Resolving spin, valley, and moir\'e quasi-angular momentum of interlayer excitons in WSe2/WS2 heterostructures

Moir\'e superlattices provide a powerful way to engineer properties of electrons and excitons in two-dimensional van der Waals heterostructures. The moir\'e effect can be especially strong for interlayer excitons, where electrons and holes reside in different layers and can be addressed separately. In particular, it was recently proposed that the moir\'e superlattice potential not only localizes interlayer exciton states at different superlattice positions, but also hosts an emerging moir\'e quasi-angular momentum (QAM) that periodically switches the optical selection rules for interlayer excitons at different moir\'e sites. Here we report the observation of multiple interlayer exciton states coexisting in a WSe2/WS2 moir\'e superlattice and unambiguously determine their spin, valley, and moir\'e QAM through novel resonant optical pump-probe spectroscopy and photoluminescence excitation spectroscopy. We demonstrate that interlayer excitons localized at different moir\'e sites can exhibit opposite optical selection rules due to the spatially-varying moir\'e QAM. Our observation reveals new opportunities to engineer interlayer exciton states and valley physics with moir\'e superlattices for optoelectronic and valleytronic applications

Single-photon detection enabled by negative differential conductivity in moiré superlattices

Detecting individual light quanta is essential for quantum information, space exploration, advanced machine vision, and fundamental science. Here, we introduce a novel single photon detection mechanism using highly photosensitive non-equilibrium electron phases in moir\'e materials. Using tunable bands in bilayer graphene/hexagonal-boron nitride superlattices, we engineer negative differential conductance and a sensitive bistable state capable of detecting single photons. Operating in this regime, we demonstrate single-photon counting at mid-infrared (11.3 microns) and visible wavelengths (675 nanometres) and temperatures up to 25 K. This detector offers new prospects for broadband, high-temperature quantum technologies with CMOS compatibility and seamless integration into photonic integrated circuits (PICs). Our analysis suggests the mechanism underlying our device operation originates from negative differential velocity, and represents an important milestone in the field of high-bias transport in two-dimensional moir\'e quantum materials

Single-photon detection enabled by negative differential conductivity in moiré superlattices

Detecting individual light quanta is essential for quantum information, space exploration, advanced machine vision, and fundamental science. Here, we introduce a novel single photon detection mechanism using highly photosensitive non-equilibrium electron phases in moir\'e materials. Using tunable bands in bilayer graphene/hexagonal-boron nitride superlattices, we engineer negative differential conductance and a sensitive bistable state capable of detecting single photons. Operating in this regime, we demonstrate single-photon counting at mid-infrared (11.3 microns) and visible wavelengths (675 nanometres) and temperatures up to 25 K. This detector offers new prospects for broadband, high-temperature quantum technologies with CMOS compatibility and seamless integration into photonic integrated circuits (PICs). Our analysis suggests the mechanism underlying our device operation originates from negative differential velocity, and represents an important milestone in the field of high-bias transport in two-dimensional moir\'e quantum materials

The effect of initial phase factor on the properties of an electro-optical bistable system

The hybrid bistable system with a delay in the feedback loop, which was originally proposed and studied by Ikeda[1], has been widely investigated[2,3,4] as this system plays many common instability behaviours of nonlinear dynamical systems. There is an initial phase factor in the equation describing the system dynamics as there are for most other bistable systems, which is equivalent to the bias in the device. We report the important role played by this phase factor in the bistability and instability behaviours, especially when the input intensity of the system is modulated harmonically.</jats:p

Mechanical behavior evaluation of corrugated steel webs (CSWs) multi-cell PC box girders

Abstract In order to optimize the design of the girder bridge, based on the CSWs PC box girders bridge design parameter, the mechanical behavior of single-room girder boxes from the single cell to five cells under four different load combinations were analyzed by using the FEA. The mid-span displacement in the bottom flange, Von-mises shear stress in both corrugated web sides, normal warping stress and dead weight of the box girder were obtained. Calculation results have shown that multiplying cell numbers could increase the efficiency of prestressing and decrease the Von-mises shear stress in both corrugated web sides in some cases. However, with the cell numbers increasing, the normal warping stress under eccentric load and the dead weight of the girder increase dramatically. Finally, by utilizing the Simple Formula Method and Principal Component Analysis Method, the proper cell number for the box girder of the specified size is suggested.</jats:p

Understanding coupling dynamics of public transportation networks

Abstract Subway and bus networks work as an integrated multiplex transportation system and play an indispensable role in modern big cities. Even though a variety of works have investigated the coupling dynamics of multiplex transportation networks, empirical data that validates the determinant coupling factors are still lacking. In this paper, we employ smartcard data of 2.4 million subway and bus passengers in Shenzhen, China to study the coupling dynamics of subway and bus networks. Surprisingly, the coupling of subway and bus networks is not notably influenced by the time-varying speed ratio of the two network layers but is jointly determined by the distribution of travel demands and transportation facilities. Our findings highlight the important role of real travel demand data in analyzing the coupling dynamics of multiplex transportation networks. They also suggest that the speed ratio of different network layers, which was regarded as a key factor in determining coupling strength, has a negligible effect on travelers’ route selections, and thus the coupling dynamics of multiplex transportation networks