We study exchange interactions in iron and nickel within the density functional theory plus dynamical mean-field theory approach with density-density and SU(2) symmetric Coulomb interaction. In particular, we analyze the representation of exchange interactions through the electron nonlocal Green's functions, connecting the local particle-hole (ph) irreducible interaction vertices. While the neglect of the local ph irreducible vertex corrections, suggested previously within the dual fermion approach [E. A. Stepanov, S. Brener, F. Krien, M. Harland, A. I. Lichtenstein, and M. I. Katsnelson, Phys. Rev. Lett. 121, 037204 (2018)], yields the result corresponding to the generalization of the magnetic force theorem approach, we argue that these vertex corrections are less important for strong localized magnets, such as iron, but become more essential for weak itinerant magnets, such as nickel. At the same time, the overall account of the local vertex and self-energy corrections in the so-called renormalized magnetic force theorem approach is essential for iron, and less important for nickel. The difference of the results of density-density and SU(2) symmetric Coulomb interaction is found to be relatively small, in contrast to the Curie temperature and the value of the local magnetic moment.

Atomic force microscopy (AFM) combined with electrical modes provides a powerful contactless approach to characterize material electrical properties at the nanoscale. However, conventional electrostatic models often overlook dynamic charge effects, which are particularly relevant for two-dimensional (2D) materials deposited on insulating substrates. In this work, we introduce a theoretical framework that extends traditional electrostatic models by incorporating charge dynamics, analyzing two key cases: nonideal conductors and nonideal insulators. Our model establishes a characteristic timescale $\tau$, which governs charge redistribution and measurement reliability. Experimental validation using graphene oxide (GO), reduced graphene oxide, and lightly reduced GO demonstrates strong dependence of frequency shift on surface conductivity, confirming our predictions. Temperature-dependent measurements further reveal conductivity variations consistent with disordered electronic materials. These findings offer valuable insight into how finite surface conductivity influences AFM-based techniques. They introduce an approach for analyzing charge dynamics on individual flakes of 2D materials while also presenting a contactless method for estimating surface conductivity.

We report on the formation of moiré patterns when observing the diffraction of surface plasmons by periodic gratings of finite extent with an imaging spectrometer that maps the light emission as a function of the wavelength and the propagation distance. This phenomenon results from the formation of standing waves upon the partial reflection of surface plasmons at the far end of the grating and their scattering by the periodic corrugations. The moiré fringes are created as a result of the incommensurability between the sampling pitch of the grating and the wavelength-dependent standing waves. We introduce a scalar model that supports these observations and provides physical insight into these results, including a method to estimate the complex Fresnel reflection coefficient of a surface plasmon at the edge of a grating.

Frustrated magnets can elude the paradigm of conventional symmetry breaking and instead exhibit signatures of emergent symmetries at low temperatures. Such symmetries arise from “accidental” degeneracies within the ground-state manifold and have been explored in a number of disparate models, in both two and three dimensions. Here we report the systematic construction of a family of classical spin models that, for a wide variety of lattice geometries with triangular motifs in one, two, and three spatial dimensions, such as the kagome or hyperkagome lattices, exhibit an emergent, continuous U(1) symmetry. This is particularly surprising because the underlying Hamiltonian actually has very little symmetry—a bond-directional, off-diagonal exchange model inspired by the microscopics of spin-orbit entangled materials (the ${\mathrm{\Gamma }}^{\prime }$ model). The construction thus allows for a systematic study of the interplay between the emergent continuous U(1) symmetry and the underlying discrete Hamiltonian symmetries in different lattices across different spatial dimensions. We discuss the impact of thermal and quantum fluctuations in lifting the accidental ground-state degeneracy via the thermal and quantum order-by-disorder mechanisms, and how spatial dimensionality and lattice symmetries play a crucial role in shaping the physics of the model. Complementary Monte Carlo simulations, for representative one-, two-, and three-dimensional lattice geometries, provide a complete account of the thermodynamics and confirm our analytical expectations.

We study Yang-Lee zeros as they approach the thermodynamic limit of the two-dimensional (2D) nearest-neighbor antiferromagnetic Ising model on square and triangular lattices. We employ the numerical linked cluster expansion (NLCE) equipped with exact enumeration (EE) of the partition function to estimate the Laplacian of the free energy, which is proportional to the zeros density. Using a modified NLCE, where the expansion can be carried directly on the Yang-Lee zeros of the involved clusters, we estimate the density of Yang-Lee zeros in the thermodynamic limit. NLCE gives significantly more zeros than EE in the complex field plane providing more insights on how the root curves look in the thermodynamic limit. For the square lattice at $T\ll T_c$, the results suggest that two vertical lines at $\pm h_c\left(T\right)$ in the complex field plane (i.e., two concentric circles in the complex fugacity plane) are the thermodynamic root curves. A similar picture is found for the triangular lattice for phase transitions at large values of magnetic field while further study is needed for phase transitions at smaller values of magnetic field. The convergence of the NLCE and (EE) calculations of the partition function to the thermodynamic limit is studied in both lattices and the temperature-field phase diagram is obtained from Yang-Lee zeros using both methods. This NLCE-based approach will facilitate the study of different types of phase transitions using Yang-Lee zeros in future research.

Instantons, semiclassical trajectories of quantum tunneling in imaginary time, have long been used to study thermodynamic and transport properties in a myriad of condensed matter and high-energy systems. A recent experiment in superconducting circuits [R. Kuzmin et al., Phys. Rev. Lett. 126, 197701 (2021)] provided first evidence for direct dynamical signatures of instantons (phase slips), manifested by order-unity inelastic decay probabilities for photons with which they interact, motivating the development of a scattering theory of instantons [A. Burshtein et al., Phys. Rev. Lett. 126, 137701 (2021)]. While this framework successfully predicted the measured inelastic decay rates of the photons for several experimental devices, it is valid only if the tunneling time of the instantons is much shorter than the relaxation time due to the environment in which they are embedded, and requires a closed analytical expression for the instanton trajectory. Here, we alleviate these restrictions by incorporating numerical methods that eliminate some of the previously applied approximations. Our results improve the agreement with the experimental measurements, also for devices with lower impedances and thus shorter relaxation times, without fitting parameters. This framework should be useful in many other quantum field theoretical contexts.

The coupling between electronic nematic degrees of freedom and acoustic phonons is known to significantly alter the universality class of a nematic quantum critical point (QCP). While non-Fermi-liquid behavior emerges in the absence of lattice coupling, the inclusion of interactions with acoustic phonons results in observables such as heat capacity and single-particle scattering rate exhibiting only subleading nonanalytic corrections to dominant Fermi-liquid terms. In this work, we demonstrate that the elastocaloric effect (ECE), the adiabatic temperature change under varying strain, and the thermal expansion deviate from this pattern. Despite lattice coupling weakening the singularity of the ECE, it preserves a dominant temperature dependence that deviates from the prediction one would obtain from Fermi-liquid theory, an effect which we will refer to as an elastocaloric anomaly. By drawing analogies between nematic systems and field-tuned altermagnets, we further show that similar responses are expected for the ECE near altermagnetic QCPs. We classify the types of piezomagnetic couplings and analyze the regimes arising from field-tuned magnetoelastic interactions. Our findings are shown to be consistent with the scaling theory for elastic quantum criticality and they further emphasize the suitability of the ECE as a sensitive probe near QCPs.

We formulate the $Z_N$ group gauging operations (or group extensions) in (smeared) boundary conformal field theories (BCFTs) and bulk conformal field theories, and study their applications to various phenomena in topologically ordered systems. We apply the resultant theories to analyze the correspondence between the renormalization group (RG) flow of CFTs and the classification of topological quantum field theories using the testable information of general classes of partition functions. One can obtain the bulk topological properties of the $2+1$ dimensional topological ordered phase corresponding to the massive RG flow of the $1+1$ dimensional systems equivalent to the smeared BCFT. We present an obstruction to mass condensation for the smeared BCFT analogous to the Lieb-Shultz-Mattis theorem for noninvertible symmetry. Corresponding to the bulk topological degeneracies in $2+1$ dimensions and gapped quantum phases in $1+1$ dimensions, we construct a new series of BCFT. We also study the implications of the massless RG flow of the $1+1$ dimensional CFTs corresponding to the domain wall or coupling problem in $2+1$ dimensional topological orders, which corresponds to the earlier proposal by L. Kong and H. Zheng [Nucl. Phys. B 966, 115384 (2021)] closely related to the integer-spin simple current by Schellekens and Gato-Rivera. We reveal that two distinct kinds of massless RG flow exist, coming from anomaly cancellation and anomaly matching related to Witt equivalence of bulk CFTs. The anomaly cancellation flows produce a new series of modular invariants as coupled models, and the anomaly matching flows produce nontrivial domain walls changing the chirality of anyons. Our paper gives a unified direction for future theoretical and numerical studies of the topological phase based on the established data of classifications of conformal field theories or modular invariants (and the corresponding category theories).

Power generation through the anomalous Nernst effect in topological Weyl materials has several advantages over conventional thermoelectrics due to the transverse geometry. However, the magnitude of the anomalous Nernst conductivity (ANC) in most known materials is too small to be of practical use, and there exist few guiding principles for finding materials with optimal thermoelectric properties. This work shows that the ANC is maximal when there is a “coactive-staggered” feature in the anomalous Hall conductivity (AHC). It is shown that a minimal arrangement of two Weyl pairs leads to such a feature, and tuning the separations between the pairs controls the temperature at which the ANC is maximal. Several methods are proposed for creating such arrangements of Weyl points starting from Dirac semimetal materials. It is also demonstrated how an existing coactive-staggered AHC in a Heusler material can be exploited, by collectively tuning the positions of the Weyl points through strain to further enhance the ANC. A modest 20% amplification of the ANC is achieved, even with relatively minor changes in Weyl point positions.

Adding spin-polarized carriers to semiconductor lasers strongly changes their properties and, through the transfer of angular momentum, leads to the emission of circularly polarized light. In such spin-lasers, the polarization of the emitted light can be modulated an order of magnitude faster than its intensity in the best conventional lasers. This ultrafast operation in spin-lasers relies on large linear birefringence, usually viewed as detrimental in spin and conventional lasers, which couples the two linearly polarized emission modes. We show that the dynamical properties of birefringent spin-lasers under intensity and polarization modulation are accurately described as coupled harmonic oscillators. Our model agrees with the intensity-equation description which, unlike the common complex field components describing the role of birefringence in laser dynamics, uses simpler real quantities and allows analytical solutions. We further predict unexplored operation regimes and elucidate the difference between the weak and strong coupling in spin-lasers.

In this study, we apply shortcut to adiabaticity pulses (time-dependent Rabi frequency and detuning) for the efficient population transfer from the ground to the exciton state in a GaAs/InGaAs quantum dot with phonon-induced dephasing. We use the time-evolving matrix product operator method to propagate system in time and find that, for temperatures below $20\text{K}$ and pulse duration up to $10\text{ps}$, a very good transfer efficiency is obtained in general. We explain these results using a Bloch-type equation derived from a generalized Lindblad equation, which adequately describes system dynamics at lower temperatures. For higher temperatures, the transfer efficiency is significantly reduced except for subpicosecond pulses, where the shortcut Rabi frequency reduces to a delta pulse attaining a fast population inversion. This work is expected to find application in quantum technologies which exploit quantum dots for single-photon generation on demand.

Longitudinal nonlinear response plays a crucial role in nonreciprocal charge transport, and it may provide a simple electrical means to probe spin-orbit coupling, magnetic order, and polarization states, etc. Here, we report on a study on the polarization and magnetic field control of longitudinal nonlinear transport in two-dimensional (2D) ferroelectrics with in-plane polarization. Based on the Boltzmann transport theory, we first study this using a general Hamiltonian model, and we show that the nonlinear conductivity can be significantly tuned by the polarization and magnetic field. In addition, the nonlinear conductivity reveals a strong spatial anisotropy. We further derive the analytical formulas for the anisotropic nonlinear conductivity in exact accordance with numerical results. Then, we exemplify those phenomena in the 2D ferroelectric SnTe monolayer in the presence of an external magnetic field based on density functional theory calculations. It is also revealed that the polarity of nonlinear conductivity is locked in the direction of polarization, thus pointing to the feasibility of the nonlinear detection of polarization states. Our work uncovers intriguing features of the longitudinal nonlinear transport in 2D ferroelectrics, and it provides guidelines for designing the polarization control of rectifying devices.

We study inversion-symmetry (IS) breaking in impurity dimers coupled to topological multi-Weyl systems in the low-energy dispersion domain. In the IS-preserved multi-Weyl semimetal phase, Hubbard bands split into symmetric and antisymmetric molecularlike subbands. Breaking IS induces a transition to a multi-Weyl metal, lifting the degeneracy of the Weyl node and closing the pseudogap. This causes opposite energy shifts: valence-band symmetric (antisymmetric) subbands red (blue) shift, reversing in the conduction band until a degeneracy point. Beyond this threshold, symmetric bands flatten near band cutoffs, whereas antisymmetric bands form quasizero energy modes asymptotically approaching—yet never crossing—the Fermi level. Crucially, identical molecular symmetries maintain nondegeneracy even as energy separation vanishes with stronger IS breaking. Our results demonstrate symmetry-selective mechanisms for topological molecular states in multi-Weyl systems.

Twisted bilayer transition metal dichalcogenides, such as ${\mathrm{MoTe}}_2$, provide a versatile platform for exploring correlated topological phases. This work investigates the interplay between perpendicular magnetic and electric fields in tuning the electronic structure and emergent topological orders of twisted bilayer ${\mathrm{MoTe}}_2$ (t-${\mathrm{MoTe}}_2$) across two distinct regimes: a low-twist-angle phase ($\theta \approx 2.1^{\circ }$) hosting multiple Chern bands of identical Chern numbers per valley, and a higher-angle phase ($\theta \approx 3.{89}^{\circ }$) featuring Haldane-like bands with opposite Chern numbers. Using a continuum model incorporating moiré potentials up to second harmonics, we compute the Hofstadter fractal spectra under applied fields, revealing Landau fan structures and magnetic-flux-dependent band topology. These fractal spectra are useful in studying emergent topological orders in terms of the composite fermion picture, where the statistical Chern-Simons flux is approximated as a uniform gauge field. We demonstrate that the system hosts both Jain-sequence fractional Chern insulators (FCIs) and non-Jain “fractal FCIs” with higher Chern numbers. The electric field suppresses composite fermion gaps and induces topological quantum phase transitions. Furthermore, our analysis extends to valley-contrasting flux attachment, proposing pathways to describe fractional quantum spin Hall states.

Following Hollins et al. [J. Phys.: Condens. Matter 29, 04LT01 (2017)], we invert the electronic ground-state densities for various semiconducting and insulating solids calculated using several density functional approximations within the generalized Kohn-Sham (GKS) scheme, which includes Hartree-Fock (HF) theory, hybrid schemes, and the $\mathrm{LDA}+U$ method. To appraise the role of locality versus nonlocality in the effective KS/GKS potential, the band structures from the resulting local exchange-correlation (LXC) Kohn-Sham potential are then compared with the band structures of the original GKS method. We find the LXC potential obtained from the HF density systematically predicts band gaps in good agreement with experiment, including for strongly correlated transition metal monoxides. Furthermore, we find that the HSE06 and PBE0 hybrid functionals yield similar densities and LXC potentials to each other. In weakly correlated systems, these potentials are also similar to PBE. For $\mathrm{LDA}+U$ densities, the LXC potential partly reverses the excessive flattening of bands caused by too-large Hubbard $U$ values. For meta-GGAs, we find only small differences between the GKS and LXC results, demonstrating that the nonlocality of meta-GGAs is weak.

Structural softness–often characterized by unstable phonon modes and large electromechanical responses–is a hallmark of ferroelectric perovskites, like ${\mathrm{BaTiO}}_3$ or $\mathrm{Pb}\left(\mathrm{Ti},\mathrm{Zr}\right){\mathrm{O}}_3$. Whether ${\mathrm{HfO}}_2$ ferroelectrics present any such structural softness is still a matter of debate. Here, using first principles calculations, we predict that it is possible to induce structural instabilities in hafnia. More specifically, our calculations show that in-plane epitaxial tensile strain causes a mechanical instability of the ferroelectric phase $\left(Pca{2}_1\right)$, which transforms discontinuously into an antipolar polymorph (Pbcn). Then, upon reduction of the tensile strain, the antipolar polymorph transforms back to the ferroelectric state through a soft phonon instability. We show that the softening is accompanied by enhancements in the dielectric and piezoelectric responses. While these transitions occur at high epitaxial strains for pure ferroelectric ${\mathrm{HfO}}_2$, we show that the required deformations are considerably lowered in superlattices with other simple oxides, which may facilitate realizing these effects experimentally.

Understanding the fundamental properties of uranium nitride (UN) is critical for the development of accident-tolerant nuclear fuel and anticorrosion technology for uranium metal. Nevertheless, more complex magnetic configurations and possible multipolar interactions remain largely unexplored. Here, by combining the density functional theory with the magnetic multipolar Hamiltonian methods, and employing multiple calculational strategies such as the treatment of strong correlation interactions, regulation of spin-orbit coupling (SOC) magnitude, control of the $5f$ occupation matrix, constraint of magnetic orientation, and decomposition of magnetic interaction energy, we examined both collinear and noncollinear magnetic configurations in the UN compound. Typically, the local magnetic vectors in the $n\mathbf{k}$ ($n$ = 1–3) configurations were comprehensively evaluated. Our calculations showed that the SOC effect plays a decisive role in stabilizing the noncollinear multi-$\mathbf{k}$ states, with the longitudinal $3\mathbf{k}$ antiferromagnetic configuration identified as the magnetic ground state. We revealed that the magnetic quadrupole-quadrupole interaction contributes to the transverse $3\mathbf{k}$ configuration, while the magnetic dipole-dipole interaction contributes to the longitudinal $3\mathbf{k}$ configuration in UN. The theoretical framework presented, incorporating multiple strategies, offers valuable guidance for further studies on multi-$\mathbf{k}$ magnetic configurations in strongly correlated magnetic systems. Additionally, the interplay between SOC and multipolar magnetic interactions enhances our understanding of magnetic behavior in systems with highly localized $f$ electrons, such as actinide compounds.

The growing demand for structural materials with superior mechanical and damping properties in dynamic applications has driven the exploration of advanced nanocomposites. In this study, we introduce a strategy to simultaneously enhance the mechanical and damping properties of metal matrix nanocomposites by embedding three-dimensional graphene origami (GOri). Molecular dynamics simulations show that GOri/Cu nanocomposites exhibit enhanced tensile mechanical properties and damping performance compared to single-crystal copper (Cu). The mechanical enhancement arises primarily from dislocation blocking at the Cu-GOri interface and the unfolding deformation of the embedded GOri. Under cyclic loading, the $Q$ factor of GOri/Cu nanocomposites is significantly lower than that of single-crystal Cu, indicating a substantial increase in energy dissipation. Detailed analysis points to interfacial friction as the dominant energy dissipation mechanism, driven by unfolding-refolding motions of the embedded GOri. Furthermore, the damping performance is shown to improve with increasing loading frequency, strain amplitude, graphene content, and ambient temperature. The degree of GOri folding plays a critical role: greater folding leads to a rougher interface, thereby enhancing interfacial energy dissipation. These findings provide valuable insights into the design of nanocomposites with improved performance for dynamic applications.