arXiv subjects

Seif Alwan

Publications and source records attributed to Seif Alwan.

3 recordsLinked to original sources

arXiv2026

Curvature-Controlled Topological Magnon Phases in a Folded Kagome Lattice

We show that geometric curvature, encoded in the folding angle between two corner-sharing triangles on a kagome lattice, provides a continuous tuning knob for topological magnon phase. Starting from an extended spin Hamiltonian with exchange, Dzyaloshinskii-Moriya (DM) interaction, and a higher-order bow-tie coupling of scalar chiralities, we derive the chirality-mediated hopping amplitude, which depends on the folding and spin canting of the bow-tie triangles. At small folding and canting angles, the bow-tie coupling surpasses DM, establishing a curvature-dominated regime. These results establish curvature as an intrinsic geometric control parameter for topological magnonics and reveal a direct analogy with chirality-induced spin selectivity in molecular systems, pointing to a unified mechanism for chirality driven transport across scales. The mechanism is particularly relevant for chiral crystals where the DM interaction is weak or forbidden by symmetry, as in systems with a six-fold screw axis.

cond-mat.mes-hall↗

arXiv2025

Emergent Topology in Kagome Ferromagnets

We investigate the emergence of a topological magnon phase in a two-dimensional kagome ferromagnet with Dzyaloshinskii-Moriya interaction (DMI) and scalar spin chirality. By incorporating a chiral interaction term proportional to the scalar triple product chi_ijk = S_i (S_j x S_k), we examine how the interplay between DMI and the topological orbital coupling kappa_TO gives rise to geometric phase, nontrivial Berry curvature, and quantized Chern numbers in the magnon bands. Using a momentum-space representation and linear spin-wave theory, we compute the orbital texture, its vorticity, and the Berry curvature across the Brillouin zone. We show that noncoplanar spin textures, driven by finite DMI, form momentum-space skyrmions that act as sources of geometric curvature. Importantly, we demonstrate that DMI alone is insufficient to break time-reversal symmetry; only the presence of finite scalar chirality terms allows the system to develop a nonzero Berry phase and topological transport signatures. We further explore the effect of a global plaquette rotation, showing that while the band structure remains invariant under this unitary transformation, the Berry curvature and Chern number are modulated, highlighting the geometric sensitivity of the topological response. Our results establish a direct correspondence between the lattice geometry, chirality, and magnon topology, providing a route toward tunable topological phases in frustrated magnetic systems.

cond-mat.mes-hall↗

arXiv2023

Temperature-dependence of the chirality-induced spin selectivity effect -- experiments and theory

The temperature dependence of the chirality-induced spin selectivity (CISS) effect can be used to discriminate between different theoretical proposals for the mechanism of the CISS effect. Here we briefly review key experimental results and discuss the effect of temperature in different models for the CISS effect. We then focus on the recently suggested spinterface mechanism and describe the different possible effects temperature can have within this model. Finally, we analyze in detail recent experimental results from Qian, et.al., (Nature, 606, 902-908 (2022)) and demonstrate that, opposite to the original interpretation by the authors, these data indicate that the CISS effect increases with decreasing temperature. Finally, we show how the spinterface model can accurately reproduce these experimental results.

cond-mat.mes-hall↗