Superconductivity often occurs close to broken-symmetry parent states and is especially common in doped magnetic insulators 1 . When twisted close to a magic relative orientation angle near !°, bilayer graphene has flat moiré superlattice minibands that have emerged as a rich and highly tunable source of strong correlation physics 2-5 , notably the appearance of superconductivity close to interaction-induced insulating states. Here we report on the fabrication of bilayer graphene devices with exceptionally uniform twist angles. We show that the reduction in twist angle disorder reveals insulating states at all integer occupancies of the four-fold spin/valley degenerate flat conduction and valence bands, i.e. at moiré band filling factors # = %, ±!, ±(, ±), and superconductivity below critical temperatures as high as ~ 3 K close to -2 filling. We also observe three new superconducting domes at much lower temperatures close to the # = % and # = ±! insulating states. Interestingly, at # = ±! we find states with non-zero Chern numbers. For # = −! the insulating state exhibits a sharp hysteretic resistance enhancement when a perpendicular magnetic field above 3.6 tesla is applied, consistent with a field driven phase transition. Our study shows that symmetry-broken states, interaction driven insulators, and superconducting domes are common across the entire moiré flat bands, including near charge neutrality.

Nanomechanical resonators are used with great success to couple mechanical motion to other degrees of freedom, such as photons, spins, and electrons [1,2]. Mechanical vibrations can be efficiently cooled and amplified using photons, but not with other degrees of freedom. Here, we demonstrate a simple yet powerful method for cooling, amplification, and self-oscillation using electrons. This is achieved by applying a constant (DC) current of electrons through a suspended nanotube in a dilution fridge.We demonstrate cooling down to 4.6 ± 2.0 quanta of vibrations. We also observe selfoscillation, which can lead to prominent instabilities in the electron transport through the nanotube. We attribute the origin of the observed cooling and self-oscillation to an electrothermal effect. This work shows that electrons may become a useful resource for quantum manipulation of mechanical resonators. * These authors contributed equally to this work. 1 arXiv:1903.04892v1 [cond-mat.mes-hall]

Mechanical resonators based on a single carbon nanotube are exceptional sensors of mass and force. The force sensitivity in these ultralight resonators is often limited by the noise in the detection of the vibrations. Here, we report on an ultrasensitive scheme based on a RLC resonator and a low-temperature amplifier to detect nanotube vibrations. We also show a new fabrication process of electromechanical nanotube resonators to reduce the separation between the suspended nanotube and the gate electrode down to ∼150 nm. These advances in detection and fabrication allow us to reach displacement sensitivity. Thermal vibrations cooled cryogenically at 300 mK are detected with a signal-to-noise ratio as high as 17 dB. We demonstrate force sensitivity, which is the best force sensitivity achieved thus far with a mechanical resonator. Our work is an important step toward imaging individual nuclear spins and studying the coupling between mechanical vibrations and electrons in different quantum electron transport regimes.

We report on a nanomechanical engineering method to monitor matter growth in real time via e-beam electromechanical coupling. This method relies on the exceptional mass sensing capabilities of nanomechanical resonators. Focused electron beam-induced deposition (FEBID) is employed to selectively grow platinum particles at the free end of singly clamped nanotube cantilevers. The electron beam has two functions: it allows both to grow material on the nanotube and to track in real time the deposited mass by probing the noise-driven mechanical resonance of the nanotube. On the one hand, this detection method is highly effective as it can resolve mass deposition with a resolution in the zeptogram range; on the other hand, this method is simple to use and readily available to a wide range of potential users because it can be operated in existing commercial FEBID systems without making any modification. The presented method allows one to engineer hybrid nanomechanical resonators with precisely tailored functionalities. It also appears as a new tool for studying the growth dynamics of ultrathin nanostructures, opening new opportunities for investigating so far out-of-reach physics of FEBID and related methods.

We report the observation of an intriguing behavior in the transport properties of nanodevices operating in a regime between the Fabry-Pérot and the Kondo limits. Using ultrahigh quality nanotube devices, we study how the conductance oscillates when sweeping the gate voltage. Surprisingly, we observe a fourfold enhancement of the oscillation period upon decreasing temperature, signaling a crossover from singleelectron tunneling to Fabry-Pérot interference. These results suggest that the Fabry-Pérot interference occurs in a regime where electrons are correlated. The link between the measured correlated Fabry-Pérot oscillations and the SU(4) Kondo effect is discussed.