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Chiral light-matter interactions supported by topological edge modes at the interface of valley photonic crystals provide a robust method to implement the unidirectional spin transfer. The valley topological photonic crystals possess a pair of counterpropagating edge modes. The edge modes are robust against the sharp bend of 60 ° and 120 ° , which can form a resonator with whispering gallery modes. Here, we demonstrate the asymmetric emission of chiral coupling from single quantum dots in a topological resonator by tuning the coupling between a quantum emitter and a resonator mode. Under a magnetic field in Faraday configuration, the exciton state from a single quantum dot splits into two exciton spin states with opposite circularly polarized emissions due to the Zeeman effect. Two branches of the quantum dot emissions couple to a resonator mode in different degrees, resulting in an asymmetric chiral emission. Without the demanding of site-control of quantum emitters for chiral quantum optics, an extra degree of freedom to tune the chiral contrast with a topological resonator could be useful for the development of on-chip integrated photonic circuits. [ABSTRACT FROM AUTHOR]

Chiral light–matter interaction between photonic nanostructures with quantum emitters shows great potential to implement spin–photon interfaces for quantum information processing. Position-dependent spin momentum locking of the quantum emitter is important for these chiral coupled nanostructures. Here, we report the position-dependent chiral coupling between quantum dots (QDs) and cross waveguides both numerically and experimentally. Four quantum dots distributed at different positions in the cross section are selected to characterize the chiral properties of the device. Directional emission is achieved in a single waveguide and in both two waveguides simultaneously. In addition, the QD position can be determined with the chiral contrasts from four outputs. Therefore, the cross waveguide can function as a one-way unidirectional waveguide and a circularly polarized beam splitter by placing the QD at a rational position, which has potential applications in spin-to-path encoding for complex quantum optical networks at the single-photon level. [ABSTRACT FROM AUTHOR]

We report an investigation of the photoresponse of a GeSn film with a graphene layer placed on top and a thin GeO2 layer sandwiched between them. Both wavelength- and power-dependent amplification of the photocurrent are demonstrated. These results are associated with the spatial separation of photoexcited electrons and holes enabled by the thin oxide layer, where electrons and holes accumulate in graphene and the GeSn film, respectively. This spatial separation of negative and positive charges generates a mutual gating that increases the number of carriers in both layers, yielding the amplification observed in the measurement. A quantitative method based on an equivalent circuit model is provided, and the numerical results agree well with the experimental data. Our results represent an advance toward the realization of high-performance heterostructured photodetectors, and the modeling provides a framework for analyzing the photodetection capability of other two-dimensional materials on semiconductor films. [ABSTRACT FROM AUTHOR]

The valley of transition metal dichalcogenides provides an additional platform to manipulate spin due to its unique selection rule. Normally, intralayer optical transitions in the magnetic field show a Zeeman splitting with a g factor of about −4. Here, we report a remarkable valley Zeeman effect exhibited by the splitting of excitonic emission in a bilayer WS2, with a value of g factor as large as −16.5. The observed large g factor results from the interlayer recombination, as the conduction band and the valence band are modified in opposite directions by the magnetic field in different layers. The interlayer recombination is due to the defect induced inversion symmetry breaking, which is theoretically not accessible in ideal bilayer WS2 with inversion symmetry. The large g factor of interlayer emission offers potential benefits for future optical spin control and detection. [ABSTRACT FROM AUTHOR]

We report on an increase in the carrier tunneling time in a single quantum dot (QD) with a magnetic field in Faraday geometry using photocurrent spectroscopy. A nearly 60% increase in hole tunneling time is observed with an applied magnetic field equal to 9 T. For a truncated pyramid QD, the hole tunnels out faster at the lateral edge of the QD due to the reduced barrier height. The magnetic field in Faraday geometry shrinks the hole wave function at the center of the QD plane, which weakens the tunneling at the lateral edge and increases the average tunneling time. This mechanism also works for the electron, but the effect is smaller. The electron wave function is more localized at the center of the QD due to the uniform confining potential; therefore, the relatively weak shrinkage caused by the magnetic field does not reduce the tunneling rate significantly. [ABSTRACT FROM AUTHOR]

We present a method to theoretically achieve multispectral ultra-narrowband near-unity absorption in metal structure with deep-subwavelength plasmonic nanocavities (i.e., volumes < λ³/20000) for high-quality sensing. The concept is based on the combined excitation of multiple plasmon resonances and high optical field confinement by an array of hexagonal non-close-packed cross-shape nanocavities on an opaque metal film. A multispectral plasmonic nano-sensor with high refractive index sensitivity (538nm/RIU) and figure of merit (58) in the optical region is obtained with the minimum bandwidth of 8nm, which offers new perspectives for achieving ultra-compact efficient biosensors. [ABSTRACT FROM AUTHOR]