C. Sinha

Signature of quantum interference and the Fano resonances in the transmission spectrum of bilayer graphene nanostructure

The well-known asymmetric Fano resonances that results from the quantum interference between the discrete and the continuum states are noted for the first time in the ballistic transmission spectrum of the bilayer graphene tunneling structures. This unconventional tunneling transmission, in stark contrast to the monolayer graphene and to the conventional heterostructures, arises due to the quadratic dispersion of the chiral charge carriers. If the Klein tunneling (the phenomenon for normal incidence) is an unusual characteristic of the massless chiral particles, then the Fano tunneling (the phenomenon for low glancing incidence) would be the specialty for the massive chiral particles. The characteristic features of the Fano line shape are found to be highly sensitive to the direction of incidence of the charge carriers, the applied homogeneous electric field, and to the barrier height. The sharp anti-resonance at the center of the tunneling band arising due to the destructive interference between the elec...

Beating oscillation and Fano resonance in the laser assisted electron transmission through graphene δ-function magnetic barriers

Abstract We investigate theoretically the transmission of electrons through a pair of δ-function magnetic barriers in graphene in presence of external monochromatic, linearly polarized and CW laser field. The transmission coefficients are calculated in the framework of non-perturbative Floquet theory using the transfer matrix method. It is noted that the usual Fabry–Perot oscillations in transmission through the graphene magnetic barriers with larger inter barrier separation takes the shape of beating oscillations in presence of the external laser field. The laser assisted transmission spectra are also found to exhibit the characteristic Fano resonances (FR) for smaller values of the inter barrier separation. The appearance of the perfect node in the beating oscillation and the asymmetric Fano line shape can be controlled by varying the intensity of the laser field. The above features could provide some useful and potential information about the light - matter interactions and may be utilized in the graphene based optoelectronic device applications.

Electron transmission through a periodically driven graphene magnetic barrier

The kinetic transport of electrons through graphene magnetic barriers is studied theoretically in presence of an external time harmonic scalar potential. The transmission coefficients are calculated in the framework of the non-perturbative Floquet theory using transfer matrix method. The time dependent scalar potential is found to suppress the usual Fabry-Perot oscillations occurring in the transmission through a constant vector potential barrier (corresponding to two oppositely directed delta-function magnetic barriers). Two types of asymmetric Fano resonances (FR) are noted and are discussed for the narrow barrier structure. One of them arises due to the oscillatory mode while the other due to the evanescent mode of the electron wave inside the barrier. In contrast, the oscillating field favors the transmission for rectangular magnetic barrier structure and also exhibits the FR due to the presence of bound state inside the barrier. The characteristic Fano line shape can be tuned by varying the amplitude of the oscillating potential. The detection of such FR offers an efficient tool for the identification of the quasi-bound and evanescent extended states inside the barrier not reported in the literature so far, for the case of graphene magnetic barrier structures.

Charge transfer in proton—positive-ion collisions producing hydrogen atoms in any arbitrary p state

Abstract The electron capture process, H + + A Z X ( Z−1 ) + →H ∗ ( n p)+ A Z X Z+ , for any arbitrary value of n including the limit n → ∞, has been investigated, taking account of the full interaction. Numerical results for the He + ion are presented.

Triple and double differential cross sections for positron impact ionization of a lithium atom

Abstract Triple (TDCS) and double (DDCS) differential cross sections are calculated for ionization of a ground state lithium atom by positron impact at medium high energies for coplanar geometry, using the correlated double continuum wave function (BBK). Some TDCS results for electron impact ionization, obtained from the present model, are also presented for a comparison with the corresponding electron TDCS experiment, and a reasonably good agreement is found. TDCS and DDCS are also calculated for positron impact ionization of a hydrogen atom from its metastable 2S state to compare with the present results of Li atom (in the ground state). A structural resemblance is always found between the two cases, as expected.

SINGLE DIFFERENTIAL AND TOTAL IONIZATION CROSS SECTION OF THE HELIUM ATOM BY POSITRON IMPACT

Abstract Single differential (SDCS) and total (TCS) cross sections are calculated for the single ionization process of a helium atom by positron impact in the intermediate and high energy range (50–300 eV). To study the charge asymmetry, cross sections for electron impact ionization are also presented for comparison with the positron data. The TCS results for positron impact have been compared with existing measurements. A good agreement is noted in the high energy regime (∼ 100–300 eV).

Double differential cross sections for electron and positron impact ionization of helium

Abstract Double differential cross sections (DDCS) for electron and positron impact ionization of helium atom have been calculated for asymmetric geometry at some selected sets of incident ( E i = 200 and 300 eV) and ejected ( E 2 = 10 and 20 eV) energies. In the present prescription, the projectile-electron correlation term in the final channel has been taken into account in the framework of the eikonal approximation and the final state wavefunction satisfies the asymptotic boundary condition for asymmetric geometry. Cross sections are presented versus the ejected angle and are compared with the experiments for electron impact. Reasonable agreement is noted with the measurements of Muller-Fiedler et al. for lower E 2 and Shyn et al. for higher E 2 .