Single-electron-resolved imaging of tunable 2D Wigner crystals and quantum spin liquids
Abstract
The main objective of this project is to spatially map the electronic and magnetic properties of tunable 2D Wigner crystal (WC) andquantum spin liquid (QSL) systems down to the atomic scale. WCs are insulating charge-ordered lattices of electrons that form at low electron density, whereas QSLs are frustrated Mott insulators that have no magnetic order down to T = 0 but that exhibit long-range quantum entanglement between spin centers. A central objective for WC systems is to directly image WC electronic wavefunctions andspin textures, as well as their behavior in the presence defects. We seek to visualize how WCs respond to strain, including pinningthresholds and glassy relaxation dynamics. Visualizing WC melting behavior and mixed phase coexistence is also a high priority. ForQSLs a central objective is to image the behavior of charge-neutral spin-1/2 spinon excitations. These are notoriously difficult tocharacterize since they typically don#t respond to applied fields. We will use new scanned probe techniques to image spinon quantum interference as spinons scatter off 2D surface structures, and we will test predictions that doping QSL systems should induce novel non-Fermi liquid ground states. We will test whether it is possible to observe gapped QSL behavior in materialswhose properties appear to be described by the Kitaev spin model. Our overall technical approach is centered around the use of 2D materials in single-layer and bilayer electricaldevices that are compatible with cryogenic atomically-resolved scanned probe microscopy. Thiscreates opportunities to tune charge carrier density in WCs and QSLs through electrostatic gating, as well as to induce lateral E-fields and current density via side gates and contacts. We will probe these systems in new ways, such as through the use of scanning tunneling potentiometry and scanning tunneling microscopy-based electron spin resonance (STM-ESR). We will also use Kelvin probe force microscopy (KPFM) techniques to overcome theelectrostatic perturbation induced by a metallic scanned-probe tip. Anticipated outcomes if successful include the mapping of WC charge order near melting transitions where solid andliquid phases are predicted to coexist in complex stripe and bubble patterns. We will similarly visualize mixed-phase QSL systems that combine novel liquid and solid spin phases detected through spinon quantum interference and spin-polarized tunnel current. This includes spinon Friedel oscillations and spinon-based RKKY-like coupling between spin defects. Use of hybrid magnetic/QSL structures will allow us to visualize and manipulate QSL-based Majorana fermion edge-states. These results are expected to impact DoD capabilities in the critical technologyareas of Microelectronics, Advanced Materials, and Quantum Science. The ability to spatially manipulate Majorana fermions represents an important step toward braiding them, and would be an impactful result in the area of Quantum Science. PerformingSTM-ESR measurements on finite Wigner #molecules# would be a useful step toward analyzing the effects of quantum decoherence on these novel electron-based qubit networks and would also help to advance the topic of Quantum Science. The ability to tune 2D materials between antiferromagnetism and QSL order would be a useful advancement for the DOD-relevant area of spintronics. Nanoscale spatial characterization of the nonlinear I-Vresponse of WCs (i.e., depinning) would also help to advance the DOD priority area of Microelectronics (including efforts to improve fast switching and low power performance). Our characterization of novel heterostructures that combine different single-layer materials would have a positive impact on DOD capabilities in the priorityarea of Advanced Materials.Approved for Public Release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 13, 2023
- Source ID
- N000142312869
Entities
People
- Michael F. Crommie
Organizations
- Office of Naval Research
- United States Navy
- University of California Regents