Towards spintronics via tunneling through asymmetric barriers

Abstract

Spin transport typically relies on direct manipulation of the spin degree of freedom via magnetic fields, spin-orbit coupling, or engineered spin-dependent potentials. We show theoretically that directional spin currents can arise in a relatively simple setting - a one-dimensional interacting fermionic ring with static, spin-independent asymmetric barriers. By introducing asymmetric potential barrier geometry, spin-resolved circulating currents emerge on a closed chain even for symmetric initial configurations. The effect can be enhanced or reversed by appropriate initial state preparation and tuning the barrier asymmetry to resonant conditions.

Figures (4)

• Figure 1: Schematic representation of the one-dimensional Fermi--Hubbard model with periodic boundary conditions and a site-dependent asymmetric external potential barrier of maximum height $h$. The hopping amplitude between neighboring sites is indicated by $J$, while $U$ represents the on-site interaction strength. Dark circles denote lattice sites.
• Figure 2: Barrier asymmetry as the essential requirement for directed spin transport. System dynamics for a symmetric initial state under asymmetric (left column, $\alpha = 0.5$) and symmetric (right column, $\alpha = 1$) barrier configurations. (a, b) Transferred charge for spin-up (blue) and spin-down (orange) components. A finite transferred charge develops only in the asymmetric case. (c, d) Site-resolved total density dynamics $\langle \hat{n}_i(t) \rangle$. The ring geometry is schematically unfolded above each panel, with the dashed cut in the top illustrations indicating where the periodic lattice is opened for visualization.
• Figure 3: Transferred charge dynamics for spin-up (blue) and spin-down (orange) components under the asymmetric barrier configuration with two distinct initial states. The doublon is positioned adjacent to (a) $h/2$ barrier and (b) $h$ barrier, with the unpaired spin-up fermion located three sites away along the ring.
• Figure 4: Control of spin directionality via barrier asymmetry. Transferred charge $Q_\sigma(t)$ as a function of time and asymmetry parameter $\alpha$ for two biased initial configurations (schematically shown above each panel set). Top row: doublon adjacent to the $\alpha h$ barrier. Bottom row: doublon adjacent to the fixed $h$ barrier. Left column corresponds to the spin-up component, right column to spin-down.