arXiv subjects

Sariah Al Saati

Publications and source records attributed to Sariah Al Saati.

6 recordsLinked to original sources

arXiv2026

Spin-Hall devices: spin relaxation spatially separates current injection from Joule dissipation

The stationary state of a spin Hall bar connected to an external load circuit is investigated through a variational approach based on the principle of minimum power dissipation generalized to the two-spin-channel model. The self-consistent distributions of longitudinal and transverse current densities, alongside the corresponding spin and charge accumulations and dissipation power in the resistance, are derived. Surprisingly, it is shown that the Joule dissipation vanishes when the load resistance is placed at a sufficiently large distance compared with the spin-relaxation length. Such a highly non-trivial global stationary state appears as the most striking characteristic of the injection of pure spin current compared with more usual current injection.

cond-mat.mes-hall↗

arXiv2026

Theory of local orbital magnetization: local Berry curvature

We develop a thermodynamic theory of local orbital magnetization based on a perturbative expansion of the magnetic-field-dependent local density of states. Applicable to periodic crystals, finite systems with open boundaries, and ribbons alike, the formalism resolves orbital magnetic textures at the sublattice scale. It further reveals a previously unidentified local Berry curvature that captures the magnetic-field-induced redistribution of electronic weight in real space. We establish the consistency of the theory across geometries, identify orbital ferro-, antiferro-, and ferrimagnetic phases in both topological and trivial insulators, and demonstrate that the local Berry curvature provides a bulk description of topology in finite systems.

cond-mat.mes-hall↗

arXiv2024

Ionospheric conductances at the giant planets of the Solar System:a comparative study of ionization sources and the impact of meteoric ions

The dynamics of giant planet magnetospheres is controlled by a complex interplay between their fast rotation, their interaction with the solar wind, and their diverse internal plasma and momentum sources. In the ionosphere, the Hall and Pedersen conductances are two key parameters that regulate the intensity of currents coupling the magnetosphere and the ionosphere, and the rate of angular momentum transfer and power carried by these currents. We perform a comparative study of Hall and Pedersen conductivities and conductances in the four giant planets of our Solar System - Jupiter, Saturn, Uranus and Neptune. We use a generic ionospheric model (restraining the studied ions to H3+, CH5+, and meteoric ions) to study the dependence of conductances on the structure and composition of these planets' upper atmospheres and on the main ionization sources (photoionization, ionization by precipitating electrons, and meteoroid ablation). After checking that our model reproduces the conclusions of Nakamura et al. (2022, https://doi.org/10.1029/2022JA030312) at Jupiter, i.e. the contribution of meteoric ions to the height-integrated conductances is non-negligible, we show that this contribution could also be non-negligible at Saturn, Uranus and Neptune, compared with ionization processes caused by precipitating electrons of energies lower than a few keV (typical energies on these planets). However, because of their weaker magnetic field, the conductive layer of these planets is higher than the layer where meteoric ions are mainly produced, limiting their role in magnetosphere-ionosphere coupling.

astro-ph.EP↗

arXiv2024

Quantum Hall and Light Responses in a 2D Topological Semimetal

We have recently identified a protected topological semimetal in graphene which presents a zero-energy edge mode robust to disorder and interactions. Here, we address the characteristics of this semimetal and show that the $\mathbb{Z}$ topological invariant of the Hall conductivity associated to the lowest energy band can be equivalently measured from the resonant response to circularly polarized light resolved at the Dirac points. The (non-quantized) conductivity responses of the intermediate energy bands, including the Fermi surface, also give rise to a $\mathbb{Z}_2$ invariant. We emphasize on the bulk-edge correspondence as a protected topological half metal, i.e. one spin-population polarized in the plane is in the insulating phase related to the robust edge mode while the other is in the metallic regime. The quantized transport at the edges is equivalent to a $\frac{1}{2}-\frac{1}{2}$ conductance for spin polarizations along $z$ direction. We also build a parallel between the topological Hall response and a pair of half numbers (half Skyrmions) through the light response locally resolved in momentum space and on the sphere.

cond-mat.mes-hall↗

arXiv2024

Power efficiency of Hall-like devices: comparison between reciprocal and anti-reciprocal Onsager relations

Two well-known Hall-like effects are occurring in ferromagnets: the Anomalous Hall effect and the Planar Hall effect. The former is analogous to the classical Hall effect and is defined by the Onsager reciprocity relation of the second kind (antisymmetric conductivity matrix), while the latter is defined by the Onsager reciprocity relation of the first kind (symmetric conductivity matrix). The difference is fundamental, as it is based on time-invariance symmetry breaking at the microscopic scale. We study the Hall current generated in both cases, together with the power that can be extracted from the edges of Hall device. The expressions of the distribution of the electric currents, the distribution of electric carriers, and the power efficiencies (i.e. the power that can be injected into a load circuit) are derived at stationary regime from a variational method based on the second law of thermodynamics. It is shown that the distribution of the transverse Hall-current is identical in both cases but the longitudinal current and the power dissipated differ at the second order in the Hall angle.

cond-mat.mes-hall↗

arXiv2022

Protected Topological Nodal Ring Semimetal in Graphene

Graphene is a two-dimensional Dirac semimetal showing interesting properties as a result of its dispersion relation with both quasiparticles and quasiholes or matter and anti-matter. We introduce a topological nodal ring semimetal in graphene with a quantized quantum Hall response, a robust one-dimensional chiral edge mode and a quadratic Fermi-liquid spectrum for the quasiparticles and quasiholes in the bulk. The bulk band degeneracy at the Fermi energy is protected through a Z2 symmetry related to the two spin polarizations of an electron and a double-orthogonality structure in the sublattice and spin quantum numbers of the two crossing eigenstates. The system may have applications in nano-electronics and in quantum mechanical entanglement applied to band theory.

cond-mat.mes-hall↗