Correlated electron-hole State in Twisted Double Bilayer Graphene

When twisted to angles near 1◦, graphene multilayers provide a window on electron correlation physics. Here we report the discovery of a correlated electron-hole state in double bilayer graphene twisted to 2.37 ◦. At this angle the moir´e states retain much of their isolated bilayer character, allow- ing their bilayer projections to be separately controlled by gates. We use this property to generate an energetic overlap between narrow isolated electron and hole bands with good nesting properties. Our measurements reveal the formation of ordered states with reconstructed Fermi surfaces, con- sistent with a density-wave state. This state can be tuned without introducing chemical dopants, enabling studies of correlated electron-hole states and their interplay with superconductivity.We acknowledge financial support from the European Graphene Flagship, the Swiss National Science Foundation via NCCR Quantum Science. P. Rickhaus acknowledges financial support from the ETH Fellowship program. Growth of hexagonal boron nitride crystals was supported by the Elemental Strategy Initiative conducted by MEXT, Japan and the CREST (JPMJCR15F3), JST. AHM and JZ were supported by the National Science Foundation through the Center for Dynamics and Control of Materials, an NSF MRSEC under Co- operative Agreement No. DMR-1720595 and by the Welch Foundation under grant TBF1473.Center for Dynamics and Control of Material

Multi-constrained optimal control of 3D robotic arm manipulators

This paper presents a generic method for optimal motion planning for three-dimensional 3-DOF multi-link robotic manipulators. We consider the operation of the manipulator systems, which involve constrained payload transportation/ capture/release, which is a subject to the minimization of the user-defined objective function, enabling for example minimization of the time of the transfer and/or actuation efforts. It should be stressed out that the task is solved in the presence of arbitrary multiple additional constraints. The solutions of the associated nonlinear differential equations of motion are obtained numerically using the direct transcription method. The direct method seeks to transform the continuous optimal control problem into a discrete mathematical programming problem, which in turn is solved using a non-linear programming algorithm. By discretizing the state and control variables at a series of nodes, the integration of the dynamical equations of motion is not required. The Chebyshev pseudospectral method, due to its high accuracy and fast computation times, was chosen as the direct optimization method to be employed to solve the problem. To illustrate the capabilities of the methodology, maneuvering of RRR 3D robot manipulators were considered in detail. Their optimal operations were simulated for the manipulators, binded to move their effectors along the specified 2D plane and 3D spherical and cylindrical surfaces (imitating for example, welding, tooling or scanning robots)