Transport of optically excited carriers in semiconductors is typically described within a quasi-equilibrium picture, where energy is carried by a single thermalized quasiparticle population characterized by well-defined transport coefficients. Here, we demonstrate that in epitaxial CsPbBr3 perovskite single crystals, this picture holds near room temperature - but breaks down dramatically at low temperature. Using transient microscopy, we show that optically measured carrier mobilities match device-scale Hall-effect and field-effect transistor measurements across a broad temperature range, resolving reported discrepancies and validating the equilibrium framework in the free-carrier regime. Below ~60 K, however, when excitonic effects become significant, equilibrium models begin to fail. We observe two coupled populations: a transient (<100 ps) hot-exciton gas with a diffusivity ~25-30 cm<sup>2</sup>/s - greatly exceeding the diffusivity expected for thermalized excitons - and a quasi-localized state that is fed by the cooling of the hot-exciton gas. These results reveal that in CsPbBr3, transport and thermalization are not separable processes: carriers move while still redistributing among internal degrees of freedom, breaking the timescale separation that underpins equilibrium transport theory in conventional semiconductors. By resolving transport at the population level, we can directly access the competing kinetics of exciton formation, interconversion, and cooling, offering a new space for controlling energy flow in perovskite materials and their photonic applications.
Efficient intrinsic spin-to-charge current conversion in an all-epitaxial single-crystal perovskite-oxide heterostructure of La0.67Sr0.33MnO3/LaAlO3/SrTiO3
Ultrafast Epitaxial Growth of Metre-Sized Single-Crystal Graphene on Industrial Cu Foil
使用单晶硅的现代技术的基础是直径高达12英寸或更大的高质量单晶硅锭的生长。对于石墨烯的许多应用，大面积高质量（理想情况下是单晶）材料将成为可能。自从十年前在铜箔上首次生长以来，已经实现了英寸大小的单晶石墨烯。我们在这里呈现了在20分钟内生长具有> 99%超高取向晶粒的5 X 50 cm 2尺寸的石墨烯膜。这一增长是通过以下方式实现的：（i）合成亚米尺寸的单晶Cu（111）箔作为衬底;（ii）在Cu（111）表面上外延生长石墨烯岛;（iii）将这样的石墨烯岛无缝合并成具有高单晶度的石墨烯膜;以及（iv）石墨烯膜的超快生长。这些成就是通过温度驱动退火技术从工业多晶铜箔生产单晶Cu（111）以及相邻氧化物连续供氧的奇妙效果实现的。所合成的石墨烯膜具有非常少的错取向晶粒（如果有的话），在4K下具有高达~ 23，000 cm 2 V-1 s-1的迁移率，并且室温薄层电阻为~ 230欧姆/平方。这种方法很有可能扩大规模，以获得具有单一结晶度的超大型和高质量的石墨烯薄膜，从而以低成本实现各种工业级应用。
Atomic-Scale Surface Imaging of bulk Epitaxial CsPbBr3 Perovskite Single Crystals on Mica using Light Assisted Scanning Tunneling Microscopy at Low-Temperature (80 K)
Institut FEMTO-ST, Univ. Marie et Louis Pasteur, CNRS（FEMTO-ST研究所，玛丽和路易·巴斯德大学，法国国家科学研究中心）；Department of Physics and Astronomy, Rutgers, the State University of New Jersey（物理与天文学系，新泽西州立罗格斯大学）；Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris Sud, Université Paris-Saclay（奥赛分子科学研究所（ISMO），法国国家科学研究中心，巴黎南大学，巴黎-萨克雷大学）
