We explore theoretically the optical response of two-dimensional (2D) materials patterned at the nanoscale into either arrays of ribbons along a planar surface or spherical particles. Fourier-Floquet decomposition of the electromagnetic fields is used in order to obtain the reflectance, transmittance and absorbance of the nanoribbon array. The spherical particles are treated with Mie theory, with the boundary conditions modified to accommodate a surface conductivity at the interface. We consider the excitonic response of hexagonal boron nitride in the ultraviolet, and of the transition-metal dichalcogenide ${\mathrm{WS}}_2$ in the visible. Unlike what is expected from graphene, where plasmons have proven very sensitive to geometry, the excitonic response of nanoribbon arrays is found to show weak tunability with the array parameters. To enhance tunability with the geometry of the system, or via hybridization with the substrate, nanospheres with a 2D semiconductor coating are demonstrated to provide a superior platform. Overall, we find that the localized nature of excitons in 2D semiconductors largely limits tunability with geometry, but their hybridization with other optical modes in the nanopatterning setup still holds promise for controllable light-matter interactions.

We propose a test of conformal invariance in critical phenomena based on the study of a two-point correlation function in the presence of a boundary. This two-point function can be studied using x-ray or neutron scattering in the conditions of total reflection (so-called grazing scattering). The conformal Ward identity in momentum space is here expressed as a differential constraint on the scattering cross section, as a function of the momentum transfer and the scattering angle. Experimental verification using x rays and binary alloys appears well within the existing techniques, while feasibility for neutron scattering requires further study. This would be the first direct experimental test of conformal invariance in critical phenomena, a symmetry widely assumed but never directly verified.

We explore nonequilibrium topological responses of symmetry-protected topological (SPT) states in open quantum systems subject to decoherence. For SPT wave functions protected by a product symmetry $G\times S$, where $G$ defects are decorated with $S$ charge, we show that full dephasing of the $S$ charge density induces spontaneous strong-to-weak symmetry breaking (SWSSB) of $G$ in the resulting mixed-state ensemble. We extend this mechanism to SPT phases protected by higher-form and spatially modulated symmetries, and further to gapless SPT states, demonstrating that dephasing-induced SWSSB persists well beyond conventional gapped zero-form settings. Our results provide a qualitative, channel-defined fingerprint of SPT order that is intrinsic to open-system dynamics and goes beyond equilibrium linear response.

Two-dimensional (2D) altermagnets have been attracting enormous research interest; however, the general guidance of global symmetry breaking poses a significant challenge of rather limited material candidates. Here, we propose a simple and widely applicable design strategy for generating both hidden and visible 2D altermagnetism in van der Waals antiferromagnetic multilayers. Based on conventional antiferromagnetic monolayers with spacetime-inversion symmetry, different types of altermagnetism can be realized, depending on interlayer magnetic interaction and local symmetry breaking. Notably, the approach has the advantage that it does not require a specific twisting/stacking order or global inversion symmetry breaking. Using a symmetry-guided framework and high-throughput computational screening, we identify diverse hidden and visible altermagnetic candidates. Beyond bilayer thicknesses, this unconventional layer-dependent nonrelativistic spin splitting mechanism exhibits a distinct odd-even effect, differing from that in conventional A-type antiferromagnets. Leveraging hidden altermagnetic order, we propose a universal multiferroic scheme for ferroelectric reversal of spin polarization. Our study greatly expands the family of 2D altermagnetic materials, circumvents stringent constraints associated with previous methods, and opens new pathways toward altermagnetic spintronics.

The band complex formed by multiple topological states has attracted extensive attention for the emergent properties produced by the interplay among the constituent states. Here, based on group theory analysis, we present a scheme for rapidly identifying the Weyl-Dirac nodal lines (a complex of Weyl and Dirac nodal lines) in bosonic systems. We find only 5 of the 230 space groups host Weyl-Dirac nodal line phonons. Notably, the Dirac nodal line resides along the high-symmetry line, whereas the Weyl nodal line is distributed on the high-symmetry plane and is interconnected with the Dirac nodal line, jointly forming a composite nodal network structure. Unlike traditional nodal nets, this nodal network exhibits markedly distinct surface states on different surfaces, which can be attributed to the fundamental differences in the topological properties between the Weyl and Dirac nodal lines. This unique property thus allows the material to present distinct surface states in a termination-selective manner. Furthermore, by first-principles calculations, we identify the materials ${\mathrm{NdRhO}}_3$ and ${\mathrm{ZnSe}}_2{\mathrm{O}}_5$ as candidate examples to elaborate the Weyl-Dirac nodal line and their related topological features. Our work provides an insight for exploring and leveraging topological properties in systems with coexisting multiple topological states.

The orbital dynamics of magnons have recently drawn interest due to their potential roles in thermal and orbital transport phenomena in magnetic insulators. In this study, we investigate the orbital magnetic moment (OMM) and orbital angular momentum (OAM) of magnons in a kagome antiferromagnet with negative vector chirality, focusing on the distinction between thermodynamic and wave-packet-based definitions. We compute the Berry curvature, the OMM, and the OAM in momentum space under an external magnetic field. Our results reveal a quantitative difference between the OMM and OAM, yet their associated Nernst coefficients exhibit similar temperature and field dependence in transport. Our results provide a quantitative comparison between the thermodynamic and wave-packet formulations of magnon orbital dynamics.

Realizing a quantum critical point (QCP) in clean ferromagnetic (FM) metals has remained elusive due to the coupling of magnetization to the electronic soft modes that drive the transition to be of first order. However, by introducing a suitable amount of quenched disorder, one can still establish a QCP in ferromagnets. In this study, we ascertain that the itinerant ferromagnet ${\mathrm{Ni}}_{1-x}{\mathrm{Mo}}_x$ exhibits a FM QCP at a critical doping of $x_c\simeq 0.125$. Through magnetization and muon-spin relaxation measurements, we demonstrate that the FM ordering temperature is suppressed continuously to zero at $x_c$, while the magnetic volume fraction remains $100\%$ up to $x_c$, indicating a second-order phase transition. The QCP is accompanied by a non-Fermi liquid behavior, as evidenced by the logarithmic divergence of the heat capacity and the linear temperature dependence of the low-temperature resistivity. Our findings reveal a minimal effect of disorder on the critical spin dynamics of ${\mathrm{Ni}}_{1-x}{\mathrm{Mo}}_x$ at $x_c$, highlighting it as one of the rare systems to exhibit a clean FM QCP.

We study an Ising model with long-range interactions undergoing a time-periodic kicking. For different initial states we observe persistent period doubling. When there is period doubling we find that the initial state has relevant overlap with Floquet states showing time-translation symmetry breaking, organized in doublets displaying $\pi$-spectral pairing (as highlighted by the $\pi$-spectral gap) and long-range order (as shown by the eigenvalues of the magnetization in the doublet). We observe period doubling for initial states with domain walls and tilted spins, and for the latter ones a finite-size scaling of the relevant $\pi$-shifted gap and magnetization eigenvalues suggests period-doubling oscillations persisting for larger system sizes and lasting a time exponential in the system size. We find that just a minority of Floquet states displays time-translation symmetry breaking while the rest is thermal, a weak-ergodicity breaking situation typical of systems with quantum scars. Although the time-translation symmetry breaking eigenstates are the minority, their number is exponential in the system size and this motivates the period doubling observed for many different initial states.

We investigate theoretically and numerically the nonreciprocal propagation and relaxation properties of magnetostatic surface spin waves (MSSWs) in dipolar-coupled ferromagnetic bilayers. The in-phase acoustic and out-of-phase optic modes are identified with distinct cross-thickness localization profiles. We trace the direction-dependent interlayer dipolar coupling strength to the intrinsic chirality of single-layer MSSWs and their associated dipolar fields, providing an intuitive physical picture for the dispersion nonreciprocity. For relaxation properties, we extend the geometry-corrected relaxation model to bilayer systems and apply the magnon-number-weighted effective damping formalism to structures with distinct Gilbert damping factors in the two sublayers. Systematic micromagnetic simulations confirm the accuracy of the quadratic energy-weighted damping scheme and quantify the relation between mode localization and total dissipation in hybrid magnonic waveguides. Combining dispersion-relation-determined characteristic frequencies and damping-related decay lengths, we establish quantitative design guidelines for nonreciprocal magnonic functionalities including frequency-division multiplexing and damping-tunable isolation. In this work, we offer quantitative reference for evaluating and optimizing the performance of multilayer magnonic waveguides and provide practical design criteria for bilayer-based nonreciprocal magnonic components.

Despite the fact that power-law interactions occur in a plethora of physical systems, their many-body dynamics is far less understood than that of nearest-neighbor interacting systems. Here, we study information scrambling in strongly disordered spin systems with power-law interactions via out-of-time-order correlators (OTOCs). Numerically, we find pronounced differences in the dynamical spreading of OTOCs between nearest-neighbor and power-law interacting systems. This deviation persists even for short-range interactions, opposing the common view that these interactions produce dynamics equivalent to the nearest-neighbor case. In a detailed experimental proposal, tailored but not limited to Rydberg tweezer setups, we present a protocol to extract OTOCs in XXZ Heisenberg spin systems with tunable anisotropy and programmable disorder based on currently available techniques.

Single-molecule magnets (SMMs) exhibit slow magnetic relaxation as a result of axial magnetic anisotropy inhibiting spin-phonon transitions. To establish a direct link between physical observables and the microscopic theory of magnetic relaxation, we here develop and numerically implement a first-principles linear response theory for open quantum systems that provides access to the complex alternating-current (ac) magnetic susceptibility in the presence of an oscillating ac magnetic field. Once combined with density functional theory and multiconfigurational electronic structure simulations, this formalism is applied in a fully first-principles fashion to three cyanido-bridged $\mathit{Ln}$/Y-based ($\mathit{Ln}$ = lanthanide) coordination polymers with general formula $\left\{{\mathit{Ln}}_x^{\text{III}}{\mathrm{Y}}_{1-x}^{\text{III}}\left[{\mathrm{Co}}^{\text{III}}{\left(\mathrm{CN}\right)}_6\right]\right\}$, where $\mathit{Ln} =$ Yb (1), Tb (2), and Dy (3). The method is able to reproduce the low-temperature direct relaxation process and its field dependence, as well as the high-temperature Orbach relaxation regime for all the investigated compounds. These results demonstrate the feasibility of ab initio simulations of magnetic ac susceptibility in lanthanide-based SMMs and support the potential of further development of ab initio open quantum systems methods toward the completion of a magnetization dynamics theory.

The first order phase transition between the nearly commensurate (NC-CDW) and commensurate (C-CDW) charge density wave phases in $1T\text{−}{\mathrm{TaS}}_2$ underpins its exotic electronic behavior, yet the spectroscopic evolution of the low energy electronic structure across this transition remains crucial to understand. Using angle resolved photoemission spectroscopy (ARPES), we investigate the low temperature C-CDW phase, characterized by a flat band commonly associated with the lower Hubbard band and a distinct in-gap state located closer to the Fermi level. Photon energy dependent measurements distinguish these two low energy features through their different spectral weight evolution. Temperature dependent ARPES across heating and cooling cycles reveals that the in-gap state undergoes an abrupt collapse upon heating into the NC-CDW phase and re-emerges sharply upon cooling back into the C-CDW phase. This pronounced thermal hysteresis provides direct spectroscopic evidence of the first order nature of the transition. Furthermore, the disappearance and recovery of the in-gap state closely track the corresponding changes in resistivity, highlighting its intimate connection to the electronic reconstruction across the C-CDW–NC-CDW phase transition.

We investigate higher-order topological insulators protected by chiral and anticommuting mirror symmetries. Using models in the BDI class, which include the prototypical topological quadrupole insulator, we show that breaking mirror symmetries that anticommute with the chiral operator leads to edge-selective bulk-boundary correspondence, with gap closings and bound states appearing only along a subset of boundaries of the same orientation and codimension. We define an edge-resolved topological invariant that distinguishes this mechanism from previous reports of termination-induced or chiral-symmetry-breaking edge-selection effects.

We introduce a neural network impurity solver for real-frequency dynamical mean-field theory that employs a multihead cross-attention mechanism to map hybridization functions to spectral functions, conditioned on impurity parameters. Trained on high-quality matrix product states data from complex contour time evolution and incorporating derivative constraints with respect to the complex-time angle, our model achieves smooth generalization to the real-frequency axis. Benchmarking on the single-band Hubbard model for the Bethe lattice demonstrates quantitative accuracy across metallic, strongly correlated, and insulating regimes.

This work examines charge ${\mathrm{\Delta }}_T$ noise in two-terminal hybrid nanostructures featuring a quantum point contact (QPC), realized either between two normal metallic leads (NQN) or between a normal metal and a superconducting lead (NQS). The energy-dependent transmission of a QPC breaks electron-hole (e-h) symmetry, leading to a finite thermovoltage under an applied temperature and voltage bias. In contrast, in earlier studies on hybrid junctions incorporating insulating barriers, as electron-hole symmetry is preserved, have vanishing thermovoltage, and consequently, charge ${\mathrm{\Delta }}_T$ noise is calculated at zero thermovoltage. In our setup, the broken e-h symmetry allows for a finite thermovoltage, at which we compute the corresponding charge ${\mathrm{\Delta }}_T$ noise. Unlike earlier studies restricted by electron-hole symmetry and vanishing thermovoltage, our work establishes a self-consistent thermoelectric noise framework in mesoscopic hybrid junctions, revealing how Andreev reflection fundamentally reshapes charge ${\mathrm{\Delta }}_T$ noise once electron-hole symmetry is broken. This broad access to charge fluctuation signatures provides a more comprehensive understanding of nonequilibrium transport in linear response. To the best of our knowledge, this is the first work that systematically explores the interplay between Andreev reflection and electron-hole symmetry breaking in the context of quantum noise and ${\mathrm{\Delta }}_T$ noise in mesoscopic hybrid structures.

We investigate the properties of a minimal two-orbital $e_g$ model of transition metal compounds featuring bond-dependent spin-orbit terms arising from the atomic spin-orbit coupling at the ligand site. We demonstrate that this model hosts a rich array of phenomena. In the noninteracting, spin-orbit-derived spin-dependent and spin-flip hopping terms produce topological bands with spin-Chern numbers $C_s=\pm 2,\pm 4$, and higher-order topological states with fractional corner charges. In the half-filled Mott insulator limit, we recover a spin-1 Hamiltonian with bond-dependent Kitaev exchange interactions. We explore the magnetoelectric effect in this two-orbital model using symmetry-based perspective and microscopic calculations, going beyond the generalized Katsura-Nagaosa-Balatsky theory for the single-orbital case. Our work may be relevant to studies of doping, strain, or pressure on compounds like nickel dihalides, $\mathrm{Ni}{X}_2$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$, and related triangular lattice materials.

Integrating altermagnetism with conventional ferroic orders simultaneously breaks spatial and time-reversal symmetries, offering a promising platform for realizing magnetoelectroelastic multifield control and for investigating light–matter interactions. Based on experimentally synthesized CrSb, alongside the theoretically predicted altermagnetic-ferroelastic biferroic NiAs-type monolayer and ferromagnetic-ferroelectric-ferroelastic triferroic wurtzite-type monolayer, we construct and investigate all-CrSb triferroic tunnel junctions (TFTJs) using NiAs/WZ heterostructures via symmetry analysis, density functional theory, and nonequilibrium Green's function approaches. Our results demonstrate that a giant tunneling magnetoresistance of 12 340%, a moderate tunneling electroresistance of 623%, a tunneling elastoresistance of 2523%, and a nearly perfect spin-filtering efficiency of 99%–100% can be achieved. Furthermore, the all-CrSb TFTJs are capable of self-powered photodetection, exhibiting a high extinction ratio of 456 and a photogalvanic effect (second-order optical nonlinearity). These findings provide a viable pathway toward miniaturized and integrated applications in magnetoelectric transport, microelectromechanical systems, optoelectronic memory, and logic devices.

Solid-state quantum simulation is a powerful approach in which the material properties of a tunable platform are used to emulate user-defined model Hamiltonians. One of the biggest challenges in materials-based quantum simulation is understanding how to exactly map material-specific changes onto model parameters in a given Hamiltonian. Here, we study the electronic structure resulting from tailored quasi-1D atomic Cs chains constructed atom by atom, using scanning tunneling microscopy and spectroscopy with the aim to uncover how Cs adatoms on InSb can be used for quantum simulation. We study the dependence of the Cs-induced confined electronic states as a function of various parameters of the chain structure. We find that the lowest-level states can be well described by a 1D confinement potential, determined by the chain length, and that the critical parameter determining the depth of the attractive potential is the Cs density. We relate the observations to a lattice model Hamiltonian with exponential long-range hopping, and compare the calculated local density of states with the experimental observations, which reproduce the lowest energy states well. We find deviations from the 1D-confinement potential description for the higher-energy states, which we detail and speculate on its origin. These studies are critical for developing this material platform toward quantum simulation of electronic structure.