On-chip single electron transistors as a thermodynamic probe of van der Waals materials

The single electron transistor (SET) is an exceptionally sensitive electrometer. It can measure important thermodynamic properties, such as the electronic compressibility and the chemical potential, which can be used to extract entropy and charge gaps in solid state systems. SETs have proven particularly powerful in characterizing two-dimensional electron gasses by, for example, identifying elusive fractional quantum hall states, measuring the thermodynamics of magnons in graphene, and recently observing fractional Chern insulators in magic-angle twisted bilayer graphene. By fabricating SETs directly on a sample, one can straightforwardly integrate this measurement capability into ultra-low temperature and high magnetic field environments. In this talk, I will discuss fabrication of these sensors on van der Waals heterostructures. I will also present compressibility data using on-chip aluminum SETs to study graphene in the quantum hall regime and discuss the relevance of this technique to elucidating open questions regarding the thermodynamics of magnon excitations in this system.