Periodic Reporting for period 2 - QUAHQ (PROBING EXOTIC QUANTUM HALL STATES WITH HEAT QUANTUM TRANSPORT)
Période du rapport: 2020-08-01 au 2022-01-31
The goal of the project QUAHQ is to tackle this experimental issue on a material that has driven a very large amount of novel research in the past decade, due to the many promises it holds both for fundamental and applied electronics. Under high magnetic field and at cryogenics temperatures, graphene can host electrically insulating, strongly correlated electronic states. These states are expected to host a number of charge neutral collective modes which can carry heat across the sample, and that directly reflect the intrinsic microscopic nature of the correlated states.
To probe these collective modes, we perform heat transport measurements in ultra-high quality graphene samples, cooled down to extremely low temperatures, and immersed in high magnetic fields. We are focusing our efforts on two classes of correlated states in graphene: the so-called "nu=0" state of the quantum Hall effect, which arises in a very peculiar point of the band structure of graphene where its valence and conduction bands touch one another; and fractional quantum Hall states, where interactions become dominant and give rise to excitations on the edge of the sample which have fractional charges.
We now routinely measure the thermal conductance of chiral edge channels of the quantum Hall effect, for fully filled Landau levels, for partially filled Landau levels where spin and valley symmetries are broken, as well as , since very recently for fractional quantum Hall states. The obtained base electronic temperature (11 mK) is very close to the base temperature of the refrigerator, and among the lowest obtained in a cryogen free system under high magnetic field. This places us in a very competitive position with respect to other groups performing heat transport measurement in graphene.