We present a comprehensive investigation of the electronic structures of the $R\mathrm{F}{\mathrm{e}}_2{X}_2$ family ($R$ = Y, La, Lu; $X$ = Ge, Si) using density functional theory (DFT) combined with dynamical mean-field theory (DMFT), with a particular focus on the origin of the flat band observed in $\mathrm{YF}{\mathrm{e}}_2\mathrm{G}{\mathrm{e}}_2$. Our calculations reveal that besides $\mathrm{YF}{\mathrm{e}}_2\mathrm{G}{\mathrm{e}}_2$, only $\mathrm{LuF}{\mathrm{e}}_2\mathrm{G}{\mathrm{e}}_2$ exhibit a nearly flat band around the M point. We demonstrate that, in addition to kinetic frustration and strong electronic correlation effects, hybridization between the $R$ and Fe $d$-orbitals plays a crucial role in the formation of flat bands. By manipulating the crystal structure and doping of $\mathrm{LuF}{\mathrm{e}}_2\mathrm{G}{\mathrm{e}}_2$ to tune the hybridization between Lu and Fe, we successfully reproduce a flat band similar to that in $\mathrm{YF}{\mathrm{e}}_2\mathrm{G}{\mathrm{e}}_2$. The high sensitivity of the flatness of the heavy band in $\mathrm{LuF}{\mathrm{e}}_2\mathrm{G}{\mathrm{e}}_2$ to structural modifications and doping provide us a new strategy for manipulating $d$-electron heavy fermion states. Our findings not only clarify how kinetic frustration, hybridization, and strong electronic correlation effects synergistically drive the emergence of flat bands in $R\mathrm{F}{\mathrm{e}}_2{X}_2$ but also pave the way for exploring new $d$-electron heavy fermion systems.

The investigation of quantum impurity models plays a crucial role in condensed matter physics because of their wide-ranging applications, such as embedding theories and transport problems. Traditional methods often fall short in producing accurate results for multi-orbital systems with complex interactions and off-diagonal hybridizations. Recently, tensor-train-based integration and summation techniques have shown promise as effective alternatives. In this study, we use tensor train methods to tackle quantum impurity problems formulated within the imaginary-time inchworm hybridization expansion framework. We identify key challenges in the inchworm expansion itself and its interplay with tensor-train-based methods. We demonstrate the accuracy and versatility of our approach by solving general quantum impurity problems. Our results suggest that tensor-train decomposition schemes offer a viable path toward accurate and efficient multi-orbital impurity solvers.

Recent advances in photonic structures with three-dimensional (3D) Weyl points offer exciting opportunities for exploring nontrivial Fermi arc surface states and enabling novel light-manipulation capabilities. However, previous studies mainly focused on exploring Fermi arc surface states operating in a single frequency band, leading to limited potential applications in multiband topological photonic routing, wave division, switching, and so on. Here, we demonstrate the existence of dual-band topological Fermi arc surface states in the 3D chiral photonic Weyl metamaterials. The dual-band gap mode physics originates from the Weyl points of different frequencies and the time-reversal symmetry is preserved. Through rigorous theoretical analysis, we study the size of the dual-band gaps that vary with the parameter $k_z$ and reveal the Weyl points as the critical points for topological phase transitions. Remarkably, the bandwidth-controllable, highly localized, and unidirectional dual-band Fermi arc surface states appear when the chiral metamaterials are in contact with the vacuum state. Moreover, a type of four-channel reconfigurable and multiband topological photonic routings is demonstrated utilizing the dual-band Fermi arc surface states. We reveal that the physical mechanism of realizing the multichannel reconfigurable topological pathways is caused by the frequency-chirality-locking of the highly localized Fermi arc surface states. Our work could offer insights into 3D Weyl semimetals and provide more flexibility for multiband topological photonic routings.

As the characteristic feature of the generalized Kerker effect in Mie theory, directional scattering elimination has been playing a pivotal role in nanophotonics and many other photonic disciplines, such as singular optics and topological photonics. Generally, zero-directional scattering can be obtained only for a specific incident polarization, and to make it fully independent of arbitrary polarizations would require scatterers that exhibit geometric (e.g., mirror) symmetries. Here, we revisit the generalized Kerker effect and directional scattering elimination not from the perspective of conventional electromagnetic multipoles, but rather quasinormal modes supported by non-Hermitian systems. We reveal how to obtain zero-directional scattering that is independent of arbitrary incident polarizations, even for scattering structures that do not exhibit the required geometric symmetries. Such geometric symmetry-free and polarization-independent responses are made accessible through a synchronous exploitation of electromagnetic reciprocity and geometric phase. Our discovery can stimulate fundamental explorations and practical applications in not only photonics, but also many other wave physics branches where scattering and geometric phases are pervasive.

Scanning tunneling microscopy (STM) at 5 K was used to study individual Au atoms adsorbed on the surface of a $\mathrm{WS}{\mathrm{e}}_2$ layer grown on epitaxial graphene. In line with theoretical predictions, scanning tunneling spectroscopy measurements reveal that the weakly bound adatom gives rise to an electronic state within the energy band gap of the $\mathrm{WS}{\mathrm{e}}_2$ layer. Adatoms in different surface locations show different gap-state energy values that follow a random distribution around the Fermi level of the sample with a standard deviation of ∼50 meV. The location-dependent shift is attributed to spatial variations in disorder potential. Tunneling via the gap state is accompanied by vibrational excitations as apparent from pronounced sideband peaks in the conductance spectra with Poisson-distributed intensities indicating significant electron-phonon coupling with a Huang-Rhys factor of $S$ ≅ 2.8. STM tunneling through single Au adatoms on two-dimensional $\mathrm{WS}{\mathrm{e}}_2$ constitutes a model case of resonant double-barrier tunneling accompanied by strong coupling to vibrational degrees of freedom.

We investigate the formation of excitonic bound states in the continuum in van der Waals (vdW) heterostructures composed of two-dimensional excitonic vdW layers and an optically resonant patterned vdW thin film. We show that the radiative losses of the exciton can be completely suppressed—not through conventional methods such as total internal reflection, Bragg mirrors, or metallic layers, but instead via destructive interference of exciton emission rates to distinct optical modes of the metasurface. We formulate the general conditions of excitonic BICs as a vanishing Purcell factor with nonvanishing vacuum local density of states at the exciton frequency. We propose a mechanism to achieve excitonic quasi-BICs with almost complete suppression of radiation via exciton coupling with a guided-mode resonance and multiple Fabry-Pérot modes. We show that in unpatterned vdW slabs, the Purcell factor suppression is defined exclusively by the slab's permittivity achieved via positioning the 2D exciton layer in the minimum of the mode electric field. We confirm through numerical simulations that, in periodically patterned heterostructure metasurfaces, the Purcell factor can be suppressed by more than five orders of magnitude, and this effect is not due to vanishing local electric fields. Our results demonstrate the formation of excitonic quasi-BICs and their potential for advancing quantum optics and information processing.

We introduce a basic formalism for computing thermal radiation by combining Waterman's $\text{T}$-matrix method with an algebraic approach to light-matter interactions. The formalism applies to nanoparticles, clusters thereof, and also molecules. In exemplary applications, we explore how a chiral structure can induce an imbalance in the circular polarization of thermal radiation. While the imbalance is rather small for a chiral molecule such as R-BINOL, a much larger imbalance is observed for an optimized silver helix of approximately 200 nm in size. Besides the directional Kirchhoff law used in this article, the formalism is suitable for implementing more nuanced theories, and also provides a straightforward path to the computation of thermal radiation spectra of astronomical objects moving at relativistic speeds with respect to the measurement devices.

The present work aims to address the effect of self-doping and a combined perturbation of self- and vacancy doping on the structural, magnetic, and magnetofunctional properties of MnNiGe-based magnetic equiatomic alloys of nominal compositions ${\mathrm{Mn}}_{1-x}{\mathrm{Ni}}_{1+x}\mathrm{Ge}$ (for $x$ = 0.2 and 0.15), ${\mathrm{Mn}}_{1+y}{\mathrm{Ni}}_{1-y}\mathrm{Ge}$ (for $y$ = 0.2 and 0.22), and ${\mathrm{Mn}}_{1+z}{\mathrm{Ni}}_{0.9-z}\mathrm{Ge}$ ($z$ = 0.03 and 0.06). Experimental findings reveal that all six alloys undergo martensitic type first-order phase transition and the transition is found to be shifted towards lower temperature with increasing doping concentration. Structural investigation reveals the incomplete nature of the martensitic phase transitions. A substantial magnetic entropy change near the martensitic phase transition temperature suggests the materials applicability as magnetic refrigerant. Interestingly, perturbation at the magnetically ordered transition metal site (Mn site) through self-doping shows larger impact on the structural and magnetic properties compared to the perturbation at the nonmagnetic transition metal site (Ni site). The introduction of vacancy at the Ni-site results in a larger impact on the incompleteness in the martensitic phase transition present in dual-doped alloys. Field-induced metamagnetic transition, nonmonotonicity in the inverse magnetocaloric effect behavior, and the presence of a possible spin-reorientation transition have also been noticed in the alloys with coexisting self- and vacancy doping.

By employing high-level quantum chemistry methods, we investigate the electronic and magnetic properties of the vanadium-vanadium (V-V) molecular Prussian blue analogue (PBA), and mainly explore the potential logic functionality based on the achieved laser-induced ultrafast spin dynamics. The results show that, with the appropriate definition of the bit information and suitable combinations of the dynamic processes, a series of logic gates (including single-bit quantum logic gates, fundamental classical logic gates and multi-bit ones) and combinational functionalities can be constructed. Notably, the proposed T gate makes a critical step towards the more general one that can be used as a complement to the Clifford gate set for universal quantum computation. The complete mappings between three-bit inputs and three-bit outputs enable the construction of any specific three-bit logic gate (which can be downward compatible into two-bit logic gate) possible. The full-adder circuit is also obtained. All these results indicate the great potential of the V-V molecular PBA structure in both classical and quantum logic functionality and, at the same time, provide novel ideas for the design and realization of molecular logic functions towards quantum information processing and spintronics applications.

Two-dimensional transition metal borides (MBenes), with orthorhombic crystals and wrinkled B-TM-B bonding networks, emerge as promising candidates for negative Poisson's ratio (NPR) materials. However, the electronic-structural synergy governing NPR in these metallic systems remains elusive. Here, using density functional theory calculations, we uncover an intrinsic strain-independent NPR in ${\mathrm{Ti}}_2{\mathrm{B}}_2$ MBene ($\nu =-0.10$ at $\theta ={45}^{\circ }$), maintaining across 0–30% strain—surpassing black phosphorus ($\nu =-0.027$) and graphene (strain-dependent $\mathrm{NPR}>18\%$). A mechanistic descriptor is established, quantifying NPR dependence on transition metal's electron affinity, electronegativity, and valence electron count. The NPR originates from synergistic wrinkle B-Ti-B bond-angle expansion and strong $p-d$ orbital hybridization. Remarkably, Cu doping further enhances the NPR of ${\mathrm{Ti}}_2{\mathrm{B}}_2$ to −0.25 via size effect and electronic modulation, enabling its potential applications for mechanically adaptive electronics and cyclic deformation-resistant Li-air battery electrodes.

Aluminum has been extensively studied under high-pressure and high-temperature conditions due to its role as a standard material in shock-wave experiments and its nearly free-electron s/p structure. In this study, we investigate the Hugoniot temperature and melting behavior of polycrystalline Al using a two-stage light-gas gun with time-resolved in situ shock temperature measurements, up to a pressure of 155.8(1.7) GPa and a temperature of 5394(543) K. Our measured Hugoniot temperature in the solid phase aligns with previous theoretical simulations. Shock-induced melting of Al is observed at 125 GPa, corresponding to a melting temperature of 4576(235) K. This value is broadly consistent with hydrostatic high-pressure experimental results when reasonably extrapolated. By integrating both static and dynamic experimental data, we derive the melting curve of Al up to 180 GPa using the Simon melting equation. Our results indicate that both dynamic and static experiments are actually consistent on the melting line of Al, if the thermal pressure is corrected in the latter.

Quasicrystal approximant $\left({\mathrm{Ce}}_x{\mathrm{Y}}_{1-x}\right){\mathrm{Cd}}_6$ ($0\le x\le 1$) forms a magnetic frustration network of corner-sharing octahedra. We report that $\left({\mathrm{Ce}}_{0.8}{\mathrm{Y}}_{0.2}\right){\mathrm{Cd}}_6$ exhibits an anomalous magnetic transition that can be classified as neither conventional static magnetic ordering nor a spin glass. The anomalous transition is characterized by the coexistence of a static order and a frequency-dependent sharp positive anomalous peak in the third-harmonic susceptibility. Based on investigations of the reference systems ${\mathrm{CeCd}}_6$ and $\left({\mathrm{Ce}}_{0.05}{\mathrm{Y}}_{0.95}\right){\mathrm{Cd}}_6$, it is suggested that the anomalous transition is induced by disorder in the potentially frustrated octahedral network system in the presence of the Kondo effect.

Electron transport combined with magnetism has gained more attention to the spintronics community in the last few decades. Among them, the topological Hall effect (THE), which arises due to the emergent magnetic field of a nontrivial object, is found to be a promising tool for probing the presence of skyrmions. A sizable interfacial Dzyaloshinskii–Moriya interaction (iDMI) with reduced effective anisotropy can stabilize skyrmions in thin films. Recently, a large iDMI has been predicted in Pt/Co/Re thin film. Here, we investigate the influence of various magnetic interactions on the THE in perpendicularly magnetized Pt/Co/$X$ ($X$ = Ta, Re) thin films. The presence of skyrmions is confirmed via THE and magnetic force microscope imaging. Notably, two distinct types of THE signals are observed in the different samples, which are explained using micromagnetic simulations. Our results reveal that exchange interaction, iDMI, effective anisotropy, and saturation magnetization contribute significantly in determining the variations in topological Hall resistivity behavior, which arise from different skyrmionic phases. These findings contribute to the development of novel material systems featuring different skyrmionic phases with potential applications in spintronics.

Using an $S$-matrix formulation, we evaluate the conductance of a one-dimensional free-electron gas in double-exchange interaction with a classical conical magnet. We find integer conductance steps depending on the energy window of the incoming electrons for conical magnets described by a fictitious magnetic field of different orientations and modulated profile. The conductance windows, which we attribute to potential or diffractive scattering, are characterized by spin selectivity depending on the fictitious magnetic field direction and chirality.

We study optical manifestations of multigap band topology in multiband superconductors with a nontrivial topological Euler class. We introduce a set of lattice models for non-Abelian superconductors with the Euler invariant signified by a nontrivial quantum geometry. We then demonstrate that the topological Bogoliubov excitations realized in these models provide for a characteristic first-order optical response distinct from those of the other known topological superconductors. We find that the spectral distribution of the optical conductivity universally admits a topological jump originating from the Euler class in the presence of $d$-wave superconducting pairings and naturally differs from the features induced by the quantum geometry in the noninteracting bands without pairing terms. Further to uncovering observable signatures in first-order optical conductivities, we showcase that the higher-order optical responses of the non-Abelian Euler superconductor can result in enhanced nonlinear currents that fingerprint the exotic topological invariant. Finally, by employing a diagrammatic approach, we generalize our findings beyond the specific models of Euler superconductors.

We introduce a quantum spin Hall semimetal or Fermi liquid characterized with a quantized ${\mathbb{Z}}_2$ topological invariant, measurable through circularly polarized light. We propose its engineering through two topological metallic band structures in crystals on the honeycomb lattice, with spin-orbit interaction, realizable from the interplay of a charge or spin density wave substrate and Zeeman effects, in between a quantum spin Hall and a quantum anomalous Hall insulators. Also, we address time-reversal symmetry and geometrical properties of the Fermi surface through light.

In this work, we argue that the antiferromagnetic spin-$\frac{1}{2}$ XXZ chain in the gapped phase with boundary magnetic fields hosts fractional spin $\frac{1}{4}$ at its edges. Using a combination of Bethe ansatz and the density matrix renormalization group we show that these fractional spins are sharp quantum observables in both the ground and the first excited state as the associated fractional spin operators have zero variance. In the limit of zero edge fields, we argue that these fractional spin operators, once projected onto the low-energy subspace spanned by the ground state and the first excited state, identify with the strong zero-energy mode discovered by Fendley [J. Phys. A: Math. Theor. 49, 30LT01 (2016)].

We explore the topological properties of extended Su-Schrieffer-Heeger (SSH) models, considering four sublattices in a unit cell and second-nearest-neighbor intercell hopping for SSH4 and SSH long-range (SSHLR) models, respectively. The additional tuning parameters cause the SSH4 (SSHLR) model to host chiral symmetry-protected two (two and four) zero-energy modes producing a richer phase diagram that we characterize by momentum-space, periodic-bulk, and open-bulk real-space winding numbers. We introduce time to study charge transport in the periodically driven SSH4 and SSHLR models under the adiabatic limit. We remarkably find that the whole parameter space turned topological for a certain choice of the remaining parameters leading to always finite quantized value of pumped charge at the end of a complete cycle. Considering time as another variable, we characterize these new phases of the driven models by momentum-space Chern number and periodic-bulk and open-bulk real-space Bott indices. We also investigate the time evolution of pumped charge for these models and connect it with the intriguing windings of the midgap energy levels with time. Interestingly, the maximum value of Chern number or Bott index for the driven models is more than that of the winding number associated with the static model, indicating the fact that there exist more zero-energy modes during the full course of a driving cycle compared to the underlying static models. We further extend our study to the quantum metric where the fluctuations in the above quantity can identify the presence of a topological phase boundary.

We introduce a method for the estimation of uncertainties in density-functional-theory (DFT) calculations for atomistic systems. The method is based on the construction of an uncertainty-aware functional distribution (UAFD) in a space spanned by a few different exchange-correlation functionals and is illustrated at the level of generalized-gradient-approximation functionals. The UAFD provides reliable estimates of errors—compared to experiments or higher-quality calculations—in calculations performed self-consistently with the Perdew-Burke-Ernzerhof functional. The scheme furthermore allows for a decomposition of the error into a systematic bias and a reduced error. The approach is applied to four different properties: molecular atomization energies, cohesive energies, lattice constants, and bulk moduli of solids. The probability distribution can be tailored to optimize the prediction of a single property or for several properties simultaneously.