Giant magnetic field from moir\'e induced Berry phase in homobilayer semiconductors

When quasiparticles move in condensed matters, the texture of their internal quantum structure as a function of position and momentum can give rise to Berry phases that have profound effects on materials properties. Seminal examples include the anomalous Hall and spin Hall effects from the momentum-space Berry phases in homogeneous crystals. Here we explore a conjugate form of electron Berry phase arising from the moir\'e pattern, the texture of atomic configurations in real space. In homobilayer transition metal dichalcogenides, we show the real-space Berry phase from moir\'e manifests as a periodic magnetic field up to hundreds of Tesla. This quantity tells apart moir\'e patterns from different origins, which can have identical potential landscape but opposite quantized magnetic flux per supercell. For low energy carriers, the homobilayer moir\'es realize topological flux lattices for the quantum spin Hall effect. An interlayer bias can continuously tune the spatial profile of moir\'e magnetic field, whereas the flux per supercell is a topological quantity that can only have a quantized jump observable at moderate bias. We also reveal the important role of the non-Abelian Berry phase in shaping the energy landscape in small moir\'e. Our work points to new possibilities to access ultra-high magnetic field that can be tailored in the nanoscale by electrical and mechanical controls

Gamma-rays from Nearby Clusters: Constraints on Selected Decaying Dark Matter Models

Recently, the Fermi-LAT collaboration reported upper limits on the GeV gamma-ray flux from nearby clusters of galaxies. Motivated by these limits, we study corresponding constraints on gamma-ray emissions from two specific decaying dark matter models, one via grand unification scale suppressed operators and the other via R-parity violating operators. Both can account for the PAMELA and Fermi-LAT excesses of e^\pm. For GUT decaying dark matter, the gamma-rays from the M49 and Fornax clusters, with energy in the range of 1 to 10 GeV, lead to the most stringent constraints to date. As a result, this dark matter is disfavored with conventional model of e^\pm background. In addition, it is likely that some tension exists between the Fermi-LAT e^\pm excess and the gamma ray constraints for any decaying dark matter model, provided conventional model of e^\pm background is adopted. Nevertheless, the GUT decaying dark matter can still solely account for the PAMELA positron fraction excess without violating the gamma-ray constraints. For the gravitino dark matter model with R-parity violation, cluster observations do not give tight constraints. This is because a different e^\pm background has been adopted which leads to relatively light dark matter mass around 200 GeV.Comment: 17 pages, 4 figures, version to appear in Phys. Lett.

Finite element analysis of coupled vibration for hoisting cable with time-varying length

The coupled axial-torsional responses of the hoisting cable with time-varying length are investigated in order to predict the longitudinal vibration more accurately. The equations of motion are formulated by Hamilton’s principle and the finite element method (FEM), in which a variable-length cable element is introduced. In order to validate this theoretical model, an ADAMS simulation model is established in the framework of the multi-body system dynamic. The result shows that the numerical solution is in reasonably good agreement with the ADAMS simulation. The frequencies of the cables with the coupling considered and neglected are analyzed by varying the excitation frequency, which indicates that the coupling effect reduces the natural frequency of the cable and the maximum amplitude shifts from the resonance region to the deceleration stage as the coupling coefficient increases

Coupled vibration of hoisting cable in cable-guided hoisting system with different swivels

In most cases, the hoisting cable in the cable-guided hoisting system is connected to the hoisting bucket with the swivel. The coupled longitudinal-torsional responses of the hoisting cable with time-varying length are investigated. The hoisting cable and two guiding cables are discretized by employing the assumed modes method, while the equations of motion are derived using Lagrange equations of the first kind, where a coefficient λ varying from 0 to 1 is introduced to represent the free spinning, proportional and self-locking swivels. The longitudinal and torsional displacements with different swivels are obtained. The results indicate the torsional displacement in the free spinning swivel is much larger than that in the proportional and there is one resonance in the former, while the longitudinal resonance in the free spinning swivel occurs earlier than that in the other two, which implies the system frequencies decrease. In addition, the presented model could also be used to describe the coupled vibration in the rigid rail-guided hoisting system but needs more modes