Dynamically Tunables Meta-Surfaces : The optical properties of atomically thin materials and complex oxides are often determined by localized modes called 'plasmons' or 'polaritons'. When these materials are structured at the nano-scale to create a 'meta-material' or, in 2D, a 'meta-surface', those localized features can drive large macroscopic changes in the index of refraction of the material, and often such effects are tunable, such that the response changes in the presence of an applied field. We seek to devise tunable 'meta-surfaces' that can control the phase and intensity of reflected or absorbed light across a wide range of frequencies. The realization of such a device would play a critical role in creating holographic displays, cloaking materials, and new incandescent light sources.
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Novel Impurity States: Donor and acceptor states in conventional semiconductors play a critical role in the creation of LEDs, transistors, diodes, solar cells, and many other solid state devices. In low dimensional materials and in materials with strong electron-electron interactions, the behavior of such impurity states is much more diverse, with states forming that have novel electronic, optical and magnetic behavior. We use scanning tunneling microscopy (STM) to search for such new states, which often cannot be detected in macroscopic measurements. In cases where a state has been theoretically predticted, but cannot be realized through conventional material growth methods, we use the STM tip to manipulate atoms in or on a material such that those states are realized, and can be probed directly. Just as donor and acceptors are critical for the creation of p-n junctions, new impurity states could allow for the creation of new classes of devices with useful properties.
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Quantum Phenomena in Highly Correlated and Layered 2D Materials: Electron-electron, spin-spin and spin-orbit interactions in materials can allow quantum phenomena to become emergent. Famous examples of such behavior includes superconductivity and topological insulators, where local interactions between particles create dramatic effects that are easily detected macroscopically. We seek to pattern and layer materials in orderings that optimize such interactions, with the aim of creating new magnetic or electronic quantum phases of matter. To guide the creation of such materials, we use local probes (such as STM and AFM) to precisely measure the interaction strength between particles as parameters are varied. Specific aims are to realize half-metallic systems, exciton insulator phases, and surface quantum spin buses.
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