The emergence of two-dimensional transition metal dichalcogenide materials has sparked intense activity in valleytronics, as their valley information can be encoded and detected with the spin angular momentum of light. We demonstrate the valley-dependent directional coupling of light using a plasmonic nanowire-tungsten disulfide (WS) layers system. We show that the valley pseudospin in WS couples to transverse optical spin of the same handedness with a directional coupling efficiency of 90 ± 1%. Our results provide a platform for controlling, detecting, and processing valley and spin information with precise optical control at the nanoscale.

Confining photons in the smallest possible volume has long been an objective of the nanophotonics community. In this Letter, we propose and demonstrate a three-dimensional (3D) gap-plasmon antenna that enables extreme photon squeezing in a 3D fashion with a modal volume of 1.3 × 10(-7) λ(3) (∼4 × 10 × 10 nm(3)) and an intensity enhancement of 400 000. A three-dimensionally tapered 4 nm air-gap is formed at the center of a complementary nanodiabolo structure by ion-milling 100 nm-thick gold film along all three dimensions using proximal milling techniques. From a 4 nm-gap antenna, a nonlinear second-harmonic signal more than 27 000-times stronger than that from a 100 nm-gap antenna is observed. In addition, scanning cathodoluminescence images confirm unambiguous photon confinement in a resolution-limited area 20 × 20 nm(2) on top of the nano gap.

The quantum plasmonics field has emerged and been growing increasingly, including study of single emitter-light coupling using plasmonic system and scalable quantum plasmonic circuit. This offers opportunity for the quantum control of light with compact device footprint. However, coupling of a single emitter to highly localized plasmonic mode with nanoscale precision remains an important challenge. Today, the spatial overlap between metallic structure and single emitter mostly relies either on chance or on advanced nanopositioning control. Here, we demonstrate deterministic coupling between three-dimensionally nanofocused plasmonic modes and single quantum dots (QDs) without any positioning for single QDs. By depositing a thin silver layer on a site-controlled pyramid QD wafer, three-dimensional plasmonic nanofocusing on each QD at the pyramid apex is geometrically achieved through the silver-coated pyramid facets. Enhancement of the QD spontaneous emission rate as high as 22 ± 16 is measured for all processed QDs emitting over ∼150-meV spectral range. This approach could apply to high fabrication yield onchip devices for wide application fields, e.g., high-efficiency light-emitting devices and quantum information processing.exciton-photon coupling | plasmonic nanofocusing | deterministic coupling | single-quantum emitter | Purcell effect S olid-state quantum photon sources based on semiconductor quantum dots (QDs) are a promising platform to realize scalable quantum technology (1-7). However, owing to the extremely small size of QDs (a few tens of nanometers) compared with the wavelength of light (a few hundreds of nanometers), the QD interaction with the photon field is very poor. This poor interaction results in rather low intrinsic spontaneous emission (SE) rates (8, 9), limiting the optical properties of single QDs: low repetition rate, higher sensitivity to thermally activated nonradiative processes and to dephasing from solid-state environment, etc. To overcome these limitations, there have been extensive efforts during the past decade to achieve deterministic coupling of a QD to intense photonic modes for strong Purcell effect (10-13), which demands spectral and spatial overlap between them. Due to the uncertainty of the size and position of the QD, it is still quite challenging and requires sophisticated control techniques, such as scanning probe microscopy and nanoscale positioning system (12,14,15). Therefore, demonstration of deterministic coupling is limited to few devices because the process has to be customized for each QD on the wafer.Nanofocusing of surface plasmon polaritons, beyond the light diffraction limit, has recently seen rapid development. This nanofocusing can be achieved using various tapered metallic structures, such as a sharp metal edge, V-shaped wedges, and tapered waveguides (16-21). Tapering a metallic structure in all three dimensions, instead of only two, is considered ideal for ultimate light focusing (20, 21). The resulting extremely small mode volume can permit strong coupl...

White light-emitting diodes (LEDs) are becoming an alternative general light source, with huge energy savings compared to conventional lighting. However, white LEDs using phosphor(s) suffer from unavoidable Stokes energy converting losses, higher manufacturing cost, and reduced thermal stability. Here, we demonstrate electrically driven, phosphor-free, white LEDs based on three-dimensional gallium nitride structures with double concentric truncated hexagonal pyramids. The electroluminescence spectra are stable with varying current. The origin of the emission wavelength is studied by cathodoluminescence and high-angle annular dark field scanning transmission electron microscopy experiments. Spatial variation of the carrier injection efficiency is also investigated by a comparative analysis between spatially resolved photoluminescence and electroluminescence.