ◽

Tight Binding ◽

Coupling Mechanism ◽

Two Dimensional ◽

Dirac Cone ◽

Two Dimensional Materials ◽

Tight Binding Method ◽

Cone Formation

The origin of Dirac cone band structure of 6,6,12-graphyne is revealed by a “mirror symmetry parity coupling” mechanism proposed with tight-binding method combined with density functional calculations.

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Temperature dependent Band gap Correction model using tight-binding approach for UTB device simulations

10.36227/techrxiv.18257963 ◽

2022 ◽

Author(s):

Nalin Vilochan Mishra ◽

Ravi Solanki ◽

Harshit Kansal ◽

Aditya S Medury

Keyword(s):

Band Structure ◽

Band Gap ◽

Tight Binding ◽

Thin Body ◽

Temperature Dependent ◽

Minor Variation ◽

Correction Model ◽

Wide Range ◽

Channel Thickness ◽

Semi Empirical

<div>Ultra-thin body (UTB) devices are being used in many electronic applications operating over a wide range of temperatures. The electrostatics of these devices depends on the band structure of the channel material, which varies with temperature as well as channel thickness. The semi-empirical tight binding (TB) approach is widely used for calculating channel thickness dependent band structure of any material, at a particular temperature, where TB parameters are defined. For elementary semiconductors like Si, Ge and compound semiconductors like GaAs, these TB parameters are generally defined at only 0 K and 300 K. This limits the ability of the TB approach to simulate the electrostatics of these devices at any other intermediate temperatures.</div><div>In this work, we analyze the variation of band structure for Si, Ge and GaAs over different channel thicknesses at 0 K and 300 K (for which TB parameters are available), and show that the band curvature at the band minima has minor variation with temperature, whereas the change of band gap significantly affects the channel electrostatics. Based on this finding, we propose an approach to simulate the electrostatics of UTB devices, at any temperature between 0 K and 300 K, using TB parameters defined at 0 K, along with a suitable channel thickness and temperature dependent band gap correction. </div>

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Electronic Structure of the Rare-Earth Nitrides

10.26686/wgtn.16968472.v1 ◽

2021 ◽

Author(s):

◽

A. R. H. Preston

Keyword(s):

Electronic Structure ◽

Rare Earth ◽

Band Structure ◽

Electronic Band Structure ◽

Electronic Band ◽

X Ray ◽

Rare Earth Nitrides ◽

Wide Range ◽

X Ray Absorption ◽

The Rare Earth

<p>The rare-earth nitrides (ReNs) are a class of novel materials with potential for use in spintronics applications. Theoretical studies indicate that among the ReNs there could be half-metals, semimetals and semiconductors, all exhibiting strong magnetic ordering. This is because of the complex interaction between the partially filled rare-earth 4f orbital and the nitrogen 2p valence and rare-earth 5d conduction bands. This thesis uses experimental and theoretical techniques to probe the ReN electronic structure. Thin films of SmN, EuN, GdN, DyN, LuN and HfN have been produced for study. Basic characterization shows that the films are of a high quality. The result of electrical transport, magnetometry, and optical and x-ray spectroscopy are interpreted to provide information on the electronic structure. SmN, GdN, DyN are found to be semiconductors in their ferromagnetic ground state while HfN is a metal. Results are compared with density functional theory (DFT) based calculations. The free parameters resulting from use of the local spin density approximation with Hubbard-U corrections as the exchange-correlation functional are adjusted to reach good agreement with x-ray absorption and emission spectroscopy at the nitrogen K-edge. Resonant x-ray emission is used to experimentally measure valence band dispersion of GdN. No evidence of the rare-earth 4f levels is found in any of the K-edge spectroscopy, which is consistent with the result of M-edge x-ray absorption which show that the 4f wave function of the rare-earths in the ReNs are very similar to those of rare-earth metal. An auxillary resonant x-ray emission study of ZnO is used to map the dispersion of the electronic band structure across a wide range of the Brillouin zone. The data, and calculations based on GW corrections to DFT, together provide a detailed picture of the bulk electronic band structure.</p>

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On the Modulation of Origami Phononic Structure for Adaptive Wave Transmission in Brillouin Zone

Volume 1: Acoustics, Vibration, and Phononics ◽

10.1115/imece2020-24498 ◽

2020 ◽

Author(s):

Megan Hathcock ◽

Bogdan-Ioan Popa ◽

K. W. Wang

Keyword(s):

Refractive Index ◽

Band Structure ◽

Brillouin Zone ◽

Environmental Changes ◽

Phononic Crystals ◽

Wave Transmission ◽

Geometric Constraints ◽

Dirac Cone ◽

Tunable Frequency ◽

Lattice Perturbation

Abstract Recently the presence of a Dirac cone within the band structure of graphene has inspired research on phononic crystals with Dirac-like behaviors — including structures mimicking zero refractive index materials. The interesting phenomena produced by these structures occur at fixed frequencies and cannot be adaptive to needs and environmental changes. To address this constraint, researchers have designed tunable phononic structures; however, the tunable frequency ranges from the studies reported to date are limited by geometric constraints. Using a reconfigurable origami structure to modulate between different classes of phononic Bravais lattices, this research numerically investigates the effects of phononic lattice perturbation to produce drastic changes in the frequency of useful accidental degeneracies.

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Investigation of the valence band structure of PbSe by optical and transport measurement

MRS Proceedings ◽

10.1557/opl.2013.150 ◽

2013 ◽

Vol 1490 ◽

pp. 75-81 ◽

Cited By ~ 2

Author(s):

Thomas C. Chasapis ◽

Yeseul Lee ◽

Georgios S. Polymeris ◽

Eleni C. Stefanaki ◽

Euripides Hatzikraniotis ◽

...

Keyword(s):

Band Structure ◽

Valence Band ◽

Room Temperature ◽

Heavy Hole ◽

Light Hole ◽

Band Model ◽

Valence Band Structure ◽

Effective Masses ◽

Wide Range ◽

Two Band Model

ABSTRACTWe investigated the valence band structure of PbSe by a combined study of the optical and transport properties of p-type Pb1-xNaxSe, with Na concentrations ranging from 0 – 4%, yielding carrier densities in a wide range of 1018 – 1020 cm−3. Room temperature infrared reflectivity studies showed that the susceptibility (or conductivity) effective mass m* increases from ∼ 0.06mo to ∼ 0.5mo on increasing Na content from 0.08% to 3%. The Seebeck coefficient scales with doping in the whole temperature range, yielding lower values for higher Na contents, while the Hall coefficient increases on heating from room temperature showing a peak close to 650 K. The room temperature Pisarenko plot is well described by the simple parabolic band model up to ∼ 1·1020 cm−3. In order to describe the behaviour in the whole concentration range, the application of the two band model, i.e. light hole and heavy hole, was used giving density of states effective masses 0.28mo and 2.5mo for the two bands respectively.

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CLASSICAL BAND STRUCTURE OF PERIODIC ELASTIC COMPOSITES

International Journal of Modern Physics B ◽

10.1142/s0217979296000398 ◽

1996 ◽

Vol 10 (09) ◽

pp. 977-1094 ◽

Cited By ~ 145

Author(s):

MANVIR S. KUSHWAHA

Keyword(s):

Band Structure ◽

Band Gap ◽

Binary Systems ◽

Spectral Gaps ◽

Wave Localization ◽

Band Theory ◽

Phononic Band Gap ◽

Rich Diversity ◽

Wide Range ◽

The Rich

The rich diversity and the fundamental character of the essential theoretical problems associated with it have given band theory a width of interest which contrasts strongly with the apparent narrowness of its subject matter. This review, dealing mainly with the classical band structures of periodic elastic and acoustic binary systems, offers briefly a systematic survey of the historical development of the principles, tools, and applications of band theory for electrons, phonons, photons, and vibrations giving what may be called the "background" to the more recent developments in the fields of photonic and phononic band-gap crystals. Attention is given to survey the physical conditions required to achieve the complete spectral gaps within which the respective propagating modes are utterly forbidden irrespective of the direction of propagation. The existence of complete spectral gaps for cleverly synthesized photonic crystals guarantees the observability of classical Anderson localization of photons and the influence on the spontaneous emission which was, until the 1980's, often regarded as a natural and uncontrollable phenomenon. The phononic band-gap crystals, on the other hand, offer the feasibility of constructing the ultrasound filters, polarization filters, and improvements in designing the transducers, as well as the observability of classical elastic or acoustic wave localization. Abiding by the central theme of the review, numerous theoretical results on the band structure related problems for periodic elastic and acoustic binary sytems have been gathered and reviewed. This survey is preceded by a detailed mathematical machinery that provides the reader with numerous useful analytical results applicable to a wide range of systems of varying interest. Finally, the report concludes with a summary of anticipated implications of photonic and phononic band-gap crystals and proposes some interesting relevant problems concerned with the spectral gaps and the classical wave localization. Our satisfaction in writing this review, like any other review which covers a considerably longer period, was to reach a reasonably self-contained unity by wanting to "leave nothing unexplained". The background provided is believed to make less formidable the task of future writers of reviews in this rather general field and hence enable them to deal more readily with particular aspects of the subject, or with recent advances in those directions in which notable progress may have been made.

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