Pomeranchuk cooling for ultralow electron temperatures in twisted bilayer graphene

• Applicant: Robin Joey Dolleman, Ph.D.
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544940953

The primary objective of this proposal is to harness the Pomeranchuk effect in twisted bilayer graphene to realize a heat cycle that is capable of lowering the material's electron temperature. The Pomeranchuk effect is a phenomenon where a change in electron density causes a large change in the entropy of the electron gas. The proposed process leverages electrostatic gating to locally induce an increase in electron gas entropy, causing the electrons to absorb heat from their environment which lowers the electron temperature of the environment. This heat is subsequently released in another part of the device to facilitate the cooling cycle. To achieve this, the project will commence with in-depth measurements of the electron gas's electrochemical potential and entropy within twisted bilayer graphene. These measurements will guide the optimization of cooling conditions. Additionally, we aim to investigate and refine fabrication techniques to minimize undesirable Joule heating. The next crucial phase involves the development of advanced temperature-sensing methods, specifically focusing on quantum dot and superconducting junctions. These sensing devices will be integrated and gate-defined within the twisted bilayer graphene, capitalizing on its electrostatic tunability as a cornerstone of the project. In the final stage, the project will concentrate on creating and detecting temperature gradients using the Pomeranchuk effect. Furthermore, we aim to reach the lowest attainable electron temperature by implementing efficient heat sinking mechanisms within the device. This multifaceted approach seeks to push the boundaries of electron temperature reduction in twisted bilayer graphene, with potential implications for 2D materials research and various applications in the realm of quantum technologies.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Christoph Stampfer