Spin-Locked Helical Currents and Pure Spin Pumping in Altermagnetic Nanotubes

Abstract

Altermagnetism has been widely explored in 3D and 2D crystals, but its one-dimensional realization remains largely unexplored. Here we propose an altermagnetic nanotube formed by rolling a 2D altermagnet, which converts momentum-odd spin polarization into spin-chirality locking enforced by the screw axis. Unlike curvature-induced magnetization in bent films, the nanotube is mirror-antisymmetric and produce no net magnetization. Two reciprocal effects emerge: (i) a single-spin injection drives a helical current whose handedness is fixed by the spin, yielding opposite-sign axial magnetic fields; and (ii) a time-varying axial flux generates a circumferential Faraday field that drives equal-magnitude but opposite axial charge currents in the two spin channels, producing a pure spin current under open-circuit conditions. As an implication, spin accumulation programs the tube's handedness and can imprint it onto otherwise achiral coaxial nanotubes in one-dimensional van der Waals assemblies. First-principles results for V2Se2O confirm spin-dependent helical wave functions near both band edges, establishing a nonrelativistic route to spin-programmable chiral nanodevices and compact flux generators/charge-neutral spin injectors without static magnetic bias.

Figures (4)

• Figure 1: Spin-programmable chiral nanosolenoid from a rolled two-dimensional altermagnet. (a),(b) Rolling imposes a screw axis that converts $k$-odd spin polarization into spin-locked axial-azimuthal motion. (c),(d) Direct effect: a single-spin injection drives a helical charge current and an axial field whose sign reverses with spin. (e) Spin-programmable chiral imprinting in coaxial altermagnetic heteronanotubes. (f) Inverse effect: a time-varying axial flux pumps equal-magnitude, opposite-sign axial currents, yielding a pure spin current.
• Figure 2: (a) Atomic structure of two-dimensional V$_2$Se$_2$O. Red and blue spheres denote V atoms with opposite spin orientations, gray spheres are O atoms, and light-purple spheres are Se atoms. The [110]-direction is shown by the black arrow. (b) Spin-polarized charge density of a V$_2$Se$_2$O nanotube, showing the alternating spin texture along the axial direction (z). The yellow line shows the mirror time-reversal symmetry $M_{z}\mathcal{T}$. (c) Cross-sectional views corresponding to three axial planes in (b), arrows highlight the helical correlation between the spin-polarized lobes around the tube circumference.
• Figure 3: Spin-resolved electronic band structures of the V$_2$Se$_2$O nanotube. Red and blue lines denote spin-up and spin-down channels, respectively. The CBM and VBM are indicated by black squares, where the “$+$” and “$-$” signs correspond to clockwise and anticlockwise helicities along the z axis.
• Figure 4: Real-space charge densities (squared modulus of the wave functions) of the VBM and CBM states for the V$_2$Se$_2$O nanotube, corresponding to the black points in Fig. \ref{['figure3']}. Panels (a,c) show the spin-down (blue) channel, and panels (b,d) show the spin-up (yellow) channel. Both VBM and CBM exhibit clear helical patterns along the tube axis, revealing opposite chiralities for the two spin channels.