We report the synthesis and comprehensive investigation of ${\mathrm{Cu}}_{1-x}{\mathrm{Cr}}_{1-x}{\mathrm{Co}}_{2x}{\mathrm{P}}_2{\mathrm{S}}_6$ (CCCPS) single crystals and powder samples, a substituted derivative of the van der Waals multiferroic ${\mathrm{CuCrP}}_2{\mathrm{S}}_6$ (CCPS) where ${\mathrm{Co}}^{2+}$ ions simultaneously substitute for $\mathrm{C}{\mathrm{u}}^{+}$ and $\mathrm{C}{\mathrm{r}}^{3+}$. Through structural and magnetic structure determination, magnetometry measurement, pyroelectric and magnetodielectric (MD) probes, we map a substitution-controlled crossover from a CCPS-like to a ${\mathrm{CoPS}}_3$ (CPS)-like regime. Co substitution rapidly suppresses long-range antiferroelectric (AFE) ordering (C2/c→Pc) of CCPS at $\sim 150\mathrm{K}$ for $\mathrm{x}\ge 0.2$, leaving short-range polar fluctuations to persist. Moreover, a structural transformation from the C2/c phase to the C2/m phase occuring near $x\approx 0.35$ is observed. In the low-substitution C2/c phase $(0.1\le x\le 0.3)$, multiple field-induced spin-flop transitions are observed, which are subtle in magnetization but pronounced in the MD response, revealing the strong coupling between spin orientation and residual polar dynamics. A double spin-flop behavior is ascribed to the synergistic effect between the strong single-ion anisotropy of $\mathrm{C}{\mathrm{o}}^{2+}$ in the low-symmetry C2/c crystal field and newly introduced antiferromagnetic (AFM) exchange interactions within the Cr triangular lattice. For intermediate substitution levels $(0.4\le x\le 0.6)$, a hybrid magnetic state emerges, characterized by a ferromagnetic component superimposed on a zigzag AFM background. In the high-substitution limit, the system converges with the zigzag antiferromagnet order of ${\mathrm{CoPS}}_3$. Our results reveal a rich interplay between lattice symmetry, competing magnetic interactions, and residual polar dynamics, offering a versatile strategy for engineering multiple spin-reorientation phases and enhanced magnetoelectric (ME) coupling in two-dimensional van der Waals thiophosphates.

Lattice thermal transport in metals is traditionally described under the assumption that a highly mobile electron gas efficiently screens ionic displacements, resulting in a predominantly harmonic interatomic potential. Here, we show that strong electron-electron correlations can profoundly disrupt this screening mechanism, promoting intrinsic phonon scattering in the kagome metal ${\mathrm{CaCu}}_5$. By comparing orbital-resolved band calculations with high-resolution angle-resolved photoemission spectroscopy, we identify a strongly correlated Cu $3d$ flat band and extract an effective Hubbard interaction of $U\approx 3\mathrm{eV}$. We demonstrate that this on-site Coulomb interaction localizes the Cu $3d$ valence charge, indicating a reduced local charge response to ionic displacements. As a consequence of the reduced electronic screening, the lattice potential and phonon spectrum are strongly renormalized, substantially expanding the three-phonon scattering phase space. Consequently, electronic correlations alone intrinsically suppress the room-temperature lattice thermal conductivity by approximately 53%. These findings identify correlation-driven anharmonicity as a significant, nonstructural factor for suppressing thermal conductivity, thereby providing a possible route to mitigate the conventional trade-off between enhanced phonon scattering and high electronic mobility.

We present an implementation of the density-functional theory $\mathrm{DFT}+U+V$ formalism within the all-electron full-potential linearized augmented–plane-wave (FLAPW) method as implemented in the FLEUR code. The $\mathrm{DFT}+U+V$ formalism extends DFT, supplemented by the on-site Coulomb interaction $U$, to address local correlation effects in localized states by incorporating intersite Coulomb interaction terms $V$. It holds promise for improving charge and bond disproportionation, charge and orbital ordering, charge-density-wave formation, charge transfer, and the intersite correlation resulting from hybridization between states of neighboring sites in a solid. $U$ and $V$ parameters are obtained from first principles using the constrained random-phase approximation (cRPA) by employing two different atom basis representations to project the screened Coulomb interaction: the Wannier and the muffin–tin basis functions. We investigate in detail the impact of the $V$ term for typical covalently bonded materials like graphene, for bulk semiconductors such as silicon and germanium, and for charge-transfer insulators like NiO. Our results demonstrate an improvement in accuracy of specific properties across these systems, providing a framework for describing materials with different interaction regimes. We compare our $\mathrm{DFT}+U+V$ results using our cRPA parameter sets with (i) previous $\mathrm{DFT}+U+V$ calculations employing pseudopotential approximations, (ii) experimental results, and (iii) our $GW$ results.

Flat-band engineering in moiré materials is highly sensitive to twist angles, while accurate large-scale simulations remain computationally prohibitive. Here, we develop a unified machine-learning framework that integrates machine-learning interatomic potentials with Hamiltonian graph neural networks to simultaneously capture the lattice reconstruction and electronic structures in twisted bilayer (tb) ${\mathrm{MoSi}}_2{\mathrm{N}}_4$. This approach enables efficient and accurate simulations of large-scale moiré superlattices beyond the capability of conventional first-principles methods. We show that flat bands in $\mathrm{tb}\text{−}{\mathrm{MoSi}}_2{\mathrm{N}}_4$ can emerge through two distinct mechanisms. When thermal lattice relaxation is included, strong in-plane reconstruction and out-of-plane corrugation generate a highly inhomogeneous moiré potential landscape, leading to strong electronic localization and ultraflat bands predominantly in the valence band. In contrast, even without lattice relaxation, reducing the interlayer spacing enhances interlayer orbital hybridization, leading to substantial band renormalization and multiple flat bands in the conduction band. Remarkably, flat bands emerge at relatively large twist angles $(\sim 6^{\circ })$, in contrast to the magic-angle condition in twisted bilayer graphene. The absence of a strict magic-angle condition originates from the distinct physical mechanisms of band flattening, where strong lattice reconstruction and stacking-dependent interlayer coupling create deep moiré potential wells without requiring fine-tuned twist angles. Beyond $\mathrm{tb}\text{−}{\mathrm{MoSi}}_2{\mathrm{N}}_4$, the framework exhibits robust transferability to multilayer and twisted multilayer systems. These results establish a unified physical picture linking lattice reconstruction, interlayer coupling, and flat-band formation; provide an efficient route for large-scale moiré simulations; and offer new opportunities for engineering flat-band physics in two-dimensional materials.

Freestanding van der Waals crystals made of single-atom carbon chains (carbynes) have been recently realized technologically. Here we investigate their electronic and optical properties theoretically and compare the results with previously reported continuous-wave and time-resolved photoluminescence data obtained by our group. Employing a fully three-dimensional tight-binding formalism benchmarked against density functional theory calculations we predict the semimetal-semiconductor transition to occur in van der Waals carbyne crystals composed by the chains of about 42 atoms long. The semiconductor phase is characterized by a hyperbolic Van Hove singularity which gives rise to unconventional hyperbolic exciton states. The previously reported experimental data probe the semiconductor phase, where resonant features associated with hyperbolic excitons are clearly visible. The exciton oscillator strength is found to be strongly sensitive to the length of carbon chains: Our previously reported experimental data show that it decreases with increasing chain length. This tendency, confirmed by the theoretical modeling, manifests the evolution of the hyperbolic exciton state on the way to the semiconductor-semimetal crossover. Our approach accounts for the actual crystalline geometry, including alternating intrachain hoppings and interchain couplings. By fitting tight-binding dispersions to density functional theory data we extract consistent parameters and establish a comprehensive framework for the physics of carbyne crystals. This study paves the way towards efficient band-gap engineering in ultimate one-dimensional carbon crystals.

A concrete question is discussed: Can there be conventional $s$-wave superconductivity (SC) in regular three-dimensional (3D) (or 2D) metals, i.e., electrons in a jellium background, interacting via the standard Coulomb coupling? We are interested in “practical” SC that can in principle be observed in experiments, so the $T=0$ ground state being superconducting is not of interest, or for that matter a $T_c$ which is exponentially small and therefore “impractical” is also not of interest in the current work. We discuss both 2D and 3D cases, focusing mostly on the 3D case. We find that almost any theory based on the Bardeen-Cooper-Schrieffer (BCS)-Migdal-Eliashberg paradigm, with some form of screened Coulomb coupling replacing the electron-phonon coupling in the BCS or Eliashberg theory, would uncritically predict absurdly high $T_c\sim 100\mathrm{K}$ for $s$-wave SC in all metals (including the alkali metals, which are well described by the jellium model) arising from the unavoidable fact that the Fermi, plasmon, and Coulomb potential energy scales are all $>{10}^4\mathrm{K}$. Therefore, we conclude, based on reduction ad absurdum, that the violation of the venerable Migdal theorem in this problem is sufficiently disruptive that no significance can be attached to numerous existing theoretical publications in the literature claiming plasmon-induced (or other similar Coulomb coupling–induced) practical SC. Using a careful analysis of the Eliashberg gap equations we find that the superconducting $T_c$ of the 3D (or 2D) electron gas can be reduced well below $\sim 1\mathrm{K}$ depending on choices of frequency cutoff parameters that are introduced to satisfy Migdall's theorem but are a priori unknown. The only believable result is the one discovered in the mid-1960s by Kohn and Luttinger [Phys. Rev. Lett. 15, 524 (1965)] predicting non-$s$-wave SC arising from Friedel oscillations with exponentially (and unobservably) low $T_c$. We provide several theoretical approaches using both BCS and Eliashberg theories and different screening models to make our point.

Quantum point contact readout theory for singlet-triplet qubits in a lateral double quantum dot is extended by including tunneling of triplet configurations in a higher-energy level of the neighboring dot. This additional channel creates energetically allowed leakage pathways that modify the branch-dependent charge and current-noise signatures, even when the Pauli blockade remains effective within the ground-state manifold. The model contains two single-particle levels in each dot. The resulting singlet and triplet block structure is derived together with a Lindblad master equation. Quantum-jump simulations are then used to resolve the dynamics of individual readout events. A complementary Liouvillian steady-state analysis identifies the regime in which tunneling to the excited level qualitatively changes the readout signatures, with the crossover determined by the level spacing.

${A\mathrm{V}}_3{\mathrm{Sb}}_5$ $(A=\mathrm{K}, \mathrm{Rb}, \mathrm{Cs})$ are kagome metals and superconductors, attracting much recent attention as the nexus of multiple quantum states. Here, through a systematic study of electric and thermal transport of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, we identify it as a metallic Fermi liquid with moderate electronic correlations and a strong electron-phonon (e-ph) collision cross section. We observe contributions to the inelastic electrical resistivity, each dominating within a distinct temperature window. The prefactor of $T^2$ is consistent with the Kadowaki-Woods scaling for a Fermi liquid with moderate correlation. By performing thermal conductivity measurements at zero and finite magnetic field, we separate the electronic and the lattice contributions to the thermal conductivity. The Wiedemann-Franz law is satisfied in the zero-temperature limit, while a downward deviation emerges at finite temperature due to the mismatch between the prefactors of the electrical and thermal quadratic resistivities, as reported in other metals. The Bloch-Grüneisen description of electron-phonon scattering successfully accounts for both electronic thermal and electrical transport, indicating a remarkably large e-ph collision cross section in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$.

We theoretically demonstrate hybrid-order topology in a two-dimensional nonsymmorphic antiferromagnet. Utilizing a generic antiferromagnetic Dirac model with a symmetry-allowed, momentum-dependent spin-density-wave mass, we show that a single bulk insulating phase exhibits distinct topological boundary manifestations governed solely by the termination geometry. For screw-compatible edges, nonsymmorphic screw symmetry protects gapless first-order edge states. In contrast, for a ${45}^{\circ }$ diamond-shaped termination, the screw symmetry is broken at the boundary, resulting in gapped edges. However, the finite geometry still preserves magnetic mirror symmetries ${\mathcal{M}}_x\mathcal{T}$ and ${\mathcal{M}}_y\mathcal{T}$, which enforce an alternating pattern of edge masses, thereby binding zero-dimensional corner states. This second-order phase is characterized by a quantized quadrupole moment, with corner states pinned to zero energy by the chiral symmetry. We further demonstrate that explicit lattice perturbations can selectively gap the first-order edge modes while robustly preserving the corner states. Our work establishes a symmetry-based route to a termination-controlled duality between first- and second-order topology in magnetic nonsymmorphic systems.

Electron irradiation and annealing treatments are a method of color center/defect creation in diamond. The depth profile of defects created by low-energy 200 keV electrons in single-crystal high-purity (type II) electronic grade diamond grown via chemical vapor deposition has been investigated. The depth profile of monovacancies created was found, using photoluminescence (PL), to decay exponentially, with a decay length $12\pm 1\mu \mathrm{m}$ and a production rate of $(1.1\pm 0.2)\times {10}^{-1}\mathrm{V}/{\mathrm{e}}^{-}/\mathrm{cm}$ at the surface. The depth distribution of the neutral and negatively charged nitrogen-vacancy $\left({\mathrm{NV}}^{0/1-}\right)$ center, and the 733 nm zero phonon line defect formed during an isochronal annealing study, have also been investigated by PL. The observed NV profiles, which do not match the vacancy profiles, can be qualitatively explained in terms of a simple model that includes the formation of vacancy clusters and the nitrogen-divacancy $\left({\mathrm{NV}}_2\right)$ defect. The production of $\left({\mathrm{NV}}^{0/-}\right)$ has been assumed to be nitrogen-limited, but this paper has shown that this is not the case, with NVs lost to the production of ${\mathrm{NV}}_2$ when the concentration of vacancies greatly exceeds that of substitutional nitrogen.

We combine first-principles density-functional theory, Berry-curvature analysis, semiclassical Boltzmann transport, and atomistic spin dynamics to establish hexagonal NiS as a compensated $3d$ altermagnetic semimetal in which topology, magnetism, and lattice dynamics are intrinsically intertwined. The rotational coset symmetry of the NiAs lattice produces the momentum-dependent spin splitting characteristic of altermagnetism. With spin-orbit coupling, gapped Dirac-like crossings generate intense Berry-curvature hot spots and nearly compensated electron-hole pockets. This leads to a large and anisotropic intrinsic spin Hall conductivity comparable to that of several $4d/5d$ metals, a symmetry-allowed anomalous Hall response despite zero net magnetization, and nonsaturating magnetoresistance exceeding ${10}^3\%$. On the magnetic side, first-principles determination of the exchange tensor reveals dominant long-range superexchange and sizable anisotropic interactions, quantitatively reproducing the experimental Néel temperature. Our results identify NiS as a model $3d$ platform in which carrier compensation, altermagnetic symmetry, Berry-curvature–driven transport, and lattice-sensitive magnetism coexist within a single symmetry framework, offering a design principle for multifunctional quantum responses in correlated transition-metal compounds.

Yield strength is used to assess nonhydrostatic conditions in diamond anvil cell experiments, serving as a critical parameter for the interpretation of high-pressure measurements. By incorporating first-principles derived high-pressure elastic properties into a thermally activated dislocation glide model, we present a method based on the superposition principle to quantitatively predict yield strength under static high-pressure conditions. Validated against representative FCC metals, Al and Ag, our theoretical predictions align well with experimental data up to 55 GPa and 40 GPa, respectively. Through the quantitative decomposition of the total yield strength into lattice friction, forest dislocation, and grain boundary components, we identify that grain boundary strengthening constitutes the dominant contribution. By analyzing the derivative of yield strength with respect to pressure ($\partial \sigma /\partial P$) under static high pressure, we demonstrate that the pressure sensitivity of yield strength is determined by the pressure-induced stiffening of the shear modulus.

The simultaneous realization of intrinsic magnetism and superhardness within a single light-element lattice represents a fundamental paradox, as the strong ${sp}^3$ covalency required for rigidity inherently suppresses the localized moments essential for magnetic ordering. Here, we resolve this dichotomy through the theoretical design of metastable 3D ${\mathrm{C}}_7{\mathrm{N}}_1$ covalent networks, constructed via a stacking engineering strategy that couples graphene with two-dimensional ${\mathrm{C}}_3{\mathrm{N}}_1$. We demonstrate that the coordination frustration imposed by nitrogen induces stable magnetic moments on threefold coordinated carbon vertices within a superhard scaffold. Crucially, we uncover a universal magnetostructural correlation: an increase in out-of-plane buckling consistently enhances the local magnetic moment. This coupling is mechanically driven by the differential compressibility between compliant interlayer C–C pillars and stiff steric N–C repulsions, and electronically governed by pyramidalization-induced localization, which narrows the defect bandwidth to satisfy the Stoner criterion. This architecture preserves exceptional mechanical integrity, yielding a Vickers hardness of 59 GPa and a Debye temperature of 1894 K. Electronic structure analysis utilizing the HSE06 hybrid functional reveals that both allotropes are intrinsic wide-gap semiconductors, exhibiting fundamental band gaps of 1.47 and 1.65 eV for the AA- and ABC-stacked phases, respectively. Beyond thermodynamics, we identify a kinetically viable synthesis pathway driven by nonhydrostatic mechanics, where shear stress significantly lowers the phase transformation barrier to an accessible threshold of $\sim 32\mathrm{GPa}$. Furthermore, a giant magnetostructural coupling is observed, where external pressure drives a reversible Stoner transition from a magnetic semiconductor to a nonmagnetic metal. This work establishes ${\mathrm{C}}_7{\mathrm{N}}_1$ as a versatile platform for exploring correlated electron physics within superhard architectures.

We investigate the time- and momentum-resolved dynamics of matter waves undergoing elastic scattering from a disordered potential in the presence of spatially uniform SU(2) gauge fields. We derive the disorder-averaged density matrix as a function of time and momentum within the weak-localization regime. By accurately approximating the frequency dependence of the ladder and maximally crossed diagram series beyond the diffusion approximation, we describe short-time spin-momentum dynamics on timescales comparable to the scattering mean free time, for arbitrary strengths of the SU(2) gauge fields and disorder. We also present a cubic equation that determines the spin isotropization time, which gives accurate asymptotic forms in the limits where the spin-orbit length is much longer (Dyakonov-Perel spin relaxation regime) or much shorter than the scattering mean free path, as well as in the SU(2)-symmetric (persistent spin helix) limit. Comparison with numerical simulations over a broad range of spin-orbit coupling strengths shows quantitative agreement for the predicted spin isotropization time. The same framework also reproduces both the relaxation of the momentum distribution and the transient backscattering peak with a momentum offset coexisting with the robust coherent backscattering dip.

Conventional Peierls theory cannot fully capture the thermal transport in strongly anharmonic compounds (e.g., lead-free halide double perovskites) because it does not account for the significant wavelike behavior of phonons—a consequence of their inherent capability to interfere and tunnel. Here, we elucidate the mechanism behind the ultralow lattice thermal conductivity in model systems ${\mathrm{Cs}}_2{\mathrm{AgInCl}}_6$ and ${\mathrm{Cs}}_2{\mathrm{AgInBr}}_6$ through a combined evaluation of the particlelike and wavelike thermal transport channels. The rattling vibrations of Cs atoms suppress the particlelike channel through enhanced anharmonicity and promote the wavelike channel by flattening phonon branches to enhance coherence. Furthermore, the $T_{1g}$ rotational mode of the ${\mathrm{InX}}_6$ octahedron induces stronger quartic anharmonicity in ${\mathrm{Cs}}_2{\mathrm{AgInBr}}_6$ than in ${\mathrm{Cs}}_2{\mathrm{AgInCl}}_6$, which primarily enhances four-phonon scattering processes to further suppress the particlelike channel. In contrast, the wavelike contributions in both compounds remain comparable due to a compensating effect between the stronger coherent coupling in ${\mathrm{Cs}}_2{\mathrm{AgInBr}}_6$ and the larger group velocities in ${\mathrm{Cs}}_2{\mathrm{AgInCl}}_6$. Overall, the dominance of the wavelike channel is more pronounced in ${\mathrm{Cs}}_2{\mathrm{AgInBr}}_6$. Finally, the dominant wavelike contribution leads to a markedly weaker temperature dependence of the total thermal conductivity in both compounds, which is more notable in ${\mathrm{Cs}}_2{\mathrm{AgInBr}}_6$ with a scaling exponent of $T^{-0.19}$ compared to $T^{-0.52}$ in ${\mathrm{Cs}}_2{\mathrm{AgInCl}}_6$. Our work establishes the wavelike channel as a vital mechanism for thermal transport in lead-free halide double perovskites, providing novel insights into their fundamental thermal properties.

Single-crystal neutron scattering and magnetic susceptibility measurements of the dilute magnetic topological insulator (${\mathrm{Sn}}_{0.9}{\mathrm{Mn}}_{0.1})\mathrm{Te}$ demonstrate the emergence of long-range ferromagnetic (FM) order below $T_{\mathrm{C}}=12\pm 1\mathrm{K}$. Through inelastic and quasielastic neutron scattering analyses, we uncover a complex interplay of competing magnetic interactions, including nearest-neighbor (NN) FM Mn-Mn exchange, second-NN antiferromagnetic (AFM) Mn-Te-Mn superexchange, and progressively weaker long-range interactions extending to at least the eighth NN. The AFM interaction mediated by the linear Mn-Te-Mn bond ($J_2\sim 0.5\mathrm{meV}$) is the strongest and leads to Mn-Mn dimer singlet states that do not contribute to FM ordering. Instead, we identify the long-range seventh-NN FM interaction $J_7$ as the most effective channel for stabilizing the FM order within a minimal model consistent with the data. Despite its relatively weak strength, its large coordination number ($Z=48$) enables percolation of exchange bonds, effectively stabilizing the FM state. Reverse Monte Carlo and atomistic spin dynamics simulations of the neutron scattering data are consistent with the observed FM state of dilute (${\mathrm{Sn}}_{0.9}{\mathrm{Mn}}_{0.1})\mathrm{Te}$. These findings underscore the critical role of long-range percolative interactions in stabilizing FM order in dilute magnetic topological systems. Beyond topological materials, the results are broadly relevant to magnetism in semiconductors and dilute magnetic alloys, where competing exchange pathways and percolative effects similarly govern the emergence of collective magnetic order.

Quorum sensing, defined as the emergence of collective behavior triggered by a critical population size or density, is a hallmark of collective biological behavior. However, it has not yet been realized in engineered quantum or classical many-body platforms. Here, we report the theoretical prediction of quorum sensing in a nonlinear cavity magnonic system, where an increase in the number of magnonic spheres drives a transition from a static state to a collectively synchronized state. We find that this synchronized state is highly sensitive to the magnon-photon coupling strength and appears as a bandlike region in the parameter space. Importantly, the quorum sensing transition is remarkably robust against parameter heterogeneity. It persists even under large mismatches in local coupling strengths, Kerr nonlinearities, and dissipation rates. These findings establish cavity magnonic platforms as a promising setting for exploring population-size-dependent collective dynamics and significantly enhance the prospects for experimental detection. By demonstrating quorum sensing in a cavity magnonic system, our work bridges concepts from biology and condensed matter physics, opening new pathways toward applications in sensing, coherent information processing, and emergent many-body technologies.

Utilizing dynamic diamond anvil cell combined with time-resolved temperature-pressure multichannel measurement system, we have measured fluid helium-4′s Grüneisen parameter between 6 and 11 GPa at around 300 K. The measurements yielded the high-pressure volumetric thermal expansion coefficient, with pressure dependence similar to that of dense hydrogen and argon. Unlike the case of low-temperature fluid helium, the unique pressure dependence of the Grüneisen parameter with pressure at room temperature and its jump near the fluid-solid transition may serve as an indicator of localized atomic aggregation of fluid helium under high pressure. This work provides crucial experimental constraints for understanding the thermodynamic behavior and microscopic interactions in dense fluid helium, offering new insights into the high-pressure physics of simple quantum fluids.