arXiv subjects

Wang Yao

Publications and source records attributed to Wang Yao.

At least 37 records · Page 2Linked to original sources

arXiv2026

Electronic procrystalline state in moire structures

Solid state materials can display varieties of atomic structural orders ranging from crystalline to amorphous, underlying their properties and diverse functionalities. Procrystal has emerged as a new category of solids, featuring a long-range ordered lattice framework tiled with disordered atomic or molecular structures on the lattice sites, arousing great interest due to its novel structural and physical properties. However, the electronic analogue of a procrystal, dubbed as an electronic procrystalline (EPC) state, has never been experimentally observed. Here, we report the observation of an EPC state in a moire superstructure formed between a monolayer metallic NiTe2 and a superconductor NbSe2 with incommensurate lattice wavevectors. The observed EPC state exhibits a long-range periodic charge modulation at the moire scale inlaid with short-range irregular orders within each moire cell. Strikingly, the short-range charge orders inside the moire unit cells have proximately root3*root3 quasi-period, which is absent in pristine NiTe2. Intriguingly, the EPC order is also observed in the superconducting state of the moire superstructure. Furthermore, the emergent EPC state and short-range charge order, coexisting with the proximity induced superconductivity, can be precisely modulated with the thickness of NiTe2. Our findings uncover the potential of moire platform for understanding and tuning novel correlated quantum phases with this exotic procrystalline order.

cond-mat.mtrl-sci↗

arXiv2025

Bosonic Laughlin and Moore-Read states from non-Chern flat bands

The rapid advances in the study of fractional Chern insulators (FCIs) raise a fundamental question: while initially discovered in flat Chern bands motivated by their topological equivalence to Landau levels, is single- particle band topology actually a prerequisite for these many-body topological orders emergent at fractional fillings? Here, we numerically demonstrate bosonic FCIs in two types of non-Chern flat bands in honeycomb lattices, using exact diagonalization and density matrix renormalization group calculations. In a gapless flat band with a singular band touching, we observe a Laughlin state at half filling, stabilized by onsite interactions from the hard-core limit down to arbitrarily small strength. Furthermore, we report the first example of a non- Abelian FCI in a non-Chern band system: a Moore-Read state at $ν$ = 1 filling of the same singular flat band with hard-core bosons. Under lattice parameters that realize a gapped trivial band (C = 0) of exact flatness, we also find the Laughlin FCI of soft-core bosons in the isolated band limit where onsite interaction is much smaller than the band gap. In this case, the FCI forms as interacting bosons spontaneously avoid the peaks in quantum metric and Berry curvature, preferentially occupying Brillouin zone region with relatively uniform quantum geometry. Our work significantly expands the landscape for (non-)Abelian FCIs and broadens the understanding of their formation beyond the Chern band paradigm.

cond-mat.str-el↗

arXiv2025

Engineering topological exciton structures in two-dimensional semiconductors by a periodic electrostatic potential

We propose to engineer topological exciton structures in layered transition metal dichalcogenides through hybridizing different Rydberg states, which can be induced by a periodic electrostatic potential remotely imprinted from charge distributions in adjacent layers. Topological phase diagrams are obtained for potentials with various strengths and wavelengths. We find the lowest band of the interlayer exciton can become topologically nontrivial, which exhibits a small bandwidth as well as quantum geometries well suited for realizing the bosonic fractional Chern insulator. For monolayer excitons, topological bands and in-gap helical edge states can emerge near the energy of 2p states.

cond-mat.mes-hall↗

arXiv2025

Fractional Chern insulator states in an isolated flat band of zero Chern number

A flat band with Chern number $C=0$, and well isolated from the rest of Hilbert space by a gap much larger than interaction strength, is a context that has not been regarded as relevant for fractional quantum Hall physics. In this work, we demonstrate the emergence of the fractional Chern insulator (FCI) states in such a trivial flat band, using large-scale exact diagonalization (ED) and infinite density matrix renormalization group (iDMRG) simulations. The $C=0$ isolated flat band is hosted by an anisotropic fluxed dice lattice. Both the quantum metric and Berry curvature of the $C=0$ flat band have a sharp peak at the $Γ$ point, whereas in the rest of the Brillouin zone (BZ) they mimic the quantum geometry of the lowest Landau level. We consider nearest-neighbor repulsion that is weak enough to ensure the isolated-band limit is always satisfied. From the projected ED simulations at $ν_\mathrm{F}=2/3$ electron filling of the flat band (i.e. $1/3$ hole filling), we find the unexpected FCI with 3-fold ground-state degeneracy and $σ_\mathrm{H}=-1/3 (e^2/h)$. The momentum space carrier distribution shows that the quantum metric peak tends to push the interacting holes away from $Γ$ point towards the BZ regions with the nearly ``ideal'' quantum geometry, underlying the formation of FCI in the $C=0$ flat band. Besides, when tuning the single-particle anisotropy such that the quantum geometry of the $C=0$ flat band becomes less sharp around $Γ$, we find the ground state becomes a charge density wave with tripled unit cell at $ν_\mathrm{F}=2/3$. Our two-band iDMRG simulations further corroborate the FCI in the isolated $C=0$ flat band, demonstrating in such parameter regime the fractionally quantized charge pumping upon flux insertion as well as the momentum-resolved entanglement spectrum characteristic of the $1/3$ Laughlin state.

cond-mat.mes-hall↗

arXiv2025

Strong Correlation Driven Quadrupolar to Dipolar Exciton Transitions in a Trilayer Moiré Superlattice

The additional layer degree of freedom in trilayer moiré superlattices of transition metal dichalcogenides enables the emergence of novel excitonic species, such as quadrupolar excitons, which exhibit unique excitonic interactions and hold promise for realizing intriguing excitonic phases and their quantum phase transitions. Concurrently, the presence of strong electronic correlations in moiré superlattices, as exemplified by the observations of Mott insulators and generalized Wigner crystals, offers a direct route to manipulate these new excitonic states and resulting collective excitonic phases. Here, we demonstrate that strong exciton-exciton and electron-exciton interactions, both stemming from robust electron correlations, can be harnessed to controllably drive transitions between quadrupolar and dipolar excitons. This is achieved by tuning either the exciton density or electrostatic doping in a trilayer semiconducting moiré superlattice. Our findings not only advance the fundamental understanding of quadrupolar excitons but also usher in new avenues for exploring and engineering many-body quantum phenomena through novel correlated excitons in semiconducting moiré systems.

cond-mat.mes-hall↗

arXiv2025

Topological domain-wall states from Umklapp scattering in twisted bilayer graphene

Twistronics, harnessing interlayer rotation to tailor electronic states in van der Waals materials, has predominantly focused on small-angle regime. Here, we unveil the pivotal role of intervalley Umklapp scattering in large-angle twisted bilayer graphene, which governs low-energy physics and drives unconventional band topology. By constructing symmetry-constrained effective $k\cdot p$ models for $\pm 21.8^{\circ}$-twisted bilayers, we demonstrate how structural chirality imprints distinct electronic responses. The $D_6$ configuration exhibits a gapped spectrum with chiral interlayer coupling, while $D_3$ symmetric stacking configuration displays semimetallic behavior. Crucially, chirality inversion creates topological domain-wall states, which manifest as counterpropagating pseudospin modes at interfaces between oppositely twisted regions. These states, absent in untwisted bilayers, emerge from a Jackiw-Rebbi-like mechanism tied to chirality reversal. Atomistic simulations confirm these topological states and demonstrate their robustness against symmetry-breaking perturbations. The interplay between twist-induced chirality and topology opens new pathways for engineering domain-wall states in twisted materials.

cond-mat.mes-hall↗

arXiv2025

Twistronics and moiré superlattice physics in 2D transition metal dichalcogenides

The moiré superlattices formed by stacking 2D semiconducting transition metal dichalcogenides (TMDs) with twisting angle or lattice mismatch have provided a versatile platform with unprecedented tunability for exploring many frontier topics in condensed matter physics, including optical, topological and correlation phenomena. This field of study advances rapidly and a plethora of exciting experimental and theoretical progresses have been achieved recently. This review aims to provide an overview of the fundamental properties of TMDs moiré superlattices, as well as highlight some of the major breakthroughs in this captivating field.

cond-mat.mes-hall↗

arXiv2025

Observation of Cavity-Mediated Nonlinear Landau Fan and Modified Landau Level Degeneracy in Graphene Quantum Transport

Recent studies on cavity-coupled two-dimensional electron gas demonstrate that vacuum-field engineering can tailor electronic transport properties of materials. By achieving ultra-strong coupling between a terahertz resonator and mesoscopic graphene, we demonstrate that cavity vacuum fields can alter the effective degeneracies of Landau levels, resulting in a nonlinear Landau fan diagram for massless Dirac fermions while preserving quantum-Hall quantization. Specifically, by leveraging graphene's gate-tunability, we observe that quantum-Hall features, minimum longitudinal and quantized Hall conductance for a given filling factor, occur at carrier densities reduced by more than 20 percent compared to systems without cavity. Theoretical analysis attributes this effect to the virtual cavity photon mediated transitions between the non-equidistant Landau levels in graphene, significantly reducing their effective degeneracy. This study paves the way for investigating cavity quantum electrodynamics in highly tunable, atomically thin two-dimensional crystals.

cond-mat.mes-hall↗

arXiv2025

Layer Coherence Origin of Planar Hall Effect: from Charge to Multipole and Valley

We uncover a new origin of the planar Hall effect - as an intrinsic property of layer coherent electrons - that exists even in bilayer and trilayer atomically thin limit. It reforms the existing theories requiring three-dimensional orbital motion, or strong spin-orbit coupling of certain forms, which are absent in van der Waals thin films. We exemplify that the effect can be triggered by strain and interlayer sliding in twisted structures with rich tunability and strong magnitudes. Furthermore, this layer coherence mechanism broadens the conceptual framework to include planar multipole Hall effect, and valley Hall effect induced by in-plane pseudo-magnetic field, outreaching the existing mechanisms. The layer mechanism also provides a new route towards quantized Hall response upon a topological phase transition induced by in-plane magnetic field. These results unveil the unexplored potential of quantum layertronics and moiré flat band for planar transport in 2D materials.

cond-mat.mes-hall↗

arXiv2025

Fractional quantum anomalous Hall effect in a singular flat band

In the search of fractional quantum anomalous Hall (FQAH) effect, the conventional wisdom is to start from a flat Chern band isolated from the rest of the Hilbert space by band gaps, so that many-body interaction can be projected to a landscape that mimics a Landau level. Singular flat bands (SFB), which share protected touching points with other dispersive bands, represent another type of flat landscapes differing from Landau levels and Chern bands in topological and geometric properties. Here we report the finding of FQAH phases in a SFB, which emerges in the bipartite limit of the nearest-neighbor tight-binding model of twisted bilayer MoTe$_2$. At 1/3 and 2/3 filling of the SFB, FQAH effects are demonstrated using density matrix renormalisation group calculations with all bands, as well as exact diagonalization calculations with the two touching bands. Gapping the band touching can turn the SFB into a nearly flat Chern band, but counter-intuitively this suppresses the FQAH effect, as the gap opening introduces strong inhomogeneity to the quantum geometry. An optical scheme to realize such SFB for cold atoms is provided. Our findings uncover a new arena for the exploration of fractional quantum Hall physics beyond the Landau level and Chern insulator paradigms.

cond-mat.mes-hall↗

arXiv2025

Förster valley-orbit coupling and topological lattice of hybrid moiré excitons

Hybrid exciton in moiré superlattices of two-dimensional (2D) semiconductors inherits the electric dipole, strong moiré trapping, and stacking optical selection rules from its interlayer part, whereas the intralayer part is intended for enhancing optical coupling strength. Here, we show that electron-hole Coulomb exchange, or Förster coupling, within the intralayer component qualitatively alters the properties of moiré excitons, enabling their coherent hopping between moiré traps laterally separated over 10 nm and/or across layers, where their kinetic propagation is completely suppressed. Valley-flip hopping channels are found as significant as the valley-conserving ones, leading to rich possibilities to tailor valley-orbit-couplings and introduce non-trivial topology to the moiré exciton superlattice. In twisted MoTe$_2$ where hybrid moiré excitons feature a symmetry protection from radiative recombination, we show that Förster valley-orbit-coupling can give rise to a rich topological phase diagram.

cond-mat.mes-hall↗

arXiv2025

Emergent Kagome lattice and non-Abelian lattice gauge field of biexcitons in t-MoTe$_2$

Non-Abelian gauge fields, characterized by their non-commutative symmetry groups, shape physical laws from the Standard Model to emergent topological matter for quantum computation. Here we find that moiré exciton dimers (biexcitons) in twisted bilayer MoTe$_2$ are governed by a genuine non-Abelian lattice gauge field. These dipolar-bound exciton dimers, formed on bonds of the honeycomb moiré superlattice, exhibit three quadrupole configurations organized into a Kagome lattice geometry, on which the valley-flip biexciton hoppings through electron-hole Coulomb exchange act as link variables of the non-Abelian lattice gauge theory. The emergence of gauge structure here is a new possibility for composite particles, where the moiré electronic structure and interactions between the electron and hole constituents jointly enforce the underlying geometric constraint. The quadrupole nature of biexciton further makes possible local gate controls to isolate designated pathways from the extended lattice for exploiting consequences of non-commutative gauge structure including the genuine non-Abelian Aharonov-Bohm effect. This also provides a new approach for quantum manipulation of excitonic valley qubit. We show path interference on a simplest loop can deterministically transform the computational basis states into Bell states.

cond-mat.mes-hall↗

arXiv2025

Initial Error Tolerant Distributed Mean Field Control under Partial and Discrete Information

In this paper, an initial error tolerant distributed mean field control method under partial and discrete information is introduced, where each agent only has discrete observations on its own state. First, we study agents' behavior in linear quadratic mean field games (LQMFGs) under heterogeneous erroneous information of the initial mean field state (MF-S), and formulate the relationships between initial errors and systemic deviations. Next, by capturing the initial error affection on the private trajectory of an agent, we give a distributed error estimation method based on maximum likelihood estimation (MLE), where each agent estimates information errors only based on discrete observations on its private trajectory. Furthermore, we establish an error-based segmented state estimation method, design the initial error tolerant distributed mean field control method (IET-DMFC), and demonstrate the consistent property of state estimation as observation frequency increases. Finally, simulations are performed to verify the efficiency of the algorithm and the consistent properties.

math.OC↗

arXiv2025

PIONM: A Generalized Approach to Solving Density-Constrained Mean-Field Games Equilibrium under Modified Boundary Conditions

Neural network-based methods are effective for solving equilibria in Mean-Field Games (MFGs), particularly in high-dimensional settings. However, solving the coupled partial differential equations (PDEs) in MFGs limits their applicability since solving coupled PDEs is computationally expensive. Additionally, modifying boundary conditions, such as the initial state distribution or terminal value function, necessitates extensive retraining, reducing scalability. To address these challenges, we propose a generalized framework, PIONM (Physics-Informed Neural Operator NF-MKV Net), which leverages physics-informed neural operators to solve MFGs equations. PIONM utilizes neural operators to compute MFGs equilibria for arbitrary boundary conditions. The method encodes boundary conditions as input features and trains the model to align them with density evolution, modeled using discrete-time normalizing flows. Once trained, the algorithm efficiently computes the density distribution at any time step for modified boundary condition, ensuring efficient adaptation to different boundary conditions in MFGs equilibria. Unlike traditional MFGs methods constrained by fixed coefficients, PIONM efficiently computes equilibria under varying boundary conditions, including obstacles, diffusion coefficients, initial densities, and terminal functions. PIONM can adapt to modified conditions while preserving density distribution constraints, demonstrating superior scalability and generalization capabilities compared to existing methods.

cs.LG↗

arXiv2025

Magnetic and nematic order of Bose-Fermi mixtures in moiré superlattices of 2D semiconductors

We investigate the magnetic orders in a mixture of Boson (exciton) and Fermion (electron or hole) trapped in transition-metal dichalcogenides moiré superlattices. A sizable antiferromagnetic exchange interaction is found between a carrier and an interlayer exciton trapped at different high symmetry points of the moiré supercell. This interaction at a distance much shorter than the carrier-carrier separation dominates the magnetic order in the Bose-Fermi mixture, where the carrier sublattice develops ferromagnetism opposite to that in the exciton sublattice. We demonstrate the possibility of increasing the Curie temperature of moiré carriers through electrical tuning of the exciton density in the ground state. In a trilayer moiré system with a p-n-p type band alignment, the exciton-carrier interplay can establish a layered antiferromagnetism for holes confined in the two outer layers. We further reveal a spontaneous nematic order in the Bose-Fermi mixture, arising from the interference between the Coulomb interaction and p-wave interlayer tunneling dictated by the stacking registry.

cond-mat.str-el↗

arXiv2025

A Constraint-Preserving Neural Network Approach for Solving Mean-Field Games Equilibrium

Neural network-based methods have demonstrated effectiveness in solving high-dimensional Mean-Field Games (MFG) equilibria, yet ensuring mathematically consistent density-coupled evolution remains a major challenge. This paper proposes the NF-MKV Net, a neural network approach that integrates process-regularized normalizing flow (NF) with state-policy-connected time-series neural networks to solve MKV FBSDEs and their associated fixed-point formulations of MFG equilibria. The method first reformulates MFG equilibria as MKV FBSDEs, embedding density evolution into equation coefficients within a probabilistic framework. Neural networks are then employed to approximate value functions and their gradients. To enforce volumetric invariance and temporal continuity, NF architectures impose loss constraints on each density transfer function.

cs.LG↗

arXiv2025

Magnetic Bloch States at Integer Flux Quanta Induced by Super-moiré Potential in Graphene Aligned with Twisted Boron Nitride

Two-dimensional electron systems in both magnetic fields and periodic potentials are described by Hofstadter butterfly, a fundamental problem of solid-state physics. While moiré systems provide a powerful method to realize this spectrum, previous experiments, however, have been limited to fractional flux quanta regime due to the difficulty of building ~ 50 nm periodic modulations. Here, we demonstrate a super-moiré strategy to overcome this challenge. By aligning monolayer graphene (G) with 1.0° twisted hexagonal boron nitride (t-hBN), a 63.2 nm bichromatic G/t-hBN super-moiré is constructed, made possible by exploiting the electrostatic nature of t-hBN potential. Under magnetic field B, magnetic Bloch states at integer flux quanta (1-9) are achieved and observed as integer Brown-Zak oscillations, expanding the flux quanta from factions to integers. Theoretical analysis reproduces these experimental findings. This work opens new avenues to study unexplored Hofstadter butterfly, explore emergent topological order at integer flux quanta and engineer long-wavelength periodic modulations.

cond-mat.mes-hall↗

arXiv2025

Spontaneous Symmetry Breaking of Cavity Vacuum and Emergent Gyrotropic Effects in Embedded moiré Superlattices

In an electronic system, spontaneous symmetry breaking can arise from many-body interaction between electrons, leading to degenerate ground states distinguishable by emergent effects otherwise prohibited by the symmetry. Here we show that ultrastrong coupling of a mesoscopic electronic system to the vacuum of a cavity resonator can lead to another paradigm of spontaneous breaking of spatial symmetries in both systems. As a pertinent example, we consider the orbital gyrotropic effects in a moiré superlattice embedded in a THz split ring cavity resonator. Our mean-field and exact diagonalization calculations consistently demonstrate a spontaneous parity symmetry breaking in both the electronic ground state and the cavity vacuum, leading to two degenerate hybrid ground states distinguished by their opposite orbital gyrotropic Hall and magnetic effects. These sizable responses in the cavity-embedded moiré superlattice are highly tunable by both the cavity field polarization and interlayer bias on the moiré superlattice, providing an advanced platform for manipulating gyrotropic effects.

cond-mat.mes-hall↗