Periodic Reporting for period 1 - NanoMagnO (Nano-Magnetic Oscillators)
Période du rapport: 2020-04-01 au 2022-03-31
Recently, it has been discovered that when two graphene monolayers are stacked and twisted at 1.1o also known as a “magic angle”, superconductivity arises due to the long-range Moiré pattern that appears at these stacking angles. Here, interactions between electrons and their band topology give rise to novel quantum states of matter, such as strongly-correlated insulators and orbital ferromagnets, when tuning the carrier concentration with an external gate. Much of the underlying physics behind such states is yet to be understood, and the strong interactions present in these devices could be exploited to observe even more novel phenomena, making this van der Waals material an ideal platform to study and engineer new physics.
Additionally, recent reports have shown that in the naturally occurring Bernal (AB stacking) bilayer graphene, when applying an in-plane magnetic field superconductivity appears at carrier concentrations where no superconductivity would otherwise be present. This is in stark contrast to conventional superconductor theory, according to which magnetic fields destabilize and destroy superconductive states. Thus, both twisted and Bernal bilayer graphene are an ideal platform to study strong correlations, superconductivity, and how these quantum states are affected by strain.
Additionally, recent reports have shown that in the naturally occurring Bernal (AB stacking) bilayer graphene, when applying an in-plane magnetic field superconductivity appears at carrier concentrations where no superconductivity would otherwise be present. This is in stark contrast to conventional superconductor theory, according to which magnetic fields destabilize and destroy superconductive states. Thus, both twisted and Bernal bilayer graphene are an ideal platform to study strong correlations, superconductivity, and how these quantum states are affected by strain.
Using state-of-art nanofabrication, we prepared electrical and electromechanical devices based on twisted bilayer graphene1 and Bernal bilayer graphene2, with the specific aim to improve the homogeneity of such devices, with both thermal and electrical means. These devices are then measured in a He4 cryostat and a dilution refrigerator, down to 15 mK, using both DC and radiofrequency techniques. These measurements show correlated peaks, which show that the twist angle is close to the magic angle and attest to the good quality of our devices. Ultimately, the project aims to suspend such devices and tune the strain while looking for changes in the electronic states of the bilayer, but to achieve this we need to overcome additional fabrication issues.
Suspending bilayer graphene stacks is something no other group has achieved before and would allow us to study different electronic states of graphene as a function of strain. In strongly-correlated materials, quantum states such as superconductivity and magnetism can be modified via strain since it directly affects the correlations themselves. This would allow us to gain insights into the physics behind these states, and ultimately how correlations appear and behave in Moiré materials.