arXiv subjects

Wang Yao

Publications and source records attributed to Wang Yao.

At least 19 recordsLinked to original sources

arXiv2026

Superradiance fingerprints of moiré exciton-biexciton condensates: path-entangled biphoton vs. supercurrent-enabled one-photon channel

Hybrid moiré excitons form a dense array of electrically tunable single-photon emitters, entailing cooperative optical responses with intriguing consequences. With the strong dipole-dipole interaction, they also realize Bose-Hubbard quantum simulators of emergent correlated matter such as Bose-Einstein condensates (BEC). Here we reveal the characteristic cooperative radiation from condensates of hybrid moiré excitons in twisted MoTe$_2$ bilayers. In each individual moiré trap, the layer hybridization selection rule dictates that the ground-state exciton is a quantum emitter of orbital-angular-momentum photons, with an exceptionally long radiative lifetime. Ground-state emission becomes pronounced only upon forming condensates, where inter-sublattice dipole attraction and intra-sublattice repulsion together lead to the coexistence of exciton and biexciton BEC with comparable weights. The biexciton (molecular-type) BEC decays through superradiance of path-entangled biphotons, whereas the exciton (atomic-type) BEC is dark at rest and becomes superradiant when it carries a supercurrent. Our findings not only uncover a novel source of entangled light but also establish unique fingerprints for exploring the cold chemistry of atomic-molecular condensates with moiré excitons.

cond-mat.mes-hall↗

arXiv2026

Real-Space Selection Rule for Moiré Exciton-Phonon Coupling

Exciton-phonon coupling (ExPC) governs energy relaxation and exciton dynamics in photoexcited quantum materials. Recent advances have revealed rich and tunable excitonic phenomena in moiré superlattices, yet the microscopic mechanisms underlying the coupling between moiré excitons and moiré phonons remain elusive. Here, we develop a real-space representation for moiré ExPC based on a unified theoretical framework combining the many-body Bethe-Salpeter equation with phonon perturbation theory. Furthermore, we uncover a general real-space selection rule: the spatial matching of a moiré exciton's electron and hole densities with the moiré-phonon-induced potential perturbations determines their individual coupling contributions, while coherent interference between the electron and hole contributions controls the total ExPC. We demonstrate this rule in prototypical WSe2/WS2 moiré heterobilayers, revealing pronounced exciton- and phonon-mode-dependent coupling, including nearly complete suppression of ExPC through destructive electron-hole interference. These findings establish the internal electron-hole spatial configuration of moiré excitons as a key degree of freedom governing the strength and mode selectivity of their coupling to moiré phonons, opening opportunities to engineer ExPC through spatially tailored moiré potentials.

cond-mat.mtrl-sci↗

arXiv2026

Realization of quantum spin Hall insulator superlattice with emergent multigap-like helical edge states

The functional quantum spin Hall insulators (QSHI), protected by time-reversal symmetry against single-particle backscattering, hold great promise for dissipationless quantum electronics. Realization of QSHI with gapped helical edge states, which would enable deterministic on/off switching of the edge-channel conductance, is a key requirement for programmable topological circuits. Here, we report realization of superlattice-modulated QSHI HfTe5 hosting emergent multigap-like helical edge states. Using scanning tunneling microscopy and spectroscopy, we identify a reconstruction-induced periodic superlattice modulation in epitaxial monolayer HfTe5 and directly observe multiple gap-like features in the edge channel, accompanied by a series of sharp peaks in the density of states. Combined with theoretical modelling, we attribute the observed edge gap to the finite-width coupling between the two edges significantly enhanced by the superlattice modulation, whereas the sharp peaks are the manifestations of mini-gaps opening at the reduced Brillouin zone boundaries by the periodic modulation of spin-orbit coupling. Notably, these sharp peaks exhibit clear Zeeman splitting under magnetic fields, consistent with the helical nature of the topological edge states. Our results establish a viable route to engineering gapped helical edge states in QSHI and provide a promising platform for topological devices with desired on/off switchability.

cond-mat.mtrl-sci↗

arXiv2026

Asynchronous Replanning in Two Population Linear Quadratic Mean Field Games: Information Requirements and Stability

We study asynchronous continuation replanning in a two-population linear--quadratic mean field game with deterministic open-loop controls and heterogeneous, possibly erroneous initial information. At exogenous opportunities, one population recomputes its continuation response from the physical aggregate state reached, with the opponent's active plan frozen. The state--plan target needed to initialize replanning is recoverable from local aggregate observations if and only if a kernel-inclusion condition holds; full recovery of the hidden initial input is unnecessary. For revisions accumulating before the terminal time, spectral stability of the limiting two-response cycle yields bounded physical execution and a finite state left limit. The zero-extended continuation plans then converge strongly to the mean field equilibrium restarted from that state. A scalar counterexample shows that well-posed continuation problems and a convergent physical state can coexist with divergent remaining plans. We also construct an exact causal implementation from local aggregate observations and establish finite-population robustness on every fixed finite opportunity prefix. Revision records match with probability tending to one, and the mean-square implementation error truncated to the matching event is $O(N_*^{-1})$, where $N_*$ is the smaller population size.

math.OC↗

arXiv2026

Cooperative Quantum Optical Effects of Moiré Exciton Superlattices

The unique properties of two-dimensional moiré systems have been widely studied from many perspectives. However, relatively little work has investigated how the real-space structure of moiré systems can directly engender novel properties and functionalities. In this Letter, we explore how intriguing cooperative optical effects can emerge from the real-space superlattice formed by moiré excitons. Particularly, we show that the collective moiré exciton states can have either strongly enhanced (superradiant) or suppressed (subradiant) radiative decay rates, depending on their in-plane wave vector. These super- and subradiant states can be efficiently switched by a gate-induced electric field gradient. Moreover, the cooperative transmittance T of the atomically thin moiré system can be switched from $T\approx 0$ (opaque) to $T \approx 1$ (transparent) with $\lesssim ~1\%$ heterostrain or a $1^{\circ}$ adjustment in the twist angle $θ$. These features are robust against nonradiative losses and disorders, making the moiré system a highly versatile platform for cooperative quantum optics with potential applications in, e.g., single photon storage and switching.

cond-mat.mtrl-sci↗

arXiv2026

Three-Dimensional Topology from Stacking-Controlled Umklapp Scattering in Large-Angle Twisted Graphite

Large-angle twisted graphene lies beyond the local-stacking description of conventional moiré systems: inequivalent rotation centers define distinct commensurate interfaces whose low-energy interlayer hybridization is governed by intervalley Umklapp tunneling. For three-dimensional twisted graphite assembled from interfaces with different crystalline symmetries, a symmetry-constrained effective model reveals that competition between nonchiral and chiral tunneling produces one-ring and two-ring nodal-line phases and a $C_3$-protected higher-order topological insulator in the presence of sublattice (chiral) symmetry. The nodal rings carry integer winding numbers, allowing oppositely wound rings to annihilate into the gapped phase. We further examine how sublattice-symmetry breaking modifies these phases. Density functional theory (DFT) and atomistic calculations for $21.8^\circ$ twisted graphite identify the equilibrium structure as a higher-order topological insulator, while compression drives it into a topological Weyl semimetal phase. These findings establish the stacking sequence of symmetry-inequivalent interfaces as a means of engineering band topology in three-dimensional twisted structures.

cond-mat.mtrl-sci↗

arXiv2026

Collective excitations in chiral spin liquid: chiral roton and long-wavelength nematic mode

Chiral spin liquid (CSL) is a magnetic analogue of the fractional quantum Hall (FQH) liquid. Collective excitations play a vital role in shaping our understanding of these exotic quantum phases of matter and their quantum phase transitions. While the magneto-roton and long-wavelength chiral graviton modes in the FQH and fractional Chern insulator (FCI) liquids have been extensively explored, whether CSLs host analogous or qualitatively different modes remains elusive. Here we explore the collective excitations in the SU(2) symmetric CSL phase. Combining exact diagonalization and time-dependent variational principle calculations, we identify two spin-singlet collective modes: a chiral p-wave roton mode at finite momentum, and a elliptically polarized d-wave nematic mode at zero momentum, both of which are prominent across the CSL phase. The chiral p-wave singlet roton has no counterpart in FQH of FCI systems, and the q = 0 d-wave mode also exhibits fingerprint distinct from those of FQH/FCI liquids. We also elucidate that both singlet modes are general for CSLs on various lattice models. By tuning J2, we find the nematic mode to be pronouncedly soft, together with the spin-triplet two-spinon bound states, potentially promoting strong nematic and spin stripe instabilities. Our work paves the way for further understanding CSL from the dynamical perspective and provides new spectroscopic signatures for future experiments of CSL candidates.

cond-mat.str-el↗

arXiv2026

Excitons probe intrinsic flat band Mottness in a van der Waals heterostructure

Excitons provide a sensitive optical probe of electronic correlations in nearby two-dimensional materials, yet their coupling to intrinsic flat-band Mott systems remains largely unexplored. Here we combine gate-tunable optical spectroscopy with first-principles calculations to study monolayer WSe$_2$ in direct contact with the van der Waals Mott insulator Nb$_3$Cl$_8$. The gate evolution of WSe$_2$ excitonic resonances reveals signatures of a correlation-reconstructed Mott gap in Nb$_3$Cl$_8$ that is absent from the single-particle band picture. In the electron-doped regime, the WSe$_2$ 2s Rydberg exciton undergoes a multistage evolution and develops into interlayer attractive and repulsive polaron branches, showing that a Rydberg exciton can be dressed by strongly correlated flat-band electrons in an adjacent Mott layer. Under an out-of-plane magnetic field, spin-polarized Nb$_3$Cl$_8$ states further induce valley-selective exciton coupling, producing a strongly enhanced circular polarization of the WSe$_2$ exciton emission. These results extend exciton-based sensing and exciton-polaron physics to intrinsic flat-band Mott materials, providing an optical route to probe and engineer correlation-driven interfacial quasiparticles.

cond-mat.mtrl-sci↗

arXiv2026

Partially Observed Mean Field Games Without Perfect Recall: Optimality Conditions and Equilibria

This paper studies partially observed mean field games without perfect recall (WPR). The representative agent observes a noisy signal, but the control at time $t$ uses only $\mathcal G_t^I=σ(y_t)$, a generally non-nested information family. The conditional population law instead uses the observation filtration $\mathbb F^Y$. These coupled levels rely on different information scales and are difficult to close within one construction. We parameterize the environment by a deterministic compatible joint law of state, driving variables, and random mean field term, thereby preserving its dependence structure without enlarging the agent's control information. For a fixed law, a reference measure and Girsanov's theorem yield a WPR stochastic maximum principle; the selected response is represented by the conditional Hamiltonian and WPR belief measure. The joint path posterior of hidden state and mean field term gives a weak Kushner-Stratonovich representation of the conditional population law. A recursive response map is continuous on a compact convex set of compatible laws, so Schauder-Tychonoff yields a weak WPR equilibrium. For a fixed equilibrium law and feedback, a compatible Yamada-Watanabe theorem lifts pathwise uniqueness to a strong realization. Finally, a linear-quadratic interbank lending example compares perfect recall (PR) with WPR. The PR response follows the Kalman-Bucy feedback, whereas the WPR response solves a Fredholm-Volterra equation and is affine in the current observation under Gaussianity. The numerical experiment illustrates how equilibrium behavior differs between PR and WPR.

math.OC↗

arXiv2026

Linear Quadratic Mean Field Games under Heterogeneous Erroneous Initial Information

We study a finite-horizon linear--quadratic mean field game with heterogeneous observations of the initial mean field. These observations may be erroneous and are used by agents to construct their feedback laws. At the population level, the heterogeneous error profile is generally infinite-dimensional. We derive exact linear sensitivity formulas showing that its closed-loop effects nevertheless admit a finite-dimensional closure: for each agent, the deviations are governed by only two n-dimensional error channels, its private error E_i and the population-average error \bar E. The population-average error determines the displacement of the actual mean field, whereas centered private errors determine agent-specific deviations and the additional cross-sectional covariance. The same representation yields quadratic cost identities and a uniform $O(N^{-1})$ mean-square approximation of the empirical aggregate. In the deterministic model, the private state history induces a linear observation problem for the initial errors. Nonsingularity of the associated observability Gramian is necessary and sufficient for exact recovery. The recovered errors reconstruct the actual mean-field state at the revision time and initialize a revised correct-information continuation from that state. We obtain an exact continuation-cost comparison; when the population-average error vanishes, revision does not increase the continuation cost. For stochastic dynamics, we take a two-component revision signal as given and study the resulting one-shot feedback relative to an oracle continuation initialized with the actual current mean field. The actual mean-field deviation is driven only by the population-average signal error, while individual deviations also retain the private signal error. Exact covariance and quadratic continuation-cost identities quantify these effects.

math.OC↗

arXiv2026

Realization of Air-Stable Two-Dimensional Superconductor Nb2Pd3Te5 With Quasi-One-Dimensional Pair Density Modulation

Two-dimensional (2D) superconductors provide a fertile platform for exploring reduced-dimensional superconductivity and emergent quantum phenomena. Incorporating quasi-one-dimensional (quasi-1D) structural motifs into 2D superconductors offers a powerful route to engineer strong electronic anisotropy, enabling unconventional superconducting states and anisotropic superconducting transport functionalities. However, such systems remain rarely realized. Here we report the realization of a 2D superconductor Nb2Pd3Te5, exhibiting an intrinsic quasi-1D pair density modulation. Monolayer and bilayer Nb2Pd3Te5 is synthesized via van-der-Waals epitaxy. Using ultralow-temperature scanning tunneling microscopy/spectroscopy, we observe the quasi-1D crystal structure and superconductivity below ~0.6 K with a pronounced quasi-1D pair density modulation. Remarkably, both monolayer and bilayer Nb2Pd3Te5 show strong air stability. Our findings establish atomically 2D Nb2Pd3Te5 as a robust and promising platform for exploring novel low-dimensional quantum phenomena and anisotropy-enabled superconducting devices.

cond-mat.mtrl-sci↗

arXiv2026

Bridging distributed quantum materials via multi-hotspot vacuum: remote Cooper pairing and Andreev teleportation

We introduce an architecture where mesoscopic quantum matter distributed over spatially separated nodes can be correlated in equilibrium, creating an unprecedented form of many-body quantum system. Central to the design is a multi-gap split-ring resonator (SRR) where the cavity photon has multiple hot spots -- each with deep-subwavelength volume at a split gap and separated by millimeter-scale distances. The cavity's vacuum fluctuations can then mediate a many-body interaction that bridges the distributed quantum materials embedded in the multiple gaps, coupling them into a single correlated mesoscopic system in equilibrium. As an example, we consider a THz SRR with two split gaps, each proximitized to a metallic moiré superlattice, where virtual exchange of a photon in the cavity vacuum mediates a current-current interaction across the gaps. The inherent attractive interaction channels lead to remote Cooper pairing reminiscent of mesoscopic superconductivity, demonstrated with density matrix renormalization group and exact diagonalization calculations. With the two constituents of a Cooper pair now paired across a millimeter-scale separation, a hole incident at one split gap can be converted into an outgoing electron at the remote gap, a process we term Andreev teleportation. The entanglement entropy between the two mesoscopic superlattices is shown to scale linearly with the area (total number of sites) of the mesoscopic lattice. Our results suggest an intriguing paradigm for equilibrium quantum networks of mesoscopic matter that enable emergent nonlocal functionalities and distributed quantum resources.

cond-mat.mes-hall↗

arXiv2026

Defect Antichains and Multigraded Symbolic Defect Series of Edge Ideals under Graph Blow-ups

In this paper, we study symbolic defect functions of edge ideals through finite antichains of exponent vectors. Let $G$ be a finite simple graph and let $I(G)$ be its edge ideal. For each symbolic degree $s$, we define the symbolic exponent region $\mathcal{P}_s(G)$, the ordinary exponent region $\mathcal{O}_s(G)$, and the symbolic defect antichain $\mathcal{D}_s(G)=\min\big(\mathcal{P}_s(G)\setminus \mathcal{O}_s(G)\big)$, where the minimum is taken with respect to the componentwise partial order. We prove that $\mathcal{D}_s(G)$ gives a finite obstruction set controlling the minimal monomial generators of the quotient $I(G)^{(s)}/I(G)^s$. Our main result is a blow-up transfer formula. If $G^{\mathbf n}$ is the graph obtained from $G$ by replacing each vertex $v_i$ by an independent set of size $n_i$, then for every $s\geq 1$, \[ \operatorname{sdefect}(I(G^{\mathbf n}),s) = \sum_{\mathbf a\in \mathcal D_s(G)} \prod_{i=1}^{r} \binom{a_i+n_i-1}{n_i-1}. \] We further refine this formula to a multigraded symbolic defect series, which records the full multidegree distribution of the minimal generators of $I(G^{\mathbf n})^{(s)}/I(G^{\mathbf n})^s$. As applications, we classify the defect antichains of complete graphs in terms of integer partitions and derive explicit symbolic defect formulas for complete multipartite graphs, complete split graphs, and blow-ups of odd cycles. We also study symbolic defect antichains under graph joins and obtain polynomiality and rational generating-function consequences in the blow-up parameters. The results provide a unified antichain-based framework for symbolic defects of edge ideals and convert several previously case-by-case computations into consequences of a single transfer principle.

math.AC↗

arXiv2026

Interlayer electric multipole Hall effect in twisted multilayers

Electrons in layered van der Waals materials possess a layer pseudospin characterizing their wave-function distribution among layers. In twisted structures, this pseudospin forms nontrivial textures, leading to intriguing phenomena such as the layer Hall effect (LHE), where distinct layer Hall currents flow despite the presence of time-reversal symmetry. In chiral bilayers, LHE manifests as an interlayer electric dipole Hall effect with Hall counterflows and a concomitant in-plane magnetic dipole. Multilayers host richer layer-dependent Hall currents, generating interlayer electric multipole Hall effects and in-plane magnetic multipoles. We start from exploring the interlayer electric quadrupole Hall effect in mirror-symmetric twisted trilayers. At small twist angles, interlayer translation efficiently tunes layer Hall current magnitudes. At large angles and low doping, the currents can be well accounted for by adding the contributions from the two individual twisted interfaces. This decomposition allows obtaining layer-resolved Hall currents in large-angle twisted multilayers even without well-defined periodicity.

cond-mat.mes-hall↗

arXiv2026

Edge Ideals of Prime Ideal Graphs over Finite Rings: Ordinary Powers, Fiber Cones, and Linear Powers

Let $R$ be a finite commutative ring with identity and let $P$ be a proper prime ideal of $R$. The prime ideal graph $Γ_P(R)$ has vertex set $R\setminus\{0\}$, where two distinct vertices $x$ and $y$ are adjacent if and only if $xy\in P$. We prove that prime ideal graphs form a ring-realizable subfamily of complete split graphs. More precisely, if $m=|P|$, $q=|R/P|$, then $q$ is a prime power and $Γ_P(R)\cong K_{m-1}\vee \overline{K}_{m(q-1)}$. We also prove a realization theorem showing that every complete split graph of this form arises from a prime ideal of a finite commutative ring. For the edge ideal $I=I(Γ_P(R))$, we determine the minimal vertex covers and obtain the irredundant primary decomposition. We characterize the minimal monomial generators of every ordinary power $I^n$ and derive a closed formula for $μ(I^n)$. We further interpret this formula as the Hilbert function of the special fiber ring $\mathcal{F}(I)$, compute the analytic spread, and prove that $\mathcal{F}(I)$ is a normal Cohen--Macaulay affine semigroup ring. Finally, we show that $I$ is matroidal and that every ordinary power $I^n$ is polymatroidal; consequently, $I^n$ has linear quotients and a $2n$-linear minimal free resolution for all $n\geq 1$.

math.AC↗

arXiv2026

Generic integer and fractional quantum anomalous Hall crystals from interaction-driven band folding

Among the extensive studies of fractional quantum anomalous Hall (FQAH) states, there recently appears a growing interest in the topological states with coexisting charge density wave (CDW) orders. Such states are referred to as Hall crystals. However, compared to those with integer Hall conductivities, the FQAH crystal (FQAHC) is still elusive even at the level of microscopic model. In this work, we numerically study a topological flat-band model on triangular lattice with spinless fermions. At fractional filling of the Chern band, the nearest-neighbor interaction leads to a commensurate and topologically trivial CDW state. Interestingly, the folded mini-band above the CDW gap is non-trivial, and we focus on the doping of it without any projection. A series of (F)QAHC states at (fractional) integer fillings of this mini-band are discovered and some FQAHC state might even exist in less "ideal" conditions. The ground-state degeneracies of such (F)QAHC states are enlarged by the CDW degeneracy and the Hall conductivities -- determined by the fillings of the mini-band -- are different from the fillings of the original Chern band. We also study the thermodynamics of an FQAHC state and find a compressible CDW phase at intermediate temperatures, which might serve as a precursor of lower temperature FQAHC phase. Moreover, we numerically demonstrate that such a generic scheme of doping CDW-folded topological mini-band could be applied to bosonic systems, broadening the platforms of Hall-crystal physics and motivating its exploration in quantum moire and cold-atom systems.

cond-mat.str-el↗

arXiv2026

Major-Minor LQ Mean Field Games with Erroneous Initial Information: Distributed Error Estimation and Strategy Modification

This paper studies major-minor linear-quadratic mean field games (MMLQMFGs) with erroneous initial information under a constrained observation structure. Each minor agent observes only its own state and the major agent's state, while the major agent observes its own state and the states of a subset of minor agents; neither side observes the mean field state directly. We show that the initial-information errors propagate linearly through the game dynamics and lead to explicit deviations in the major state, the actual mean field, and the agents' internally updated mean field states. Based on this structure, we formulate distributed error identification as a parameter-estimation problem from discrete-time local observations and construct maximum-likelihood estimators for unknown initial errors. We then propose an estimate-based strategy modification at an intermediate time by reconstructing the current mean field from the estimated errors and switching to the corresponding control law. We also characterize the resulting estimation errors and show that, in the present symmetric setting, the major agent's estimation precision depends on the number of observed minor agents but not on their identities. Numerical results illustrate the proposed method.

math.OC↗

arXiv2026

Fractional quantization by interaction of arbitrary strength in gapless flat bands with divergent quantum geometry

Fractional quantum anomalous Hall (FQAH) effect, a lattice analogue of fractional quantum Hall effect, offers a unique pathway toward fault-tolerant quantum computation and deep insights into the interplay of topology and strong correlations. The exploration has been successfully guided by the paradigm of ideal flat Chern bands, which mimic Landau levels in both band topology and local quantum geometry. Yet, given the boundless potential for Bloch bands in lattice systems, it remains a significant open question whether FQAH states can arise in scenarios fundamentally distinct from this paradigm. Here we turn to a class of gapless flat bands, featuring (i) ill-defined band topology, (ii) non-quantized Berry flux, (iii) divergent quantum geometry at singular band touchings, (iv) highly fluctuating and far-from-ideal quantum geometry across the Brillouin zone (BZ). Our exact diagonalization and density matrix renormalization group calculations unambiguously demonstrate FQAH phase that is virtually independent of the interaction strength, persisting from the weak-interaction to the strong-interaction limit. We find the stability of the FQAH states does not uniquely correlate with the singularity strength or the BZ-averaged quantum geometric fluctuations. Instead, the many-body topological order can adapt to the singular and fluctuating quantum geometric landscape by spontaneously developing an inhomogeneous carrier distribution, while its quenching accompanies the drop in the occupation-weighted Berry flux. Our work reveals a profound interplay between local quantum geometry and many-body correlation, and significantly expands the exploration space for FQAH effect and correlated phenomena in general.

cond-mat.mes-hall↗