Engineering chiral-induced spin selectivity in an artificial topological quantum well

Abstract

Chiral-induced spin selectivity (CISS) is a striking phenomenon in which spin-unpolarized electrons become spin-polarized after traversing a chiral medium. Theoretical studies have shown that spin-orbit coupling, geometric chirality, and dephasing act cooperatively for this effect to emerge. Inspired by this, we demonstrate a solid-state realization of CISS in an engineered InAs/GaSb quantum well where geometric chirality and dephasing can be introduced controllably. Introducing a chiral structure produces a clear spin polarization whose sign reverses when the chirality is flipped, and whose magnitude grows systematically with the number of dephasing electrodes, while achiral configurations exhibit no spin selectivity. The polarization remains robust even under strong Anderson disorder, showing that the engineered chiral structures provides an intrinsically stable route to spin-selective transport. These results establish a solid-state platform in the topological quantum well system for controllably generating the CISS effect.

Figures (5)

• Figure 1: Schematic of two chiral configurations of the InAs/GaSb quantum well device used to demonstrate the CISS effect. (a) Left-chirality configuration: the InAs layer lies above GaSb, and the bottom dephasing electrode (Lead 1) is attached to the lower boundary. (b) Right-chirality configuration: the layer sequence is inverted, with GaSb on top of InAs, corresponding to an opposite (right-chirality) chirality. In both cases, the transport current flows from Lead L to Lead R.
• Figure 2: (a,b) Helical-edge transport in the InAs/GaSb quantum well under the two opposite chiral configurations corresponding to Fig. \ref{['fig1']}(a) (left chirality) and Fig. \ref{['fig1']}(b) (right chirality). Spin-up (red) and spin-down (blue) channels propagate along opposite boundaries due to spin-momentum locking. (c) Spin-resolved conductances $G_\uparrow(E)$ and $G_\downarrow(E)$ for the left-chirality configuration under dephasing ($\Gamma_d = 0.5$), showing a clear splitting within the bulk-gap region. (d) Resulting spin polarization $P_s(E)$. The central region contains 90 $\times$ 50 unit cells, and dephasing electrode covers 30 unit cells.
• Figure 3: (a) Spin-resolved conductances $G_{\uparrow}(E)$ and $G_{\downarrow}(E)$ for the left-chirality InAs/GaSb device with two bottom dephasing electrodes (inset) and $\Gamma_d = 0.5$. (b) Spin polarization $P_s(E)$ for devices with two (cyan) and three (magenta) bottom dephasing electrodes. The central scattering region contains $150\times 50$ (two electrodes) or $210\times 50$ (three electrodes) unit cells, and each bottom dephasing electrode covers $30$ unit cells.
• Figure 4: (a) Two-terminal device with dephasing electrodes attached symmetrically to the top and bottom edges. (b) Configuration in which dephasing electrodes are distributed uniformly within each $5 \times 5$ bulk plaquette. (c,d) Corresponding spin-resolved conductances $G_{\uparrow}$ and $G_{\downarrow}$ versus the Fermi energy $E$. The other parameters are the same as in Fig. \ref{['fig2']}.
• Figure 5: (a) Spin-resolved conductances $G_{\uparrow}(E)$ and $G_{\downarrow}(E)$ of the InAs/GaSb quantum-well device with a single dephasing electrode under a representative disorder strength $W=1$. (b) Spin polarization $P_s(E)$ versus the Fermi energy $E$ for different disorder strengths $W$. Both $\Gamma_d=0.5$ and $W$ are in units of energy $E_0$. The other parameters are the same as in Fig. \ref{['fig2']}.