Hexagonal Boron Nitride Slab Waveguides for Enhanced Spectroscopy of Encapsulated 2D Materials.

The layered insulator hexagonal boron nitride (hBN) is a critical substrate that brings out the exceptional intrinsic properties of two-dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDs). In this work, the authors demonstrate how hBN slabs tuned to the correct thickness act as optical waveguides, enabling direct optical coupling of light emission from encapsulated layers into waveguide modes. Molybdenum selenide (MoSe ) and tungsten selenide (WSe ) are integrated within hBN-based waveguides and demonstrate direct coupling of photoluminescence emitted by in-plane and out-of-plane transition dipoles (bright and dark excitons) to slab waveguide modes.

High-speed metamagnetic switching of FeRh through Joule heating.

Due to its proximity to room temperature and demonstrated high degree of temperature tunability, FeRh's metamagnetic ordering transition is attractive for novel high-performance computing devices seeking to use magnetism as the state variable. We demonstrate electrical control of the antiferromagnetic-to-ferromagnetic transition via Joule heating in FeRh wires. The magnetic transition of FeRh is accompanied by a change in resistivity, which can be probed electrically and allows for integration into switching devices.

Ultrasharp Lateral p-n Junctions in Modulation-Doped Graphene.

We demonstrate ultrasharp (≲10 nm) lateral p-n junctions in graphene using electronic transport, scanning tunneling microscopy, and first-principles calculations. The p-n junction lies at the boundary between differentially doped regions of a graphene sheet, where one side is intrinsic and the other is charge-doped by proximity to a flake of α-RuCl across a thin insulating barrier. We extract the p-n junction contribution to the device resistance to place bounds on the junction width.

Acoustic cavities in 2D heterostructures.

Two-dimensional (2D) materials offer unique opportunities in engineering the ultrafast spatiotemporal response of composite nanomechanical structures. In this work, we report on high frequency, high quality factor (Q) 2D acoustic cavities operating in the 50-600 GHz frequency (f) range with f × Q up to 1 × 10. Monolayer steps and material interfaces expand cavity functionality, as demonstrated by building adjacent cavities that are isolated or strongly-coupled, as well as a frequency comb generator in MoS/h-BN systems.

Direct-Write of Nanoscale Domains with Tunable Metamagnetic Order in FeRh Thin Films.

We have directly written nanoscale patterns of magnetic ordering in FeRh films using focused helium-ion beam irradiation. By varying the dose, we pattern arrays with metamagnetic transition temperatures that range from the as-grown film temperature to below room temperature. We employ transmission electron microscopy, X-ray diffraction, and temperature-dependent transport measurements to characterize the as-grown film, and magneto-optic Kerr effect imaging to quantify the He irradiation-induced changes to the magnetic order.

Unveiling Electron Optics in Two-Dimensional Materials by Nonlocal Resistance Mapping.

We propose a technique based on nonlocal resistance measurements for mapping transport in electron optics experiments. Utilizing tight-binding transport methods, we show how to use a four-terminal measurement to isolate the ballistic transport from a single lead of interest and reconstruct its contribution to the local density of states. This enables us to propose an experimentally tractable four-terminal device with via contacts for measuring Veselago lensing in a graphene - junction.

Gate-Tunable Graphene-WSe Heterojunctions at the Schottky-Mott Limit.

Metal-semiconductor interfaces, known as Schottky junctions, have long been hindered by defects and impurities. Such imperfections dominate the electrical characteristics of the junction by pinning the metal Fermi energy. Here, a graphene-WSe p-type Schottky junction, which exhibits a lack of Fermi level pinning, is studied.