Magnetic quasiparticles, such as skyrmions and merons in van der Waals (vdW) magnets, have attracted great attention due to their potential applications in low dimensional high-density memory storage. However, controlling the transition between different magnetic solitons is still a challenge. Here, we observed a multistep topological transition in monolayer $1H$-type magnets under magnetic field. The different magnetic states, including helical spiral spin textures, meron-antimeron pairs, and skyrmion-antiskyrmion lattices, are fully analyzed from the real-space spin textures, the propagation vectors in reciprocal-space, and the topological charges. Moreover, the formation of these special meron-antimeron pairs is demonstrated to originate from the competition between Dzyaloshinskii-Moriya (DM) interaction and Heisenberg-type frustration. A phase diagram shows that a weak frustration would lower the critical transition field between different topological states. Our results enable the realization of multistep transitions in vdW magnets and provide a promising material platform for studies on different magnetic solitons.

We investigate the finite-temperature phase diagram of the classical $J_1-J_2$ XY model on a square lattice using a tensor network approach designed for frustrated spin systems. This model, characterized by competing nearest-neighbor and next-to-nearest-neighbor interactions, exhibits a complex interplay between $U\left(1\right)$ and $Z_2$ symmetries. Our study reveals an emergent intermediate phase around $J_2/J_1\sim 0.505$, which is characterized by a $Z_2$ long-range stripe order without phase coherence in the XY spins. The intermediate phase features two well-separated phase transitions: a higher-temperature Ising transition and a lower-temperature Berezinskii-Kosterlitz-Thouless (BKT) transition. The relative separation between these transitions is significantly larger than previously reported, enabling a clearer investigation of their distinct thermodynamic properties. For $0.5<J_2/J_1<0.501$, two transitions merge into a single first-order phase transition, a phenomenon that cannot be explained solely by mapping to the Ising-XY model. As $J_2/J_1\to \infty$, the transition evolves continuously into the BKT universality class. These findings advance the understanding of the mechanisms driving phase transitions in frustrated spin systems, and they suggest potential experimental realizations in platforms such as ultracold atoms, Josephson junction arrays, and optical lattices.

We investigate the two-dimensional Hubbard model using a real-frequency implementation of the $\mathrm{TPSC}+\mathrm{DMFT}$ approach. This hybrid method combines the nonlocal correlations captured by the two-particle self-consistent (TPSC) approach with the local dynamical correlations of dynamical mean field theory (DMFT). The results demonstrate that $\mathrm{TPSC}+\mathrm{DMFT}$ effectively describes pseudogap physics and nonlocal fluctuations in the moderately correlated regime, while also reproducing the Mott insulating state at larger interaction strengths. For doped Mott insulators, we find that $\mathrm{TPSC}+\mathrm{DMFT}$ captures the evolution of Fermi pockets into Fermi arcs, consistent with the results from cluster DMFT and photoemission studies. These findings highlight the capability of $\mathrm{TPSC}+\mathrm{DMFT}$ to bridge the gap between weak and strong coupling physics in Hubbard models, providing insights into spin and charge fluctuations, as well as their role in the pseudogap formation.

Here we report on low temperature transport measurements of encapsulated bilayer graphene nanoconstrictions fabricated employing electrode-free atomic force microscope based local anodic oxidation nanolithography. This technique allows for the creation of constrictions as narrow as 20 nm, much smaller than in previous studies. In constrictions wider than ∼120 nm, we observe bulk transport characteristics. However, as the constriction's width is reduced, a transport gap appears. Single quantum dot (QD) formation is observed within the narrowest constriction with addition energies exceeding 100 meV, which surpass previous experiments on patterned QDs. Our results suggest that transport through the narrower constrictions is primarily governed by edge disorder combined with quantum confinement effects.

Recently, the quantum anomalous Hall effect (QAHE) has been theoretically proposed in compensated antiferromagnetic systems by using the magnetic topological insulator model [Phys. Rev. Lett. 134, 116603 (2025)]. However, the related and systematic study based on a realistic material system is still limited. As the only experimentally realized antiferromagnetic topological insulator, ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ becomes a vital platform for exploring various topological states. In this work, by using comprehensive first-principles calculations, we illustrate that the QAHE can also be realized in compensated antiferromagnetic even-septuple-layer ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ without combined parity-time ($\mathcal{PT}$) symmetry. Using a magnetic topological insulator model, the layer-resolved Chern number is calculated to further understand the presence of different Chern numbers. The application of external hydrostatic pressure will strengthen the Te-Te quasicovalent bond due to the dramatic compression of the van der Waals gap. Thus, the topological nontrivial gap exceeds the room-temperature energy scale in a wide range of pressures. Additionally, we find that constructing ${\mathrm{MnBi}}_2{\mathrm{Te}}_4/{\mathrm{CrI}}_3$ heterostructure can realize the compensated antiferromagnetic configurations with QAHE. Our work demonstrates the realization of QAHE in compensated antiferromagnetic even-septuple-layer ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ and provides a reliable strategy to obtain the corresponding magnetic configurations.

We investigate bilayer and trilayer systems composed of topologically distinct, vertically stacked layers, forming topological heterostructures based on the Benalcazar-Bernevig-Hughes model. We find that a topological phase transition induced by interlayer coupling significantly alters the number of corner states in these topological structures. Furthermore, we find that traditional nested Wilson loop analysis inaccurately classifies certain phases, leading us to evaluate multipole chiral numbers (MCNs) as a more appropriate topological invariant for this scenario. The MCNs not only enable accurate classification of topological phases but also directly correspond to the number of zero-energy corner states, effectively characterizing $\mathbb{Z}$-class higher-order topological insulator phases. Our study proposes the concept of topological heterostructures, providing critical insights into the control of localized corner states within multilayer systems and expanding potential research directions avenues.

A minimal Kitaev chain, consisting of two quantum dots connected via a superconductor, can host highly localized near-zero-energy states, known as poor man's Majoranas (PMMs). These states have been proposed as promising candidates to study Majorana bound states (MBSs) in a highly tunable setup. However, it is unclear whether and how PMMs observed in real systems are actually connected to the topological phase of the full Kitaev chain. Here, we study PMMs using a microscopic model and show that, in the long chain limit, not all PMMs are related to topological states. Rather, in long chains, some PMMs evolve into trivial highly localized low-energy states. We provide an explanation for the occurrence of these states and show that there is no clear conductance signature that is able to distinguish PMMs that evolve into true topological states from PMMs that evolve into trivial states.

In a recent paper by Reed et al. [Phys. Rev. B 105, 205304 (2022)], angle resolved photoemission spectroscopy (ARPES) experimental results as well as density functional theory (DFT) calculations performed on the diamond C(111)-($2\times 1$) surface, both clean and graphene covered, are presented. We only address the first part of the paper (clean surface). On the basis of their photoemission data, the authors claim that the C(111)-($2\times 1$) surface is metallic, adding that “our ARPES measurements do not compare well” with previous experimental results. Indeed, in the literature one can find a number of results obtained with different techniques, including ARPES, proving the semiconducting character of this surface. In this Comment we disagree with the interpretation of the experimental data given in the paper and conclude that the surface is semiconducting and any disagreement with published results is almost completely eliminated. We also discuss the theoretical approach used, placing it in a wider framework. When well founded, also the theoretical simulation shows the semiconducting character of the C(111)-($2\times 1$) surface.

In the Comment by Goletti et al. [Phys. Rev. B 111, 117301 (2025)], concerns are raised regarding the interpretation of our experimental findings, as well as the application of basic ground-state density functional theory (DFT) models pertaining to the $\mathrm{C}\left(111\right)\text{−}(2\times 1)$ surface presented in our earlier publication [Reed et al., Phys. Rev. B 105, 205304 (2022)]. These concerns are addressed and our interpretation of the results is ultimately reconfirmed. We present further analysis of the original data and introduce new measurements on previously unreported regions of the surface reconstructed ($2\times 1$) Brillouin zone, aiding in the evaluation of the dispersion relation at other high-symmetry points. We gain insights relating to the current use of DFT calculations that include many-body theories when relating to the occupied electronic structure of this surface as measured by angle-resolved photoelectron spectroscopy.

Near-hydrodynamic electron flows have been realized in a number of recent experiments, where momentum-conserving collisions dominate the flow behavior. We analyze these flows using a matched asymptotic expansion of the governing linearized Boltzmann equation to second order in the rarefaction parameter—the Knudsen number—with arbitrary diffusely scattering boundaries. We find corrections to the bulk governing equations, boundary conditions, and near-boundary dynamics unreported in the literature. The developed theory is used to solve two-dimensional Poiseuille flow in the near-hydrodynamic regime. Nonhydrodynamic corrections are found to compete with the classical Hall or odd viscosity. Our results are in excellent agreement with high-fidelity numerical solutions of the linearized Boltzmann equation.

Attosecond time-resolved photoelectron spectroscopy reveals photoemission dynamics, for example, via reconstruction of attosecond beating by interference of two-photon transitions (RABBITT). However, the multitude of photoemission peaks in a RABBITT spectrogram often limits the applicability of the method to well-separated photoemission channels. Here, we derive relations between RABBITT oscillations of sidebands and principal bands within strong field approximation. This allows extracting timing information on the photoemission dynamics for rather convoluted RABBITT spectra, for which the common analysis would fail. This improvement is demonstrated for simulated overlapping RABBITT spectrograms based on a solid-state photoemission model showing the robust reconstruction of the individual photoemission delays.

Inspired by the hunt for new phases of matter in quantum mixed states, it has recently been proposed that the equivalence of microcanonical and canonical ensembles in statistical mechanics is a manifestation of strong-to-weak spontaneous symmetry breaking (SWSSB) in an underlying many-body quantum description. Here, we build an effective field theory for SWSSB of a global U(1) symmetry; the answer exactly reproduces the Schwinger-Keldysh effective field theory of diffusion for the conserved charge. We conclude that hydrodynamics can be understood as a theory of superfluidity for the broken strong symmetry: a nonvanishing susceptibility is a measurable order parameter for SWSSB, the diffusion mode is the Goldstone boson of the spontaneously broken continuous symmetry, and a generalization of Goldstone's theorem implies that the diffusion mode is always long lived. This perspective provides a transparent physical explanation for the unusual reparameterization symmetries, which are a necessary ingredient of Schwinger-Keldysh effective field theories for normal fluids.

Low-energy excitations of a two-dimensional electron gas (2DEG) in modulation-doped multiple (ten) quantum wells (QWs) was studied using far-infrared magnetotransmission technique at liquid helium temperatures. A large distance between neighboring QWs of 54 nm excluded a direct interaction of electron wave functions confined in the wells. In four samples which differed in the spacer width and the level of doping with iodine donors, supplied with a metallic grid coupler, a uniform picture of excitations of the 2DEG was observed. These involved the cyclotron resonance (CR), its second harmonic (2CR), and magnetoplasmon modes (MPMs). MPMs with a small amplitude originated from excitations of the 2DEG in a single QW and these with a high amplitude resulted from a coherent excitation of the 2DEG in all wells. A polaron effect resulting from the interaction of the CR, 2CR, and MPMs with an optical phonon was observed and described with appropriate models. Both types of MPMs exhibited gaps in the disperion relations at the frequency close to the 2CR, leading to Bernstein modes, which was described with an appropriate (nonlocal) theoretical model.

The magnetic ground-state configuration of iron selenide (FeSe) has been a topic of debate, with experimental evidence suggesting the stripe spin fluctuations as predominant at low temperatures, while density functional theory calculations using the exchange-correlation (XC) functional of the generalized gradient approximation (GGA) have historically predicted the antiferromagnetic (AFM) dimer configuration. In this study, we utilize the restored-regularized SCAN $\left({\mathrm{r}}^2\mathrm{SCAN}\right)$ functional, a variant of the strongly constrained and appropriately normed (SCAN) meta-GGA, to investigate the magnetic configurations of FeSe. It is found that ${\mathrm{r}}^2\mathrm{SCAN}$ predicts a stripe-AFM ground-state configuration with an antiparallel spin alignment between layers. The energy difference between the parallel and antiparallel interplanar spin alignments is approximately 1.7 meV/atom, predicting a significant but previously unreported interlayer spin coupling not yet observed by experiments. The present study underscores the importance of accurate XC functionals, such as ${\mathrm{r}}^2\mathrm{SCAN}$, in predicting the magnetic ground-state configuration of complex materials like FeSe, highlighting its potential to predict magnetic interactions more reliably than traditional GGA functionals by adhering to exact constraints.

Topological disclinations (TDs), derived from the cut-and-glue process in topological crystalline insulators, have been effectively employed to localize fractional charges in classical wave systems. However, most existing strategies primarily focus on TD modes within the lowest band gap, neglecting the higher-orbital states. As the bands become entangled, higher band gaps are too narrow to support distinguished TD modes from bulk modes. In this work, we successfully demonstrate TD modes within the $s$-, $p$-, $d$-, and higher-orbital band gaps. In addition, we build photonic waveguides under the interplay between valley-Hall topology and TD defects. Unlike the traditional topological edge states confined on the outer boundary of the model, this TD-induced optical paths can hold hybrid-orbital topological waveguides within the sample. Furthermore, a wave propagation network is achieved by interconnecting different TD states, enabling more versatile wave transmission modes across various band gaps. This study paves the way for the manipulation of TD states and waveguides within hybrid-orbital band gaps in photonic crystals, offering promising applications in the design and fabrication of multimode optical devices, such as beam splitters and embedded topological cavities.

Non-Abelian braiding has attracted substantial attention because of its pivotal role in describing the exchange behavior of anyons, in which the input and outcome of non-Abelian braiding are connected by a unitary matrix. Implementing braiding in a classical system can assist the experimental investigation of non-Abelian physics. However, the design of non-Abelian gauge fields faces numerous challenges stemming from the intricate interplay of group structures, Lie algebra properties, representation theory, topology, and symmetry breaking. The extreme diversity makes it a powerful tool for the study of condensed matter physics. Whereas the widely used artificial intelligence with data-driven approaches has greatly promoted the development of physics, most works are limited on the data-to-data design. Here we propose a self-reasoning assistant learning framework capable of directly generating non-Abelian gauge fields. This framework utilizes the forward diffusion process to capture and reproduce the complex patterns and details inherent in the target distribution through continuous transformation. Then the reverse diffusion process is used to make the generated data closer to the distribution of the original situation. Thus, it owns strong self-reasoning capabilities, allowing us to automatically discover the feature representation and capture more subtle relationships from the data set. Moreover, the self-reasoning eliminates the need for manual feature engineering and simplifies the process of model building. Our framework offers a disruptive paradigm shift to parse complex physical processes, automatically uncovering patterns from massive data sets.