Graphene-Based Nanodevices in the Superconducting and Strongly Correlated Regimes
The ability to isolate and manipulate high-quality few-atoms-thick materials represents a major advance in condensed matter physics. Assembling these ultra-thin materials into van der Waals heterostructures, i.e., artificial meta-materials with atomically sharp interfaces, markedly increases the ric...
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| Format: | Thesis |
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Massachusetts Institute of Technology
2023
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| Online Access: | https://hdl.handle.net/1721.1/150713 https://orcid.org/ 0000-0001-5345-7774 |
| Summary: | The ability to isolate and manipulate high-quality few-atoms-thick materials represents a major advance in condensed matter physics. Assembling these ultra-thin materials into van der Waals heterostructures, i.e., artificial meta-materials with atomically sharp interfaces, markedly increases the rich variety of physical properties accessible in 2D systems.
Graphene, a carbon-based 2D hexagonal lattice, possesses exceptional properties that since its discovery in 2004 have attracted wide attention from the scientific and engineering communities. In this work, I present a series of experiments via two different approaches, i.e., proximity effect and twist angle design, to induce superconductivity and strong correlations in graphene-based systems—two phenomena that do not intrinsically occur in this material.
In the first part of this thesis, graphene is flanked by two superconductors and inherits their superconducting properties by proximity effect. Initially, the underlying microscopic mechanism of this phenomenon is investigated using planar tunneling spectroscopy. Then, a superconductor-graphene-superconductor junction is coupled to a superconducting circuit to create and manipulate the first graphene-based transmon qubit.
In the second part of this dissertation, the electronic properties of graphene-based systems are engineered by controlling the relative twist angle between the atomic planes. In particular, when two graphene sheets are stacked on top of each other near the “magic angle,” θ ≈ 1.1°, nearly flat bands develop, featuring superconductivity and correlated insulating states. I begin by showing that local electrostatic control over the different electronic phases of magic-angle twisted bilayer graphene (MATBG) enables the creation of versatile hyper-tunable quantum devices. I also present low-temperature transport experiments to demonstrate the emergence of two exotic electronic phases in MATBG previously observed in other strongly correlated systems: nematicity and strange metal behavior. Next, I discuss local electronic compressibility measurements, evidencing that the low-temperature correlated phases originate from a high-energy state with an unusual band population sequence. Then, I describe nano-optics studies, probing plasmonic collective excitations in MATBG. Last, the study of a novel 2D moiré system beyond MATBG, i.e., twisted bilayer-bilayer graphene, is discussed.
The contributions of this thesis to the field pertain to graphene-based superconducting devices and the MATBG rich phase diagram and may find applications in next-generation superconducting electronics. |
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