Li Yan

Kondo insulators are paradigmatic strongly correlated materials, traditionally found in f-electron compounds. They originate from the hybridization between itinerant conduction electrons and localized magnetic moments, which opens a gap in the electronic spectrum. Two-dimensional moiré systems provide a new route to flat bands with strong electron correlation, which host localized moments at half filling. Here we report signatures, based on local conductivity measurements using microwave impedance microscopy, of a Kondo insulator in a moiré superlattice of monolayer WS ₂ / bilayer WSe ₂ , in which one WSe ₂ layer carries flat moiré bands and the other dispersive ones. When both layers are partially doped with two holes per moiré unit cell in total, an insulating state appears when the moiré band contains less than one hole. The insulator becomes metallic above a certain threshold magnetic field, evidence for the singlet nature of the Kondo insulator, and the observed behavior is reproduced by a periodic Anderson model. Our results open a route to simulating Kondo physics in tunable moiré systems.

Semiconducting transition metal dichalcogenide (TMDC) moiré superlattices provide an unprecedented platform for manipulating excitons. The in-situ control of moiré excitons could enable novel excitonic devices but remains challenging. Meanwhile, as dipolar composite bosons, interlayer excitons in the type-II aligned TMDC moiré superlattices exhibit strong interactions with fermionic charge carriers. Here, we demonstrate active manipulation of exciton diffusivity by tuning their interplay with correlated carriers in moiré potentials. When electrons form Mott insulators, the interlayer exciton energy is blueshifted due to strong electron-exciton repulsion, leading to the enhancement of diffusivity by as much as two orders of magnitude. In contrast, exciton diffusivity is suppressed at fractional fillings, where carriers form generalized Wigner crystals. In between fractional fillings, electrons populate all moiré traps, resulting in enhanced diffusivity with increasing carrier density, owing to the effectively reduced moiré potential confinement experienced by excitons. Our study inspires further engineering and controlling exotic excitonic states in TMDC moiré superlattices for fascinating quantum phenomena and novel excitonic devices.

In order to account for the realistic situation where herbivory increases with plant density, we present a novel delayed Gauss-type plant–herbivore model in this study that incorporates a Holling type-III functional response. The Allee effect, which greatly influences the growth of plant populations at low densities, is also taken into consideration in the model. One important development in plant growth regulation is the addition of a time delay parameter ([ ], which significantly changes system dynamics and gives rise to intricate behaviors such as Hopf bifurcation, limit cycles and periodic oscillations. Using the delay parameter as a bifurcation trigger, we analytically determine the feasible nontrivial equilibrium point and examine its stability. Our analysis shows that, as [ ] varies, the system behavior undergoes a critical transition from global stability to asymptotic stability and, ultimately, to instability via Hopf bifurcation at the interior equilibrium [ ]. These shifts provide insights into how ecological interactions and time delays influence population dynamics, and they are both analytically verified and graphically depicted. MATLAB-based numerical simulations clearly show how changes in system parameters affect stability and produce complex dynamic patterns.