CAREER: Microwave transmission spectroscopy of van der Waals materials

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Nontechnical abstract: We often consider electricity as flowing like water in a pipe, but this analogy breaks down when electrons interact strongly. This so-called "collective behavior" of electrons in a material often leads to exciting new electronic properties. This project uses microwave radiation to characterize these electronic phases. By understanding the collective behavior, new technology can be developed around it. This project involves early career STEM undergraduate researchers in every aspect of the research. A nanofabrication course that is cross-listed between Physics and Engineering extends the impact of this research by engaging undergraduate and graduate students in related technical fields. Educational outreach components of this project focus on K-12 students in the greater Philadelphia area through partnerships with local libraries as well as public and private schools. These events expose students to hands-on STEM activities that are directly related to the project’s research areas: nanotechnology, electronics, cryogenics, and quantum mechanics. Technical abstract: Measuring the properties of fragile electronic states in highly-interacting electronic systems is a difficult task. This project employs microwave transmission spectroscopy to study collective electronic states in van der Waals materials at low temperatures and high magnetic fields by coupling microwave radiation to the two-dimensional electron system through an adjacent coplanar waveguide. The transmission of microwave radiation is sensitive to carrier conductivity and the collective oscillations of solid phases associated with pinning to crystal impurities. This project characterizes several electronic solids in graphene and compares these results with transition metal dichalcogenides that have strong spin-orbit interaction. The research also expands the spectroscopic technique to investigate two-dimensional superconductors. This investigation revolves around the recently-questioned dissipationless state that exists below the Berezinskii–Kosterlitz–Thouless transition by measuring the frequency-dependent conductance. Several phases of both electrons and composite fermions are studied: Wigner and Skyrme crystals, stripe phases, superconducting condensates, superconducting vortex lattices, and possibly never-before-seen quantum states. This project addresses fundamental questions at the frontiers of highly interacting electronic systems in materials that will advance the field of quantum electronics and are therefore of the highest interest to broad academic and industrial communities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.