The recently discovered spin defects in hexagonal boron nitride (hBN), a layered van der Waals material, have great potential in quantum sensing. However, the photoluminescence and the contrast of the optically detected magnetic resonance (ODMR) of hBN spin defects are relatively low so far, which limits their sensitivity. Here we report a record-high ODMR contrast of 46% at room temperature, and simultaneous enhancement of the photoluminescence of hBN spin defects by up to 17-fold by the surface plasmon of a gold-film microwave waveguide. Our results are obtained with shallow boron vacancy spin defects in hBN nanosheets created by low-energy He + ion implantation, and a gold-film microwave waveguide fabricated by photolithography. We also explore the effects of microwave and laser powers on the ODMR, and improve the sensitivity of hBN spin defects for magnetic field detection. Our results support the promising potential of hBN spin defects for nanoscale quantum sensing.

The recently proposed concept of graphene photodetectors offers remarkable properties such as unprecedented compactness, ultrabroadband detection, and an ultrafast response speed. However, owing to the low optical absorption of pristine monolayer graphene, the intrinsically low responsivity of graphene photodetectors significantly hinders the development of practical devices. To address this issue, numerous efforts have thus far been made to enhance the light-graphene interaction using plasmonic structures. These approaches, however, can be significantly advanced by leveraging the other critical aspect of graphene photoresponsivity enhancement-electrical junction control. It has been reported that the dominant photocarrier generation mechanism in graphene is the photothermoelectric (PTE) effect. Thus, the two energy conversion mechanisms involved in the graphene photodetection process are light-to-heat and heat-to-electricity conversions. In this work, we propose a meticulously designed device architecture to simultaneously enhance the two conversion efficiencies. Specifically, a gap plasmon structure is used to absorb a major portion of the incident light to induce localized heating, and a pair of split gates is used to produce a p-n junction in graphene to augment the PTE current generation. The gap plasmon structure and the split gates are designed to share common key components so that the proposed device architecture concurrently realizes both optical and electrical enhancements. We experimentally demonstrate the dominance of the PTE effect in graphene photocurrent generation and observe a 25-fold increase in the generated photocurrent compared to the un-enhanced cases. While further photocurrent enhancement can be achieved by applying a DC bias, the proposed device concept shows vast potential for practical applications.

No abstract

Magnetism in two-dimensional van der Waals materials has received significant attention recently.The Curie temperature reported for those materials, however, has been so far remained relatively low. Here, we measure magneto-optical Kerr effects (MOKE) under perpendicular magnetic field for van der Waals ferromagnet Cr2Ge2Te6 as well as its heterostructure with antiferromagnetic insulator NiO. We observe a notable increase in both Curie temperature and magnetic perpendicular anisotropy in Cr2Ge2Te6/NiO heterostructures compared to those in Cr2Ge2Te6.Measurements on the same exfoliated Cr2Ge2Te6 flake (on a SiO2/Si substrate) before and after depositing NiO show that the hysteresis loop can change into a square shape with larger coercive field for Cr2Ge2Te6/NiO. The maximum Curie temperature (TC) observed for Cr2Ge2Te6/NiO reaches ~120 K, is nearly twice the maximum TC ~ 60 K reported for Cr2Ge2Te6 alone. Both enhanced perpendicular anisotropy and increased Curie temperature are observed for Cr2Ge2Te6 flakes with a variety of thicknesses ranging from ~5 nm to ~200 nm. The results indicate that magnetic properties of two-dimensional van der Waals magnets can be engineered and controlled by using the heterostructure interface with other materials.

Atom-like defects in two-dimensional (2D) hexagonal boron nitride (hBN) have recently emerged as a promising platform for quantum information science. Here, we investigate single-photon emissions from atomic defects in boron nitride nanotubes (BNNTs). We demonstrate the first, to the best of our knowledge, optical modulation of the quantum emission from BNNTs with a near-infrared laser. This one-dimensional system displays a bright single-photon emission, as well as high stability at room temperature, and is an excellent candidate for optomechanics. The fast optical modulation of a single-photon emission shows multiple electronic levels of the system and has potential applications in optical signal processing.