arXiv subjects

Hasna Chnafa

Publications and source records attributed to Hasna Chnafa.

8 recordsLinked to original sources

arXiv2026

Strain- and potential-controlled tunneling in monolayer MoS$_2$

We present a theoretical study of spin- and valley-resolved quantum transport in monolayer MoS$_2$ under the combined influence of mechanical strain and an external scalar potential, a combination whose simultaneous unexplored. Within an effective massive Dirac Hamiltonian that incorporates intrinsic spin--orbit coupling, strain induces valley-dependent momentum shifts that lift the degeneracy between the $K$ and $K'$ valleys and strongly modify the transport characteristics. The scalar potential modifies the tunneling spectrum, leading to pronounced changes in resonant transmission, Fabry--P\'erot interference, and conductance. We show that the interplay between strain and electrostatic potential enables efficient control of both valley and spin polarization of the transmitted current. In particular, we identify a dual-knob control scheme in which the barrier width governs the frequency of conductance oscillations while strain independently controls their phase and amplitude. Furthermore, we predict electrostatic spin inversion -- a sign reversal of spin polarization achievable purely by gate tuning at finite strain, requiring no geometric reconfiguration. Depending on the strain orientation, the transmission probability and conductance can be selectively suppressed or enhanced, resulting in highly tunable valley- and spin-polarized transport. These findings demonstrate that strain and potential engineering provide orthogonal and independently operable mechanisms for controlling conductance as well as spin and valley degrees of freedom in monolayer MoS$_2$, offering promising prospects for spintronic and valleytronic device applications.

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arXiv2026

Tuning quantum tunneling in WSe$_2$ via strain engineering

We present a comprehensive theoretical study of strain-engineered quantum transport in monolayer tungsten diselenide (WSe$_2$) in the presence of an electrostatic scalar potential. By incorporating strain effects within a low-energy Dirac framework, we analyze their impact on spin- and valley-resolved transmission, conductance, and polarization. The applied potential barrier partitions the system into three distinct regions, allowing for an analytical derivation of the wave functions in each domain. Enforcing continuity conditions at the interfaces yields exact expressions for the transmission and reflection amplitudes. The transmission probability is evaluated from the corresponding current densities, while the conductance is obtained using the Landauer-B\"uttiker formalism, enabling a quantitative determination of spin and valley polarizations. Our numerical analysis reveals that strain acts as a powerful tuning parameter that reshapes the electronic dispersion and strongly modifies transport characteristics. In particular, the transmission and conductance exhibit pronounced oscillatory behavior driven by quantum interference and resonant tunneling mechanisms. More importantly, both spin and valley polarizations display substantial and highly controllable variations as functions of strain, barrier height, and incident energy. These results demonstrate that strain and electrostatic engineering provide an efficient and versatile platform for manipulating spin-valley degrees of freedom in WSe$_2$. The ability to tailor polarization and interference effects suggests promising opportunities for the design of next-generation spintronic, valleytronic, and optoelectronic devices based on two-dimensional transition-metal dichalcogenides.

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arXiv2026

Quantum transport in gapped graphene under strain and laser--electrostatic barriers

Electron transport in graphene under a laser-modulated barrier is studied in the presence of an energy gap, a scalar potential, and a uniaxial zigzag strain. The transfer-matrix approach is used with the boundary conditions to derive the transmission probabilities as functions of different system parameters. Without strain, raising either the energy gap or the potential generally reduces transmission in the central and lower sidebands. Moderate zigzag strain generates pronounced Fano-type oscillations that vanish at large strain, while transmission increases for low potential and decreases for high values. In the upper sideband, the incidence energy shifts the resonance peaks to the right, and growing the barrier width generates characteristic oscillatory patterns. Furthermore, increasing the laser field amplitude enhances transmission, whereas higher laser frequencies tend to suppress it. These findings offer new perspectives on controlling electronic transport in gapped graphene via external fields, strain, and potential applications in optoelectronic devices.

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arXiv2026

Energy-gap--controlled current oscillations in graphene under periodic driving

We investigate the impact of an induced mass term $\Delta$ on the current density in graphene subjected to a space- and time-dependent periodic potential $U(x,t)$. By solving the Dirac equation and deriving both the quasi-energy spectrum and the corresponding eigenspinors, we obtain explicit analytical expressions for the current density, which exhibits a clear dependence on $\Delta$. We show that $\Delta$ acts as a tunable control parameter that governs the amplitude, sign, and resonance structure of Josephson-like current oscillations. For normal incidence and a purely time-periodic potential, our results reveal that the oscillations within the energy gap gradually diminish as the mass term $\Delta$ increases. This suppression leads to a weakening of the Josephson-like effect typically observed in such systems. When the potential $U(x,t)$ is periodic in both space and time, the behavior becomes more complex. The current density can take either positive or negative values depending on the magnitude of the induced gap, and it generally decreases over time. As a result, the resonance phenomena--prominent at lower gap values--become progressively less significant as $\Delta$ increases. These findings underscore the tunable nature of light-matter interactions and quantum transport in gapped graphene, suggesting potential applications in terahertz (THz) nanoelectronic devices and optically controlled quantum switches.

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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-P\'erot resonance, and the transmissions move to the right when the energy gap is tuned.

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arXiv2022

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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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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arXiv2020

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 $\theta$ compared to linear and circular polarizations where its values change oppositely.

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