Ultrafast Spatiotemporal Dynamics of Room-Temperature Exciton Spins in a Two-Dimensional Layered Halide Perovskite

When and Where

Apr 12, 2023
9:45am - 10:00am

Moscone West, Level 3, Room 3004

Presenter

Go Yumoto

Fumiya Sekiguchi

Ruito Hashimoto

Tomoya Nakamura

Atsushi Wakamiya

Yoshihiko Kanemitsu

Co-Author(s)

Go Yumoto¹,Fumiya Sekiguchi¹,Ruito Hashimoto¹,Tomoya Nakamura¹,Atsushi Wakamiya¹,Yoshihiko Kanemitsu¹

Institute for Chemical Research, Kyoto University¹

Abstract

Go Yumoto¹,Fumiya Sekiguchi¹,Ruito Hashimoto¹,Tomoya Nakamura¹,Atsushi Wakamiya¹,Yoshihiko Kanemitsu¹

Institute for Chemical Research, Kyoto University¹

Spin-polarized excitons in atomically thin two-dimensional (2D) semiconductors have attracted great interest for spin-optoelectronic applications because of their large exciton binding energies and unique spin-dependent characters. Spatially resolved optical measurements have revealed the formation of spatial patterns and long-range transport of the exciton spins in 2D transition metal dichalcogenides [1-3]. This spatial controllability of the exciton spins shows the potential of 2D semiconductors for exciton-based spin-optoelectronic applications. However, observations of such spatial dynamics have been restricted to cryogenic temperatures because the short exciton spin relaxation times at room temperature prevent formation of a spatial pattern and transport of the exciton spins. The absence of spatial evolution of spin-polarized excitons at room temperature limits the potential for applications such as information and signal processing and chiral nanophotonics. This limitation could be overcome by utilizing exciton-exciton exchange interactions, where the repulsive force between excitons with the same spin drives fast expansion of a spatial profile of spin-polarized excitons. From this point of view, 2D Ruddlesden-Popper lead halide perovskites (RPPs) are promising candidates for demonstrating spatial evolution of exciton spins at room temperature. This is because 2D RPPs have stable excitons characterized by a total exciton angular momentum projection of ±1 [4-9] and exhibit substantial exciton-exciton interactions [10] and relatively long exciton spin relaxation times at room temperature [11]. We synthesized phase-pure 2D RPP single crystals of (C4H9NH3)2(CH3NH3)3Pb4I13, and mechanically exfoliated the crystal flakes and transferred them onto a glass substrate. To investigate the spatial and temporal dynamics of the exciton spins in 2D RPPs at room temperature, we developed polarization-resolved pump-probe microscopy with millidegree, submicrometer, and subpicosecond resolutions [12]. Because the pump-induced Faraday rotation angle is proportional to the spin-polarized exciton population, we measured the images of the time-resolved Faraday rotation angle. At low pump intensity, the spin-polarized exciton population decays keeping its isotropic Gaussian spatial profile, which reflects the pump beam profile. In contrast, at high pump intensity, we observed that the spatial profile of the spin-polarized exciton population evolves into a halo-like spatial pattern with increasing pump-probe delay time and ultrafast exciton spin transport occurs [12]. We found that the rapidly expanding halo-like spatial profile is caused by density-dependent nonlinear relaxation and repulsive interaction between excitons with the same spin, both of which are induced by exciton-exciton exchange interactions. Our findings reveal the impact of the exciton-exciton interactions on the spatiotemporal dynamics of exciton spins at room temperature and suggest the potential of 2D RPPs for spin-optoelectronic applications. Part of this study was supported by JSPS KAKENHI (Grant no. JP19H05465). References 1) P. Rivera et al., Science 351, 688-691 (2016). 2) M. Onga et al., Nat. Mater. 16, 1193-1197 (2017). 3) D. Unuchek et al., Nat. Nanotechnol. 14, 1104-1109 (2019). 4) D. Giovanni et al., Sci. Adv. 2, e1600477 (2016). 5) J. C. Blancon et al., Nat. Commun. 9, 2254 (2018). 6) T. Yamada et al., J. Chem. Phys. 151, 234709 (2019). 7) K. Ohara et al., Phys. Rev. B 103, L041201 (2021). 8) G. Yumoto et al., Nat. Commun. 12, 3026 (2021). 9) G. Yumoto and Y. Kanemitsu, Phys. Chem. Chem. Phys. 24, 22405-22425 (2022). 10) S. A. Bourelle et al., Nano Lett. 20, 5678-5685 (2020). 11) X. Chen et al., ACS Energy Lett. 3, 2273-2279 (2018). 12) G. Yumoto et al., Sci. Adv. 8, eabp8135 (2022).