Transient circular dichroism and exciton spin dynamics in all-inorganic halide perovskites

Abstract

All-inorganic metal halides perovskites (CsPbX3, X = Br or Cl) show strong excitonic and spin-orbital coupling effects, underpinning spin-selective excitonic transitions and therefore exhibiting great promise for spintronics and quantum-optics applications. Here we report spin-dependent optical nonlinearities in CsPbX3 single crystals by using ultrafast pump-probe spectroscopy. Many-body interactions between spin-polarized excitons act like a pseudo-magnetic field and thus lift the degeneracy of spin states resulting in a photoinduced circular dichroism. Such spontaneous spin splitting between “spin-up” and “spin-down” excitons can be several tens of milli-electron volts under intense excitations. The exciton spin relaxation time is ~20 picoseconds at very low pump fluence, the longest reported in the metal halides perovskites family at room temperature. The dominant spin-flip mechanism is attributed to the electron-hole exchange interactions. Our results provide essential understandings towards realizing practical spintronics applications of perovskite semiconductors.

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

“…The BAP model is also suitable for description of CVD‐deposited all‐inorganic 3D CsPbX 3 perovskites film system, leaving the spin relaxation dynamics exhibiting excellent balance of robust exciton resonances, optical nonlinearities and relatively long exciton spin lifetimes; [ 63 ] strong dependence on pump fluence; and temperature independence feature. [ 41 ] This work constructs fundamental understanding of exciton spin transient photophysics in 2D perovskites, which is essential to explore their untapped application in spintronic devices at room‐temperature, including, quantum computing and nonvolatile memory devices.…”

“…As discussed above, perovskites (2D or 3D) emerge as prospective spintronic materials, due to defect tolerance, solution processability, large SOC, and allowance of circularly‐polarized light pump of J ‐(spin) polarized carriers/excitons with 100% spin selection. However, the reported spin relaxation lifetime, to date, is limited to several to tens of ps at room‐temperature, [ 36,41 ] hampering the effective spin transport in such perovskites systems. Comparatively, Ruddlesden–Popper perovskites (RPP) with mixed phases (between 2D and 3D) provide viability of ultrafast spin funneling, owing to self‐formation of natural multiple QW system and tunable thickness with phase number ( n ).…”

“…[ 31,32 ] Red‐shift phenomenon (Figure 2j) can be triggered by following the former three ways of pumping absorption (Figure 2a–c), dominatingly rooting from bandgap renormalization, [ 54 ] bi‐exciton‐induced red‐shift, [ 55 ] hot‐carrier‐induced Stark effect, [ 56 ] and photo‐induced circular dichroism. [ 41 ]…”

“…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.…”

Optical switching of topological phase in a perovskite polariton lattice

“…In our experiment, the CsPbBr 3 perovskite active medium is grown by a vapor-phase deposition technique as discussed before (38,43,44), with excellent optical properties and flat surface (see the Supplementary Materials). Robust exciton polariton condensates have been previously demonstrated in this type of perovskite microcavity at room temperature (36,39).…”