Strong electric-field transients resonant to intersubband transitions in n-type modulation-doped GaAs/AlGaAs quantum wells induce coherent Rabi oscillations, which are demonstrated by a phase-resolved measurement of the light emitted by the sample. The time evolution of the intersubband polarization is influenced by Coulomb-mediated many-body effects. The subpicosecond period and the phase of the Rabi oscillations are controlled by the properties of the midinfrared driving pulse.

of more than 20% in the last few years. [1,2] Hybrid lead halide perov skites typically have a 3D ABX 3 (where, A = CH 3 NH 3 + (MA), B = Pb, and X = Cl, Br, and I) crystal structure con sisting of [PbI 6 ] and MA + units in their lattice framework and their band gaps can be tuned by halide engineering. [3][4][5] However, the key challenge in commer cializing 3D organic-inorganic hybrid perovskite photovoltaics is related to well known issues with longterm instability of devices under ambient conditions. [6,7] Recently, another class of 2D organicinorganic hybrid perovskite counterparts have attracted attention owing to their superior ambient stability and prom ising optoelectronic properties. [8][9][10][11][12][13][14] There is now considerable interest in 2D hybrid perovskite compounds, typi cally represented by the generic for mula (Aʹ) 2 (MA) n−1 M n X 3n+1 , where Aʹ is a longchain organic spacer, MA is small organic cation, M is a divalent metal, and n is the number of perovskite layers per unit cell. [15,16] These 2D hybrid halide perovskites exhibit a characteristic quantum well (QW)like structure owing to the selfassembled periodic array of perovskite [PbI 6 ] This work reveals the intrinsic carrier transport behavior of 2D organolead halide perovskites based on phase-pure homologous (n = 1, 2, and 3) Ruddelsden-Popper perovskite (RPP) (BA) 2 (MA) n−1 Pb n I 3n+1 single crystals. The 2D perovskite field effect transistors with high-quality exfoliated 2D perovskite bulk crystals are fabricated, and characteristic output and transfer curves are measured from individual single-crystal flakes with various n values under different temperatures. Unipolar n-type transport dominated the electrical properties of all these 2D RPP single crystals. The transport behavior of the 2D organolead halide hybrid perovskites exhibits a strong dependence on the n value and the mobility substantially increases as the ratio of the number of inorganic perovskite slabs per organic spacer increases. By extracting the effect of contact resistances, the corrected mobility values for n = 1, 2, and 3 are 2 × 10 −3 , 8.3 × 10 −2 , and 1.25 cm 2 V −1 s −1 at 77 K, respectively. Furthermore, by combining temperature-dependent electrical transport and optical measurements, it is found that the origin of the carrier mobility dependence on the phase transition for 2D organolead halide perovskites is very different from that of their 3D counterparts. Our findings offer insight into fundamental carrier transport behavior of 2D organic-inorganic hybrid perovskites based on phase-pure homologous single crystals. Field Effect Transistors

Self-assembled nanocomposites have gained much attention over the past decade due to their intriguing properties and functionalities. In this work, we developed a self-assembled nanocomposite photoanode composed of an epitaxial BiVO 4 matrix embedded with WO 3 mesocrystals for photoelectrochemical (PEC) applications in the visible-light regime. The orientation of the crystal facet and interface provides a superior template to understand the intimate contact between the two constituent phases. We demonstrate that the interfacial coupling of the mesocrystal and matrix improves the separation of photoexcited carriers and the properties of charge transfer, resulting in a greatly enhanced PEC performance compared with their parent compounds. The current study demonstrates that the utilization of the interface-to-volume ratio to optimize charge interactions in the nanocomposite is essential for the advanced design of novel mesocrystal-embedded nanocomposite photoelectrodes.

In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] with the Drude model in the 200–5000 cm−1 region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm−1 especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.

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