Mathematics and Natural Sciences
Sergei Urazhdin, PhD
PROFESSOR, EMORY COLLEGE OF ARTS AND SCIENCES, PHYSICS
Direct observation of the Berezinskii-Kosterlitz-Thouless state
Kosterlitz and Thouless received the 2016 Nobel prize in Physics for the prediction of the Berezinskii-Kosterlitz-Thouless (BKT) transition – a topological phase transition expected for two-dimensional (2d) systems characterized by the single-parameter continuous [U(1)] symmetry. Instead of the typical transition from a disordered high-temperature state to the ordered low-temperature state, such systems are expected to exhibit a unique strongly-interacting vortex-antivortex plasma state at temperatures above a certain transition temperature TBKT, which becomes frozen below TBKT. This state has far-reaching implications for our understanding of symmetry and topology in collective phenomena, as well as applications, but it has been never directly observed.
The project will create and directly observe the BKT state in magnetic systems by utilizing a state-of-art magnetic imaging setup designed and nearly completed in the PI’s laboratory. Three main issues prevent the BKT state in magnetic systems: i) dipolar fields, ii) anisotropy favoring the multidomain state, and iii) history-dependence of the magnetic state (glassiness). The first two issues will be overcome by developing magnetic materials characterized by almost vanishing magnetization and random magnetic anisotropy and/or frustration of exchange interaction which are expected to destabilize the domain state and stabilize the BKT state. The last issue will be overcome by utilizing a specially devised magnetic field sequence enabling generation of vortex-antivortex pairs. The proposed observation of the magnetic BKT state will provide the first direct confirmation of the long-standing predictions, and facilitate the development of novel highly efficient analog magnetic memory for neuromorphic device applications.
Lili Wang, PhD
ASSISTANT PROFESSOR, EMORY COLLEGE OF ARTS AND SCIENCES, CHEMISTRY
Pseudo-Solid-State Optical Upconversion for Solar Energy Harvesting
Optical upconversion is a process that converts two or more low-energy photons into a singular, high-energy photon. By exploiting sub-bandgap photons, optical upconversion holds significant promise in overcoming the Shockley–Queisser limit imposed on the maximum power conversion efficiencies of conventional single-junction solar cells. Among various upconversion approaches, quantum dot (QD)-sensitized triplet–triplet annihilation is the most promising avenue toward achieving upconversion beyond the silicon bandgap. Despite the superior upconversion efficiency demonstrated in solution, the translation to solid-state upconversion is hindered by a notable decrease in performance. This decrease is attributed to restricted exciton diffusion and parasitic back energy transfer near the device interface, limiting the practical application of solid-state upconversion devices. In this proposal, we will employ chemical design at the mesoscale to develop pseudo-solid-state devices, effectively mitigating the efficiency constraints in solid-state devices. Specifically, we plan to confine the QD-sensitized upconversion process within nanodroplet-containing organic glasses, leveraging the high efficiency of solution-phase upconversion while simultaneously providing the structural integrity required for seamless integration with devices—something that the solution phase alone lacks. Fundamental photophysics of these devices featuring different nanodroplet sizes will be investigated to reveal the influence of mesoscale confinement on diffusion-mediated upconversion processes and inform the optimal design strategy. Our approach represents a pivotal advancement in expediting the integration of upconversion into commercial applications. We anticipate preliminary results from the proposed research to lead to competitive funding from federal agencies.
Kristin Williams, PhD
ASSISTANT PROFESSOR, EMORY COLLEGE OF ARTS AND SCIENCES, COMPUTER SCIENCE
Tangible Access to Data Physicalization
Data permeates every corner of society, but is largely communicated through visual graphics. To those without data literacy skill (32% of the US population) or who are blind or visually impaired (BVI), this visual bias impacts central daily activities like those found in learning, consuming news media, and synthesizing financial trends. To provide alternative routes to access data, data physicalization represents data tangibly to communicate via tactile perception. However, through its visual bias, data physicalization relies wholly on visual expression. The role of tangible access could be better leveraged for data physicalization’s communication by investigating ways to provide tangible access to data exploration and synthesis. The project advances a research agenda to both uncover fundamental features of data physicalization that enable tangible access and to use this work to inform the design of toolkits for composing data physicalizations. To do so, it will 1) uncover the constraints tactile perception imposes on data physicalization designs, 2) chunk and group both active and passive touch to develop exploration command sets and features sets for data physcalizations, and 3) develop a toolkit and fabrication pipeline for composing the primitive building blocks of data physicalizations to support data synthesis. The results of this project will contribute a form of tangible communication that is informed by the route from low-level tactile perception to the elementary building blocks of data physicalization. This will enable effective guidance on tactile encodings to support both active and passive touch when exploring data physicalizations.