Sharp Resonant States Research Articles

Improved pharmacological properties of nitrotyrosine drug via fluorination: A theoretical study

It has become obvious that fluorinated drugs have a significant role in medicinal applications. In this study, the fluorination of 3-nitrotyrosine as an anti-Parkinson and anti-Alzheimer drug was explored using density functional theory calculations. We have investigated the most important chemical properties of 3-nitrotyrosine that affect the pharmacological activity of the drug. We found that the intramolecular hydrogen bonding and intramolecular charge of the drug were influenced by fluorine substitution. Our results also reveal that the fluorination altered the stability, solubility, and molecular polarity of the 3-nitrotyrosine drug. The density of state analysis also determines sharp resonance states of fluorine atoms with the 3-nitrotyrosine drug states particularly in the highest molecular orbital reigns, suggesting hybridization of the fluorine states with the state of the drug. Moreover, our results show that the electronic spectra of fluorinated derivatives of 3-nitrotyrosine drug exhibit a red shift toward higher wavelengths (lower energies). Our calculations show that the free energy transfers of fluorinated derivatives of the 3-nitrotyrosine drug in water were negative that it meant that the designed molecules dissolving in aqueous phase occurred simultaneously. Consequently, the results of the present study show that the fluorination of 3-nitrotyrosine drug could be considered as a promising strategy to design useful drugs with better pharmacological properties.

Charmed dibaryon resonances in the potential quark model

Charmed dibaryon states with the spin-parity [Formula: see text], and [Formula: see text] are predicted for the two-body [Formula: see text] ([Formula: see text], [Formula: see text], or [Formula: see text]) systems. We employ the complex scaling method for the coupled channel Hamiltonian with the [Formula: see text]-CTNN potentials, which were proposed in our previous study. We find four sharp resonance states near the [Formula: see text] and [Formula: see text] thresholds. From the analysis of the binding energies of partial channel systems, we conclude that these resonance states are Feshbach resonances. We compare the results with the [Formula: see text] resonance states in the heavy quark limit, where the [Formula: see text] and [Formula: see text] thresholds are degenerate, and find that they form two pairs of the heavy-quark doublets in agreement with the heavy quark spin symmetry.

Quark model estimate of hidden-charm pentaquark resonances

A quark model, which reproduces the ground-state mesons and baryons, i.e., the threshold energies, is applied to the $qqqc\bar c$ configurations, where $q$ is a light quark and~$c$ the charmed quark. In the calculation, several open channels are explicitly included such as $\Jpsi +N$, $\eta_c+N$, $\Lambda_c +D$, etc. To distinguish genuine resonances and estimate their width, we employ Gaussian Expansion Method supplemented by the real scaling method (stabilization). No resonance is found at the energies of the $P_c(4380)$ and $P_c(4450)$ pentaquarks. On the other hand, there is a sharp resonant state at 4690\,MeV with $J=1/2^-$ state and another one at 4920\,MeV with $J=3/2^-$ state, which have a compact structure.

Magnetic moments in graphene with vacancies.

Vacancies can induce local magnetic moments in graphene, paving the way to make magnetic functional graphene. Due to the interaction between magnetic moments and conduction carriers, the magnetotransport properties of graphene can be modulated. Here, the effects of vacancy induced magnetic moments on the electrical properties of graphene are studied via magnetotransport measurements and spin-polarized density functional theory calculations. We show by quantum Hall measurements that a sharp resonant Vπ state is introduced in the midgap region of graphene with vacancies, resulting in the local magnetic moment. The coupling between the localized Vπ state and the itinerant carrier is tuned by varying the carrier concentration, temperature, magnetic field, and vacancy density, which results in a transition between hopping transport and the Kondo effect and a transition between giant negative magnetoresistance (MR) and positive MR. This modulated magnetotransport is valuable for graphene based spintronic devices.

Theoretical and experimental evidence of Fano-like resonances in simple monomode photonic circuits

A simple photonic device consisting of two dangling side resonators grafted at two sites on a waveguide is designed in order to obtain sharp resonant states inside the transmission gaps without introducing any defects in the structure. This results from an internal resonance of the structure when such a resonance is situated in the vicinity of a zero of transmission or placed between two zeros of transmission, the so-called Fano resonances. A general analytical expression for the transmission coefficient is given for various systems of this kind. The amplitude of the transmission is obtained following the Fano form. The full width at half maximum of the resonances as well as the asymmetric Fano parameter are discussed explicitly as function of the geometrical parameters of the system. In addition to the usual asymmetric Fano resonance, we show that this system may exhibit an electromagnetic induced transparency resonance as well as well as a particular case where such resonances collapse in the transmission coefficient. Also, we give a comparison between the phase of the determinant of the scattering matrix, the so-called Friedel phase, and the phase of the transmission amplitude. The analytical results are obtained by means of the Green's function method, whereas the experiments are carried out using coaxial cables in the radio-frequency regime. These results should have important consequences for designing integrated devices such as narrow-frequency optical or microwave filters and high-speed switches. This system is proposed as a simpler alternative to coupled-micoresonators.

Impurity states in multibands-wave superconductors: Analysis of iron pnictides

We examine the effect of a single, nonmagnetic impurity in a multiband, extended $s$-wave superconductor allowing for anisotropy of the gaps on the Fermi surfaces. We derive analytic expressions for the Green's functions in the continuum and analyze the conditions for the existence of sharp impurity-induced resonant states. Underlying band structure is more relevant for the multiband than for the single-band case, and mismatch between the bands generically makes the formation of the impurity states less likely in the physical regime of parameters. We confirm these conclusions by numerically solving the impurity problem in a tight-binding parametrization of the bands relevant to pnictide superconductors.

Evidence of Fano-like resonances in mono-mode magnetic circuits

In the frame of long-wavelength Heisenberg model, a simple magnonic device is designed to obtain possibly transmission stop bands (where the propagation of spin waves is forbidden). This simple device is composed of an infinite one-dimensional mono-mode waveguide (the backbone) along which $N({N}^{\ensuremath{'}})$ side resonators are grafted at two sites. Contrary to all known systems of this kind, a spectral transmission gap of nonzero width occurs here even with this simple structure. This is obtained by combining appropriately the zeros of transmission of the side resonators. Sharp resonant states inside the gaps can be achieved without introducing any defects in the structure. This results from an internal resonance of the structure when such a resonance is situated in the vicinity of a zero of transmission or placed between two zeros of transmission, the so-called Fano resonances. A general analytical expression for the transmission coefficient is given for various systems of this kind within the framework of the Green's function method. The amplitude, the phase, and the phase time of the transmission are discussed as a function of frequency and it is shown that the width of the stop bands is very sensitive to the number of the side resonators. These results should have important consequences for designing integrated devices such as narrow-frequency optical or microwave filters and high-speed switches.

Transmission gaps and Fano resonances in an acoustic waveguide: analytical model

A simple acoustic device consisting of two dangling side resonators grafted at two sites on aslender tube is designed possibly to obtain transmission stop bands (where the propagationof longitudinal acoustic waves is forbidden). In contrast to all known systems ofthis kind, a spectral transmission gap of nonzero width occurs here even withthis simple structure. This is obtained by combining appropriately the zeros oftransmission of the side resonators. Sharp resonant states inside the gaps canbe achieved without introducing any defects in the structure. This results froman internal resonance of the structure when such a resonance is situated in thevicinity of a zero of transmission or placed between two zeros of transmission, theso-called Fano resonances. A general analytical expression for the transmissioncoefficient is given for various systems of this kind within the framework of theGreen’s function method. The amplitude and the phase of the transmission arediscussed as a function of frequency and it is shown that the width of the stopbands is very sensitive to the number of side resonators. These results should haveimportant consequences for the suppression of low-frequency noise and for designingfilters.

Transmission gaps and Fano resonances in a simple acoustic waveguide: Analytical model

A simple acoustic device consisting of two dangling side resonators grafted at two sites on a slender tube is designed to obtain possibly transmission stop bands where the propagation of longitudinal acoustic waves is forbidden. Contrary to all known systems of this kind, a spectral transmission gap of nonzero width occurs here even with this simple structure. This is obtained by combining appropriately the zeros of transmission of the side resonators. Sharp resonant states inside the gaps can be achieved without introducing any defects in the structure. This results from an internal resonance of the structure when such a resonance is situated in the vicinity of a zero of transmission or placed between two zeros of transmission, the so-called Fano resonances. A general analytical expression for the transmission coefficient is given for these systems within the framework of the Green's function method. The amplitude and the phase time of the transmission are discussed as a function of frequency and it is shown that the width of the stop bands is very sensitive to the number of the side resonators. These results should have important consequences for the suppression of low-frequency noise and for designing filters.

First-Principles Study of Carbon Nanotubes with Bamboo-Shape and Pentagon–Pentagon Fusion Defects

A first-principles study of single-walled carbon nanotubes with bamboo-shape (BS) and pentagon-pentagon fusion defects was conducted. Sharp resonances occur on the BS-nanotubes as strong density of electronic states (DOS) localized at carbon atoms adjacent to the partitions, while at the partition the localized DOS was greatly depleted. A strong defect state at -0.1 eV below the Fermi level was generated and the band gap was narrowed for BS-(10, 0) nanotube. Sharp resonant states are observed in the valence and conduction bands of BS-(12, 0) nanotube. The resonant states are attributed to the pentagon defects as exemplified by the study of a (5, 5) nanotube with pentagon-pentagon fusion ring. The high chemical reactivity of the topological defects of the BS-nanotubes is correlated to the presence of localized resonant states.

Magnon nanometric filters in quasi-one-dimensional cluster chains

In the frame of the discrete dipole approximation, the propagation of magnons in quasi-one-dimensional resonant structures made of nanometric magnetic clusters is examined theoretically. These resonant structures, composed of a nanometric magnetic cluster chain and adsorbed clusters near the chain, may exhibit sharp peaks (dips) in the magnon transmission spectrum. Stop bands and sharp resonant magnonic states in the gaps can be created with an appropriate choice of the geometrical or magnetic parameters of the structure. These resonant states result from an internal resonance of the structure when such a resonance is situated in the vicinity of a zero of transmission or placed between two zeros of transmission. This model may have potential applications in constructing magnon filter devices.

Transmission gaps and sharp resonant states in the electronic transport through a simple mesoscopic device

A simple electronic circuit consisting of a single symmetric or asymmetric loop with dangling resonators is designed to obtain possibly large stop bands (where the propagation of electrons is forbidden). Contrary to all known systems of this kind, a spectral transmission gap of nonzero width occurs here even with a single loop. This is obtained by combining appropriately the zeros of transmission of the loop and of the dangling resonators. Sharp resonant electronic states inside the gaps can be achieved without introducing any defects in the structure. This results from an internal resonance of the structure when such a resonance is situated in the vicinity of a zero of transmission or squeezed between two zeros of transmission, the so-called Fano resonances. A general expression for the transmission coefficient is given for various systems of this kind within the framework of the interface response theory. The amplitude and the phase of the transmission are discussed as a function of the wave vector or energy and it is shown that the width of the stop bands is very sensitive to the number of grafted resonators, while the magnitude of the resonant states in the transmission coefficient is very sensitive to the lengths of the different arms constituting the loop and the dangling resonators. These structures may have potential applications in microelectronic devices.

Computation of 2+ resonance in 6He: bound state in the continuum

Calculation of the 2+ resonance state of 6He in a three-body model (4He + n + n) is done by adopting a novel theoretical technique. The effective three-body potential for the 2+ state of 6He is obtained using hyperspherical harmonics and it presents a shallow well followed by a low and wide barrier. Numerical diffculties present in the calculation of the resonance energy of such a shallow well–barrier combination are overcome by the construction of a one-parameter (λ) isospectral potential having a bound state in the continuum. This potential develops a deep well followed by a high barrier for small positive values of λ. This effectively traps the system in a sharp resonant state and facilitates calculation of the resonance energy accurately. We obtain the first 2+ resonance at 1.814 MeV with a width of 135 keV. We also get a second 2+ resonance at 4.9 MeV.

Soluble complex potential model for heavy-ion collision: resonance and fusion in 12C+ 12C reaction

The optical model for nucleus–nucleus scattering is treated explicitly by means of a new form of complex composite potential which permits an exact solution of s-wave Schrödinger equation. The real part of the potential being everywhere smooth possesses a pocket followed by a barrier and the imaginary part can be viewed distinctly as volume and surface terms as envisaged in the study of heavy-ion collision. The closed form of the S-matrix obtained from the logarithmic derivative of the wave functions in two different parts of the potential depends explicitly on the parameters of the potential. While the pocket generate molecular or shape resonances, the barrier can support number of sharp resonance states in the above-barrier region of energy. This new states of resonance from the barrier along with the pocket resonances successfully account for the large number of experimentally observed resonances in light heavy-ion system namely 12C+ 12C and their manifestation as oscillatory structures in the data of fusion cross section.

Electronic properties of selected BN nanocones

The electronic properties of selected BN nanocones are investigated. In particular, we have proposed one configuration for BN nanocones associated with the 240° disclination as the most stable one presenting as characteristic four pentagons at the apex and termination in two atoms. This structure is simulated by clusters containing 58 B plus N atoms and additional 12 H atoms to saturate the dangling bonds at the edge. The geometric structure is obtained through molecular mechanics optimization calculations. The density-functional theory is employed to perform total energy calculations. The most stable termination is obtained when the two terminating atoms are one B and one N. For those cases where the two apex atoms are of the same kind, the apex with B atoms is determined to present lower binding energy than with N atoms. For the topologies studied, the local densities of states are investigated near the apex of the nanocones and sharp resonant states are found to dominate the electronic structure in the region close to the Fermi energy. These BN nanocones with pentagonal sites at their apex are proposed as good candidates for nanoprobes in scanning microscopy and also for electron field emitters.

Structural and Electronic Properties of 240° Nanocones

An original nanocone with 240° disclination arises naturally from a planar hexagonal sheet when four 60° segments originating from adjacent hexagonal centers are cut out of the plane and the severed edges of the segments are rejoined. The comparison among the calculated total energies of several pure carbon nanocones with this same 240° disclination but built from different growth modes shows that the cone with four 60° segments is the most stable one. The geometric structures are optimized and the density-functional theory is employed to perform total energy calculations. Defined the designability and the stability of this carbon structure, with four pentagons sharing two atoms at the apex, we simulate a similar BN nanocone by clusters containing 58 B plus N atoms and additional 12 H atoms to saturate the dangling bonds at the edge. Depending on the choice of the sharing atoms (BN, BB, or NN), the local densities of states near the apexes are investigated and sharp resonant states are found to dominate the electronic structure in the region close to the Fermi energy.

Particle–hole interaction effect on an Auger-electron spectrum

Abstract Auger-electron spectroscopy (AES) spectral-lineshape governed by a final-state interaction of a localized two-hole (2h) state with a three-hole one-particle (3h1p) continuum or bound state, is studied by a Green’s function method. The particle–hole interaction U in a 3h1p state can affect the AES spectral-lineshape significantly. Even when the coupling between a 2h state and a 3h1p continuum is strong, there can be a sharp resonant 2h state. When the coupling is “weak”, the quasi-particle approximation for a 2h state can break down. As an example, the M 45 –N 23 N 45 AES spectra of elements Pd to Ba are studied. The effect of particle–hole interaction on an AES spectral-lineshape of a charge transfer system is also discussed.

Electronic structure of carbon nanocones.

Topology related changes in the local density of states near the apex of carbon nanocones are investigated using both tight-binding and ab initio calculations. Sharp resonant states are found to dominate the electronic structure in the region close to the Fermi energy. The strength and the position of these states with respect to the Fermi level depend sensitively on the number and the relative positions of the pentagons constituting the conical tip. Carbon nanocones are thus proposed as good candidates for nanoprobes in scanning probe microscopy.

Particle–hole interaction effect on a core-level XPS spectrum II

Abstract X-ray photoelectron spectroscopy (XPS) spectral behavior of an initial discrete core-hole state embedded or nearly embedded in a continuum is studied by a Green’s function model calculation. The particle–hole interaction U in the final two-hole one-particle state is included in the initial core-hole self-energy by the ladder and ring approximation. With an increase of U, the transition to an unoccupied (particle) state near the double-ionization threshold increases in the final state. With a further increase of U, the transition to an empty bound level below the Fermi level dominates. It is shown that even when the coupling between the initial discrete core-hole state and the final continuum state is strong there can be a sharp resonant state. When the coupling is weak, there is a possibility of the breakdown of the quasi-particle approximation for the initial core-hole state. U can substantially affect the initial core-hole spectral function.

Resonant states in quantum wells: theoretical analysis of the density of states and phase times

The existence of sharp resonant states in a single quantum well separated from its semi-infinite substrate by a barrier layer is reported here. These resonances appear as well defined peaks in the density of states. The local and total densities of states are obtained from an analytical determination of the Green functions. The expressions of the transmission and reflection phase times are also derived and compared to the density of states. The positions of the peaks in the density of states enable us to study the energy levels of resonant states as a function of the thicknesses of the barrier and well layers. Specific applications of our analytical results are given in this paper for a bilayer sandwiched between two semi-infinite GaAs and media.