Two-dimensional multiferroics promise low-power, multifunctional devices, yet the intrinsic coexistence and mutual control of three coupled ferroic orders in a single layer remains elusive. Here, we identify pentagonal monolayer $\mathrm{Fe}{\mathrm{O}}_2$ as an intrinsic triferroic altermagnet where ferroelectric (FE), ferroelastic (FA), and altermagnetic (AM) orders coexist and are tightly coupled, accompanied by a competing antiferroelectric (AFE) phase using first-principles calculations. The sole presence of glide mirror ${\mathrm{M}}_x$ symmetry in a $\mathrm{Fe}{\mathrm{O}}_2$ sublayer, with the breaking of fourfold rotation ${\mathrm{C}}_{4z}$ symmetry, induces in-plane vector ferroelectricity and twin-related ferroelastic strains. Both FE and AFE phases break combined parity-time symmetry and display sizable altermagnetic spin splitting with Néel temperatures over 200 K. Electric-field induced rotation of the FE polarization reverses the sign of the spin splitting, while in-plane uniaxial strain triggers ferroelastic switching that simultaneously rotates the FE polarization vector by 90° and reverses the AM state. These electric-field- and strain-mediated pathways interlink six distinct polarization states that can be selected purely by electric fields and/or mechanical strain. This work extends intrinsic triferroicity to pentagonal monolayers and outlines a symmetry-based route toward mechanically and electrically configurable altermagnetic spintronics.

Clifford circuits augmented matrix product states (CAMPS) was recently proposed to leverage the advantages of both Clifford circuits and matrix product states (MPS). Clifford circuits can support large entanglement and can be efficiently simulated classically according to the Gottesman-Knill theorem. So in CAMPS, MPS needs only to handle the so-called nonstabilizerness entanglement entropy which significantly improves the simulation accuracy for a given bond dimension. In this work, we generalize CAMPS to study the fermion system by taking advantage of the Jordan-Wigner transformation which can map the studied fermion system to a spin system. We benchmark the method on both the spinless $t\text{−}V$ model and the spinful Hubbard model. Our test results show significant improvement of the accuracy of CAMPS over MPS, especially when the interactions are strong. Fermionic CAMPS provides a useful tool for the accurate study of many-body fermion systems in the future and has the potential to help resolve long-standing issues.

Achieving precise control of the topological phases spanning normal insulators, topological insulators (TIs), and second-order TIs (SOTIs) is still rare in two-dimensional atomic crystals. Herein, through a low-energy effective model, we propose a generalized design strategy that enables the systematic control of nontrivial topology in heterobilayers under ferroelectric polarization reversal and an external magnetic field. Our analysis reveals that the polarized state not only induces the band inversion to form a TI phase but also breaks its out-of-plane mirror symmetry, thereby enabling the realization of SOTIs under weak magnetic fields. Moreover, first-principles calculations and topological analysis have confirmed that a series of heterobilayers exhibit switchable topological states manifested through quantized spin Hall conductance, edge states, and spatially resolved zero-dimensional corner states. This work not only provides a practical framework for engineering a normal insulator to achieve the TI/SOTI phase but also opens up a technological avenue bridging first-order and higher-order band topologies.

Shuttling of spin qubits between different locations is a key element in many prospective semiconductor systems for quantum information processing, but the shuttled qubits should be protected from decoherence caused by by time- and space-dependent noise. Since the paths of different spin qubits are interrelated, the noise acting on the shuttled spins exhibits complex and unusual correlations. We appraise the role of these correlations using the concept of trajectories on random sheets, and demonstrate that they can drastically affect the efficiency of coherence protection. These correlations can be exploited to enhance the shuttling fidelity, and we show that by encoding a logical qubit in a state of two sequentially shuttled entangled spins, high fidelity can be achieved even for very slow shuttling. We identify the conditions favoring this encoding, and quantify improvement in the shuttling fidelity in comparison with single-spin shuttling.

In a classic Mott system, the transition from the insulating to the metallic state occurs when the lattice spacing is reduced such that the increase in bandwidth $W$ overcomes the local Coulomb repulsion $U$. In this picture, both $W$ and the ratio $W/U$ become larger with decreasing the distance between correlated sites. Here we show that, in transition-metal compounds, there is another path to metallization. It is associated with an expansion (instead of a compression) of the lattice and thus with a decrease in $W$. In this scenario $W/U$ grows with increasing distance—the opposite of the classical Mott case. Such a surprising inversion can be obtained by decoupling the main factors controlling $W$ and screening. This mechanism explains the electronic behavior of the $t_{2g}^2$ triangular lattice series $\mathrm{LiV}{X}_2$ ($X=\mathrm{O}$, S, and Se) with increasing anionic size.

We study many-body quantum geometric effects in a time-dependent system with emergent quantum integrable field theory instantaneously. We establish a theorem stating that the Berry connection matrix, and thus all associated geometric and topological quantities of the system, can be precisely characterized by excitations up to two particles from the initial emergent quantum integrable field theory. To illustrate the many-body geometric influence, we analyze an Ising chain subjected to both a small longitudinal field and a slowly rotating transverse field, whose low-energy physics in the scaling limit is instantaneously governed by the quantum $E_8$ integrable field theory. Focusing on the quantum geometric potential (QGP), we show the QGP continuously suppresses the instantaneous energy gaps with decreasing longitudinal field, thereby enhancing many-body Landau-Zener tunneling as evidenced by the Loschmidt echo and its associated spectral entropy. The critical threshold for the longitudinal field strength is determined, where the spectral entropy linearly increases with system size and exhibits hyperscaling behavior when approaching the threshold. As the longitudinal field passes the threshold and decreases toward zero, the QGP continuously leads to vanishing instantaneous energy gaps involving more low-energy excitations, resulting in increasing spectral entropy indicative of many-body Landau-Zener tunneling. Our results unveil telltale quantum geometric signatures in time-dependent many-body systems, elucidating the intricate interplay between quantum geometry, integrability, and dynamics.

In electronic devices based on two-dimensional (2D) materials that utilize surface acoustic waves (SAWs), it is crucial to understand the interaction between 2D materials and piezoelectric substrates. Here, we systematically investigate this interaction through numerical modeling of a van der Waals heterostructure comprising graphene encapsulated by hexagonal boron nitride. Our simulations focus on the role of dielectric thickness and gate-layer conductivity in determining the strength and efficiency of SAW-driven electric potentials. Results reveal that the amplitude of the SAW-induced electric potential in graphene decline exponentially with increasing dielectric thickness. Conducting-gate layers introduce pronounced screening effects, with back-gate significantly reducing the amplitude of the SAW-induced electric potential compared to top-gate due to their direct screening of electric fields. Additionally, conducting graphene layer itself leads to a self-intrinsic screening that reduces the amplitude of the SAW-induced electric potential. Our study provides quantitative insights into optimizing device configurations and conductivity parameters, offering clear strategies for improving the sensitivity and effectiveness of SAW-based 2D electronic devices for quantum and sensing applications.

In electronic systems with strong electron-electron interactions, charge carriers can exhibit fluidlike behavior governed by viscosity. While such hydrodynamic regimes have been observed in pristine graphene, realizing similar behavior in moiré superlattices has been challenging due to enhanced momentum-relaxing umklapp electron-electron scattering. Here, we show that placing a graphene/hBN superlattice in close proximity to a conductive screening layer suppresses umklapp momentum relaxation, creating favorable conditions for the observation of viscous electron flow. The hydrodynamic response near the first Dirac point remains largely insensitive to the moiré potential, allowing clear observation of the viscous Hall effect and extraction of the electron-electron scattering length. These results identify proximity screening as a practical route to tune scattering processes and enable quantitative measurement of electron viscosity in moiré superlattices. In contrast, transport near the secondary Dirac points is strongly affected by narrow bandwidth, which hinders reliable measurements of the viscous Hall effect in this regime. This limitation highlights the need for multicomponent hydrodynamic frameworks to describe narrow-bandwidth moiré systems.

Many complex intermetallic structures possess cagelike environments that can host additional guest atoms. In ${\mathrm{Al}}_{10}\mathrm{V}$, these atoms give rise to low-frequency, localized vibrations (Einstein modes) that dominate the thermodynamic response at low temperature. They become imaginary under volume expansion as temperature rises, invalidating the harmonic approximation. We develop a framework to incorporate these strongly anharmonic vibrational modes into first-principles thermodynamic calculations. By explicitly modeling the cage potential and solving the associated Schrödinger equation numerically, we compute the full anharmonic free energy contribution and demonstrate its impact on the thermodynamic behavior of ${\mathrm{Al}}_{10}\mathrm{V}$. This allows us to examine structures with different cage fillings and construct the Al-V phase diagram in the relevant composition range. Our results reproduce key experimental signatures, including the anomalous rise in the thermal expansion coefficient and heat capacity at low temperatures, and reveal that the presence and the extent of cage filling by guest atoms is essential to stabilizing the ${\mathrm{Al}}_{10}\mathrm{V}$ phase at elevated temperatures.

We investigate polarization-coupled magnetization ($P$-coupled-$M$) switching and strain-induced metal-to-insulator transition in ${\mathrm{AA}}^{\prime }{\mathrm{BB}}^{\prime }{\mathrm{O}}_6$ double perovskites, using ${\mathrm{Sr}}_2{\mathrm{FeMoO}}_6$ as an example. First-principles calculations and ab initio molecular dynamics simulations reveal an unconventional octahedral tilt precession ($Q_{Tp}$) facilitating efficient $P$-coupled-$M$ switching with a lower energy barrier compared to conventional hybrid improper ferroelectric modes. In ${\mathrm{KLaFeMoO}}_6$, strain engineering effectively modulates electronic and magnetic properties, demonstrating a strain-induced transition from a ferroelectric half-metallic ferromagnet to an antiferroelectric insulator. In this system, we have observed $P$-coupled-$M$ switching at 450 K. Monte Carlo simulations confirm the thermal stability and Néel temperature of the antiferromagnetic phase as 480 K. These results highlight the potential of ${\mathrm{KLaFeMoO}}_6$ for high-temperature spintronic applications.

The presence of phonon instabilities that leads to the formation of charge modulations in kagome metals has allowed their classification based on the atomic displacements of the imaginary modes. Here, we use diffuse and inelastic x-ray scattering (IXS), backed by Monte Carlo simulations to describe a type-I instability in the kagome metal ${\mathrm{Yb}}_{0.5}{\mathrm{Co}}_3{\mathrm{Ge}}_3$. We find that the in-plane displacement of Co in the kagome plane drives a structural transition with the appearance of new Bragg peaks at odd $L$. The in-plane odd Bragg reflections are surrounded by an anisotropic hexagonal diffuse scattering, characteristic of a highly frustrated triangular lattice, that can be modeled following a combination of an Ising model and Lennard-Jones potential. The inelastic spectra reveal no softening but an anomalous broadening of the $\mathrm{\Gamma }$–$A$ low energy acoustic mode, and demonstrate that the structural phase transition in ${\mathrm{Yb}}_{0.5}{\mathrm{Co}}_3{\mathrm{Ge}}_3$ is of an order-disorder transformation type. Our results allow disentangling the structural ordering from the geometric frustration-induced correlated disorder in kagome lattices, and highlight the power of combined diffuse scattering and IXS to differentiate between displacive and order-disorder scenarios.

We present a first-principles investigation of strain-driven vacancy clustering in aluminum. Specifically, we perform Kohn-Sham density functional theory calculations to study the influence of hydrostatic strains on clustering in tri-, quad-, and heptavacancies. We find that compressive strains are a key driving force for vacancy aggregation, particularly for collapse of clusters on the (111) plane, consistent with prior experimental observations of vacancy clusters on this plane. Notably, we find that the heptavacancy on the (111) plane collapses to form a prismatic dislocation loop for hydrostatic compressive strains exceeding 5%, highlighting the critical role of such strains in prismatic dislocation loop nucleation in aluminum.

The spectra of particles in disordered lattices can either be completely extended or localized or can be intermediate, which hosts both the localized and extended states separated from each other. In this work, however, we show that in the case of a one-dimensional lattice with long-range hopping and non-Hermitian quasiperiodic on-site potential, the localized and extended states in the spectrum are intermixed with each other rather than well separated. As a result, an atypical intermediate phase appears where extended states intermittently appear in the pool of localized states. We also argue that such anomalous spectral intermixing can be realized in the short-range hopping limit by appropriate engineering of the on-site potential. Moreover, we obtain that the nature of the spectrum also reveals nonstandard scenarios in the complex energy plane where the complex energies encircle real ones. These findings shed light on the intricate interplay between the non-Hermiticity and quasiperiodic disorder in the system.

We theoretically investigate criticality and multifractal states in a one-dimensional Aubry-André-Harper model coupled to electromagnetic cavities. We focus on two specific cases where the photon frequencies are ${\omega }_0=1$ and 2, respectively. Phase transitions are analyzed using both the average and minimum inverse participation ratio to identify metallic, fractal, and insulating states. We provide numerical evidence to show that the presence of the optical cavity induces a critical, intermediate phase in between the extended and localized phases, hence drastically modifying the traditional transport phase diagram of the Aubry-André-Harper model, in which critical states can only exist at the well-defined metal-insulator critical point. We also investigate the probability distribution of the inverse participation ratio and conduct a multifractal analysis to characterize the nature of the critical phase, in which we show that extended, localized, and fractal eigenstates coexist. Altogether, our findings reveal the pivotal role that the coupling to electromagnetic cavities plays in tailoring critical transport phenomena at the microscopic level of the eigenstates.

Dynamical axion (quasi-) particles are emergent collective excitations in topological magnetic insulators or in Weyl semimetals that break parity and time-reversal invariance. They couple to electromagnetism via a topological Chern-Simons term, leading to their decay into two photons. We extend the Weisskopf-Wigner formulation of atomic spontaneous emission to the quantum field theory of dynamical axion quasiparticles, allowing us to obtain the quantum two-photon state emerging from axion decay in real time. This state features hyperentanglement in momentum and polarization with a distinct polarization pattern, a consequence of the parity and time-reversal breaking of the axion-photon interaction. Polarization aspects of this two-photon state are studied by introducing quantum Stokes operators. Although the two-photon quantum state features vanishing averages of the degree of polarization and polarization asymmetry, there are nontrivial momentum correlations of the Stokes operators. In particular momentum correlations of the polarization asymmetry can be obtained directly from coincident momentum- and polarization-resolved two-photon detection. Correlations of Stokes operators are directly related to momentum- and polarization-resolved Hanbury-Brown Twiss second-order coherences. This relationship suggests two-photon correlations as a direct probe of dynamical axion quasiparticles. Similarities and differences with parametrically down converted photons and other systems where spontaneous emission yield hyperentangled two-photon states are recognized, suggesting experimental avenues similar to tests of Bell inequalities to probe dynamical axion quasiparticles with coincident two-photon detection.

We study the Green's functions in non-Hermitian systems that exhibit the critical non-Hermitian skin effect (critical NHSE) using a double-chain Hatano-Nelson model with interchain coupling $\mathrm{\Delta }$. When $\mathrm{\Delta }=0$, the system decomposes into two independent chains and, in this case, the Green's functions follow predictable patterns based on the generalized Brillouin zone (GBZ) theory. For small $\mathrm{\Delta }$ $(\mathrm{\Delta }=1/10000)$, there are two cases. In conventional regions with trivial open-boundary conditions spectral winding numbers, the interchain coupling induces a zigzag scaling structure in the Green's functions, which can be explained by the first-order perturbation theory. In anomalous regions with nontrivial winding numbers, the actual Green's functions and the GBZ-based predictions match in the bulk but diverge near the boundaries and this deviation turns out to be derived from the influence of the GBZ of the $\mathrm{\Delta }=0$ case. These results reveal the unique nonperturbative features of the critical NHSE and highlight the limitations of the GBZ theory in capturing the boundary effects of finite-size systems and thus emphasize the need to consider both bulk and boundary dynamics in such systems.

Dirac nodal lines (DNLs), whose fourfold degenerate nodes with linear dispersion form a continuous line in reciprocal space, have been extensively investigated in the condensed matter community due to their intriguing topological and transport properties. However, a uniform approach to efficiently and expediently exploring the symmetry-enforced DNLs is quite lacking in bosonic systems, especially for the recently proposed topological phonons. Here, based on the group representation theory analysis, we present a recipe for discovering the DNL phonons along high symmetry lines (HSLs) in all space groups. The results show that only five space groups with inversion symmetry are identified to host the DNL phonons along seven HSLs. Furthermore, using first-principles calculations, we screen out a set of realistic materials as the ideal candidates to realize the DNL phonons along HSLs. The Zintl phase ${\mathrm{K}}_2{\mathrm{BaSi}}_4$ and pyrite-type ${\mathrm{PdAs}}_2$ are selected as examples to elaborate the DNLs and their related topological features. Our work not only paves the way to explore the novel DNL phonons, but also provides realistic material candidates to facilitate the possible experimental observation of DNLs in phonon systems.

In the ongoing research for two-dimensional (2D) ferromagnetic materials with strong intrinsic Dzyaloshinskii–Moriya interaction (DMI), most of the efforts are focused on doping, Janus engineering, or heterostructure formation to break inversion symmetry and enhance spin–orbit coupling (SOC). Here, we demonstrate that a pristine 2D material monolayer $H\text{−}{\mathrm{FeTe}}_2$ can naturally host robust DMI and magnetic anisotropy due to its intrinsic broken inversion symmetry and the strong SOC of Te atoms. We explore the effect of biaxial strain and electron correlation on $H\text{−}{\mathrm{FeTe}}_2$ using first principles $\mathrm{DFT}+U$ calculations. We systematically investigate the Heisenberg exchange interaction, magnetic anisotropy, and DMI in the space spanned by strain and correlation. Our results reveal a distinct, nonmonotonic strain dependence of both magneto anisotropy energy (MAE) and DMI, including a strain-tunable crossover between in-plane and out-of-plane magnetic easy axes. A remarkable enhancement of the in-plane DMI is observed under the combined influence of strain and strong correlations, which is unusual for pristine 2D materials and suggests a favorable regime for spintronic applications. Notably, even in the absence of strain, $H\text{−}{\mathrm{FeTe}}_2$ exhibits finite DMI and considerable anisotropy rare for a pure 2D material. Through these findings, we present $H\text{−}{\mathrm{FeTe}}_2$ as a unique pristine 2D system with robust and tunable spin interactions for exploring fundamental spin orbit-driven magnetic phenomena.