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

Abstract: We show that rolling a two-dimensional altermagnet into a nanotube turns it into a spin-programmable chiral nanosolenoid with two reciprocal, SOC-free functionalities. (i) Direct: injecting a single-spin-polarized current produces a steady helical current whose handedness is locked to the spin orientation, yielding opposite axial magnetic fields for opposite spins. (ii) Inverse: a time-varying axial flux Phi(t) induces a circumferential Faraday field E_theta = -(dPhi/dt)/(2 pi R) that drives equal-magnitude, opposite-sign axial charge currents in the two spin channels, Iz^up = - Iz^down, thereby pumping a pure spin current Is = (hbar/2e)(Iz^up - Iz^down) with zero net charge flow. Both effects arise from the interplay between momentum-odd spin polarization inherent to altermagnets and the screw symmetry of the rolled geometry, and persist in the complete absence of spin-orbit coupling. Using V2Se2O as a prototype, first-principles calculations reveal spin-dependent chiral wave functions near both the conduction- and valence-band edges. These results establish a nonrelativistic route toward compact spin-controlled flux generators and charge-neutral spin injectors in light-element materials without static magnetic bias.