arXiv subjects

Miloud Mekkaoui

Publications and source records attributed to Miloud Mekkaoui.

At least 19 recordsLinked to original sources

arXiv2026

Magnetic control of Goos-Hänchen shifts and group delay time in monolayer WSe$_2$

We study the influence of an external magnetic field on the Goos-Hänchen (GH) shift and the group delay time (GDT) in monolayer WSe$_2$ in the presence of a magnetic barrier. The transport properties of Dirac-like carriers are obtained by solving the effective low-energy Hamiltonian and evaluating the corresponding transmission amplitudes. The GH shift and the GDT are subsequently extracted from the phase of the transmission coefficient. We systematically analyze their dependence on the magnetic field strength, incident energy, angle of incidence, and barrier width, with particular emphasis on the spin and valley degrees of freedom associated with the $K$ and $K'$ valleys. Our results show that the magnetic barrier strongly modulates both the GH shift and the GDT, leading to oscillatory behavior and pronounced spin-valley-dependent transport characteristics. Remarkably, the magnetic field enables selective control of the lateral shift and traversal time of carriers for each spin and valley channel, allowing for tunable spatial and temporal separation of electronic wave packets. This provides a mechanism for manipulating fermionic trajectories after transmission through the barrier in a highly controllable manner. Such tunability opens promising avenues for designing nanoscale devices based on spin and valley filtering, as well as for potential applications in information storage and processing within spintronic and valleytronic platforms.

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arXiv2025

Laser-induced modulation of conductance in graphene with magnetic barriers

We study how electrons move across a graphene sheet when it encounters two magnetic barriers with a region in between that is continuously driven by laser light. Rather than acting as a static obstacle, this illuminated middle section becomes a Floquet cavity that opens new transport channels through controlled photon absorption and emission. By combining Floquet theory with the transfer matrix method, we track electron transmission through both the main energy band and the emerging photon-assisted sidebands. We find that the laser does more than modify the potential--it reshapes how electrons interact between the magnetic barriers, enabling a switch from ordinary transmission to transport dominated by photon exchange. Because the magnetic field and the optical drive are applied to separate sections of the device, the system supports interference between cyclotron-filtered motion and discrete photon-pumping channels, producing Fano resonances and angle-dependent transmission zeros that cannot appear in double magnetic or double laser barrier systems alone. Under well-defined conditions, the distance between the magnetic barriers controls the coupling between Floquet channels, allowing highly tunable resonances and even perfect transmission, despite strong magnetic confinement. We also observe that low-energy carriers are efficiently blocked by the magnetic regions, while conductance steadily rises with energy until it reaches a clear saturation plateau. This hybrid design provides a versatile way to steer graphene electrons by balancing optical pumping and magnetic momentum filtering.

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arXiv2024

Conductance in graphene through double laser barriers and magnetic field

Photon-assisted charge transport through a double barrier laser structure, separated by a region assisted by a magnetic field, is studied. Employing Floquet theory and matrix formalism, the transmission probabilities for the central band and sidebands are calculated. The temporal periodicity of the laser fields creates an infinite number of transmission modes due to the degeneracy of the energy spectrum. The challenge of numerically addressing all modes necessitates the limitation to the first sideband corresponding to energies $\varepsilon\pm\varpi$. A critical phase difference between the two laser fields is found to cancel the transmission through the sidebands due to quantum interference. Varying the width of the region where the magnetic field is applied allows for the suppression of lateral transmission and control over the transmission mode. The intensity of the laser fields also allows for suppressing Klein tunneling and blocking transmission processes with zero photon exchange, as well as activating transmission processes with photon exchange. The conductance is also affected by changes in the system parameters. Increasing the intensity of the laser field reduces the conductance due to the confinement of the fermions by the laser fields. In addition, increasing the size of the region where the magnetic field is applied reduces the conductance because the increased distance gives the fermions a greater chance of diffusion and increases their interaction with the magnetic field.

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arXiv2024

Transmissions in gapped graphene exposed to tilting and oscillating barriers

We investigate the transmissions of fermions through gapped graphene structures by employing a combination of double barrier tilting and a time-oscillating potential. The latter introduces additional sidebands into the transmission probability, which manifest at energy levels determined by the frequency and incident energy. These sidebands arise from the absorption or emission of photons generated by the oscillating potential. We demonstrate that the tilting and positioning of the scattering events within the barriers play a crucial role in determining the peak of tunneling resistance. In particular, the presence of a mid-barrier-embedded scatter leads to a transition from a peak to a cusp when the incident energy reaches the Dirac point within a barrier. Additionally, we illustrate that introducing a time-varying potential results in transmissions dispersing across both the central band and the sidebands.

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arXiv2024

Transmission in graphene through a double laser barrier

We study the tunneling behavior of Dirac fermions in graphene subjected to a double barrier potential profile created by spatially overlapping laser fields. By modulating the graphene sheet with an oscillating structure formed from two laser barriers, we aim to understand how the transmission of Dirac fermions is influenced by such a light-induced electric potential landscape. Using the Floquet method, we determine the eigenspinors of the five regions defined by the barriers applied to the graphene sheet. Applying the continuity of the eigenspinors at barrier edges and using the transfer matrix method, we establish the transmission coefficients. These allow us to show that oscillating laser fields generate multiple transmission modes, including zero-photon transmission aligned with the central band $\varepsilon$ and photon-assisted transmission at sidebands $\varepsilon+ l\varpi$, with $l=0,\pm1, \cdots$ and frequency $\varpi$. For numerical purposes, our attention is specifically directed towards transmissions related to zero-photon processes ($l=0$), along with processes involving photon emission ($l=1$) and absorption ($l=-1$). We find that transmission occurs only when the incident energy is above the threshold energy $\varepsilon>k_y+2\varpi$, {with transverse wave vector $k_y$}. We find that the variation in distance {$d_1$ separating two barriers of widths $d_2-d_1$} suppresses one transmission mode. Additionally, we show that an increase in laser intensity modifies transmission sharpness and amplitude.

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arXiv2023

Tuned gap in graphene through laser barrier

We study the effect of the energy gap on the transmission of fermions in graphene exposed to linearly polarized light as a laser barrier. We determine the energy spectrum, apply boundary conditions at interfaces, and use the transfer matrix approach to obtain transmissions for all energy modes. We show that when the energy gap increases, the oscillations of transmissions decrease dramatically until they vanish entirely. However, when the barrier width varies, the oscillations become more significant and exhibit sharp peaks. By increasing the incident energy, the laser field suppresses the Fabry-Pérot resonance, and the transmissions move to the right when the energy gap is tuned.

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arXiv2023

Transport properties in gapped graphene through magnetic barrier in a laser field

We study the transport properties of Dirac fermions through gapped graphene through a magnetic barrier irradiated by a laser field oscillating in time. We use Floquet theory and the solution of Weber's differential equation to determine the energy spectrum corresponding to the three regions composing the system. The boundary conditions and the transfer matrix approach {are} employed to explicitly determine the transmission probabilities for multi-energy bands and the associated conductance. As an illustration, we focus only on the three first bands: the central band $T_0$ (zero photon exchange) and the two first side bands $T_{\pm1}$ (photon emission or absorption). It is found that the laser field activates the process of translation through photon exchange. Furthermore, we show that varying the incident angle and energy gap strongly affects the transmission process. The conductance increases when the number of electrons that cross the barrier increases, namely when there is a significant transmission.

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arXiv2023

Transmission in graphene through tilted barrier in laser field

We study the transmission of Dirac fermions in graphene through a tilted barrier potential in the presence of a laser field of frequency $ω$. By using Floquet theory, we solve the Dirac equation and then obtain the energy spectrum. The boundary conditions together with the transfer matrix method allow us to determine the transmission probabilities corresponding to all energy bands $E+l\hbarω$ $(l=0,\pm1, \cdots)$. By limiting to the central band $l=0$ and the two first side bands $l=\pm 1$, we show that the transmissions are strongly affected by the laser field and barrier. Indeed, it is found that the Klein effect is still present, a variety of oscillations are inside the barrier, and there is essentially no transmission across all bands.

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arXiv2023

Transmission in strained graphene subjected to laser and magnetic fields

We investigate the effect of strain along armchair and zigzag directions on electrical transport in graphene through a magnetic barrier and a linearly polarized electromagnetic wave. In the context of Floquet theory, the eigenvalues and related eigenspinors are calculated analytically. The transmission probabilities are expressed as a function of different parameters using the transfer matrix approach and boundary conditions at two interfaces with current densities. We see that as the barrier width and incident energy change, the transmission via the center band oscillates less at zero strain. The transmission across the first sidebands begins at 0 and follows the pattern of a sinusoidal function that grows with increasing barrier width and becomes nearly linear for larger incident energy. When the strain magnitude is activated, the number of oscillations in all transmission channels drops marginally in the armchair direction but increases dramatically in the zigzag direction. The behavior of the total transmission is found to be comparable to that of the central band, with the exception that it exhibits a translation to the up. The suppression of Klein tunneling at normal incidence is another result seen in all strain settings.

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arXiv2022

Effect of strain on tunneling time in graphene magnetic barrier

We solve the Dirac equation in three regions of graphene to get the solutions of the energy spectrum in connection to the strain, energy gap, and magnetic field. The Goos-Hänchen shifts and group delay time will be obtained by applying the stationary phase approximation after the wave functions at the interfaces have been matched. Our results suggest that the group delay time is influenced by the presence of strain along the armchair and zigzag directions. We show that the gate voltage and strain have the ability to change the group delay from subluminality to superluminality. This may have significant uses in high-speed graphene-based nanoelectronics.

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arXiv2022

Group delay time of fermions in graphene through tilted potential barrier

The group delay time of Dirac fermions subjected to a tilting barrier potential along the $ x $-axis is investigated in graphene. We start by finding the eigenspinor solution of the Dirac equation and then relating it to incident, reflected, and transmitted beam waves. This relationship allows us to compute the group delay time in transmission and reflection by obtaining the corresponding phase shifts. We discovered that the barrier width, incident energy, and incident angle can all be used to modify the group delay time, and that the particles travel through the barrier at the Fermi velocity $ v_F $. Our findings also show that the transmission group delay might be controlled, and that gate voltage control could be useful in graphene-based tilting barriers.

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arXiv2022

Strain effect on Goos-Hänchen shifts and group delay time in gapped graphene barrier

We investigate the strain effect on the Goos-Hänchen (GH) shifts and group delay time for transmitted Dirac fermions in gapped graphene through a single barrier potential. The solutions of energy spectrum are used to compute the transmission probabilities together with the GH shifts and group delay time. Our results show that the two last quantities are strongly depending to weather the strain is applied along armchair or zigzag directions. In particular it found that both of quantities can be enhanced with the applied strain.

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arXiv2021

Strain Effect on Transmission in Graphene Laser Barrier

We investigate the strain effect along armchair and zigzag directions on the tunneling transport of Dirac fermions in graphene laser barrier through a time dependent potential along y-axis. Our system is composed of three regions and the central one is subjected to a deformation of strength S. Based on Dirac equation and the Floquet approach, we determine the eigenvalues and eigenspinors for each region. Using the boundary conditions at interfaces together with the transfer matrix method we identify the transmission in the different Floquet sideband states as function of the physical parameters. In the strainless case, we show that the transmisson of central band decreases for smaller values of the barrier width and rapidly oscillates with different amplitude for larger ones. Whereas the transmission for the first sidebands increases from zero and shows a damped oscillatory profile. It is found that the number of oscillations in all transmission channels reduces with increasing the strength of armchair strain but becomes more important by switching the deformation to zigzag. Moreover, it is observed the appearance of Fano type resonance peaks by altering the amplitude and the frequency of the laser field.

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arXiv2021

Klein tunneling through double barrier in ABC-trilayer graphene

Klein tunneling and conductance for Dirac fermions in ABC-stacked trilayer graphene (ABC-TLG) through symmetric and asymmetric double potential barriers are investigated using the two and six-band continuum model. Numerical results for our system show that the transport is sensitive to the height, the width and the distance between the two barriers. Klein paradox at normal incidence and resonant features at non-normal incidence in the transmission result from resonant electron states in the wells or hole states in the barriers and strongly influence the ballistic conductance of the structures.

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arXiv2021

Tunneling of Electrons in Graphene via Double Triangular Barrier in External Fields

We study the transmission probability of Dirac fermions in graphene scattered by a triangular double barrier potential in the presence of an external magnetic field. Our system made of two triangular potential barrier regions separated by a well region characterized by an energy gap. Solving our Dirac-like equation and matching the solutions at the boundaries allowed us to express our transmission and reflection coefficients in terms of transfer matrix. We show in particular that the transmission exhibits oscillation resonances that are manifestations of the Klein tunneling effect. The triangular barrier electrostatic field was found to play a key role in controlling the peak of tunneling resistance. However, it only slightly modifies the resonances at oblique incidence and leaves Klein paradox unaffected at normal incidence.

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arXiv2021

Effect of Strain on Band Engineering in Gapped Graphene

We study the effect of strain on the band engineering in gapped graphene subject to external sources. By applying the Floquet theory, we determine the effective Hamiltonian of electron dressed by a linearly, circularly and an elliptically polarized dressing field in the presence of strain along armchair and zigzag directions. Our results show that the energy spectrum exhibits different symmetries and for the strainless case it takes an isotropic and anisotropic forms whatever the values of irradiation intensity, whereas it is linear as in the case of pristine graphene. It increases slowly when strain is applied along the armchair direction but rapidly for the zigzag case. Moreover, it is found that the renormalized band gap changes along different strain magnitudes and does not change for the polarization phase $θ$ compared to linear and circular polarizations where its values change oppositely.

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arXiv2021

Gap-tunable of Tunneling Time in Graphene Magnetic Barrier

We study the tunneling time of Dirac fermions in graphene magnetic barrier through an electrostatic potential and a mass term. This latter generates an energy gap in the spectrum and therefore affects the proprieties of tunneling of the system. For clarification, we first start by deriving the eigenspinors solutions of Dirac equation and second connect them to the incident, reflected and transmitted beam waves. This connection allows us to obtain the corresponding phases shifts and consequently compute the group delay time in transmission and reflection. Our numerical results show that the group delay time depends strongly on the energy gap in the tunneling process through single barrier. Moreover, we find that the group approaches unity at some critical value of the energy gap and becomes independent to the strengths of involved physical parameters.

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arXiv2020

Goos-Hänchen Shifts in Gapped Graphene subject to External Fields

We study Dirac fermions in gapped graphene that are subjected to a magnetic field and a potential barrier harmonically oscillating in time. The tunneling modes inside the gap and the associated Goos-Hänchen (GH) shifts are analytically investigated. We show that the GH shifts in transmission for the central band and the first two sidebands change sign at the Dirac points $ε+l\hbar\tildeω$ $(l=0,\pm 1)$. We also find that the GH shifts can be either negative or positive and becomes zero at transmission resonances.

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