Dynamical quantum systems both driven by unitary evolutions and monitored through measurements have proved to be fertile ground for exploring new dynamical quantum matters. While the entanglement structure and symmetry properties of monitored systems have been intensively studied, the role of topology in monitored dynamics is much less explored. In this work, we investigate novel topological phenomena in the monitored dynamics through the lens of free-fermion systems. Free-fermion monitored dynamics were previously shown to be unified with the Anderson localization problem under the Altland-Zirnbauer symmetry classification. Guided by this unification, we identify the topological area-law-entangled phases in the former setting through the topological classification of disordered insulators and superconductors in the latter. As examples, we focus on $1+1\mathrm{D}$ free-fermion monitored dynamics in two symmetry classes: DIII and A. We construct quantum circuit models to study different topological area-law phases and their domain walls in the respective symmetry classes. We find that the domain wall between topologically distinct area-law phases hosts dynamical topological modes whose entanglement is protected from being quenched by the measurements in the monitored dynamics. We demonstrate how to manipulate these topological modes by programming the domain-wall dynamics. In particular, for topological modes in class DIII, which behave as unmeasured Majorana modes, we devise a protocol to braid them and study the entanglement generated in the braiding process.

A material in possession of localized $4f$-electron magnetism and delocalized $3d$-electron or band magnetism can often present enigmatic physical phenomena, and there has been a longstanding interest in the kagome metal ${\mathrm{YbFe}}_6{\mathrm{Ge}}_6$. More recently, because of an investigation of a so-called anomalous Hall effect, or topological Hall effect, and magnetic neutron Bragg diffraction [Yao et al., Phys. Rev. Lett. 134, 186501 (2025)]. Iron moments in the two-dimensional layers of a hexagonal nuclear structure undergo collinear antiferromagnetic order below a temperature $\approx 500$ K. The moments depart from the $c$ axis in a spontaneous transition at $\approx 63$ K to an orthorhombic structure. The magnetism of Yb ions appears to behave independently, which can be confirmed using resonant x-ray Bragg diffraction enhanced by a Fe atomic resonance. The inferred magnetic structure is P(parity)T(time)-symmetric (anti-inversion $\overline{1{}^{\prime }}$) collinear antiferromagnetism that does not couple to circular polarization (helicity) in primary x-rays, unlike altermagnetism. A linear magnetoelectric effect is allowed, and Kerr rotation and the piezomagnetic effect are forbidden. Symmetry informed Bragg diffraction patterns for future x-ray and neutron experiments are shown to be rich in Fe magnetic properties of orthorhombic ${\mathrm{YbFe}}_6{\mathrm{Ge}}_6$, including space-spin correlations, anapoles, and Dirac quadrupoles familiar in high-${\mathrm{T}}_{\mathrm{c}}$ ceramic superconductors.

We report the discovery of scaling in the mesoscale magnetic microstructure of bulk ferromagnets. Supported by analytical micromagnetic theory, we introduce the field-dependent scaling length $l_{\mathrm{C}}\left(H\right)$, which describes the characteristic long-wavelength magnetization fluctuations that are caused by microstructural defects by means of magnetoelastic and magnetocrystalline anisotropy. The scaling length $l_{\mathrm{C}}$ is identified to consist of the micromagnetic exchange length of the field $l_{\mathrm{H}}$, which depends on the magnetic interactions, and a field-independent contribution that reflects the properties of the magnetic anisotropy field and the magnetostatic fluctuations. The latter finding is rooted in the convolution relationship between the grain microstructure and micromagnetic response functions. We validated the scaling property by analyzing experimental data for the magnetic neutron scattering cross section. When plotted as a function of the dimensionless scaled scattering vector $\mathfrak{q}\left(H\right)=q{l}_{\mathrm{C}}\left(H\right)$, the field-dependent amplitude-scaled neutron data of nanocrystalline Co and a Nd-Fe-B-based nanocomposite collapse onto a single master curve, demonstrating universal behavior. The scaling length $l_{\mathrm{C}}$ provides a framework for analyzing the field-dependent neutron scattering cross section, highlighting the existence of critical length scales that govern the mesoscale microstructure of magnetic materials.

The sign reversal of Hall effects has attracted considerable research interest in both fundamental physics and device applications. Here, we utilize the low-energy condensation-type deposition technique to fabricate cluster-assembled NiCo nanomagnets to maximize surface effects, attempting to establish an optimal platform for exploring nontrivial magnetotransport. As the cluster size decreases, both the ordinary and anomalous Hall effects exhibit sign reversal behavior, especially completely reversed behavior over the entire temperature range below the characteristic size of 16.09 nm. Based on scaling laws and theoretical analysis, we demonstrate that the synchronous sign reversal of both Hall effects originates from the switching of dominance between bulk and surface effects. The size-dependent magnetoresistance and magnetic properties also change significantly at the characteristic size, further confirming the evolution of the two effects. This study provides an effective route to engineer Hall effects in nanomagnets, which is beneficial for improving the performance and functionality of spintronic devices.

We investigate spin wave behavior in chiral magnonic quasicrystals (MQCs) based on Ir/Fe/Pt(Ir) and Au/Fe/Pt(Au) multilayers using wave vector resolved Brillouin light scattering (BLS). By systematically tuning the geometric structure and tailoring the interfacial Dzyaloshinskii-Moriya interaction (i-DMI), we obtain both the spin wave dispersion and the density of states (DOS). The results show that the Fibonacci sequence in chiral MQCs significantly enhances frequency modulation effects and promotes the formation of flat band structures. The position and number of local flat bands can be easily tuned, which has never been observed in conventional periodic magnonic crystals (MCs). Furthermore, the engineered i-DMI leads to pronounced nonreciprocal spin wave propagation, expanding the functional capabilities of MQCs. Moreover, a comprehensive analysis reveals that chiral MQCs exhibit unique dispersion characteristics, including multiple band gaps and fractal features, opening avenues for spin wave manipulation. These findings offer valuable insights for designing high-selectivity spintronic devices and establish a solid theoretical foundation for understanding spin wave dynamics, thereby accelerating the development of spin wave technologies for information processing and quantum computing.

We investigate the effects of fluxon cotunneling and quantum Coulomb drag in a system of two small Josephson junctions coupled by means of mutual capacitance $C_m$. Depending on the value of $C_m$ we identify three different regimes of strong, intermediate, and weak coupling. Focusing our attention on the last two regimes we develop a perturbation theory in the interaction and explicitly derive fluxon cotunneling amplitudes at sufficiently small mutual capacitance values. We demonstrate that the Coulomb drag effect survives at any nonzero $C_m$ and evaluate the nonlocal voltage response that is in general determined by a trade-off between two different cotunneling processes. Our predictions can be straightforwardly generalized to bilinear Josephson chains and directly verified in future experiments.

Inversion asymmetry in bilayer graphene can be tuned by the displacement field. As a result, the band dispersion in biased bilayer graphene acquires flatband regions near the Dirac points along with a nontrivial band geometry. We analyze the effect of inversion asymmetry on the critical temperature and superfluid stiffness of the superconducting state of AB-stacked graphene bilayer and the exciton condensate in double layers formed by two AB-stacked graphene bilayers. We find that the geometric superfluid stiffness in bilayer graphene superconductors is negligible due to the small superconducting gap. Furthermore, since the geometric superfluid stiffness is maximized for a constant order parameter, it can be neglected in biased bilayer graphene superconductors with any pairing symmetry. In contrast, the displacement field enhances the geometric superfluid stiffness in exciton condensates. It is most prominent at low densities and high displacement fields. A consequence of the geometric superfluid stiffness is a modest enhancement of the Berezinskii-Kosterlitz-Thouless transition temperature in bilayer graphene's exciton condensate.

We investigate the magnetic phases of semiconductor-based artificial triangular graphene quantum dots (TGQDs) with zigzag edges using variational and diffusion Monte Carlo methods. These systems serve as quantum simulators for bipartite lattices with broken sublattice symmetry, providing a platform to study the extended Hubbard model's emergent magnetic phenomena, including Lieb's magnetism at half filling, edge depolarization upon single-electron addition, and Nagaoka ferromagnetism. Our nonperturbative quantum Monte Carlo simulations, performed for finite-sized TGQDs modeled as nanopatterned GaAs quantum wells, with system sizes up to $N_s=61$ lattice sites, reveal a transition from metallic to insulating regimes as a function of the quantum well radius $\rho$, while preserving edge-polarized ground states at half filling. Notably, edge depolarization occurs upon single-electron doping in both metallic and insulating phases, in contrast to the Nagaoka ferromagnetism observed in hexagonal armchair geometries.

We investigate the Mott transition in a two-band Hubbard-Kanamori model using dynamical mean-field theory with the density matrix renormalization group and the numerical renormalization group (NRG) as impurity solvers. The study focuses on the case where the intraorbital and interorbital Coulomb interactions are equal ($U=U_2$) and the Hund's coupling is absent ($J=0$). Our spectral analysis for this case confirms the absence of an orbital-selective Mott transition (OSMT) even in systems with very distinct bandwidths ($t_1$ and $t_2$ parameters for wide and narrow band, respectively) indicating a simultaneous Mott transition occurring in both bands. Notably, the NRG results show the emergence of a pseudo-gap-like feature and a central peak in the narrow band, whose characteristics depend on the hopping parameter $t_2$. These spectral features may act as precursors to OSMT in more realistic systems with finite Hund's coupling ($J>0$). Furthermore, in the Mott insulating phase, the self-energies for both bands diverge, indicating that the Mott transition represents a topological phase transition for both bands. Our results underscore the importance of accurate impurity solvers in capturing the density of states and detailed spectral structures.

Ferrimagnetism appears in the temperature-field phase diagrams of several candidate Kitaev materials, such as the honeycomb cobaltates ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ and ${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$. In a number of instances, however, the exact nature of the corresponding ground states remains the subject of ongoing debate. We show that general symmetry considerations can rule out candidate states that are incompatible with the observed ferrimagnetic behavior. In particular, we demonstrate that a ferrimagnetic response cannot be reconciled with a collinear zigzag ground state, owing to the combined time-reversal and translational symmetry inherent to that configuration. Instead, the observed behavior is fully compatible with the symmetries of noncollinear multi-$\mathbf{q}$ states, such as the triple-$\mathbf{q}$ discussed in the context of ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$. We exemplify this general result by computing the ferrimagnetic response of an extended Heisenberg-Kitaev-Gamma model with explicit sublattice symmetry breaking within linear spin-wave theory. If the model realizes a triple-$\mathbf{q}$ ground state, the calculated magnetization curve is well consistent with the low-temperature behavior observed in ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$. In this case, a finite magnetization remains in the zero-temperature limit as a consequence of quantum fluctuations, even if the $g$ factors on the different sublattices are identical. For a zigzag ground state, by contrast, the total magnetization vanishes both at zero and finite temperatures, independent of possible sublattice-dependent $g$ factors, as expected from the symmetry analysis. The implications of our general result for other Kitaev materials exhibiting ferrimagnetic behavior are also briefly discussed.

An efficient mixed deterministic and sparse-stochastic plane-wave approach is developed for periodic generalized-Kohn-Sham density functional theory band-structure calculations with extensive $k$-point sampling, for any hybrid-exchange density functional. The method works for very large elementary cells over many $k$ points, and we benchmark it on covalently bonded solids and molecular crystals with nonbonded interactions, for systems of up to 33 000 atoms. Memory and CPU requirements scale quasilinearly with the number of atoms.

The topological flat band (TFB) at the charge neutrality point (CNP) has attracted much recent interest for its physical properties in realizing exotic quantum states, while its implication on materials’ chemical properties remains largely unknown. Here, we predict the TFB@CNP in two-dimensional covalent and metal organic frameworks (COFs and MOFs) can enhance catalysis. Using density-functional theory and tight-binding calculations, we show that in a class of COFs and MOFs underlined by a diatomic kagome lattice model, TFB@CNP can be designed by tuning the relative intra- and interkagome lattice hopping in correlation with electron filling. Remarkably, using hydrogen evolution reaction as an example, we illustrate that the catalytic activity of abundant active sites in COFs and MOFs can be significantly enhanced when they are involved in forming the TFB@CNP. Our findings open a promising direction that integrates topological physics with reaction chemistry in the new platform of high-performance TFB-enhanced catalysis.

The frustrated magnet $\alpha \text{−}{\mathrm{RuCl}}_3$ is one of the prime candidates for realizing a Kitaev quantum spin liquid (QSL). However, the existence of a field-induced intermediate QSL phase in this material remains under debate. Here, we employ sign-free numerically exact quantum Monte Carlo simulations to investigate the Kitaev-Heisenberg (KH) model on the honeycomb lattice with $K=-2J$ under an applied magnetic field along the $z$ direction. Our findings reveal that the system undergoes a direct quantum phase transition from a zigzag magnetically ordered phase to a spin-polarized phase at zero temperature, which belongs to the 3D XY universality class. At finite temperatures, a Berezinskii-Kosterlitz-Thouless transition line separates the spin-polarized phase from a quasi-long-range ordered state, eventually terminating at the quantum critical point. Our results convincingly show that there is no intermediate QSL phase in the KH model with a $z$-direction magnetic field, which we believe will shed important light on understanding experimental observations in $\alpha \text{−}{\mathrm{RuCl}}_3$.

In recent years, the negatively charged group-IV–vacancy defects in diamond, labeled as $\mathrm{G}4\mathrm{V}(-$) or G4V centers, have attracted significant attention in quantum information processing. In this study, we investigate the magneto-optical properties of G4V centers under high compressive hydrostatic pressures up to 180 GPa. The spin-orbit splitting of the electronic ground and excited states, as well as the hyperfine tensors, are calculated using plane-wave supercell density functional theory, providing distinctive fingerprints that uniquely characterize these defects. To this end, we develop a theory for calculating the hyperfine tensors when the electronic states are subject to the Jahn–Teller effect. We find that the zero-phonon-line energy increases with hydrostatic pressure, with the deformation potential increasing from $\mathrm{SiV}(-$) to $\mathrm{PbV}(-$). On the other hand, our calculated photoionization threshold energies indicate that $\mathrm{PbV}(-$)-based quantum sensors can operate only up to 32 GPa, whereas $\mathrm{SnV}(-$), $\mathrm{GeV}(-$), and $\mathrm{SiV}(-$) remain photostable up to 180 GPa. We also find that the spin-orbit splitting increases in both the electronic ground and excited states with increasing pressure. The optical transitions associated with the hyperfine fine structure of the dopant atoms are interpreted using our theoretical framework, which reproduces existing experimental data at zero strain. We show that the hyperfine levels are weakly dependent on magnetic field, and increasing pressure leads to optical transitions at longer wavelengths. Finally, we estimate the spin coherence times of the G4V centers under increasing hydrostatic pressure across different temperature regimes.

Here, the electron-phonon coupling (EPC) in polycrystalline nanostructures is systematically studied using Langevin dynamics simulations with spatial correlations. The EPC constant in polycrystalline nanostructures is found to be larger than that in their single-crystalline counterparts and increases with the decrease of the grain size and carriers’ concentration. The EPC constant for polycrystalline silicon with a grain size of $\sim 5\mathrm{nm}$ and a carriers’ concentration of $6.9\times {10}^{21}{\mathrm{cm}}^{-3}$ is improved from its bulk counterpart value of $\sim 1.44\times {10}^{17}\mathrm{W}/{\mathrm{m}}^3\mathrm{K}$ to $\sim 1.84\times {10}^{17}\mathrm{W}/{\mathrm{m}}^3\mathrm{K}$. The temperature of phonon modes in polycrystals therefore increases faster than that in the corresponding single crystals. Our spectral analysis shows that additional high-frequency phonon modes are activated in polycrystals and therefore provide more possible coupling channels for electrons. Meanwhile, the overall temperature of optical phonon modes is observed to increase faster than that of acoustic phonon modes in both polycrystals and single crystals. Our calculated scattering rates show that the scattering rate between optical phonons and electrons is generally larger than that between acoustic phonons and electrons. The scattering rate between optical phonons and acoustic phonons is much larger than that between phonons and electrons. This indicates that the energy of hot electrons is transferred to optical phonon modes, and acoustic phonon modes gain thermal energy from optical phonon modes through their interactions. As a result, the temperature of optical phonon modes increases faster than that of acoustic phonon modes in the systems. Further increase of carriers’ concentration can increase the scattering rate between electrons and phonons, and thus increase the EPC constant. Our study here highlights the influence of grain boundaries and carriers’ concentration on EPC in polycrystalline nanostructures, which benefits future carrier dynamics investigations.

Current progress in electro-optical modulation within silicon integrated photonics, driven by the unique capabilities of advanced functional materials, has led to significant improvements in device performance. However, inherent constraints in dimensionality and tunability still pose challenges for further innovation. In this work we propose a strategy that exploits the principles of non-Hermitian physics—specifically, the concept of exceptional points (EPs)—to transcend these limitations and pave the way for the next generation of versatile, high-performance photonic devices. Our multilayer structure supports hybrid plasmonic waveguide modes that can manifest as various orders of quasiparticles. By judiciously setting spatial parameters, the system can be tuned to exhibit both weak and strong coupling regimes between the plasmonic and dielectric modes, leading to the controlled formation of EP degeneracies. Furthermore, the integration of low-loss phase-change materials (${\mathrm{Sb}}_2{\mathrm{S}}_3$ and ${\mathrm{Sb}}_2{\mathrm{Se}}_3$) enables dynamic electrical tuning, resulting in pronounced modulation of propagation loss and transmission coefficients over submicron distances. This superior performance not only sets a new benchmark for device responsivity and compactness but also opens promising avenues for future research, including the incorporation of gain media for loss compensation at EPs and the exploration of alternative tunable materials for next-generation ultracompact photonic devices.

We present the analytical solution of the mean-field Hubbard model of undoped and doped graphene rectangulenes. These are nonchiral graphene rectangles of arbitrary length and width, and nanoribbons are thus narrow rectangulenes. We rewrite the Hubbard model on the basis of exact bulk and edge noninteracting eigenstates, and we provide analytical expressions for the Coulomb integrals. We also present a general mean-field decoupling of the Hamiltonian that is valid at any temperature and doping. We introduce the edge-only doping regime and discuss the paramagnetic, ferromagnetic, and antiferromagnetic mean-field solutions in this regime. We calculate explicitly at zero temperature the eigenenergies, occupations, spin densities, and the addition energies of rectangulenes with lengths and widths ranging from a nanometer to several hundreds of them. We rewrite the exact mean-field tight-binding Hamiltonian back in the site-occupation basis.

Spin helix states with spatially modulated spin textures are exact eigenstates of the one-dimensional anisotropic spin-$\frac{1}{2}$ Heisenberg model under specific parameter conditions. In this work, we extend this framework by constructing exact eigenstates of the fully anisotropic XYZ Heisenberg model, with spin helix structures modulated by elliptic functions, across all spatial dimensions and spin quantum numbers. The XXZ and XY cases are also analyzed to clarify the conditions for the emergence of spin helix eigenstates and their key properties. Within the subspace spanned by these elliptic spin helix states, a family of analytically tractable states can be identified. Our results broaden the class of exactly solvable eigenstates in nonintegrable systems and deepen the understanding of spin modulation states in many-body systems.