arXiv subjects

C. Sinha

Publications and source records attributed to C. Sinha.

15 recordsLinked to original sources

arXiv2025

The effect of duty cycle on electron transmission through a graphene electrostatic barrier

We investigated theoretically the transmission properties of Dirac Fermions tunneling through a periodically (sinusoidal and rectangular) driven electrostatic barrier in Monolayer graphene. For the time harmonic potential with moderate to high alpha (=amplitude/frequency) the central Floquet band is found to be almost cloaked for the Klein transmitted electron in contrast to electron at higher grazing incidences. As a time periodic drive, we mainly focused on the use of rectangular wave electric signal to modulate the transparency of the barrier. It is noted that the asymmetric Fano resonance, a characteristic feature of photon assisted tunneling, is more likely to occur for rectangular drive in contrast to the harmonic one. The height of the modulating potential is particularly responsible for the dressing effect of the barrier. The position and nature of the FR can be tailored by changing the height and frequency of the rectangular drive. Moreover, the duty cycle of the driving potential turns out to be an important controlling parameter for the transmission process. Thus, the rectangular modulation plays an important role for the occurrence and detection of the Fano resonances which is vital for the use of graphene nanostructure in the field of detectors, sensors, modulators etc. The present findings attempt for the first time, to realize the effect of duty cycle on the quantum interference in semiconductor nanostructures.

cond-mat.mes-hall↗

arXiv2022

Formation of Anti hydrogen ion in Positronium-Antihydrogen collision with screened Coulomb Potential

The present theoretical work addresses the study of the formation of a positive Antihydrogen ion in a single charge exchange reaction where a positronium ( ground or excited state) interacts with a ground state anti-hydrogen atom, being embedded in a dense Debye plasma. The calculations are carried out in the frame work of a Coulomb Distorted Eikonal Approximation. The result shows that Ps(3S) is the most interesting state to enhance the anti H^+ production at the energy close to the reaction threshold. Regarding the Debye screening, it may be inferred that in lower energy regime, the screening effect enhances the TCS for the 1S and 2S states while reduces the same for the 2P and 3S states of Ps.

quant-ph↗

arXiv2020

Quenching effect of oscillating potential on anisotropic resonant transmission through a phosphorene electrostatic barrier

The anisotropy in resonant tunneling transport through an electrostatic barrier in mono layer black phosphorus either in presence or in absence of an oscillating potential is studied. Non-perturbative Floquet theory is applied to solve the time dependent problem and the results obtained are discussed thoroughly. The resonance spectra in field free transmission are Lorentzian in nature although the width of the resonance for the barrier along the zigzag direction is too thinner than that for the armchair one. Resonant transmission is suppressed for both the cases by the application of oscillating potential that produces small oscillations in the transmission around the resonant energy particularly at low frequency range. Sharp asymmetric Fano resonances are noted in the transmission spectrum along the armchair direction while a distinct line shape resonance is noted for the zigzag direction at higher frequency of the oscillating potential. Even after the angular average, the conductance along the armchair direction retains the characteristic Fano features that could be observed experimentally. The present results are supposed to suggest that the phosphorene electrostatic barrier could be used successfully as switching devices and nano detectors.

cond-mat.mes-hall↗

arXiv2019

Laser induced suppression of transmission in magnetically strained black phosphorus

Charge transport through a rectangular vector potential barrier modulated by a continuum laser in monolayer phosphorene is studied theoretically in the ballistic regime along the line of Floquet formalism. Laser free transmission profile displays strong directional behavior exhibiting collimation depending on the incident energy and width of the barrier. However, the application of laser, polarized along the zig-zag direction, creates a sharp anti-resonance in the transmission spectrum and reveals a strong light matter interaction due to broken symmetry in presence of the magnetic vector potential. Transmission properties through a vector barrier are found to be sensitive particularly for lower frequency and higher intensity of the laser. For a thin barrier, the laser assisted conductance is suppressed remarkably in contrast to its oscillatory nature for a thicker one.

cond-mat.mes-hall↗

arXiv2017

Dynamic cloaking effect of a vector barrier in bilayer graphene

Transmission profiles in bilayer graphene have been studied theoretically in presence of a pair of delta function magnetic barriers. Two types of asymmetric Fano resonances are discussed in connection to the electronic cloaking effect in graphene nanostructures. One arises in a static (time independent) vector barrier due to the quantum interference between the discrete hole like state inside the barrier and the electron like continuum outside. In this case the computed results for normal incidence indirectly verify that the cloaking effect is a manifestation of the chirality conservation in charge transport through bilayer graphene scalar barriers. While the other arising due to discrete continuum coupling via the exchange of photon under the application of an external time periodic scalar potential. The study of Fano resonances in transmission spectrum is very much urgent in regards of localization of charge carriers in graphene nano structures for its application in digital device fabrication.

cond-mat.mes-hall↗

arXiv2016

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.

cond-mat.mes-hall↗

arXiv2016

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

We investigate theoretically the transmission of electrons through a pair of δ- function magnetic barriers in graphene in presence of external monochromatic, linearly polarised 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.

cond-mat.mes-hall↗

arXiv2015

Positronium impact ionization of Alkali atoms

Target ionization processes of alkali atoms by Positronium impact are investigated. Calculations are performed in the frame work of model potential formalism using the Coulomb distorted eikonal approximation. Interesting qualitative features are noted both in the scattered Ps and the ejected electron distributions in differential as well as double differential levels of the collision cross sections.

physics.atom-ph↗

arXiv2015

Spin orbit splitting of the photon induced Fano Resonance in an oscillating graphene electrostatic barrier

We investigate theoretically the effect of a time dependent oscillating potential on the transport property of the Dirac Fermion through a monolayer graphene electrostatic barrier under the influence of the Rashba spin orbit interaction. The time dependent problem is solved in the frame work of the non perturbative Floquet approach. It is noted that the dynamic condition of the barrier may be controlled by tuning the Rashba parameter. Introduction of the spin orbit interaction causes splitting of the Fano resonance(FR), a characteristic feature in photon assisted tunneling. The separation between the spin split FR gives an indirect measure of the fine structure of the quasihole bound state inside the barrier. The present findings on the Rashba splitting of the FR and its external control by tuning the oscillating field parameters might have potential for applications in spintronic devices, especially in the spin field effect transistors. The spin polarization of different Floquet sidebands is found to be quite sensitive to the spin pseudospin interaction.

cond-mat.mes-hall↗

arXiv2012

Complete Break Up of Ortho Positronium (Ps)- Hydrogenic ion System

The dynamics of the complete breakup process in an Ortho Ps - He+ system including electron loss to the continuum (ELC) is studied where both the projectile and the target get ionized. The process is essentially a four body problem and the present model takes account of the two centre effect on the electron ejected from the Ps atom which is crucial for a proper description of the ELC phenomena. The calculations are performed in the framework of Coulomb Distorted Eikonal Approximation. The exchange effect between the target and the projectile electron is taken into account in a consistent manner. The proper asymptotic 3-body boundary condition for this ionization process is also satisfied in the present model. A distinct broad ELC peak is noted in the fully differential cross sections (5DCS) for the Ps electron corroborating qualitatively the experiment for the Ps - He system. Both the dynamics of the ELC from the Ps and the ejected electron from the target He+ in the FDCS are studied using coplanar geometry. Interesting features are noted in the FDCS for both the electrons belonging to the target and the projectile.

physics.atom-ph↗

arXiv2010

Enhancement in Ground State Antihydrogen Formation via Three Body Recombination through Multiphoton effects

Laser- assisted antihydrogen formation cross sections (differential and total) via the three - body recombination (TBR) process in a plasma of antiprotons and positrons are studied for the ground and excited states . Significantly large cross sections are obtained for low energies. The ground state antihydrogen cross section dominates throughout the energy range, essential for high precision spectroscopics studies in order to test the CPT theorem. The formation cross section are found to be much higher for unequal energies of the two positrons than for equal energies.

physics.atom-ph↗

arXiv2008

Fragmentation of Positronium (Ps) in collision with Li ion

Fragmentation of ground state ortho Positronium (Ps) in collision with Li ion (Li+) is studied in the framework of post collisional Coulomb distorted eikonal approximation (CDEA) for the target elastic case . The present model takes account of the two center effect on the ejected e which is crucial for a proper description of the projectile ionization involving an ionic target. Both the fully differential (TDCS) and the doubly differential (DDCS) cross sections (energy spectra) are investigated at intermediate and high incident energies. A broad distinct Electron loss peak (ELP) centered around v_e ~ v_p is noted in the e energy spectrum in contrast to the sharp ELP for a heavy projectile. Two salient features are noted in the present study: i) the shift of the e DDCS peak (summed over e+ angles) towards higher ejection energy with respect to half the residual energy of the system, ii) comparison of the e& e+ energy spectra reflect a strong e - e+ asymmetry with respect to the ratio v_e/v_p =1 >. Both these features could be attributed to the post collisional two center effect on the e due to its parent nucleus (e+) and the screened target ion . Two different wave functions of the Li ion are chosen in order to test the sensitivity of the present results with respect to the choice of the wave function.

physics.atom-ph↗

arXiv2008

Formation of antihydrogen in antiproton - positron collision

A quantum mechanical approach is proposed for the formation of antihydrogen in the ground and excited states (2s, 2p) via the mechanism of three body recombination (TBR) inside a trapped plasma of anti proton and positron or in the collision between the two beams of them. Variations of the differential (DCS) as well as the total (TCS) formation cross sections are studied as a function of the incident energies of both the active and the spectator positrons. Significantly large cross sections are found at very low incident energies in the TBR process as compared to other processes leading to antihydrogen. The present formation cross section decreases with increasing positron energy (temperature) but no simple power law could be predicted for it covering the entire energy range, corroborating the experimental findings qualitatively. The formation cross sections are found to be much higher for unequal energies of the two positrons than for equal energies, as expected physically.

physics.atom-ph↗

arXiv2008

Electron loss to the Continuum in the Projectile ionization for Positronium - Helium atom collision

The dynamics of the electron loss to the continuum (ELC) from the light neutral projectile positronium (Ps) atom in collision with the He atom is studied in the framework of the post collisional Coulomb Distorted Eikonal Approximation (CDEA). Both the fully differential (TDCS) and the double differential (DDCS) cross sections are investigated in the intermediate and high incident energies. Results are compared with the existing experiment and other theories, where possible.

physics.atom-ph↗

arXiv2008

Laser-assisted multiphoton ionization of a hydrogen atom by electron impact

The dynamics of the electron impact multiphoton ionization of a hydrogen atom in the presence of an intense laser field has been studied theoretically, with a view to comparing (qualitatively) the results with the recent kinematically complete experiments of Horr et al [ Phys. Rev. Lett., vol. 94, 153201, (2005) ] for the He target. Significant laser modifications are noted in the present doubly (DDCS) and the fully differential cross sections (TDCS). For most of the explored kinematics (chosen in accordance with the experiment), the present binary peak intensity of the laser-assisted TDCS is significantly enhanced with respect to the field free ones, in agreement with the experiment but in contradiction with the existing first order theories. Importance of the multiphoton effects are also studied.

physics.atom-ph↗