Search

Magneto-band structures of AA-stacked bilayer graphene nanoribbons with armchair and zigzag (BLAGNR and BLZGNR) edges are calculated by the p z -orbital tight-binding model. At zero field, BLAGNR is a semiconductor or metal determined by its width. Magnetic field can reduce band-gap and exhibit crossing bands. For metallic BLZGNRs, crossing bands shift and parabolic bands are separated more widely with magnetic field; however, partial flat bands keep unchanged. Temperature significantly increases plasmon frequency and strength for semiconducting BLAGNRs, but slightly affects those of metallic BLAGNRs and BLZGNRs. Magnetic field, for gapped BLAGNRs, can effectively reduce the threshold temperature for inducing plasmon. Whether magneto-plasmon frequency and critical momentum of dispersion relation increase or decrease is strongly sensitive to nanoribbon's geometry. Field-modulated plasmons with a wide range of frequency could provide potential applications in waveguides and optical sensors. • Band-gaps are determined by the edge geometry and width of BLGNRs. • Magnetic field significantly modulates energy dispersions and reduces band-gaps. • Plasmon frequency and strength increase with temperature and magnetic field for gapped BLAGNRs. • Plasmon spectra of metallic BLAGNRs and BLZGNRs have a weak temperature-dependence. • Plasmon frequency decreases with magnetic field for metallic BLAGNRs and BLZGNRs. [ABSTRACT FROM AUTHOR]

In this work, we aim to control the electronic heat capacity (EHC) of bilayer P6 mmm borophene through a perpendicular electric field, excitonic effects, and external dopants. To achieve this, we employ the tight-binding model within a semi-classical framework. Our findings reveal a decrease in EHC under all stimuli due to decreased total electronic states in the system, while the coexistence of electric field and excitonic effects leads to an enhancement of EHC in the strong regime. Additionally, our study highlights a shift in the Schottky anomaly peak at low temperatures only in the strong regime of stimuli. This study is crucial for the design of thermoelectric materials based on borophene. • Control of the electronic heat capacity of bilayer P6 mmm borophene through a perpendicular electric field, excitonic effects, and external dopants. • Shift in the Schottky anomaly peak at low temperatures only in the strong regime of stimuli. • Enhancement of electronic heat capacity in the strong regime with the coexistence of electric field and excitonic effects. • Reduction of electronic heat capacity under all stimuli. [ABSTRACT FROM AUTHOR]

We investigate the transport properties in T-shaped armchair graphene nanoribbons with a zigzag-edge sidearm connected to two normal-conducting leads. For semiconducting armchair graphene nanoribbons, the conduction peaks can be introduced into the gap regime, which may be used as an energy filter. The metallic armchair graphene nanoribbons with a sidearm are proposed for a field-effect transistor where the on and off states are switched by tuning the length or the width of the sidearm. In addition, we demonstrate that both the on and off states are robust to the tunneling barrier between the leads and the graphene nanoribbons. • A simple T-shaped armchair GNRs with a zigzag-edge sidearm is constructed. • The semiconducting armchair grapheme nanoribbons may be used as an energy filter. • The metallic armchair graphene nanoribbons are advised for a field-effect transistor. • It is certified that both the on and off states are robust to the tunneling barrier. [ABSTRACT FROM AUTHOR]

We consider manifolds of the tunable electronic density of states in single-layer β 12 -borophene, parameterized by a manifold electron hopping amplitude. We study the hybridization properties of orbitals in the presence of gas molecules (GM) with a tight-binding model and Green's function approach. Independent of how we dope the layer by GM, van Hove singularities are significantly generated and associated with various broadness and flatness features of bands. We demonstrate that β 12 -borophene with GM-doped { a , e } , { a , c } , { b , d } , and { b , c } atoms is described by a semimetallic phase, where the metallic phase is washed out in the vicinity of Fermi level. We also find a gapless semiconducting phase at the Fermi energy for GM-doped c atoms; however, the most inherent character of the system remains unchanged once all atoms are simultaneously doped with GM. These findings can apply to tuning field-effect transistor-based gas sensors. • Investigation of the metallic phase of beta_12-borophene (with five {a,b,c,d,e} atoms in the unit cell) via van Hove singularities in the vicinity of the Fermi energy in the presence of adsorbed gas molecules (GM). • Appearance of semimetallic phase for GM-doped {a,e}, {a,c}, {b,d}, and {b,c}. • Appearance of a gapless semiconducting phase at the Fermi energy for GM-doped {c} atoms. [ABSTRACT FROM AUTHOR]

We investigate the effects of disorder on the electron transport properties of graphene nanoribbons (GNs) with armchair edges described in tight-binding (TB) model. We try to compare the electronic properties of armchair graphene nanoribbons (AGNs) subjected to two types of disorder with different distributions. In this regard, the tight-binding model of electron transport in the presence of hopping to nearest and next-nearest neighbors is investigated. With the aid of the spectral and multifractal analyses, we find that for the case of ordered distribution of disorder the AGNs acts as an insulator and for disordered distribution AGN behaves as a semi-metal. Our results can report different regimes of conductivity and addresses the transition between semi-metallic and insulator phases. [ABSTRACT FROM AUTHOR]

The energy spectrum and electronic density of states (DOS) of zigzag graphene nanoribbons with edges reconstructed with topological defects are investigated within the tight-binding method. In case of the Stone–Wales zz (57) edge the low-energy spectrum is markedly changed in comparison to the pristine zz edge. We found that the electronic DOS at the Fermi level is different from zero at any width of graphene nanoribbons. In contrast, for ribbons with heptagons only at one side and pentagons at another one the energy gap at the Fermi level is open and the DOS is equal to zero. The reason is the influence of uncompensated topological charges on the localized edge states, which are topological in nature. This behavior is similar to that found for the structured external electric potentials along the edges. [ABSTRACT FROM AUTHOR]

The tight-binding model is used to study the electronic and optical properties of armchair and zigzag boron nitride nanoribbons (ABNNRs and ZBNNRs) in electric field. Electric field could significantly change dispersion relations, degeneracy, edge-states, band crossings, and energy gaps. The field-modulation of energy gaps is more effective and covers wider energy range for BNNRs than graphene nanoribbons. The critical electric field that induces zero-gap transition strongly depends on geometric structures of BNNRs. At zero field, the selection rule and the absorption frequency range of spectral functions are different between ABNNRs and ZBNNRs. Electric field would change state functions that constructs new selection rule and further exhibits more absorption peaks. [ABSTRACT FROM AUTHOR]

Abstract: We study the magnetism of an adatom adsorbed on AA-stacked bilayer graphene (BLG) in both unbiased and biased cases using the Anderson impurity model. We find different magnetic phase diagrams for the adatom, depending on its energy level. The magnetic phase of the adatom varies from that in normal metals to that in graphene. This is because of the individual energy dependence of the density of states (DOS) of AA-stacked BLG and anomalous broadening of the adatom energy level. We also investigate the effect of a bias voltage on the DOS of AA-stacked BLG and show that adatom magnetization can be controlled by applying a bias voltage. This allows the possibility of using AA-stacked BLG in spintronic devices. [Copyright &y& Elsevier]

Abstract: For a newly discovered iron-based high superconducting parent material , we present an effective three-dimensional five-orbital tight-binding model by fitting the band structures. The three -symmetry orbitals of the five Fe 3d orbitals mainly contribute to the electron-like Fermi surface, which has a three-dimensional character, in agreement with recent angle-resolved photoemission spectroscopy experiments. To understand the groundstate magnetic properties, the two- and three-dimensional spin and charge susceptibilities within the random phase approximation are investigated. It obviously shows a sharp peak at wave vector , indicating the magnetic instability of Néel-type antiferromagnetic rather than (, )-type or stripe (, 0)-type antiferromagnetic ordering, while it exhibits a ferromagnetic instability between the nearest neighboring FeSe layers along c axis. The three-dimensional spin fluctuation may play an important role in pairing symmetry in superconducting materials , etc.). [Copyright &y& Elsevier]

Abstract: The symmetry group (magnetic translation group) of a Bloch electron in a finite two-dimensional lattice in a perpendicular magnetic field is discussed. The details of the structure of this group depend on a gauge of a vector potential of a magnetic field. For two gauges, symmetric and Landau, the group elements are presented in terms of generators, and the relation between the group properties and the number of magnetic fluxes through the elementary cell of the lattice is pointed out. [Copyright &y& Elsevier]

I theoretically determine the electronic and optical signatures of CdSe/CdS core/shell dot-in-hexagonal platelet nanocrystals with experimentally synthesized dimensions exploiting the atomistic tight-binding theory. With the increasing lateral sizes and thicknesses of the CdS hexagonal platelets, the reduction of excitonic band gaps is ascribed to the quantum confinement consequence. The excitonic band gaps emitting the visible spectra are carried out by CdS shell sizes. The optical characteristic of CdSe/CdS dot-in-hexagonal platelet nanocrystals is advanced when comparing with bare CdSe nanocrystal. The reduction of oscillator strengths, excitonic binding energies and stokes shift with the increasing sizes of CdSe shell is ascribed to the electron-hole wave function overlaps. The key findings from the tight-binding analysis agree well with the experimental observation. Finally, this theoretical study delivers the essential direction to predesign of core/shell dot-in-hexagonal platelet nanocrystals with specific characteristics for various optoelectronic technologies. [ABSTRACT FROM AUTHOR]

Thermoelectric power of the Kondo insulators is analyzed theoretically. It is pointed out that Kelvin''s relation found in 1851 must be modified for insulators at low temperatures. A realistic tight-binding model is constructed for the description of the conduction bands of the most typical Kondo insulator YbB12. It will be a good starting point for the development of a realistic theory of the Kondo insulators with strong correlation. [Copyright &y& Elsevier]

We study the thermoelectric properties of zigzag-edge phosphorene nanoribbon with N chains (N -ZPNR) under a perpendicular electric field (PEF). By adopting the tight-binding Hamiltonian combined with the nonequilibrium Green's function method, it is demonstrated that the maximum value of the Seebeck coefficients for both 40- and 41-ZPNRs can reach 4 mV/K. Interestingly, there is an even–odd effect on the thermoelectric properties when a PEF is applied, which originates from the structure symmetry of N -ZPNR and can result in different behavior of edge states for even and odd cases. Specifically, the increasement induced by the external field of the Seebeck coefficient for 41-ZPNR with odd number of chains is much more pronounced than that for 40-ZPNR with even number. Moreover, the introduction of the Anderson disorder to the system can suppress the transmission but enhance the Seebeck coefficients for both even and odd cases. • The maximum value of the Seebeck coefficients for both 40- and 41-ZPNRs can reach 4 mV/K. • There is an even–odd effect on the thermoelectric properties when an external field is applied. • The Anderson disorder can suppress the transmission but enhance the Seebeck coefficients for both even and odd cases. [ABSTRACT FROM AUTHOR]

Band structures of armchair graphene nanoribbons (AGNRs) under crossed external fields are calculated within the tight-binding model. Magnetic field reduces energy-gap and flattens energy dispersions of band-edge states. Electric field strongly distorts energy dispersions leading to a reduction of energy-gap, a shift in band-edge states and many local maxima and minima. The complex dielectric function is further calculated in long-wavelength limit in which many peak-dip structures reveal characteristics of transparency and absorption. Furthermore, plasmon spectra are determined by frequency-position, sharpness, and number of peak-dip structures those are related to field strength and ribbon's geometry. The field-induced extra transition channels could make a change in the frequency, peak-height, and number of branch of plasmons that can make AGNRs into a tunable terahertz nano-material. The photoninduced plasmons are further reflected in the edge-structures of reflectance spectra, unveiling the transition between transparency and absorption. Reflectance spectra strongly depend on external fields and ribbon's geometry that will be verified by experimental measurements. • Magnetic and electric fields significantly modulate electronic properties of AGNRs. • Plasmon spectra strongly depend on field strength and ribbon's geometry. • External fields make AGNRs into tunable terahertz nano-materials in plasmonics. • Field-tuned reflectance spectra reflect the transition between transparence and absorption. [ABSTRACT FROM AUTHOR]