arXiv subjects

Nassima Benchtaber

Publications and source records attributed to Nassima Benchtaber.

5 recordsLinked to original sources

arXiv2026

Intrinsic (non)-Gilbert damping in magnetic insulators calculated from a minimal model and \textit{ab initio} spin Hamiltonians

We present an analytically solvable minimal model for the relaxation of low-frequency magnons in magnetic insulators arising from magnon-phonon and magnon-magnon interactions. The model establishes a direct connection between microscopic relaxation processes and Gilbert damping, and reveals how magnon decay evolves from bulk systems to the monolayer limit. We find that magnon-phonon coupling produces Gilbert damping of comparable magnitude in three- and two-dimensional magnets, with qualitative differences between flexural phonons in free-standing monolayers and three-dimensional phonons in substrate-supported layers. By contrast, non-Gilbert damping due to four-magnon scattering is strongly enhanced in two dimensions, where it becomes independent of spin-orbit coupling. To benchmark the model against real materials, we introduce a numerical approach for computing magnon damping from ab initio-derived spin Hamiltonians. We demonstrate that the central conclusions of the model remain valid for magnons in bulk YIG and in a monolayer of the van der Waals magnetic insulator CrSBr.

cond-mat.mtrl-sci↗

arXiv2025

Anisotropic Phonon Dynamics and Directional Transport in Actinide van der Waals Semiconductor USe$_3$

Direction-dependent charge transport and optical responses are characteristic of van der Waals (vdW) materials with strong in-plane anisotropy. While transition-metal trichalcogenides (TMTCs) exemplify this behavior, heavier analogs remain largely unexplored. In this study we examine USe$_3$ as an anisotropic vdW material and a heavier analog of the well-studied TMTCs. We reveal strong in-plane anisotropy using polarization-resolved Raman spectroscopy, investigate strain-induced shifts of phonon modes, and quantify direction-dependent charge-carrier mobility through transport measurements on field-effect devices. First-principles calculations based on density-functional theory corroborate our findings, providing a theoretical basis for our experimental observations. Casting USe$_3$ as an actinide analog of a TMTC establishes a platform for exploring low-dimensional semiconductors that combine strong in-plane anisotropy with f-electron physics.

cond-mat.mtrl-sci↗

arXiv2022

Trivial and topological bound states in bilayer graphene quantum dots and rings

We discuss and compare two different types of confinement in bilayer graphene by top and bottom gating with symmetrical microelectrodes. Trivial confinement corresponds to the same polarity of all top gates, which is opposed to that of all bottom ones. Topological confinement requires the polarity of part of the top-bottom pairs of gates to be reversed. We show that the main qualitative difference between trivial and topological bound states manifests itself in the magnetic field dependence. We illustrate our finding with an explicit calculation of the energy spectrum for quantum dots and rings. Trivial confinement shows bunching of levels into degenerate Landau bands, with a non-centered gap, while topological confinement shows no field-induced gap and a sequence of state branches always crossing zero-energy.

cond-mat.mes-hall↗

arXiv2021

Geometry effects in topologically confined bilayer graphene loops

We investigate the electronic confinement in bilayer graphene by topological loops of different shapes. These loops are created by lateral gates acting via gap inversion on the two graphene sheets. For large-area loops the spectrum is well described by a quantization rule depending only on the loop perimeter. For small sizes, the spectrum depends on the loop shape. We find that zero-energy states exhibit a characteristic pattern that strongly depends on the spatial symmetry. We show this by considering loops of higher to lower symmetry (circle, square, rectangle and irregular polygon). Interestingly, magnetic field causes valley splittings of the states, an asymmetry between energy reversal states, flux periodicities and the emergence of persistent currents.

cond-mat.mes-hall↗

arXiv2021

Scattering of topological kink-antikink states in bilayer graphene structures

Gapped bilayer graphene can support the presence of intragap states due to kink gate potentials applied to the graphene layers. Electrons in these states display valley-momentum locking, which makes them attractive for topological valleytronics. Here, we show that kink-antikink local potentials enable modulated scattering of topological currents. We find that the kink-antikink coupling leads to anomalous steps in the junction conductance. Further, when the constriction detaches from the propagating modes, forming a loop, the conductance reveals the system energy spectrum. Remarkably, these kink-antikink devices can also work as valley filters with tiny magnetic fields by tuning a central gate.

cond-mat.mes-hall↗