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The growth of VO2 epitaxial films has been researched extensively for obtaining excellent phase-transition performance. However, previous methods typically necessitate high temperatures or post-annealing processes, which elevate both experimental complexity and cost. In this work, we prepared high-quality VO2 epitaxial films by reactive magnetron sputtering directly under a low growth temperature. Benefiting from the determination of the oxygen pressure ratio from the theoretical analysis of the sputtering process model, single-stoichiometric VO2 epitaxial films could be prepared under 450 °C with a resistance change of 103, and above 500 °C with a resistance change exceeding 104. The mechanism of achieving low-temperature growth of VO2 epitaxial films was analyzed utilizing Thornton's zone model; finally, the epitaxial characteristics of VO2 on the sapphire substrate were confirmed from in-plane and out-of-plane directions. This work presents a guideline for the low-temperature growth of VO2 epitaxial films with enhanced phase-transition performance, thereby reducing both the cost and the requirements associated with the epitaxial growth of VO2 films. [ABSTRACT FROM AUTHOR]

Organic molecular vibrations, typically occurring in the terahertz (THz) regime, can resonate with a metastructure. A hallmark Rabi splitting occurs when the coupling strength is sufficiently strong. In this work, we observe the strong coupling of localized surface plasmons (LSPs) and intermolecular vibration mode at THz on a metasurface spin-coated with organic molecule α-lactose monohydrate. Excited by transverse-electric THz waves, dispersive localized surface plasmons interact with nondispersive intermolecular vibrations and form two vibro-polariton modes. The angle-resolved transmission spectra of the coupled system are detected by using a terahertz time-domain spectrometer, demonstrating an anti-crossing effect with a clear Rabi splitting. By retrieving the coupling strength and Hopfield coefficients of polariton bands from the measured data, we further verify that these two bands originate from the strong coupling between LSPs and molecular vibration mode. Moreover, we show that it is possible to implement molecular concentration sensing based on this strong coupling effect. This study demonstrates a unique approach to investigate vibro-polaritons at the terahertz regime and provides a testbed for future applications of strong coupling effects in chemical detection and biosensing. [ABSTRACT FROM AUTHOR]

Traditional optical elements, such as waveplates and polarization beam splitters, are essential for quantum state tomography (QST). Yet, their bulky size and heavy weight are prejudicial for miniaturizing quantum information systems. Here, we introduce nondiffractive silicon metasurfaces with high transmission efficiency to replace the traditional optical elements for QST of polarization-entangled states. Two identical silicon metasurfaces are employed, and each metasurface comprises four independent districts on a micrometer scale. The unit cell of each district consists of two silicon nanopillars with different geometrical sizes and orientation angles, and the interference of the scattered waves from the nanopillars leads to a single output beam from the district with a specific polarization state with a transmission efficiency above 92%. When the two-photon polarization-entangled state shines on different districts of two metasurfaces, each photon of the photon pair interacts with the local nanopillars within the district, and the two-photon state is projected onto 16 polarization bases for state reconstruction. We experimentally demonstrate the reconstruction of four input Bell states with high fidelities. This approach significantly reduces the number of conventional optical components in the QST process and is inspiring for advancing quantum information technology. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) photodetection has attracted much attention for applications like monitoring ozone holes and light communication. Although UV photodetectors based on conventional inorganic semiconductors have been widely investigated, fast response devices with high sensitivity remain needed for UV communication systems. This Letter reports on flexible ultrathin methylammonium lead bromide(MAPbBr3)-based UV photodetectors. In the UV regime, the response time reaches 3.3/4.0 μs, and the 3 dB bandwidth is 0.22 MHz. No current degradation is detected after repeated bending cycles, indicating the excellent mechanical flexibility and reliability of flexible high-speed UV photodetectors. Moreover, MAPbBr3 nanosheet-based photodetectors have been integrated into a UV communication system as signal receivers transmitting messages encrypted by international Morse codes. These results reveal the potential of ultrathin perovskite nanosheets in developing flexible optoelectronic devices for UV communications and related applications. [ABSTRACT FROM AUTHOR]