Imaging Electronic Wavefunctions in 2D Semiconducting Devices at High Magnetic Field

Nontechnical Description: The goal of this project is to better understand how electrons behave in two-dimensional (2D) electrical devices fabricated from single-layer materials that are only a few atoms thick. This will be accomplished by using scanning tunneling microscopy (STM) to directly image the electrons in these devices in the presence of strong magnetic fields. This topic has broad significance because 2D devices are strong candidates for enabling new technological applications that offer better device miniaturization, higher energy efficiency, faster communications, and new methods for manipulating quantum information. Much of the promise of 2D devices stems from the fact that electrons in 2D devices behave very differently than electrons in more conventional “bulk” three-dimensional (3D) devices. Such new behavior provides technological opportunity but also creates the need for new scientific methods to characterize it effectively. This research is aimed at performing precisely such characterization. For example, the ability to directly visualize what electrons are doing in these devices allows theoretical predictions to be tested in an unambiguous way. In addition to providing new insight into the electronic properties of 2D devices through such testing, this project is also aimed at training students and postdocs in cutting-edge experimental techniques that will increase the technical capabilities of the US workforce. Technical Description: This project is focused on performing scanning tunneling microscopy (STM) based visualization of correlated electron behavior in single-layer and bilayer transition metal dichalcogenide (TMD) field-effect transistor (FET) devices at low temperature and in high magnetic field. The main goals of the project are to explore how applied fields affect electronic wave-functions in both single-layer and moiré-based homobilayer systems, including local quantum spin behavior. The main approach involves fabricating ultraclean 2D devices from exfoliated layers of TMD materials by incorporating them into stacked, open-face (i.e., surface accessible) FET device arrangements. These devices are integrated into a cryogenic STM that allows electronic wave-functions to be imaged with atomic resolution. Such an approach allows the measurement of fundamental quantities such as Landau level formation, quasiparticle interference, and Wigner crystal formation. Visualizing the competition between topological physics and strongly correlated behavior is uniquely effective for testing theoretical predictions involving both strong spin-orbit coupling and strong electron-electron interactions. Such imaging, for example, allows competing groundstates that exist in inhomogeneous systems, such as charge density wave formation, novel magnetism, and superconductivity, to be clearly differentiated. Direct characterization of local magnetic excitations in these materials are also essential for evaluating their potential use in manipulating quantum information for future technological applications. The main intellectual merit of this research lies in the insights gained by imaging new physical regimes of local electronic and magnetic behavior for 2D semiconducting devices in high field, an area that has been largely unexplored by STM techniques up to now. 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. NSF Award ID: 2528960 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Michael Crommie | Institution: University of California-Berkeley, BERKELEY, CA | Award Amount: $412,800 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2528960 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2528960.html