arXiv subjects

Seungyun Han

Publications and source records attributed to Seungyun Han.

10 recordsLinked to original sources

arXiv2026

Emergence of the magnetic octupole Rashba-Edelstein effect from spin-orbit entanglement

Magnetic multipoles have attracted growing interest as order parameters and dynamical degrees of freedom in unconventional magnets, yet it remains unclear how broadly they can emerge as active electronic degrees of freedom. Here, we show that spin-orbit-entangled multiorbital states can host magnetic octupole (MO) degrees of freedom. In Rashba systems, this gives rise to an MO Rashba texture accompanying the J-Rashba texture. Remarkably, spin-orbital entanglement can realize a pure-MO limit in which the spin and orbital-angular-momentum textures vanish while the MO texture remains finite. An applied electric field converts this texture into a nonequilibrium MO polarization through an MO Rashba-Edelstein effect. Around the pure-MO regime, the MO Edelstein response dominates over the conventional spin response, showing that multipolar responses need not be small corrections to dipolar spin physics. Our results establish an interface-based route for electrically generating nonequilibrium multipolar magnetic polarization in spin-orbit-coupled systems.

cond-mat.mes-hall↗

arXiv2026

Intra-atomic magnetic octupoles and their coupling to cluster magnetic octupoles in Chiral antiferromagnets Mn$_3$Sn

We demonstrate that Mn$_3$Sn hosts finite intra-atomic magnetic octupoles (AMOs) $\mathbf{o}$ in addition to the well-established cluster magnetic octupole (CMO) $\mathbf{O}$. In contrast to the cluster-scale CMO, the AMO is a site-localized magnetic multipole associated with the anisotropic intra-atomic spin density. Symmetry analysis shows that the CMO and AMO transform in the same representation, allowing a bilinear interaction of the form $-g\,\mathbf{O}\cdot\mathbf{o}$. Using first-principles calculations, we confirm the presence of finite AMO densities and show that the AMO transforms concomitantly with the CMO under rotations of the noncollinear magnetic structure, providing microscopic evidence for the coupling between them. We further show that the magnetic band splitting can be represented by projected AMO operators, with manifold-dependent effective octupolar exchange coefficients in realistic Mn$_3$Sn. The presence of AMOs has three important implications. First, we show that the nonrelativistic spin splitting of Mn$_3$Sn can be described in terms of projected AMO operators, with manifold-dependent effective octupolar exchange coefficients, establishing the AMO as a microscopic operator underlying the spin splitting. Second, the AMO reveals a close connection between Mn$_3$Sn and $d$-wave altermagnets from the magnetic-octupole perspective. Third, the $\mathbf{O}\cdot\mathbf{o}$ coupling suggests a new route to manipulate the CMO using AMO currents, opening a direction for controlling the multipolar order in Mn$_3$Sn.

cond-mat.mtrl-sci↗

arXiv2026

Deterministic Néel vector switching of altermagnets via magnetic octupole torque

Altermagnets have recently emerged as promising materials for next-generation spintronic devices. For their device applications, realizing a single-domain configuration is essential but remains challenging. We theoretically consider injecting magnetic multipoles into altermagnets, which can be achieved by applying an in-plane current to an altermagnet/normal metal bilayer. We demonstrate for $d$-wave altermagnets that the torque generated by the magnetic octupole injection can achieve magnetic-field-free deterministic switching of the altermagnets' Néel vector and transform their multidomain configurations into a single domain. This method allows the switching in diverse altermagnets, thereby facilitating their device applications and fundamental studies. This work also exemplifies the usefulness of magnetic multipole currents.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic octupole Hall effect in heavy transition metals

d-wave altermagnets have the magnetic octupole as their primary order parameter. A recent study [Han et al. arXiv 2409.14423 (2024)] demonstrated that magnetic octupole current can induce Néel vector dynamics. Therefore, identifying materials that can efficiently generate a magnetic octupole current is essential. In this paper, we investigate the magnetic octupole Hall effect in 4d and 5d transition metals. By employing atomic magnetic octupole operators, we calculate the magnetic octupole Hall conductivity using first-principles calculations. We also explore the microscopic origin of the magnetic octupole Hall effect and find that it results from the combined effect of orbital texture and spin-orbit coupling. Additionally, we analyze the ratio of spin Hall conductivity to magnetic octupole Hall conductivity across various materials and identify those that are optimal for observing magnetic octupole physics. We also discuss potential applications arising from the magnetic octupole Hall effect. Our work serves as a valuable reference for identifying materials suitable for studying magnetic octupole physics.

cond-mat.mtrl-sci↗

arXiv2025

Orbital Pumping Incorporating Both Orbital Angular Momentum and Position

We develop a theory of adiabatic orbital pumping, highlighting qualitative differences from spin pumping. An oscillating magnetic field pumps not only orbital angular momentum current but also orbital angular position current. The latter, which has no spin counterpart, underscores the incompleteness of existing orbital torque theories. Importantly, both types of orbital currents can be detected as transverse electric voltages, which contain considerable second harmonic components unlike in spin pumping. Moreover, orbital currents can be pumped by lattice dynamics that carry phonon angular momentum, implying that orbital currents can, in turn, induce phonon angular momentum. Our work open up new possibilities for generating orbital currents and provides a broader understanding of the interplay between spin, orbital, and phonon dynamics.

cond-mat.mes-hall↗

arXiv2025

Gigantic current control of coercive field and magnetic memory based on nm-thin ferromagnetic van der Waals Fe3GeTe2

Controlling magnetic states by a small current is essential for the next-generation of energy-efficient spintronic devices. However, it invariably requires considerable energy to change a magnetic ground state of intrinsically quantum nature governed by fundamental Hamiltonian, once stabilized below a phase transition temperature. We report that surprisingly an in-plane current can tune the magnetic state of nm-thin van der Waals ferromagnet Fe3GeTe2 from a hard magnetic state to a soft magnetic state. It is the direct demonstration of the current-induced substantial reduction of the coercive field. This surprising finding is possible because the in-plane current produces a highly unusual type of gigantic spin-orbit torque for Fe3GeTe2. And we further demonstrate a working model of a new nonvolatile magnetic memory based on the principle of our discovery in Fe3GeTe2, controlled by a tiny current. Our findings open up a new window of exciting opportunities for magnetic van der Waals materials with potentially huge impacts on the future development of spintronic and magnetic memory.

cond-mat.mtrl-sci↗

arXiv2024

Harnessing magnetic octupole Hall effect to induce torque in altermagnets

d-wave altermagnets have magnetic octupoles as their order parameters [Phys. Rev. X 14, 011019 (2024)]. We theoretically show that magnetic octupoles injected from outside generate torque on the d-wave altermagnets. The injection can be achieved by the magnetic octupole Hall effect in an adjacent layer. We calculate the magnetic octupole Hall conductivity of the heavy metal Pt and find a sizable value comparable to its spin Hall conductivity. Our work generalizes the spin Hall phenomenology (generation by heavy metals and detection by torque in ferromagnets) to the magnetic octupole Hall phenomenology (generation by heavy metals and detection by torque in altermagnets), which can be utilized to electrically control magnetic configurations of altermagnets.

cond-mat.mes-hall↗

arXiv2024

Nonlinear Orbital and Spin Edelstein Effect in Centrosymmetric Metals

Nonlinear spintronics combines nonlinear dynamics with spintronics, opening up new possibilities beyond linear responses. A recent theoretical work [Xiao et al., Phys. Rev. Lett. 130, 166302 (2023)] predicts the nonlinear generation of spin density [nonlinear spin Edelstein effect (NSEE)] in centrosymmetric metals based on symmetry analysis combined with first principle calculation. However, its microscopic mechanism is limited to a specific set of materials with local inversion symmetry breaking and is not applicable to general materials. This paper focuses on the fundamental role of orbital degrees of freedom for the nonlinear generation in centrosymmetric systems. Using a combination of tight-binding model and density functional theory calculations, we demonstrate that nonlinear orbital density can arise independently of spin-orbit coupling. In contrast, spin density follows through spin-orbit coupling. We further elucidate the microscopic mechanism responsible for this phenomenon, which involves the NSEE induced by electric-field-induced orbital Rashba texture. In addition, we also explore the potential applications of the nonlinear orbital and spin Edelstein effect for field-free switching of magnetization.

cond-mat.mtrl-sci↗

arXiv2022

Microscopic study of orbital textures

Many interesting spin and orbital transport phenomena originate from orbital textures, referring to $\vec{k}$-dependent orbital states. Most of previous works are based on symmetry analysis to model the orbital texture and analyze its consequences. However the microscopic origins of orbital texture and its strength are largely unexplored. In this work, we derive the orbital texture Hamiltonians from microscopic tight-binding models for various situations. To form an orbital texture, $\vec{k}$-dependent hybridization of orbital states are necessary. We reveal two microscopic mechanisms for the hybridization: (i) lattice structure effect and (ii) mediation by other orbital states. By considering the orbital hybridization, we not only reproduce the orbital Hamiltonian obtained by the symmetry analysis but also reveal previously unreported orbital textures like orbital Dresselhaus texture and anisotropic orbital texture. The orbital Hamiltonians obtained here would be useful for analyzing the orbital physics and designing the materials suitable for spin-orbitronic applications. We show that our theory also provides useful microscopic insight into physical phenomena such as the orbital Rashba effect and the orbital Hall effect. Our formalism is so generalizable that one can apply it to obtain effective orbital Hamiltonians for arbitrary orbitals in the presence of periodic lattice structures.

cond-mat.mes-hall↗

arXiv2022

Orbital Dynamics in Centrosymmetric Systems

Orbital dynamics in time-reversal-symmetric centrosymmetric systems is examined theoretically. Contrary to common belief, we demonstrate that many aspects of orbital dynamics are qualitatively different from spin dynamics because the algebraic properties of the orbital and spin angular momentum operators are different. This difference generates interesting orbital responses, which do not have spin counterparts. For instance, the orbital angular momentum expectation values may oscillate even without breaking neither the time-reversal nor the inversion symmetry. Our quantum Boltzmann approach reproduces the previous result on the orbital Hall effect and reveals additional orbital dynamics phenomena, whose detection schemes are discussed briefly. Our work will be useful for the experimental differentiation of the orbital dynamics from the spin dynamics.

cond-mat.mes-hall↗