Content of SPECIAL TOPIC — Moiré physics in two-dimensional materials in our journal

Published in last 1 year |  In last 2 years |  In last 3 years |  All Please wait a minute... For selected: Download citations EndNote Ris BibTeX Toggle thumbnails Select Valley-selective manipulation of moiré excitons through optical Stark effect Chenran Xu(徐晨燃), Jichen Zhou(周纪晨), Zhexu Shan(单哲旭), Wenjian Su(苏文健), Kenji Watanabe, Takashi Taniguchi, Dawei Wang(王大伟), and Yanhao Tang(汤衍浩) Chin. Phys. B, 2025, 34 (1): 017102.   DOI: 10.1088/1674-1056/ad7c32 Abstract （446）   HTML （418）    PDF （4387KB）（291）       Knowledge map    Semiconductor moiré superlattices provide great platforms for exploring exotic collective excitations. Optical Stark effect, a shift of the electronic transition in the presence of a light field, provides an ultrafast and coherent method of manipulating matter states, which, however, has not been demonstrated in moiré materials. Here, we report the valley-selective optical Stark effect of moiré excitons in the WSe$_{2}$/WS$_{2}$ superlattice by using transient reflection spectroscopy. Prominent valley-selective energy shifts up to 7.8 meV have been observed for moiré excitons, corresponding to pseudo-magnetic fields as large as 34 T. Our results provide a route to coherently manipulate exotic states in moiré superlattices. Select Chiral phonons of honeycomb-type bilayer Wigner crystals Dingrui Yang(杨丁睿), Lingyi Li(李令仪), Na Zhang(张娜), and Hongyi Yu(俞弘毅) Chin. Phys. B, 2025, 34 (1): 017301.   DOI: 10.1088/1674-1056/ad8eca Abstract （357）   HTML （3）    PDF （1392KB）（305）       Knowledge map    We theoretically investigated the chiral phonons of honeycomb-type bilayer Wigner crystals recently discovered in van der Waals structures of layered transition metal dichalcogenides. These chiral phonons can emerge under the inversion symmetry breaking introduced by an effective mass imbalance between the two layers or a moiré potential in one layer, as well as under the time-reversal symmetry breaking realized by applying a magnetic field. Considering the wide tunability of layered materials, the frequencies and chirality of phonons can both be tuned by varying the system parameters. These findings suggest that bilayer honeycomb-type Wigner crystals can serve as an exciting new platform for studying chiral phonons. Select Correlated physics, charge and magnetic orders in moiré kagomé systems Zhaochen Liu(刘兆晨) and Jing Wang(王靖) Chin. Phys. B, 2025, 34 (2): 027304.   DOI: 10.1088/1674-1056/ad9ffa Abstract （311）   HTML （3）    PDF （1747KB）（304）       Knowledge map    Moiré systems have emerged as an ideal platform for exploring interaction effects and correlated states. However, most of the experimental systems are based on either triangular or honeycomb lattices. In this study, based on the self-consistent Hartree-Fock calculation, we investigate the phase diagram of the kagomé lattice in a recently discovered system with two degenerate $\varGamma$ valley orbitals and strong spin-orbit coupling. By focusing on the filling factors of $1/2$, $1/3$ and $2/3$, we identify various symmetry-breaking states by adjusting the screening length and dielectric constant. At the half filling, we discover that the spin-orbit coupling induces Dzyaloshinskii-Moriya interaction and stabilizes a classical magnetic state with $120^\circ$ ordering. Additionally, we observe a transition to a ferromagnetic state with out-of-plane ordering. In the case of $1/3$ filling, the system is ferromagnetically ordered due to the lattice frustration. Furthermore, for $2/3$ filling, the system exhibits a pinned droplet state and a $120^\circ$ magnetic ordered state at weak and immediate coupling strengths, respectively. For the strong coupling case, when dealing with non-integer filling, the system is always charge ordered with sublattice polarization. Our study serves as a starting point for exploring the effects of correlation in moiré kagomé systems. Select Orbital XY models in moiré superlattices Yanqi Li(李彦琪), Yi-Jie Wang(王一杰), and Zhi-Da Song(宋志达) Chin. Phys. B, 2025, 34 (2): 027303.   DOI: 10.1088/1674-1056/ad9ffc Abstract （303）   HTML （3）    PDF （1036KB）（453）       Knowledge map    Moiré superlattices provide a new platform to engineer various many-body problems. In this work, we consider arrays of quantum dots (QD) realized on semiconductor moiré superlattices with a deep moiré potential. We diagonalize single QD with multiple electrons, and find degenerate ground states serving as local degrees of freedom (qudits) in the superlattice. With a deep moiré potential, the hopping and exchange interaction between nearby QDs become irrelevant, and the direct Coulomb interaction of the density-density type dominates. Therefore, nearby QDs must arrange the spatial densities to optimize the Coulomb energy. When the local Hilbert space has a two-fold orbital degeneracy, we find that a square superlattice realizes an anisotropic $XY$ model, while a triangular superlattice realizes a generalized $XY$ model with geometric frustration.