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Stacking two-dimensional crystals with a small twist produces flat electronic bands in which interactions dominate, giving correlated insulators, magnetism and superconductivity. Transport reveals where these states occur; thermodynamics reveals what they are — how much energy it costs to add an electron, how large the gaps are, and what kind of excitation closes them.
Using a scanning single-electron transistor as a local electrometer, I measured the chemical potential of these systems directly, with the spatial resolution to separate intrinsic behaviour from twist-angle disorder.
Selected results
- The many-body Hofstadter spectrum and flavour phase diagram of magic-angle twisted bilayer graphene
- Spin skyrmion gaps, evidence that the correlated insulators are strong-coupling states
- Correlated insulators and Hofstadter states in moiré semiconductors, including reentrant charge order
Approach
- Scanning SET operating in a cryogen-free dilution refrigerator
- Local chemical-potential and inverse-compressibility measurements in high magnetic fields
- Close collaboration with theory