Coherent Spin Precession and Lifetime-Limited Spin Dephasing in CsPbBr₃ Perovskite Nanocrystals

Abstract

Carrier spins in semiconductor nanocrystals are promising candidates for quantum information processing. Using a combination of time-resolved Faraday rotation and photoluminescence spectroscopies, we demonstrate optical spin polarization and coherent spin precession in colloidal CsPbBr 3 nanocrystals that persists up to room temperature. By suppressing the influence of inhomogeneous hyperfine fields with a small applied magnetic field, we demonstrate inhomogeneous hole transverse spin-dephasing times (! ! *) that approach the nanocrystal photoluminescence lifetime, such that nearly all emitted photons derive from coherent hole spins. Thermally activated LO phonons drive additional spin dephasing at elevated temperatures, but coherent spin precession is still observed at room temperature. These data reveal several major distinctions between spins in nanocrystalline and bulk CsPbBr 3 and open the door for using metal-halide perovskite nanocrystals in spin-based quantum technologies.

Ultrafast Pump‐Probe Spectroscopy—A Powerful Tool for Tracking Spin‐Quantum Dynamics in Metal Halide Perovskites

“…Very recently, Crane et al. [ 37 ] demonstrated carrier spin‐dephasing dynamics and coherent spin precession in colloidal CsPbBr 3 nanocrystals up to room‐temperature, by performing TRFR and PL measurements. At low temperatures, spin coherence is restricted by inhomogeneous hyperfine fields, but the spin‐dephasing time ( T 2 * ) can be extended dramatically under a small magnetic field, as plotted in Figure 9e.…”

“…In contrast, the spin‐quantum mechanisms of perovskites revealed by circularly‐polarized pump‐probe technique are still controversial that is related to composition, size, and layers of perovskites. [ 37,40,45,48 ] Hence, it is urgent to conduct more comprehensive investigation by circularly‐polarized pump‐probe technique and simultaneously need assistance of other measurement approaches. Currently, ultrafast spin‐quantum dynamics were predominately studied in metal Pb atoms based perovskites which determines SOC and spin switching processes, but it deserves to replace Pb atoms with part of other metal atoms (such as, Sn, Bi, and Ag‐In) [ 107 ] for spin information transport with long relaxation time and spin manipulation, which can also avoid strong toxicity of Pb atoms.…”

“…Alternatively, perovskites also exhibit outstanding spin‐dependent photophysical performances owing to giant spin‐orbital coupling (SOC) in heavy Pb atoms and interactions between spin‐orbit and electron‐hole exchange. [ 24–27 ] Experimentally, large­scale Rashba and Dresselhaus splitting, [ 26–29 ] large optical Stark effect (OSE), [ 30–32 ] magneto­optical effect, [ 29,33–37 ] triplet formation, [ 38 ] and polarized light related effects, [ 39 ] have recently been observed in perovskites. Such experimental observations have triggered extensive research interest on perovskites spintronics, promising for construction of next‐generation integrated perovskites optoelectronic and photonic devices with spin functions.…”

“…However, fundamental understanding of spin‐dependent photo‐physics in perovskites, in particular of, hyperfine description of spin relaxation, magnetic spin effect, and spin polarization processes, which is plausible for manipulation of spin electrons by spin photons leveraging circularly‐polarized pump‐probe technique, is still at its nascent stage. [ 30–32,34–37,40–48 ] Moreover, up to date, few review papers have been reported on systematic, complete, and insightful summary and discussion of such emerging ultrafast spin‐quantum dynamics and phenomena in various perovskites from the aspect of study via this technique. [ 23,49,50 ] Hence, it is highly desirable for providing a systemic review on this rapidly developing field in recent few years, to evoke extraordinary research on spintronic properties in perovskites for truly practical spintronic devices in future.…”

Perspectives of Organic and Perovskite‐Based Spintronics

“…[ 159,166 ] Leveraging this excitonic structure, many studies reported the successful injection of spin‐polarized excitons and carriers into perovskite NCs for a wide variety of sizes and compositions. [ 159,167–169 ] Analogously to bulk HPs, spin lifetimes in NCs were reported to be in the ps‐regime (see Figure 4d).…”