Signatures of Spin Coherence in Chiral Coupled Quantum Dots

TL;DR

This work addresses the challenge of observing quantum-coherent spin dynamics in ambient conditions by constructing multilayer quantum-dot assemblies connected with chiral linkers and probing spin coherence via field- and angle-dependent photoluminescence lifetimes. By circularly polarizing excitation and applying a transverse magnetic field, the authors reveal a field-orientation–dependent modulation of the long-lived PL component, consistent with spin precession along the chiral axis and chiral-mediated spin delocalization. A two-channel spin-decay model incorporating precession phase, initial spin state, and ensemble inhomogeneity reproduces the key trends, linking spin-selective coupling to coherent dynamics. The results establish chiral QD assemblies as a room-temperature platform to study coherent manifestations of the chiral-induced spin selectivity effect, with potential implications for spintronics and quantum technologies.

Abstract

Chiral-induced spin selectivity (CISS) enables spin selectivity of charge carriers in chiral molecular systems without magnetic materials. While spin selectivity has been widely investigated, its quantum coherence has not yet been explored. Here, we investigate spin-dependent photoluminescence (PL) dynamics in multilayer quantum-dot (QD) assemblies coupled by chiral linkers. Using circularly polarized excitation in the presence of an external magnetic field, we observe a pronounced modulation of the PL lifetime that depends on the magnetic field magnitude and geometry. The lifetime difference between left- and right-circularly polarized excitations exhibits a field-angle dependence, consistent with spin precession driven by the transverse magnetic-field component relative to the chiral axis. A model incorporating coupled spin precession and decay processes reproduces the experimental trends. These results establish chiral QD assemblies as a room-temperature platform for probing quantum coherent manifestations of the CISS effect, with implications for spintronic and quantum technologies.

Figures (6)

• Figure 1: (a) Schematic illustration of spin-modulated photoluminescence (PL) decay in a chiral–quantum-dot (QD) system, where a transverse magnetic field (B) induces coherent spin precession along the chiral molecular axis, resulting in an oscillatory PL lifetime. (b) Schematic of the chiral–QD sample structure, consisting of three QD sizes (3.3, 4.2, and 4.9 nm) with absorption peaks at 520, 560, and 580 nm, respectively, interconnected by left- or right-handed (L/D) chiral molecular linkers.
• Figure 2: Symmetry breaking in a chiral system. Comparison of photoluminescence lifetime decay under a magnetic field of $B = 280$ Gauss for a multilayer of D-chiral or L-chiral QD assemblies, excited by LCP or RCP light.
• Figure 3: Lifetimes constants for the D-chiral sample. Lifetime constants extracted for LCP and RCP light are plotted in blue and red respectively, as a function of the applied magnetic field. The magnetic field is oriented in a polar angle $\theta = 45\degree$ relative to the sample surface. The magnet's azimuthal angles $\phi$ are aligned to (a) $\phi = 0\degree$; (b) $\phi = 20\degree$; (c) $\phi = 40\degree$ and (d) $\phi = 60\degree$
• Figure 4: PL lifetime differences between RCP and LCP excitation light as a function of the magnetic field for the D-chiral sample. The magnetic field is oriented in a polar angle $\theta = 45\degree$ relative to the sample surface and the optical axis. The magnet is rotated around the sample in different azimuthal angles (a) $\phi = 0\degree$; (b) $\phi = 20\degree$; (c) $\phi = 40\degree$ and (d) $\phi = 60\degree$.
• Figure 5: PL lifetime differences between RCP and LCP light as a function of the azimuthal angle $\phi$, plotted for magnetic fields B = 160 (blue), 200 (red), 240 (yellow) and 280 (purple) Gauss. (a) D-chiral sample; (b) L-chiral sample.