AQP Seminar: Thermal effects in graphene Josephson junctions: heat flow and prospects for ultra-sensitive bolometers

Aalto Quantum Physics Seminar (Nanotalo). Speaker: Mr. Matti Tomi (Nano, Aalto University).

Monolayer graphene has an extremely small electronic heat capacity due to its tiny volume. The heat capacity depends on carrier concentration, and reaches its minimum at the charge neutrality point, where it is limited by the concentration of residual charge carriers. The absorption of a single microwave photon can increase the temperature of a small graphene device by hundreds of millikelvins, which makes graphene a promising material for single-photon detectors and other ultra-sensitive thermal sensors. Another key parameter in bolometry and calorimetry is thermal conductance from the detector to its surroundings. Electron-phonon coupling in graphene is very weak at low temperatures and low carrier concentrations, and is often thought to form the bottleneck for thermal relaxation in graphene devices.
I will present results of our recent measurements concerning heat flow in encapsulated graphene Josephson junctions. For the thermal coupling coefficient from the electrons in graphene to the heat bath, we obtain a value that is several orders of magnitude larger than electron-phonon coupling in ideal graphene. I will also discuss different methods of detecting temperature increase in graphene, which typically does not have a resistance that would depend on temperature. 

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