Understanding heating and cooling mechanisms in mesoscopic hybrid superconductor−semiconductor devices is crucial for their application in quantum technologies. Indeed, self-heating effects could potentially impact quasiparticle poisoning and qubit decoherence, and therefore the performance of hybrid quantum devices. In a previous work, we showed that Joule heating effects can be significant in hybrid superconductor-semiconductor devices owing to the poor thermal conductivity of superconductors. Here, we study the nature of the cooling mechanisms in different parts of a hybrid device and observe distinct behaviours for grounded and floating superconductors. To this end, we employ Joule spectroscopy, a technique developed by our group that detects superconductor-to-normal transitions in a device through the loss of Andreev excess current. We demonstrate that cooling of superconducting islands is limited by the rather inefficient electron−phonon coupling, as opposed to grounded superconductors that primarily cool by quasiparticle diffusion. Finally, we show that applied microwaves lead to similar heating effects but are affected by the interplay of the microwave frequency and the effective electron−phonon relaxation time. [Full article]
