Encouraged by experimental reports of diamond precipitation in carbon-containing materials under warm dense matter conditions and in shock compression experiments, we examine the behavior of carbon in TiC using density functional theory–molecular dynamics simulations. Two polymorphs of TiC are considered, the ambient-pressure $B1$ ($Fm\overline{3}m$) structure in which C-C interactions are prevented by geometric constraints and a high-pressure $Cmcm$ structure in which C atoms condense into zigzag chains. Chemistry-inspired bonding analyses confirm the covalently bound nature of these chains and further illuminate important interatomic interactions in both structures. Upon melting of $B1$ TiC, new short-range C-C interactions develop in the liquid, while the preexisting C-C interactions in $Cmcm$ TiC persist in the liquid. The resulting carbon networks in the melt provide a promising environment for eventual diamond nucleation.

We derive analytical expressions for the spin-wave frequencies and precession amplitudes in monolayer and antiferromagnetically coupled bilayer CrSBr under in-plane external magnetic fields. The analysis covers the antiferromagnetic, ferromagnetic, and canted phases, demonstrating that the spin-wave frequencies in all phases are tunable by the applied magnetic field. We discuss the roles of intra- and interlayer exchange interactions, triaxial anisotropy, and intralayer dynamic dipolar fields in controlling the magnetization dynamics.

Dirac-Weyl semimetals host both Dirac and Weyl fermions and the exploration of material candidates with tunable topological properties is essential to realize topological spintronic devices. In this work, we propose CaAgBi as a Dirac-Weyl semimetal with tunable type-I and type-II Weyl points based on first-principles calculations. In addition to the three pairs of Dirac points located along the rotational axis as previously reported, our calculations reveal 18 additional pairs of dual-type Weyl points distributed across three distinct planes: type I in the $k_z=0$ plane and type II in the $k_z=\pm 0.0698\frac{2\pi }{c}$ planes. The topological features are further confirmed through chirality of the Weyl points as well as the existence of surface Fermi arcs. Moreover, we find that the position and annihilation of Dirac and Weyl points are tunable by the alloy engineering and external strains. The alloy engineering is employed to modulate the positions of Weyl points, revealing different annihilation concentrations for type-I and type-II Weyl points, potentially offering other experimental strategies for Weyl point manipulation. Under tensile biaxial strain, the Weyl points in the $k_z=0$ plane annihilate along the $\mathrm{\Gamma }\text{−}M$ path at $2.1\%$ strain, whereas the Weyl points in the $k_z\ne 0$ planes remain robust within $6\%$ strain. This work provides a versatile platform for manipulating Dirac/Weyl interactions, with spin-orbit coupling driven alloy control and strain-selective engineering opening avenues for topological electronics.

Identifying model Hamiltonians is a vital step toward creating predictive models of materials. Here, we combine Bayesian optimization with the EDRIXS numerical package to infer Hamiltonian parameters from resonant inelastic x-ray scattering (RIXS) spectra within the single atom approximation. To evaluate the efficacy of our method, we test it on experimental RIXS spectra of ${\mathrm{NiPS}}_3, {\mathrm{NiCl}}_2, {\mathrm{Ca}}_3{\mathrm{LiOsO}}_6$, and ${\mathrm{Fe}}_2{\mathrm{O}}_3$, and demonstrate that it can reproduce results obtained from hand-fitted parameters to a precision similar to expert human analysis while providing a more systematic mapping of parameter space. Our work provides a key first step toward solving the inverse scattering problem to extract effective multi-orbital models from information-dense RIXS measurements, which can be applied to a host of quantum materials. We also propose atomic model parameter sets for two materials, ${\mathrm{Ca}}_3{\mathrm{LiOsO}}_6$ and ${\mathrm{Fe}}_2{\mathrm{O}}_3$, that were previously missing from the literature.

Recent advances in fluorescence imaging have enabled direct measurements of doublon, singlon, and holon correlation functions in cold-atom experiments. We demonstrate that these correlators provide a powerful probe of the extended crossover from metallic to insulating behavior at intermediate and high temperatures. To this end, we carry out determinantal quantum Monte Carlo simulations of the two-dimensional repulsive Fermi-Hubbard model on a square lattice, varying doping, interaction strength $U$, and temperature $T$. Our results reveal clear signatures of a crossover from the metallic regime at small $U$ to the Mott insulating regime at large $U$. Specifically, we note the following: (1) At half-filling, we distinguish three regimes (metallic, non-Fermi-liquid, and Mott insulating) by analyzing the temperature dependence of the thermodynamic density of states $\tilde{\kappa }=\frac{\partial n}{\partial \mu }$ in comparison with the low-energy single-particle density of states $N\left(\omega \right)$. (2) At finite doping, although $N\left(\omega \right)$ remains gapless, a sign change in $\frac{\partial \tilde{\kappa }}{\partial T}$ marks a transition from insulating to metallic behavior at a critical density $n_{\text{cr}}(U,T)$. (3) These crossovers can also be tracked using experimentally accessible correlators, such as density-density, moment-moment, and doublon-holon correlations, providing valuable diagnostics in settings where direct spectral information is difficult to obtain.

The enigmatic strange metal remains one of the central unsolved problems of 21st century science. Understanding this phase of matter requires knowledge of the momentum- and energy-resolved dynamic charge susceptibility $\chi (q,\omega )$, especially at finite momentum. Inelastic electron scattering (EELS), performed in either transmission or reflection geometry, is a powerful probe of $\chi (q,\omega )$. For the prototypical strange metal ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+x}$, transmission- and reflection EELS, and infrared (IR) spectroscopy agree at $q\sim 0$, all revealing a highly damped plasmon near 1 eV. At larger $q$, however, EELS results show unresolved discrepancies. Since IR data are highly reproducible, it is advantageous to use IR data to calculate what the expected EELS response should be at modest $q$. Building on prior momentum-resolved reflection geometry M-EELS work [Chen et al., Phys. Rev. B 109, 045108 (2024)], we extend this approach to transmission EELS for finite stacks of metallic layers, comparing a “textbook” Lindhard metal to a strange metal. In the Lindhard case, the low-$q$ response is dominated by long-lived, standing wave plasmon modes arising from interlayer Coulomb coupling, with in-plane dispersions that resemble the well-known Fetter modes of layered metals. This behavior depends only on the geometry and the long-range nature of the Coulomb interaction and is largely insensitive to layer details. At larger $q$, the response reflects the microscopic properties of individual layers. For the strange metal, calculations based on IR data predict a highly damped plasmon with weak dispersion and no distinct surface mode. While our results match IR and M-EELS at low $q$, they do not reproduce any published EELS spectra at large $q$, highlighting unresolved discrepancies that demand further experimental investigation.

Most of the fundamental concepts of topological classification and characterization are based on an assumption of short-range coupling. These cognitions may largely fail for long-range systems with power-law decay exponent $\beta$, which have received increasing attention with the fast progress in artificial assembled quantum simulators. Especially, the bulk-boundary correspondence may weaken $(0<\beta <1)$ or completely break down $(\beta =0)$, cases where the bulk topological invariant alone is insufficient to determine the number of edge modes. Here, we propose a mapped bulk-boundary correspondence to characterize topological edge modes of nonlocal systems with strong long-range coupling $0\le \beta <1$. The analytic results show that strong long-range hoppings can induce infinitely large topological regions. Our method is also applicable to the Rydberg-dressed systems with an infinite dressing radius.

We report the observation of unconventional transport phenomena in a spin-1 model that supports a tower of quantum many-body scars, and we discuss their properties uncovering their peculiar nature. In quantum many-body systems, the late-time dynamics of local observables are typically governed by conserved operators with local densities, such as energy and magnetization. In the model under investigation, however, there is an additional dynamical symmetry restricted to the subspace of the Hilbert space spanned by the quantum many-body scars. The latter significantly slows the decay of autocorrelation functions of certain coherent states of quantum many-body scars and is responsible for the unconventional form of transport that we detect numerically. We show that excited states with energy close to that of the quantum many-body scars play a crucial role in sustaining the transport. Finally, we propose a generalized eigenstate thermalization hypothesis to describe specific properties of states with energy close to the scars.

Variational Monte Carlo simulations have been crucial for understanding quantum many-body systems, especially when the Hamiltonian is frustrated and the ground-state wavefunction has a nontrivial sign structure. In this paper, we use recurrent neural network (RNN) wavefunction ansätze to study the triangular-lattice antiferromagnetic Heisenberg model (TLAHM) for lattice sizes up to $30\times 30$. In a recent study [M. S. Moss et al., Phys. Rev. B 112, 134450 (2025)], the authors demonstrated how RNN wavefunctions can be iteratively retrained in order to obtain variational results for multiple lattice sizes with a reasonable amount of compute. That study, which looked at the sign-free, square-lattice antiferromagnetic Heisenberg model, showed favorable scaling properties, allowing accurate finite-size extrapolations to the thermodynamic limit. In contrast, our present results illustrate in detail the relative difficulty in simulating the sign-problematic TLAHM. We find that the accuracy of our simulations can be significantly improved by transforming the Hamiltonian with a judicious choice of basis rotation. We also show that a similar benefit can be achieved by using variational neural annealing, an alternative optimization technique that minimizes a pseudo-free energy. Ultimately, we are able to obtain estimates of the ground-state properties of the TLAHM in the thermodynamic limit that are in close agreement with values in the literature, showing that RNN wavefunctions provide a powerful toolbox for performing finite-size scaling studies for frustrated quantum many-body systems.

Machine-learning-based variational Monte Carlo simulations are a promising approach for targeting quantum many-body ground states, especially in two dimensions and in cases where the ground state is known to have a nontrivial sign structure. While many state-of-the-art variational energies have been reached with these methods for finite-size systems, little work has been done to use these results to extract information about the target state in the thermodynamic limit. In this work, we employ recurrent neural networks (RNNs) as a variational ansätze, and leverage their recurrent nature to simulate the ground states of progressively larger systems through iterative retraining. This transfer learning technique allows us to simulate spin-$\frac{1}{2}$ systems on lattices with more than 1,000 spins without beginning optimization from scratch for each system size, thus reducing the demands for computational resources. In this study, we focus on the square-lattice antiferromagnetic Heisenberg model, where it is possible to carefully benchmark our results. We show that we are able to systematically improve the accuracy of the results from our simulations by increasing the training time, and obtain results for finite-sized lattices that are in good agreement with the literature values. Furthermore, we use these results to extract accurate estimates of the ground-state properties in the thermodynamic limit. This work demonstrates that RNN wavefunctions are able to extract accurate information about quantum many-body systems in the thermodynamic limit.

A crystal-structure match (CSM), the atom-to-atom correspondence between two crystalline phases, is used extensively to describe solid-solid phase transition (SSPT) mechanisms. However, existing computational methods cannot account for all possible CSMs. Here, we propose a formalism to classify all CSMs into a tree structure, which is independent of the choices of unit cell and supercell. We rigorously proved that only a finite number of noncongruent CSMs are of practical interest. By representing CSMs as integer matrices, we introduce the crystmatch method to exhaustively enumerate them, which uncontroversially solves the CSM optimization problem under any geometric criterion. For most SSPTs, crystmatch can reproduce all known deformation mechanisms and CSMs within 10 CPU minutes, while also revealing thousands of new candidates. The resulting database can be further used for comparing experimental phenomena, high-throughput energy barrier calculations, or machine learning.

The effect of tetragonal distortion on spin-gapless semiconducting (SGS) behavior in thin films of inverse Heusler compound $\text{T}{\text{i}}_2\text{CoSi}$ was investigated by first-principles calculations. Cubic $\text{T}{\text{i}}_2\text{CoSi}$ exhibits SGS characteristics with a 0.7-eV energy gap in the spin-down band and a zero-width gap in the spin-up band, consistent with prior studies. Substrate-induced tetragonal distortion in $\text{T}{\text{i}}_2\text{CoSi}$ thin film, arising from lattice mismatch, profoundly impacts its electronic structure and stability. Owing to the energy preference, volume-relaxed tetragonal distortion models align more closely with experimental observations. The weakened interatomic covalent hybridization due to tetragonal distortion is responsible for the volume expansion and decreased phase stability. Notably, robust half-metallicity persists across a broad distortion range, as evidenced by stable integer magnetic moments and preserved band gaps near the Fermi level. This magnetic stability stems from distortion-dependent moment compensation between Co and Ti/Si atoms. By contrast, the SGS state survives only within a narrow distortion level window ($-2\%-+2\%$), beyond which valence and conduction bands cross the Fermi level, destroying the spin-gapless feature. The associated energy penalty for maintaining these characteristics within this window was modest (22–27 meV), suggesting that thermal annealing could enable films to overcome this barrier and approach more stable, less-distorted configurations. Therefore, current study provides suggestions to grow high-quality thin-film samples for spintronic applications by selecting suitable substrate to obtain the least lattice distortion, and annealing samples at high-enough temperature to endow samples with a more relaxed state. These results advance fundamental understanding of the effect of tetragonal distortion on SGS property and the related physics mechanism while offering practical strategies for developing high-performance spintronic devices.

We present a combined magnetometry, muon spin-relaxation $\left(\mu \mathrm{SR}\right)$, and neutron-scattering study of the insulating spin glass ${\mathrm{Zn}}_{0.5}{\mathrm{Mn}}_{0.5}\mathrm{Te}$, for which magnetic ${\mathrm{Mn}}^{2+}$ and nonmagnetic ${\mathrm{Zn}}^{2+}$ ions are randomly distributed on a face-centered cubic lattice. The magnetometry and $\mu \mathrm{SR}$ results confirm a spin freezing transition around $T_f\approx 23$ K, with the spin-fluctuation rate decreasing gradually and somewhat inhomogeneously through the sample volume as the temperature decreases toward $T_f$. Characteristic spin-correlation times well above $T_f$ are on the order of ${10}^{-10}$ s, much slower than typically observed in canonical spin glasses but in line with expectations for a cluster spin glass. Using magnetic pair distribution function (mPDF) analysis and reverse Monte Carlo (RMC) modeling of the magnetic diffuse neutron-scattering data, we show that the spin-glass ground state consists of clusters of spins exhibiting short-range-ordered type-III antiferromagnetic correlations with a locally ordered moment of $3.1\left(1\right){\mu }_{\mathrm{B}}$ between nearest-neighbor spins. The type-III correlations decay exponentially as a function of spin separation distance with a correlation length of approximately 5 Å. The diffuse magnetic scattering and corresponding mPDF show no significant changes across $T_f$, indicating that the dynamically fluctuating short-range spin correlations in the paramagnetic state retain the same basic type-III configuration that characterizes the spin-glass state; the only change apparent from the neutron-scattering data is a gradual reduction of the correlation length and locally ordered moment with increasing temperature. Taken together, these results paint a unique and detailed picture of the local magnetic structure and dynamics in ${\text{Zn}}_{0.5}{\text{Mn}}_{0.5}\text{Te}$ and provide strong evidence that this material is best described as a cluster spin glass. In addition, this work showcases a statistical method for extracting diffuse scattering signals from neutron powder diffraction data, which we developed to facilitate the mPDF and RMC analysis of the neutron data. This method has the potential to be broadly useful for neutron powder diffraction experiments on a variety of materials with short-range atomic or magnetic order.

The shift current photovoltaic effect is conventionally understood as the real-space displacement of a wave packet induced by photoexcitation. However, this interpretation becomes insufficient in flat-band systems, where quasiparticles are too massive to accelerate in real space under the optical electric field. Here, we developed a physically consistent method to decompose the shift current into real-space and momentum-space components. A surprising pure momentum-space shift current is found theoretically in flat-band Mott insulator ${\mathrm{Nb}}_3{X}_8$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$ monolayers. This work underscores that significant shift current responses can emerge even in systems with zero polarization change, highlighting the potential for exploring novel bulk photovoltaic effects in flat-band Mott insulators.

Metaconnected benzene shows destructive quantum interference in charge transport. Whether metaconnection always indicates destructive quantum interference is not yet well understood. Herein, we compare two meta structures, meta-terminated paraterphenyl (meta1) and metaterphenyl (meta2), through tight-binding modeling of simplified structures, as well as synthesis, single-molecule conductance measurements, and self-energy corrected density-functional theory calculations of three series of molecules. Meta2 exhibits a much stronger quantum interference effect than meta1 in single-molecule junction charge transport. When the second-nearest neighbor interaction between the molecule and the electrodes $\left({\mathrm{\Gamma }}_1\right)$ is included, the tight-binding model successfully captures the difference between meta1 and meta2. Through tight-binding modeling of benzene, biphenyl, and tetraphenyl structures, we suggest that when ${\mathrm{\Gamma }}_1$ enables coupling between para or ortho positions on the terminal benzene to the electrode, overall destructive quantum interference is suppressed; when ${\mathrm{\Gamma }}_1$ continues to be a coupling between meta positions to the electrode, destructive quantum interference remains. Our findings highlight that different degrees of destructive quantum interference effect can be readily achieved through the design of varied metaconnected molecular structures.

Flexoelectricity, an electromechanical coupling between strain gradient and polarization, offers a promising dimension to enrich silicon-based devices. Although the flexoelectricity of silicon is known, some fundamental aspects remain ambiguous, such as the discrepancy between experimental results and theoretical predictions, the influence of doping concentration, and the role of the band gap. Here, we measured the flexoelectricity of intrinsic and heavily doped Si over the temperature range of $-50–200{}^{\circ }\mathrm{C}$. The flexoelectric coefficient is of ∼2.6 µC/m and barely varies with temperature in doped silicon, while in intrinsic silicon, it varies by nearly two orders of magnitude from ∼15.2 nC/m to 1.8 µC/m as temperature increases. We show that their different temperature dependencies correspond to the temperature-insensitive donor ionization in doped silicon and the temperature-sensitive intrinsic excitation in intrinsic silicon, with the latter captured by a quantitative relationship between flexoelectricity, temperature, and band gap. Furthermore, similar experimental results on germanium (Ge) suggest the universality of this relationship in first-generation semiconductors. These findings would offer valuable reference for developing Si-based electromechanical devices as well as understanding the strain-gradient effects on semiconductor band structures (flexoelectronics).

Thermal measurements of heat capacity and thermal conductivity in a wide range of insulators and superconductors exhibit a “thermal paradox”: a large linear specific heat reminiscent of neutral Fermi surfaces (associated with fractionalized quasiparticles) in nonmetallic samples that exhibit no corresponding linear temperature coefficient to the thermal conductivity. At first sight, these observations appear to support the formation of a continuum of thermally localized many-body excitations, a form of many-body localization that would be fascinating in its own right. Here, by mapping thermal conductivity measurements onto thermal $RC$ circuits, we argue that the development of extremely long thermal relaxation times, a “thermal bottleneck,” is likely in systems with either many-body localization or neutral Fermi surfaces due to the large ratio between the electron and phonon specific heat capacities. We present a reevaluation of thermal conductivity measurements in materials exhibiting a thermal paradox that can be used in future experiments to deliberate between these two exciting alternatives.