arXiv subjects

Narjes Kheirabadi

Publications and source records attributed to Narjes Kheirabadi.

10 recordsLinked to original sources

arXiv2026

Strain-Tunable Harmonic Responses in Valley-Polarized Bilayer Graphene

We theoretically investigate the linear and second-order nonlinear optical responses of valley-polarized bilayer graphene under uniaxial strain. Employing a low-energy effective Hamiltonian that incorporates trigonal warping and strain-induced anisotropy, we calculate the optical susceptibilities within the quantum kinetic formalism. We show that, while the second-order response vanishes in valley-balanced bilayer graphene owing to the cancellation of contributions from opposite valleys, a finite valley polarization lifts this cancellation and enables a net second-harmonic generation (SHG) signal. Uniaxial strain substantially modifies the nonlinear response by distorting the low-energy electronic structure and altering the pseudospin texture, producing a highly anisotropic SHG spectrum. Pronounced resonant enhancements occur at photon energies $\hbarω\approx E_f$ and $\hbarω\approx 2E_f$, associated with two-photon and one-photon interband resonances, respectively. Remarkably, changing the sign of the strain parameter reverses the direction of the induced second-harmonic current, providing a mechanically controlled switching mechanism for nonlinear optical transport. These results establish strain engineering as an effective route for manipulating valley-dependent nonlinear optical phenomena in bilayer graphene and suggest new opportunities for tunable mid-infrared photonic and valley-optoelectronic applications.

cond-mat.mes-hall↗

arXiv2025

General solution for the response of materials under radiation and tilted magnetic field: semi-classical regime

The Berry curvature dipole is well-known to cause Hall conductivity. This study expands on previous results to demonstrate how two- and three-dimensional materials react under a tilted magnetic field in the linear and nonlinear regimes. We show how the Hall effect has a quantum origin by deriving the general form of intrinsic and extrinsic currents in materials under a tilted magnetic field. Our focus is on determining the linear and nonlinear response of two-dimensional materials. We also demonstrate that as the result of the perpendicular component of the magnetic field a current resulted by both velocity and Berry curvature can occur in two-dimensional materials and topological crystalline insulators in second harmonic generation and ratchet responses. The findings of this research may provide insight into the transport characteristics of materials in the semi-classical regime and initiate a new chapter in linear and nonlinear Hall effects.

cond-mat.mes-hall↗

arXiv2024

Engineering of Chern number of topological bands in bilayer graphene by in-plane magnetic field and electrical bias

Based on the full Hamiltonian of bilayer graphene, phase transitions are realized by the change of the in-plane magnetic field and the electrical bias in bilayer graphene. We show that the engineering of Chern numbers of four bands is possible by an applied in-plane magnetic field and an electrical bias in bilayer graphene. Our results are promising for the exploration of new topological phenomena in 2D materials.

cond-mat.mes-hall↗

arXiv2022

Quantum nonlinear planar Hall effect in bilayer graphene: an orbital effect of a steady in-plane magnetic field

We study the quantum nonlinear planar Hall effect in bilayer graphene under a steady in-plane magnetic field. When time-reversal symmetry is broken by the magnetic field, a charge current occurs in the second-order response to an external electric field, as a result of the Berry curvature dipole in momentum space. We have shown that a nonlinear planar Hall effect originating from the anomalous velocity is deduced by an orbital effect of an in-plane magnetic field on electrons in bilayer graphene in the complete absence of spin-orbit coupling. Taking into account the symmetry analysis, we derived the dominant dependence of Berry curvature dipole moment on the magnetic field components. Moreover, we illustrate how to control and modulate the Berry curvature dipole with an external planar magnetic field, gate voltage, and Fermi energy.

cond-mat.mes-hall↗

arXiv2021

Current induced by a tilted magnetic field in phosphorene under terahertz laser radiation

In this study, we investigate the cyclotron resonance effect in the first-order AC current, magnetic ratchet effect, and second harmonic generation in phosphorene in the presence of a steady tilted magnetic field and under THz laser radiation. We establish that various cyclotron resonances exist in the deduced currents based on the angular frequency of the incoming light. These resonances are dependent on the $ω_{c_{+}}$ value, a function of the carrier charge, the perpendicular magnetic field, and the effective masses along the armchair or zigzag edges. We discuss the direction and the magnitude of the deduced currents for various radiation polarizations. We compare the results with a zero perpendicular magnetic field. Cyclotron resonance for the first order AC current occurs at $ω= \pm ω_{c_{+}}$. The deduced current declines if the perpendicular magnetic field is zero. Meanwhile, for the ratchet current, cyclotron resonances occur at $ω= \pm ω_{c_{+}}$, $ω= \pm 2ω_{c_{+}}$, and radiation helicity affects the deduced current for circularly polarized light. Cyclotron resonance for the second harmonic generation current occurs at $ω= \pm ω_{c_{+}}$, $ω= \pm 2 ω_{c_{+}}$ and $ω= \pm ω_{c_{+}}/2 $ and the current is stronger compared to the case with no perpendicular magnetic field. As the magnetic field rotates in the plane of anisotropic phosphorene, separate directions are predicted for the second harmonic generation--related current. It is noteworthy that the magnitude of the ratchet and second harmonic generation current are within the same range and comparable to the magnetic ratchet current in monolayer graphene, $μA / cm$.

cond-mat.mes-hall↗

arXiv2021

Interaction of hydrogen-edged boron nitride flakes with lithium: boron nitride as a protecting layer for a lithium-ion battery and a spin-dependent photon emission device

The current rechargeable battery technologies have a failure in their performance at high pressure and temperature. In this article, we have brought theoretical insights on using boron nitride flakes as a protecting layer for a lithium-ion battery device and extended its application for a spin-dependent photon emission device. Hence, the electronic properties of pristine and lithium-doped hydrogen-edged boron nitride flakes have been studied by the first principle density functional theory calculations. In this study, we have discussed the stability, adsorption energies, bond lengths, electronic gaps, frontier molecular orbitals, the density of states, charge distributions, and dipole moments of pristine and lithium hydrogen-edged doped boron nitride flakes.

physics.app-ph↗

arXiv2021

Magnetic ratchet effect in phosphorene

The magnetic ratchet effect has been studied in phosphorene by the use of the Boltzmann kinetic equation that is a semi-classical approach. The Hamiltonian of phosphorene in a steady parallel magnetic field is derived using the tight-binding model. We consider the effect of the magnetic field on non--linear dynamics in the presence of an ac laser field and spatial inversion asymmetry. We have shown that for anisotropic 2D materials and phosphorene, the ratchet current has the response to three different light polarizations: linearly polarized light, circularly polarized light, and unpolarized light.

cond-mat.mes-hall↗

arXiv2018

Cyclotron resonance of the magnetic ratchet effect and second harmonic generation in bilayer graphene

We model the magnetic ratchet effect in bilayer graphene in which a dc electric current is produced by an ac electric field of frequency $ω$ in the presence of a steady in-plane magnetic field and inversion-symmetry breaking. In bilayer graphene, the ratchet effect is tunable by an external metallic gate which breaks inversion symmetry. For zero in-plane magnetic field, we show that trigonal warping and inversion-symmetry breaking are able to produce a large dc valley current, but not a non-zero total dc charge current. For the magnetic ratchet in a tilted magnetic field, the perpendicular field component induces cyclotron motion with frequency $ω_c$ and we find that the dc current displays cyclotron resonance at $ω_c = ω$, although this peak in the current is actually smaller than its value at $ω_c = 0$. Second harmonic generation, however, is greatly enhanced by resonances at $ω_c = ω$ and $ω_c = 2ω$ for which the current is generally much larger than at $ω_c = 0$.

cond-mat.mes-hall↗

arXiv2016

Magnetic ratchet effect in bilayer graphene

We consider the orbital effect of an in-plane magnetic field on electrons in bilayer graphene, deriving linear-in-field contributions to the low-energy Hamiltonian arising from the presence of either skew interlayer coupling or interlayer potential asymmetry, the latter being tunable by an external metallic gate. To illustrate the relevance of such terms, we consider the ratchet effect in which a dc current results from the application of an alternating electric field in the presence of an in-plane magnetic field and inversion-symmetry breaking. By comparison with recent experimental observations in monolayer graphene [C. Drexler et al., Nature Nanotech. 8, 104 (2013)], we estimate that the effect in bilayer graphene can be two orders of magnitude greater than that in monolayer, illustrating that the bilayer is an ideal material for the realization of optoelectronic effects that rely on inversion-symmetry breaking.

cond-mat.mes-hall↗

arXiv2015

Lithium doped graphene as spintronic devices

Generating spintronic devices has been a goal for the nano-science. We have used density function theory to determine magnetic phases of single layer and bilayer lithium doped graphene nanoflakes. We have introduced graphene flakes as single molecular magnets, spin on/off switches and spintronic memory devices. To aim this goal, adsorption energies, spin polarizations, electronic gaps, magnetic properties and robustness of spin-polarized states have been studied in the presence of dopants and second layers. We find that for bilayer SMMs with two layers of different sizes the highest occupied molecular orbital and the lowest unoccupied molecular orbital switch between the layers. Based on this switch of molecular orbitals in a bilayer graphene SMM, spin on/off switches and spintronic memory devices could be achievable.

cond-mat.mes-hall↗