Local magnetic measurements of superconductivity in van der Waals heterostructures

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Non-technical Abstract: The growing family of so-called van der Waals (vdW) materials offers a versatile platform to discover and explore new electronic phenomena in two dimensions which may enable significant advances in future electronic devices. A vdW material has strong bonding within the plane, while the planes are held together by weak vdW forces. This makes it possible to isolate individual sheets through mechanical exfoliation from a bulk crystal and build heterostructures containing different vdW materials by stacking one sheet at a time. In heterostructures, physical properties going beyond the intrinsic properties of a single material may be realized. This project focuses on superconductivity in vdW heterostructures. The main tool the team uses is a scanning magnetic probe, a superconducting quantum interference device, that offers the sensitivity required to measure the magnetic signatures of superconductivity in vdW heterostructures. This tool allows the team to explore how the superconducting state in a vdW material is modified through electrostatic gating, tuning the twist angle between stacked layers, number of layers, applied uniaxial strain as well as proximity with a magnetic layer and layers that have strong spin-orbit coupling. The ultimate goal is to realize, enhance and understand novel superconducting states in vdW heterostructures. This project trains graduate and undergraduate students in areas of scientific and technological importance including materials science, scanning probe microscopy and nanoscience. In addition, this project includes an education and outreach component that will provide hands-on science activities aimed at K-12 students. Technical Abstract: Van der Waals (vdW) materials and heterostructures offer a versatile platform to explore and realize unconventional superconductivity, due to the large library of layered materials available for stacking and a range of available tuning parameters that can further modify electronic properties. The extremely low sample volume of vdW devices poses a challenge in using conventional techniques beyond electrical transport to characterize their superconducting properties. This project uses local magnetic measurements enabled by scanning superconducting quantum interference device microscopy to directly probe properties of the superfluid in a large range of vdW superconductors. These measurements provide insights in how the superconducting order can be modified through electrostatic gating, tuning the twist angle between stacked layers, the number of layers, applied uniaxial strain as well as through proximity with a magnetic layer and layers that have strong spin-orbit coupling. This project also takes first steps towards phase-sensitive measurements of the superconducting order parameter in vdW superconductors, which can provide unambiguous characterization of the superconducting pairing symmetry.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.