Research

Metasurface for Laser Sail Applications: Laser sails are a proposed type of spacecraft –propelled by a high-power laser– that can potentially reach relativistic speeds. Such a scheme, however, faces many challenges, and among those are the strict limitations on the sail’s mass, density, and absorptivity, as well as the ability of the sail to self-stabilize within the beam. Our research is focused on developing a thin dielectric optical metasurface as a self-stabilizing, non-absorptive laser sail. A metasurface is a material that has its optical properties dramatically altered by structuring the material on the sub-wavelength scale. The reflection and refraction of the light is controlled by engineering the local, microscopic scattering properties and arbitrary optical wave-fronts can be engineered. This local control can be used as a means of passive orientation correction and positioning of laser sails, with the deflected light imparting both forward and lateral forces selectively on various parts of the sail.

Van der Waals Hetero-structures for STM: Van der Waals hetero-structures are stacks of two-dimensional crystals. An example of this is Bilayer Graphene (BLG), which like other 2D Crystals has a melting temperature that decreases with thickness. Stacking BLG on Hexagonal Boron Nitride (hBN) allows us to see a clear topography compared to putting BLG on SiO2. Devices can be made from these stacks such as tunable transistors and optical instruments with tunable absorption properties. Studying these stacks using the STM also allows us to discover new physics such as Exciton Condensates Superconductivity and Mott Insulation. The goal of our STM measurements of BLG is to demonstrate the best possible understanding of dI/dV spectra to discover new physics. A problem with this is that the tip acts as a top gate and both band structure and doping change with the voltage probed. By extending earlier work on optics and transport measurements to the STM we will be able to discover new physics.

Screening in 2D Van Der Waals Materials: Charge interactions in atomically thin materials can be much stronger than in their 3D counterparts.  These interactions lead to novel many-body phenomena, as well as strong excitonic effects.  We develop local probe methods that can be used to directly measure the strength of those interactions by analyzing the how charge impurities perturb the local potential in 2D materials.

Coulomb Drag: By placing two sheets of conducting material close to each other with a thin insulating spacer, a system that favors highly correlated charge carriers can be created. These types of systems promote behavior that, under the right conditions, lead to a “Coulomb Drag” mechanism where current through a ‘drive’ layer is able to induce a voltage across a second ‘drag’ layer due to interlayer electron-electron scattering leading to momentum and energy transferral. Using mono or bilayer graphene as our conducting sheets and hexagonal boron nitride as our insulating spacer, we are able to tune carrier density and perform a wide range of transport measurements. When strong magnetic fields are applied to the system, such structures are theorized to host exotic states known as exciton condensate.