Research on charge density waves (CDWs) in 2D transition-metal dichalcogenides like $\mathrm{Ta}{\mathrm{S}}_2$ has predominantly focused on acoustic mode softening, largely overlooking the impact of crystal field effects (CFEs). This oversight has neglected crucial phenomena such as the formation of a flat band and the roles of flat bands in metal–insulator transitions. Our study shows that CFEs are essential for the formation of flat bands, the stability of the CDW phase, and the accompanying metal–insulator transition. These findings provide pivotal insights and pave the way for rational manipulation of CDW phases in 2D materials, offering substantial benefits for practical applications.

We use an exact Moreau-Yosida regularized formulation to obtain the exchange-correlation potential for periodic systems. We reveal a profound connection between rigorous mathematical principles and efficient numerical implementation, which marks a successful application of a Moreau-Yosida-based inversion for physical systems. We develop a mathematically rigorous inversion algorithm that is demonstrated for representative bulk materials, specifically bulk silicon, gallium arsenide, and potassium chloride. Our inversion algorithm allows the construction of rigorous error bounds that we are able to verify numerically. This unlocks a pathway to analyze Kohn-Sham inversion methods, which we expect in turn to foster mathematical approaches for developing approximate functionals.

Swift electrons passing near or through metallic structures have proven to be an excellent tool for studying plasmons and other types of confined optical modes involving collective charge oscillations in the material structures hybridized with electromagnetic fields. In this work, we provide a general analytical framework for the simulation of electron energy-loss spectroscopy (EELS) in infinite systems with cylindrical symmetry, such as wires, holes, and optical fibers. While EELS theory is well developed for electrons moving parallel to the direction of translational symmetry, we introduce closed-form analytical solutions for perpendicular electron trajectories. These analytical results are corroborated by comparison to numerical simulations based on a frequency-domain boundary-element method and a discontinuous-Galerkin time-domain finite-element method. Numerical solutions further allow us to study termination effects in finite-sized cylindrical objects such as nanorods. The present study of the interaction between free electrons and cylindrically symmetric photonic systems can find application in the analysis of EELS spectra and the design of free-electron–photonic hybrid systems.

Recent advancements have established self-intercalation as a powerful technique for manipulating quantum material properties, with precise controllable intercalation concentrations. Given the inherently rich phase diagrams of transition metal dichalcogenides (TMDCs), studying the self-intercalated TMDCs can offer promising candidates for investigating the interplay between various orderings. This paper focuses on fully intercalated bilayer ${\mathrm{TaSe}}_2$ (${\mathrm{Ta}}_3{\mathrm{Se}}_4$), which has recently been fabricated experimentally. By performing first-principles calculations, we demonstrate the suppression of an intrinsic $3\times 3$ charge density wave (CDW) in parent ${\mathrm{TaSe}}_2$ layers, and emergence of $2\times 2$ and $\sqrt{3}\times \sqrt{3}$ or absence of a CDW in the intercalated layers, depending on the stacking sequence and intercalation sites being occupied. Particularly, the $2\times 2$ CDW shows an increase in electronic states at the Fermi level compared to its non-CDW phase. This unusual behavior contrasts with that of typical CDW materials in TMDCs. Furthermore, superconductivity is preserved in these ${\mathrm{Ta}}_3{\mathrm{Se}}_4$ structures, with superconducting transition temperatures comparable to those of ${\mathrm{TaSe}}_2$. Spin-orbit coupling is found to enhance the density of states at Fermi levels while simultaneously reducing the electron-phonon coupling matrix elements. These two competing effects result in varying impacts on superconductivity across different ${\mathrm{Ta}}_3{\mathrm{Se}}_4$ structures. Moreover, our calculations indicate that magnetic order is absent. Our paper deepens the understanding of underlying physics in ${\mathrm{Ta}}_3{\mathrm{Se}}_4$, and provides experimentally feasible candidates for studying CDW, superconductivity, and their interplay.

The common model to describe exciton-plasmon interaction phenomenologically is the coupled oscillator model. Originally developed for atomic systems rather than solid-state matter, this model treats both excitons and plasmons as single harmonic oscillators coupled via a constant which can be fitted to experiments. In this paper, we present a modified coupled oscillator model specifically designed for exciton-plasmon interactions in hybrids composed of two-dimensional excitons, such as in transition metal dichalcogenide (TMDC) monolayers and metal nanoparticles while maintaining the simplicity of the commonly applied coupled oscillator models. Our approach is based on the self-consistent solution of a microscopic material model and Maxwell's equations, allowing us to analytically derive an effective exciton-plasmon coupling constant. Our findings highlight the importance of the spatial dispersion, i.e., the delocalized nature of TMDC excitons, necessitating the distinction between bright and momentum-dark excitons. Both types of excitons occur at different resonance energies and exhibit a qualitatively different coupling with localized plasmons. We find a strong coupling between the plasmon and momentum-dark excitons, while a weakly coupled bright exciton manifests as an additional, third peak in the spectrum. Consequently, we propose a realistic modeling of the primary spectral features in experiments incorporating three harmonic oscillator equations instead of the conventional two. However, we also shed light on the limitations of the three coupled oscillator model in describing the line shape of extinction and scattering cross section spectra.

Scrambling unitary dynamics in a quantum system transmutes local quantum information into a nonlocal web of correlations which manifests itself in a complex spatiotemporal pattern of entanglement. In such a context, we show there can exist three distinct dynamical phases characterized by qualitatively different forms of quantum correlations between two disjoint subsystems of the system. Transitions between these phases are driven by the relative sizes of the subsystems and the degree scrambling that the dynamics effects. Besides a phase which has no quantum correlations as manifested by vanishing entanglement between the parts and a phase which has nontrivial quantum correlations quantified by a finite entanglement monotone, we reveal a new phase transition within the entangled phase which separates phases wherein the quantum correlations are invisible or visible to measurements on one of the subsystems. This is encoded in the qualitatively different properties of the ensemble of states on one of the subsystems conditioned on the various measurement outcomes on the other subsystem. This provides a new characterization of entanglement phases in terms of their response to measurements instead of the more ubiquitous measurement-induced entanglement transitions. Our results have implications for the kind of tasks that can be performed using measurement feedback within the framework of quantum interactive dynamics.

Two-particle interferometry is an important tool for extracting the exchange statistics of quantum particles. We theoretically investigate the prospects of such interferometry to probe the statistics of pointlike anyonic excitations injected in a Hong-Ou-Mandel (HOM) setup based on a quantum point contact device in the fractional quantum Hall regime. We compute the standard HOM ratio, i.e., the ratio of tunneling noises for two- and one-particle injections, and find that for pointlike anyons it only depends on the temperature and the anyon scaling dimension. Importantly, the latter is not necessarily related to the exchange phase. In fact, we establish that the HOM ratio does not reveal the exchange phase of the injected anyons: For injection-time delays that are small compared to the thermal timescale, we find that the exchange phase accumulated due to time-domain braiding between injected and thermally activated anyons is erased due to two mutually canceling subprocesses. In contrast, for time delays large compared to the thermal time, only a single subprocess contributes to the braiding, but the accumulated phase is canceled in the HOM ratio. These findings suggest caution when interpreting HOM interferometry experiments with anyons, and approaches beyond the standard HOM ratio are thus necessary to extract anyonic statistics with two-particle interferometry experiments.

We explore the critical properties of the localization transition in the non-Hermitian Aubry-André-Stark (AAS) model with quasiperiodic and Stark potentials, where the non-Hermiticity comes from the nonreciprocal hopping. The localization length, the inverse participation ratio, and the energy gap are adopted as the characteristic quantities. We perform a scaling analysis to derive the scaling functions of the three quantities with critical exponents in several critical regions, with respect to the quasiperiodic and Stark potentials and the nonreciprocal strength. We numerically verify the finite-size scaling forms and extract the critical exponents in different situations. Two groups of critical exponents for the non-Hermitian AAS model and its pure Stark limit are obtained, which are distinct from those for the non-Hermitian Aubry-André model and their Hermitian counterparts. Our results indicate that the Hermitian and non-Hermitian AAS, Aubry-André, and Stark models belong to different universality classes. We demonstrate that these critical exponents are independent of the nonreciprocal strength, and remain the same in different critical regions and boundary conditions. Furthermore, we establish a hybrid scaling function with a hybrid exponent in the overlap region between the critical regions for the non-Hermitian AAS and Stark models.

Understanding light-induced hidden orders is relevant for nonequilibrium materials control and future ultrafast technologies. Hidden superconducting order, in particular, has been a focus of recent experimental and theoretical efforts. In this study, we investigate the stability of light-induced $\eta$ pairing. Using a memory truncated implementation of nonequilibrium dynamical mean field theory (DMFT) and entropy-cooling techniques, we study the long-time dynamics of the photoinduced superconducting state. In the presence of coupling to a cold phonon bath, the photodoped system reaches a quasi-steady state, which can be sustained over a long period of time in large-gap Mott insulators. We show that this long-lived prethermalized state is well described by the nonequilibrium steady-state implementation of DMFT.

Frustrated spin models may lead to the formation of both classical noncollinear spin structures and unique quantum phases including highly entangled quantum spin liquids. Here, we study the entanglement and spatial quantum correlations in linear spin-wave theory around a classical spin spiral ground state. We find that the entanglement between pairs of sites is short-ranged, and is completely absent in certain cases. In contrast, the entanglement hidden in multisite clusters is peaked close to phase transitions and shows an asymptotic behavior modulated by the period of the magnetic structure. These findings motivate further exploring the connection in the entanglement properties of fully quantum and of quasiclassical spin models.

We investigate the easy-axis Heisenberg model on the triangular lattice by numerically studying excitations and the dynamical spin structure factor $S^{\mu \mu }(\mathbf{q},\omega )$. Results are analyzed within the supersolid scenario, characterized by the translation-symmetry-breaking parameter $m_z$ and the supersolid offdiagonal order parameter $m_{\perp }$. We find very robust $m_z>0$ in the whole easy-axis anisotropy regime $\alpha =J_{\perp }/J_z>0$, even enhanced by the magnetic field $h>0$, as well as $m_{\perp }>0$ for intermediate $\alpha <1$ and $h>0$. Still, at small $\alpha \lesssim 0.2$, relevant for recent experiments on the magnetic material ${\mathrm{K}}_2\mathrm{Co}{\left({\mathrm{SeO}}_3\right)}_2$, we find at $h=0$ rather vanishing $m_{\perp }\sim 0$, which appears compatible with the numerically established finite magnon excitation gap ${\mathrm{\Delta }}_1\sim 0.25\alpha J$.

Using the combination of a new effective Hamiltonian approach and hybrid Monte Carlo simulations, we unveil a variety of partially magnetically ordered (PMO) phases in the Kondo lattice model. Our approximation is motivated by two crucial features of the Hamiltonian: (i) formation of Kondo singlets leading to vanishing local magnetic moments, and (ii) spatially correlated nature of the effective single-particle kinetic energy. We discover PMO phases with fractional values $1/4$, $3/8$, and $1/2$ of Kondo-screened sites. A common understanding of these states emerges in terms of a nonlocal ordering mechanism. Our semiclassical approach can be generalized to study other interacting quantum systems in the intermediate coupling regime.

We report the magnetic properties of the quantum triangular lattice antiferromagnet ${\mathrm{PrMgAl}}_{11}{\mathrm{O}}_{19}$ through magnetization and specific-heat measurements. Strong magnetic anisotropy indicates the realization of an Ising-like magnetism in ${\mathrm{PrMgAl}}_{11}{\mathrm{O}}_{19}$ single crystal while no long-range magnetic ordering is realized down to 0.4 K. The splitting of the low-lying quasidoublet of the non-Kramers ion $\mathrm{P}{\mathrm{r}}^{3+}$ into two singlets, suggested by experimental data, is consistent with an effective pseudospin-1/2 scenario. Single-crystal x-ray diffraction shows the repartition of $\mathrm{P}{\mathrm{r}}^{3+}$ ions between two slightly different positions in their oxygen cage, and specific-heat measurements consistently show a double-Schottky anomaly, attributed to excitations between the two singlets of the low-lying quasidoublet from the two distinct sites. The observed gapless excitations in zero field are attributed to induced quantum magnetism, predicted when the magnetic interactions are of an energy scale comparable with the splitting between the two singlets. Based on these results, we find that the magnetic ground state of ${\mathrm{PrMgAl}}_{11}{\mathrm{O}}_{19}$ can be modeled by a quantum Ising magnet with an intrinsic transverse field rather than a quantum spin liquid.

Currently, antiferromagnetic spintronics is mostly studied for antiferromagnets with special antiferromagnetic crystal structures originating from symmetry breaking involving time-reversal and inversion symmetries. Here, we report the surface-induced topological Hall effect in antiferromagnet $\gamma$-FeMn films. $\gamma$-FeMn with a noncoplanar magnetic structure has long been thought to have no special Hall effect transport properties due to its highly symmetrical spin structure. However, experimental evidence suggests that the unexpected Hall effect of epitaxial (polycrystalline) $\gamma$-FeMn has a source other than the magnetization. The anisotropic rotation of the FeNi films caused by $\gamma$-FeMn suggests that the noncoplanar spin structure may preserve its characteristic at the surface, resulting in the topological Hall effect. By fitting the unexpected Hall effect of $\gamma$-FeMn films with thicknesses, it is shown that the anomalous transverse signal originates from the surface in the epitaxial films, while it originates from the bulk in the polycrystalline films. Combining with the scaling analysis, we experimentally demonstrate the existence of the surface topological Hall effect in noncoplanar antiferromagnet $\gamma$-FeMn. Our work provides perspectives for investigating the fascinating physical properties of triple-Q antiferromagnets.

In two dimensional magnets, the interplay of thermal fluctuations and spin anisotropy control the existence of long-range magnetic order. In the van der Waals antiferromagnets ${\mathrm{FePX}}_3$, orbital degeneracy in the $t_{2g}$ levels of the ${\mathrm{Fe}}^{2+}$ ions in octahedral coordination yields strong uniaxial anisotropy, which stabilizes magnetic order up to $T\approx 100$ K. Recent inelastic neutron scattering measurements around the magnetic ordering transition have shown the existence of a broad spectrum of magnetic fluctuations with nontrivial momentum dependence, which has been interpreted as evidence for localized entangled cluster excitations. In this paper, we offer an alternative interpretation using classical nonlinear spin dynamics simulations. We present stochastic Landau Lifshitz dynamics simulations that reproduce the neutron scattering measurements of Chen et al. [npj Quantum Mater. 9, 40 (2024)] on ${\mathrm{FePSe}}_3$. These calculations faithfully explain the dynamical structure factor's momentum and energy dependence and point to a classical origin for the excitations observed in neutron spectroscopy and that the order-disorder transition can be understood in terms of thermal fluctuations overcoming the anisotropy energy.

Anisotropic magnetoresistance (AMR) is a well-known magnetoelectric coupling phenomenon, commonly exhibiting twofold symmetry with respect to the angle of the magnetization relative to the current. In this study, we reveal the existence of high-order AMRs in two-dimensional (2D) magnetic monolayers. Based on density functional theory (DFT) calculations of ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ and ${\mathrm{CrTe}}_2$ monolayers, we find that different energy bands contribute uniquely to AMR behavior. The high-order AMR is attributed to strong spin mixing at band crossing points, which induces significant Berry curvature. This curvature also contributes to the AMR for electrons with dominant spin-up or spin-down polarization characteristics. However, for electrons exhibiting strong spin mixing, the Berry curvature effect becomes nontrivial, resulting in high-order AMR. Our findings provide an effective approach to identifying and optimizing materials with high-order AMR, which is critical for designing high-performance spintronic devices.

Recent experiments on planar superconductor-topological insulator-superconductor (S-TI-S) junctions, e.g., in the Corbino geometry, have reported low-temperature nonzero Josephson currents in states with integer fluxoid (flux) induced in the junction by a perpendicular magnetic field. This effect was discussed in connection with Majorana zero modes localized in Josephson vortices of such junctions. Here, we provide an explanation for this phenomenon, attributing it to imperfections. We focus on the “atomic” limit in which the low-energy bound states of different vortices do not overlap. In this limit, we can associate the nonvanishing critical current with the irregularities, e.g., in the junction's width. The low-temperature contribution to the current is provided by the bound states with low but nonzero energy. We also propose clear experimental tests based on microwave spectroscopy, revealing distinctive selection rules for vortex transitions.

Supercurrent field-effect transistors made from thin metallic films are a promising option for next-generation high-performance computing platforms. Despite extensive research, there is still no complete quantitative microscopic explanation for how an external dc electric field suppresses superconductivity in thin films. This study aims to provide a quantitative description of superconductivity as a function of film thickness based on Eliashberg's theory. The calculation considers the electrostatics of the electric field, its realistic penetration depth in the film, and its effect on the Cooper pair, which is described as a standard $s$-wave bound state according to BCS theory. The estimation suggests that an external electric field of approximately ${10}^8$ V/m is required to suppress superconductivity in films 10–30 nm thick, which aligns with experimental observations. Ultimately, the study offers “materials-by-design” guidelines for suppressing supercurrent when an external electric field is applied to the film surface. Furthermore, the proposed framework can be easily extended to investigate the same effects for ultrathin films.

${\mathrm{HfO}}_2$-based ferroelectric materials are promising for the next generation of memory devices, attracting significant attention. However, their potential applications are significantly limited by fatigue and imprint phenomena, which affect device lifetime and memory capabilities. Here, to accurately describe the dynamics and field effects of ${\mathrm{HfO}}_2$, we adopt our newly developed DREAM-Allegro network scheme and develop a comprehensive machine-learning model for ${\mathrm{HfO}}_2$. Such a model can predict not only the interatomic potential, but also the Born effective charges for any structures. Applying such model, we explore the role of domain dynamics in ${\mathrm{HfO}}_2$ and find that the fatigue and imprint phenomena are closely related to the domain and domain-wall dynamics, where the dynamics can be summarized into two pivotal switching pathways. Based on the different atomic motions in the two paths, we propose that an inclined electric field can sufficiently suppress fatigue and enhancing the performance of ${\mathrm{HfO}}_2$-based ferroelectric devices.