arXiv subjects

Adel Abbout

Publications and source records attributed to Adel Abbout.

15 recordsLinked to original sources

arXiv2026

Gauge transformation for pulse propagation and time ordered integrals

We investigate a gauge transformation based on the successive elimination of time-dependent onsite potentials at individual sites in finite or infinite systems. Our analysis shows that this transformation renormalizes the inward hoppings by a phase factor $e^{i \phi(t)}$ and the outward hoppings by $e^{-i \phi(t)}$. We further demonstrate how this procedure facilitates the reduction and simulation of pulse propagation in scattering systems, while significantly simplifying the time-ordered integrals involved in the time evolution operator for time-dependent Schrodinger equation.

cond-mat.mes-hall↗

arXiv2024

Carbon nanotube as quantum point contact valley-filter and valley-splitter

The electrical characteristics of a carbon nanotube can be significantly modified by applying elastic strain. This study focuses on exploring this phenomenon in a single-walled carbon nanotube (SWNT) using tight-binding transport calculations. The results indicate that, under specific strains, an armchair SWNT can act as a filter, separating the two valley electrons K and Kp. Notably, when subjected to deformation, the SWNT exhibits intriguing behaviors, including a quantized conductance profile that varies with the strength of the strain. Consequently, precise control of the width of the quantized plateaus allows for the generation of a polarized valley current. Furthermore, when both K-types are conducted, the strain is demonstrated to completely separate them, directing each K-type through a distinct pathway.

cond-mat.mes-hall↗

arXiv2024

Topological spin-torque in non-collinear anti-ferromagnetic 3Q state

We investigate the spin torque in the topological phase of the 3Q antiferromagnetic (AFM) configuration. We first obtain the band structure to identify the topology and nature of the different gaps of the system and then calculate the spin density in the whole system. We demonstrate the presence of a non-vanishing spin-torque component at the edge of the system and analyze its effect on the texture. Moreover, we show that the direction of the torque depends hugely on the way we cut the system to define the edge.

cond-mat.mes-hall↗

arXiv2023

Pseudo Electric Field and Pumping Valley Current in Graphene Nano-bubbles

The extremely high pseudo-magnetic field emerging in strained graphene suggests that an oscillating nano-deformation will induce a very high current even without electric bias. In this paper, we demonstrate the sub-terahertz (THz) dynamics of a valley-current and the corresponding charge pumping with a periodically excited nano-bubble. We discuss the amplitude of the pseudo-electric field and investigate the dependence of the pumped valley current on the different parameters of the system. Finally, we report the signature of extra-harmonics generation in the valley current that might lead to potential modern devices development operating in the nonlinear regime

cond-mat.mes-hall↗

arXiv2022

Deep learning of deformation-dependent conductance in thin films: nanobubbles in graphene

Motivated by the ever-improving performance of deep learning techniques, we design a mixed input convolutional neural network approach to predict transport properties in deformed nanoscale materials using a height map of deformations (from scanning probe information) as input. We employ our approach to study electrical transport in a graphene nanoribbon deformed by a number of randomly positioned nano-bubbles. Our network is able to make conductance predictions valid to an average error of 4.3\%. We demonstrate that such low average errors are achieved by including additional inputs like energy in a highly redundant fashion, which allows predictions that are 30-40\% more accurate than conventional architectures. We demonstrate that the same method can learn to predict the valley-resolved conductance, with success specifically in identifying the energy at which inter-valley scattering becomes prominent. We demonstrate the robustness of the approach by testing the pre-trained network on samples with deformations differing in number and shape from the training data. We employ a graph theoretical analysis of the structure and outputs of the network and conclude that a tight-binding Hamiltonian is effectively encoded in the first layer of the network. We confirm our graph theoretical analysis numerically for different hopping processes in a trained network and find the result to be accurate within an error of 1\%. Our approach contributes a new theoretical understanding and a refined methodology to the application of deep learning for the determination transport properties based on real-space disorder information.

cond-mat.mes-hall↗

arXiv2022

Tunneling phase diagrams in anisotropic Multi-Weyl semimetals

Motivated by the exciting prediction of Multi-Weyl topological semimetals that are stabilized by point group symmetries [Phys. Rev. Lett. 108 (2012) 266802], we study tunneling phenomena for a class of anisotropic Multi-Weyl semimetals. We find that a distant detector for different ranges of an anisotropy parameter $λ$ and incident angle $θ$ will measure a different number of propagating transmitted modes. We present these findings in terms of phase diagrams that is valid for an incoming wave with fixed wavenumber $k$--energy is not fixed. To gain a deeper understanding of this phenomenon we then focus on the simplest case of an anisotropic quadratic Weyl-semimetal and analyze tunneling coefficients analytically and numerically to confirm the observations from the phase diagram. Our results show non-analytical behavior, which is the hallmark of a phase transition. This serves as a motivation to make a formal analogy with phase transitions that are known from statistical mechanics. Specifically, we argue that the long distance limit in our tunneling problem takes the place of the thermodynamic limit in statistical mechanics. More precisely, find a direct formal connection to the recently developed formalism for dynamical phase transitions [Reports on Progress in Physics 81 (5) (2018) 054001]. We propose that this analogy to phase transitions can help classify transport properties in exotic semimetals.

cond-mat.mes-hall↗

arXiv2019

Artificial gauge fields and topological insulators in Moire superlattices

We propose an innovative quantum emulator based on Moire superlattices showing that, by employing periodical modulation on each lattice site, one can create tunable, artificial gauge fields with imprinting Peierls phases on the hopping parameters and realize an analog of novel Haldane-like phase. As an application, we provide a methodology to directly quantify the topological invariant in such a system from a dynamical quench process. This design shows a robustly integrated platform which opens a new door to investigate topological physics.

cond-mat.quant-gas↗

arXiv2018

Quantum Anomalous Hall Effect and Anderson Chern Insulating Regime in Noncollinear Antiferromagnetic 3Q State

We investigate the emergence of both quantum anomalous Hall and disorder-induced Anderson Chern insulating phases in two dimensional hexagonal lattices, with antiferromagnetically ordered 3Q state and in the absence of spin-orbit coupling. Using tight-binding modeling, we show that such systems display not only a spin-polarized edge-localized current, the chirality of which is energy dependent but also an impurity-induced transition from trivial metallic to topological insulating regimes, through one edge mode plateau. We compute the gaps' phase diagrams, and demonstrate the robustness of the edge channel against deformation and disorder. Our study hints at the 3Q state as a promising building block for dissipationless spintronics based on antiferromagnets.

cond-mat.mes-hall↗

arXiv2018

Cooperative Charge Pumping and Enhanced Skyrmion Mobility

The electronic pumping arising from the steady motion of ferromagnetic skyrmions is investigated by solving the time evolution of the Schrodinger equation implemented on a tight-binding model with the statistical physics of the many-body problem. It is shown that the ability of steadily moving skyrmions to pump large charge currents arises from their non-trivial magnetic topology, i.e. the coexistence between spin-motive force and topological Hall effect. Based on an adiabatic scattering theory, we compute the pumped current and demonstrate that it scales with the reflection coefficient of the conduction electrons against the skyrmion. Finally, we propose that such a phenomenon can be exploited in the context of racetrack devices, where the electronic pumping enhances the collective motion of the train of skyrmions.

cond-mat.mtrl-sci↗

arXiv2016

Statistical analysis of the figure of merit of a two-level thermoelectric system: a random matrix approach

Using the tools of random matrix theory we develop a statistical analysis of the transport properties of thermoelectric low-dimensional systems made of two electron reservoirs set at different temperatures and chemical potentials, and connected through a low-density-of-states two-level quantum dot that acts as a conducting chaotic cavity. Our exact treatment of the chaotic behavior in such devices lies on the scattering matrix formalism and yields analytical expressions for the joint probability distribution functions of the Seebeck coefficient and the transmission profile, as well as the marginal distributions, at arbitrary Fermi energy. The scattering matrices belong to circular ensembles which we sample to numerically compute the transmission function, the Seebeck coefficient, and their relationship. The exact transport coefficients probability distributions are found to be highly non-Gaussian for small numbers of conduction modes, and the analytical and numerical results are in excellent agreement. The system performance is also studied, and we find that the optimum performance is obtained for half-transparent quantum dots; further, this optimum may be enhanced for systems with few conduction modes.

cond-mat.mes-hall↗

arXiv2013

Mesoscopic thermoelectric transport near zero transmission energies

We study the thermoelectric transport coefficients of a one-dimensional (1D) electron waveguide connected to one and then two off-channel cavities, in the presence of dephasing phonons. The model system is that of a linear chain described as a 1D lattice. For simplicity we consider single-mode cavities, which may be tuned with external gates. While the presence of only one off-channel cavity yields a nearly symmetric transmission profile, which is canceled around the cavity mode, an additional cavity modifies this profile strongly and results in an asymmetric shape characterized by oscillations. In both cases, we consider electron-phonon interactions in our calculations and analyze their effects on the transmission function around the Fermi energy. Knowledge of the energy-dependent transmission function allows the numerical computation of thermoelectric transport coefficients, including the thermopower. In the presence of a second off-channel cavity, the sign of the thermopower depends on the relative position of this cavity energy level with respect to the Fermi energy: the thermopower is positive when low-energy electrons in the vicinity of the Fermi level are not transmitted, and becomes negative when the higher-energy electrons are not transmitted.

cond-mat.mes-hall↗

arXiv2013

Delay-Time and Thermopower Distributions at the Spectrum Edges of a Chaotic Scatterer

We study chaotic scattering outside the wide band limit, as the Fermi energy $E_F$ approaches the band edges $E_B$ of a one-dimensional lattice embedding a scattering region of M sites. We show that the delay-time and thermopower distributions differ near the edges from the universal expressions valid in the bulk. To obtain the asymptotic universal forms of these edge distributions, one must keep constant the energy distance $E_F-E_B$ measured in units of the same energy scale proportional to $\propto M^{-1/3}$ which is used for rescaling the energy level spacings at the spectrum edges of large Gaussian matrices. In particular the delay-time and the thermopower have the same universal edge distributions for arbitrary M as those for an M=2 scatterer, which we obtain analytically.

cond-mat.mes-hall↗

arXiv2013

Level spacing distribution of a Lorentzian matrix at the spectrum edge

Effective Hamiltonians can explain in a much simpler way the physics behind a scattering process. Chaotic scattering is directly related to Lorentzian Hamiltonians which, because of their properties, can be reduced to a $2\times 2$ matrix problem in the case of two modes scattering. In this framework, we provide the distribution of level spacing of its eigenvalues and show that this special kind of distribution has no mean level spacing (divergent) and is characterized by a geometrical decay law. We discuss the relation of this distribution to the averaged level spacing at the edge of the spectrum of $N \times N$ Lorentzian matrices.

cond-mat.dis-nn↗

arXiv2012

Time delay matrix at the spectrum edge and the minimal chaotic cavities

Using the concept of minimal chaotic cavities, we give the distribution of the proper delay times of $Q=-i\hbar S^\dagger \frac{\partial S}{\partial E}$ at the spectrum edge with a scattering matrix $S$ belonging to circular ensembles CE. The three classes of symmetry ($β=1$, 2 and 4) will be analyzed to show how it differs from the distribution obtained in the bulk of the spectrum. In this new class of universality at the spectrum edge, more attention will be given to the Wigner time $τ_w=tr(Q)$ and its distribution will be given analytically in the case of 2 modes scattering. The results will be presented exactly at all the Fermi energies without any approximation. All this will be tested numerically with an excellent precision.

cond-mat.dis-nn↗

arXiv2010

Thermal Enhancement of Interference Effects in Quantum Point Contacts

We study an electron interferometer formed with a quantum point contact and a scanning probe tip in a two-dimensional electron gas. The images giving the conductance as a function of the tip position exhibit fringes spaced by half the Fermi wavelength. For a contact opened at the edges of a quantized conductance plateau, the fringes are enhanced as the temperature T increases and can persist beyond the thermal length l_T. This unusual effect is explained assuming a simplified model: The fringes are mainly given by a contribution which vanishes when T -> 0 and has a decay characterized by a T-independent scale.

cond-mat.mes-hall↗