Competing interlayer magnetic interactions in kagome magnets can lead to diverse magnetic phases, which enable promising topological or quantum material properties. Here, the electronic structure and magnetic properties are studied using first-principles calculations for the $\mathrm{Li}{\mathrm{Fe}}_6\mathrm{G}{\mathrm{e}}_6, \mathrm{Li}{\mathrm{Fe}}_6\mathrm{G}{\mathrm{e}}_4$, and $\mathrm{Li}{\mathrm{Fe}}_6\mathrm{G}{\mathrm{e}}_5$ compounds sharing the kagome $\mathrm{F}{\mathrm{e}}_3\mathrm{Ge}$ layer motif but with different interlayer arrangements. For $\mathrm{Li}{\mathrm{Fe}}_6\mathrm{G}{\mathrm{e}}_4$ and $\mathrm{Li}{\mathrm{Fe}}_6\mathrm{G}{\mathrm{e}}_5$, the predicted magnetic ground states are collinear antiferromagnetic (AFM) states involving a mix of ferromagnetic (FM) and AFM interlayer orientations. In contrast, for $\mathrm{Li}{\mathrm{Fe}}_6\mathrm{G}{\mathrm{e}}_6$, an incommensurate cycloidal spin spiral ground state is stabilized, although its energy is close to a collinear A-type AFM state. The analysis of magnetic RKKY exchange coupling confirms the results of calculations. The values of atomic magnetic moments are in good agreement with existing experimental estimations. Our experiments on $\mathrm{Li}{\mathrm{Fe}}_6\mathrm{G}{\mathrm{e}}_6$ single crystals reveals AFM ordering at ∼540 K and transition to another magnetic phase with a small FM component, possibly with spin canting, below ∼270 K.

This work presents electronic and magnetic properties of selected members in the cubic Laves phase series ${\mathrm{Nd}}_{1-x}{\mathrm{Pr}}_x\mathrm{CoNi}$ (0 $\le x \le$ 1) and ${\mathrm{Ce}}_{0.25}{\mathrm{Pr}}_{0.75}\mathrm{CoNi}$, together with the corresponding binary compositions (${\mathrm{NdCo}}_2, {\mathrm{NdNi}}_2, {\mathrm{PrCo}}_2, {\mathrm{PrNi}}_2, {\mathrm{CeCo}}_2, {\mathrm{CeNi}}_2$), using soft x-ray absorption spectroscopy, x-ray magnetic circular dichroism (XMCD), density-functional theory, and crystal field multiplet calculations. All transition-metal moments saturate below 1 T, while the rare-earth moments do not saturate even at 5 T, consistent with van Vleck paramagnetic contributions and crystal field suppression. While the sum rules are widely used to extract element-specific magnetic moments from XMCD, we show that for $3d$ transition metals, their application requires accurate estimates of the number of unoccupied $3d$ states. We observe a finite magnetic moment on Ni, challenging the common assumption of its nonmagnetic character in Laves phases. The orbital magnetic moments were determined using the spin rules, while the spin moments were estimated from single-ion values from multiplet calculations, due to the invalidity of the spin sum rule for light rare-earth elements. The magnetic moments of Nd and Pr are found to be suppressed relative to their free-ion values, with multiplet theory indicating that this is due to crystal field effects. Our results confirm that Nd and Pr maintain localized $4f^3$ and $4f^2$ configurations, respectively, and that their element-specific magnetic moments are robust to rare-earth substitution. Ce, on the other hand, exhibits a tuneable mixed-valent ground state with both magnetic $4f^1$ and nonmagnetic $4f^0$ components. The relative fraction of these states varies with the electronegativity of the surrounding $3d$ transition metals, revealing a pathway to tune Ce magnetism via composition. This work establishes a framework for accurately interpreting XMCD in light rare-earth-based intermetallics and provides insight for designing light rare-earth-based magnetocaloric materials.

Transition metal-based layered organic-inorganic hybrid perovskites (OIHPs) exhibit diverse magnetic phenomena, yet the atomistic origin of magnetism in this class of materials remains elusive after decades of study. Here we demonstrate a notable ligand tunability of magnetism in two new quasi-two-dimensional OIHPs (${\mathrm{C}}_7{\mathrm{H}}_9\mathrm{NBr}$)${}_2{\mathrm{CuX}}_4$ (${\mathrm{C}}_7{\mathrm{H}}_9\mathrm{NBr}$ = 4-Bromobenzylammonium = A, X = Cl, Br) from comprehensive magnetic measurements and provide its microscopic understanding supported by ab initio DFT calculations. Despite being isostructural and having easy plane magnetocrystalline anisotropy (MCA), the Cl and Br analogs exhibit contrasting magnetic response. While ${\mathrm{A}}_2{\mathrm{CuCl}}_4$ shows an in-plane ferromagnetic and out-of-plane antiferromagnetic-like response, ${\mathrm{A}}_2{\mathrm{CuBr}}_4$ follows the reverse trend. The origin of this intriguing behavior is argued to stem from Dzyaloshinskii-Moriya interaction (DMI) present in these layered systems. We quantify DMI by employing constrained noncollinear DFT calculations in the presence of SOC which otherwise is challenging in the domain of OIHPs due to their large system size. Based on the competition between DMI and MCA, we propose a canted and transverse conical spiral spin structure for ${\mathrm{A}}_2{\mathrm{CuCl}}_4$ and ${\mathrm{A}}_2{\mathrm{CuBr}}_4$, respectively, which captures the observed magnetic response. Our study provides an effective way of tailoring and understanding the occurrence of nontrivial spin textures in this class of OIHPs.

Chiral spin liquids (CSLs) are exotic phases of interacting spins in two dimensions, characterized by long-range entanglement and fractional excitations. We construct a local Hamiltonian on the triangular lattice that stabilizes the Kalmeyer-Laughlin CSL without requiring fine-tuning. Our approach employs coupled-wire constructions and introduces a lattice duality to construct a solvable chiral sliding Luttinger liquid, which is driven toward the CSL phase by generic perturbations. By combining symmetry analysis and bosonization, we make sharp predictions for the ground states on quasi-one-dimensional cylinders and tori, which exhibit a fourfold periodicity in the circumference. Extensive tensor network simulations demonstrating ground-state degeneracies, fractional quasiparticles, nonvanishing long-range order parameters, and entanglement signatures confirm the emergence of the CSL in the lattice Hamiltonian.

We present a theoretical study of the spin-resolved Josephson diode effect in junctions comprising strongly spin-polarized conical magnets (FM) coupled to singlet superconductors (SC). The system is treated by making use of the Gor'kov and quasiclassical Green's function methods. Modeling the SC/FM interfaces as spin-dependent $\delta$ potentials, we apply our model to an SC/FM/SC junction and account for the Josephson current-phase relation (CPR). The nontrivial coupling between the spin bands in the conical magnet gives rise to a strong Josephson diode effect with an efficiency greater than $40\%$. The effect essentially depends on the quantum spin-geometric phase that enters the Josephson CPR in a very similar manner to the superconducting phase difference. The former is generated nonlocally by the intrinsically noncoplanar spin arrangement of the conical magnet, which breaks the time-reversal and inversion symmetries. Strong spin polarization and a helical pitch of the conical magnet comparable to the superconducting coherence length are essential for the effect. We perform a harmonic analysis of the Josephson CPR and interpret the effect in terms of coherent transfer of multiple equal-spin triplet Cooper pairs across the conical magnet.

We report a comprehensive investigation of CeGaSi single crystals, including magnetic, thermodynamic, electronic, and magnetotransport properties. The powder x-ray diffraction refinement reveals that CeGaSi crystallizes in LaPtSi-type tetragonal structure with space group $I{4}_{1}md$. The electrical resistivity data show a metallic nature with a sharp drop occurring around $T_m\sim$ 11 K, revealing a magnetic phase transition, which is confirmed by magnetic susceptibility and heat capacity data. The magnetic susceptibility, magnetization, and heat capacity data are analyzed through the crystalline electric field based on the point charge model, suggesting that the six degenerate ground states of ${\mathrm{Ce}}^{3+}$ ($J=5/2$) ions split into three doublets with an overall splitting energy $\sim 288$ K. The maximum negative magnetoresistance in CeGaSi for both $B\parallel c$ and $B\parallel ab$ field directions is observed near $T_m$, attributed to the suppression of spin-disorder scattering by the magnetic field. The Hall resistivity data for $B\parallel c$ and $B\parallel ab$ show anomalous Hall signal. Our scaling analysis suggests that anomalous Hall effect in CeGaSi is dominated by the skew scattering mechanism. In addition, first-principles calculations identify CeGaSi as a nodal-line metal.

Since the development of the nonlocal correlation functional vdW-DF, the family of van der Waals density functionals has grown to better describe a wide variety of systems. A recent generation of the vdW-DF family, vdW-DF3, featured a newly constructed form of the nonlocal correlation that more accurately modeled molecular dimers, layered structures, and surface adsorption. However, it also revealed an intrinsic trade-off in vdW-DF3's parametrization and inflexibility of exchange in the generalized gradient approximation, limiting its accuracy for molecular crystals. In this paper we propose an optimization of vdW-DF3 that is tailored to three-dimensional molecular crystals. This functional, called vdW-DF3-mc, contains a tunable form of the exchange enhancement factor with parameters that directly correspond to physically relevant qualities. In addition, within the nonlocal correlation, we prioritize smoothness of the kernel switching function as a means of restoring flexibility to vdW-DF3's design. Testing vdW-DF3-mc on several benchmark sets, we achieve highly accurate energetics and geometries for molecular crystals. This is particularly evident for the case of polymorphs of ice, for which errors in the volume and cohesive energy are on the order of only 1%, indicating very promising performance for important subcategories of molecular crystals, such as polymorphism and hydrogen-bonded solids.

Non-Hermitian systems exhibit unique boundary phenomena absent in their Hermitian counterparts, most notably the non-Hermitian skin effect (NHSE). In this work, we explore a lattice model consisting of two coupled nonreciprocal chains, focusing on the interplay between system size, interchain coupling, and spectral topology. Using both analytical and numerical approaches, we systematically examine the evolution of the complex energy spectra and spectral winding numbers under periodic and open boundary conditions. Our results uncover a variety of size-dependent localization transitions, including the emergence and instability of concurrent bipolar skin effects in the $W=0$ region, and their crossover to unipolar and conventional bipolar NHSEs as the system size increases. Notably, we demonstrate that these size-dependent behaviors persist even beyond the weak-coupling regime, highlighting their universality in non-Hermitian systems with complex spectral structures. This study provides insights into the mechanisms governing skin effects and offers practical guidelines for engineering non-Hermitian topological phases in synthetic lattices.

Charge order in the kagome superconductor ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ exhibits a complex three-dimensional organization and intermediate-temperature anomalies whose bulk character has remained unsettled. We use orientation-dependent ${}^{51}\mathrm{V}$ NMR as a site-selective probe to determine the stacking of the charge density wave (CDW) state and its thermal evolution. Below $T_{\mathrm{CDW}}\approx 94\mathrm{K}$, the field-linear splitting of the ${}^{51}\mathrm{V}$ central transition together with the anisotropy of the Knight shift tensor identify an interlayer-modulated $3\mathit{q}$ CDW whose local environments are consistent with a four-layer $2\times 2\times 4$ stacking with mixed trihexagonal/Star-of-David distortions, in agreement with synchrotron x-ray determinations. For comparison, ${\mathrm{RbV}}_3{\mathrm{Sb}}_5$ serves as a reference exhibiting a uniform trihexagonal $2\times 2\times 2$ stacking, allowing us to isolate features unique to the $2\times 2\times 4$ state in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$. With ${\mathit{H}}_0\parallel c$, the ${}^{51}\mathrm{V}$ quadrupolar satellites through the intermediate temperature scale near $T_{\mathrm{CO}}\approx 65\mathrm{K}$ reorganize into two well-resolved electric-field-gradient manifolds that coexist over a finite interval; their relative spectral weights interchange on cooling while the total integrated satellite intensity remains conserved and ${\nu }_Q$ within each manifold is nearly temperature independent. The coexistence without critical broadening, together with conserved intensity, provides bulk evidence consistent with a first-order charge-order transition near $T_{\mathrm{CO}}$. Our measurements do not resolve whether this lower-temperature transition corresponds to a distinct in-plane order or a reorganization of the $3\mathit{q}$ state; rather, they delimit this window and provide bulk, site-resolved constraints that connect prior reported anomalies to a thermodynamic first-order transition.

The Mott transition is primarily characterized by an isostructural insulator-metal transition in a correlated system under pressure, which is at the heart of many emergent phenomena. The associated transition mechanism, however, has been a long-standing challenge. Here we present a study of the mechanism underlying Mott transition in $\mathrm{PbCr}{\mathrm{O}}_3$ by exploring its bonding and electronic behaviors under pressure, which involves intricate lattice-charge interactions. We find that its Mott transition is mainly dictated by the Cr–O sublattice with largely tunable electronic and elastic properties under tensile stress, as exerted by the contracted Pb–O sublattice due to the presence of bond-length mismatch. Pressure can effectively balance tensile stress in the Cr–O sublattice for shortening its bond to a critical length, at which the $\mathrm{Cr}3d\text{–O}2p$ covalent hybridization occurs to form strong Cr–O bonds with a profoundly enhanced stiffness. As a response, extra bond shrinking spontaneously takes place to drive $3d$-electron delocalization and lattice collapse for the Mott transition. In addition, the electronic stability and structural symmetry of this material are also revealed to be closely related to its valence-electron density. These discoveries provide powerful insights into the atomistic mechanism of the Mott transition, which could also be applicable for understanding structural transitions in many other perovskite compounds.

The nitrogen vacancy (NV) center in diamond is an intriguing electronic spin system with applications in quantum radiometry, sensing, and computation. In those experiments, a bias magnetic field is commonly applied along the NV symmetry axis to eliminate the triplet ground-state manifold's degeneracy ($S=1$). In this configuration, the eigenvectors of the NV spin's projection along its axis are called strong-axial-field states. Conversely, in some experiments, a weak magnetic field is applied orthogonally to the NV symmetry axis, leading to eigenstates that are balanced linear superpositions of strong-axial-field states, referred to as dressed states. The latter are sensitive to environmental magnetic noise at the second order, allowing to perform magnetic field protected measurements while providing increased coherence times. However, if a small axial magnetic field is added in this regime, the linear superposition of strong-axial-field states becomes unbalanced. This paper presents a comprehensive study of free induction decay (FID) measurements performed on an NV center ensemble in the presence of strain and weak orthogonal magnetic field, as a function of a small magnetic field applied along the NV symmetry axis. The simultaneous detection of dressed states and unbalanced superpositions of strong-axial-field states in a single FID measurement is shown, gaining insight into coherence time, nuclear spin, and the interplay between temperature and magnetic field sensitivity. The discussion concludes by describing how the simultaneous presence of magnetically sensitive and insensitive states opens up appealing possibilities for both sensing and quantum computation applications.

The diffuse states in acceptor systems mean they are still largely inaccessible to fully ab initio treatments, so the field largely relies on effective-mass theory. However, it has not been clear whether local departures from the cubic symmetry of the bulk semiconductors are important. Here, we present a detailed first-principles study of the central cell corrections for Group III acceptors (B, Al, Ga, and In) in silicon and in particular analyze the noncubic contributions. We simulate an array of nearly isolated acceptors within density functional theory (DFT) and study the resulting band structure of the doped systems. Based on the self-consistent one-electron potentials, we compute central cell corrections for a distorted lattice, where both structures are separately relaxed to the minimum-energy configuration. We find that, although noncubic corrections are substantial close to the acceptor, their influence on the long-range structure of the bound states is minimal because the corrections are localized in a very small range, in contrast with the case of donors in silicon. The corrected states are more localized than the uncorrected ones, so previous estimates of the inter-acceptor distances at which different interactions dominate need to be reduced; our corrections lead to improved agreement with experiment and also allow the different characteristics of different Group III acceptors to be accounted for.

Due to their well-suited optoelectronic properties, metal halide perovskites are emerging semiconductor materials with potential applications in solar cells, detectors, and light-emitting diodes. Beyond the traditional 3D perovskites, low-dimensional counterparts have more attractive effects such as excitonic emissions and quantum confinements that are enhanced by the reduced dimensionality, which involve the electron-phonon coupling (EPC). Such phenomenon, which comprehends the interaction between charge carriers and lattice vibrations, usually strongly impacts the photoluminescence (PL) response in low-dimensional frameworks. In this paper, we investigated the intrinsic EPC onto low-temperature PL of the zero-dimensional (0D) ${\mathrm{Rb}}_2{\mathrm{SnBr}}_6$ perovskite. Temperature-dependent PL measurements, complemented by various characterization techniques and theoretical calculations, revealed broadband emission with a significant Stokes shift attributed to self-trapped excitons (STEs). The Fröhlich mechanism, mediated by interactions between excitonic charge carriers and longitudinal optical (LO) phonons, primarily accounts for the emission broadening through phonon-assisted radiative recombination. The EPC strength was evaluated through the Huang-Rhys factor $S=34$, confirming strong correlations between electronic and vibrational properties and supporting the STE emission assumption. The possible mechanism of STE formation was evaluated by the Fröhlich parameter $\alpha$ of 2.78 for electrons and 4.41 for holes, which points out a major contribution of the hole-polaron quasiparticle on exciton trapping. Our findings give insights regarding the influence of EPC in 0D perovskites and STE formation, which leads to the assessment of ${\mathrm{Rb}}_2{\mathrm{SnBr}}_6$ for light-harvesting applications.

We present a high-throughput, real-time study of PTCDI-${\mathrm{C}}_8$ thin film growth using quick x-ray reflectivity (qXRR) with 12 ms time resolution, combined with machine learning-based analysis. In situ qXRR enables monitoring of vacuum deposition at growth rates from 1 to $30\AA /\mathrm{s}$, accessing a previously unexplored regime in molecular beam deposition. To efficiently analyze the resulting $\sim 20000$ reflectivity curves, we employ a convolutional neural network trained on a physics-informed multilayer model. This approach robustly extracts key structural parameters—including thickness, roughness, and crystalline versus amorphous content—from noisy data. We quantify interface roughness as a function of both film thickness and growth rate, identifying rapid roughening with a scaling exponent of $\beta =0.62$ with film thickness and a secondary scaling exponent of $\gamma =0.21$ with growth rate. Additionally, we observe a reduction in the coherently ordered film thickness and a rise in amorphous content at higher deposition rates. These results demonstrate that combining qXRR with machine learning provides quantitative access to fast kinetic growth processes, offering a powerful tool for in situ characterization and morphological control in organic thin film fabrication.

Spins confined in optically active quantum dot molecules (QDMs) can be used for the deterministic generation of photonic graph states with tailored entanglement structures. Their usefulness for the generation of such nonclassical states of light is determined by orbital and spin decoherence mechanisms, particularly phonon-mediated processes dominant at energy scales up to a few millielectronvolts. Here, we directly measure the spectral function of orbital phonon relaxation between the energy states of the neutral exciton in a QDM and benchmark our findings against microscopic $\mathit{k}·\mathit{p}$ theory. Our results reveal pronounced resonances and antiresonances in the phonon-relaxation rates, ranging from tens of $\mu {\mathrm{s}}^{-1}$ up to tens of ${\mathrm{ns}}^{-1}$. Comparison with a kinetic model reveals the voltage (energy) dependent phonon coupling strength and fully explains the interplay between phonon-assisted relaxation and radiative recombination. The resonances and antiresonances enable further tunability of the exciton lifetime which can be leveraged to increase the lifetime of energetically unfavorable charge configurations needed for realizing efficient spin-photon interfaces and multidimensional cluster states.

Layered van der Waals (vdW) antiferromagnetic (AFM) topological insulators (TIs), particularly the recently discovered $\mathrm{MnBi}{}_2\mathrm{Te}{}_4$-family materials, have attracted significant attention. The gapped surface states in $\mathrm{MnBi}{}_2\mathrm{Te}{}_4$ are one of its key properties. However, whether the surface states in $\mathrm{MnBi}{}_2\mathrm{Te}{}_4$ are gapped or gapless remains a persistent and unresolved issue. A recently proposed intrinsic explanation is that a slight expansion of the topmost vdW gap can transform initially gapped surface states into gapless ones, potentially resolving this controversy. Despite this insight, how to experimentally comfirm the signal of the topmost vdW gap expansion in AFM TI is a problem worthy of investigation. In this work, we employ a multi-Dirac model to investigate the evolution of the band structure and Landau levels (LLs) in an AFM TI as the topmost vdW gap expands, revealing a range of intriguing phenomena. Our findings provide interesting perspectives on the tunability of LLs in layered vdW AFM TIs.

Building on the recent advancements on moiré superlattices, we propose an exactly solvable model with Kitaev-type interactions on a bilayer honeycomb lattice for both AA stacking and moiré superlattices. Using Monte Carlo simulations and variational analysis, we uncover a rich variety of phases where the intra and interlayer ${\mathbb{Z}}_2$ fluxes (visons) are arranged in a periodic fashion in the ground state, tuned by interlayer coupling and out-of-plane external magnetic field. We further extend our model to moiré superlattices at various commensurate twist angles around two distinct twist centers represented by $C_{3z}$ and $C_{6z}$ of the honeycomb lattice. Our simulations reveal generalized arrangements of plaquette values that correlate with the AA or AB stacking regions across the moiré unit cell. Moreover, we find that, depending on the twist angle, twist center and interlayer coupling, moiré superlattices exhibit to a variety of gapped and gapless spin liquid phases and can also host corner and edge modes. Our results highlight the rich physics in bilayer and twisted bilayer models of exactly solvable quantum spin liquids.