The generic Mott transition in one-dimensional quantum systems can be described by the $(1+1)D$ sine-Gordon model with a tilt via bosonization. Because the configuration space of the sine-Gordon model separates into distinct topological sectors, standard local Monte Carlo schemes are limited to very small system sizes ($\sim 15\times 15$). To overcome this limitation, we introduce the smooth worm (SmoWo) Monte Carlo algorithm which enlarges the configuration space to allow smooth transitions between topological sectors. The method combines worm updates with event-chain Monte Carlo moves. We explicitly prove its validity and quantify its performance. Thanks to the substantial acceleration achieved by the SmoWo algorithm, we are able to simulate large system sizes up to $256\times 256$, providing a precise picture of the different phases and critical behavior of the sine-Gordon model.

In obstructed atomic insulators, fractionally quantized charges appear at the corners of the crystals in the shapes of vertex-transitive polyhedra and are given by the filling anomaly divided by the number of corners. Authors of recent studies have revealed that the filling anomaly for the cases with genus 0 is universally given by the total charge at the Wyckoff position (WP) $1a$. In this study, we rewrite the formula in terms of the degree of sharpness of the corner and show that the corner charge formula also holds for cases with arbitrary genus. We also extend our formula to vertex-transitive shell polyhedra, which are closed or open polyhedra without the bulk region, with all the vertices related by symmetry. Then we show that the corner charges of such shell polyhedra are equal to the two-dimensional disclination charges of the corresponding disclinations. By identifying it with the disclination charge under the Wen-Zee action, we show that the coupling constant of the Wen-Zee action for a crystalline insulator is given by the total charge at the WP at the disclination core.

The strong-interaction functionals $W_{\infty }\left[n\right]$ and $W_{\infty }^{\prime }\left[n\right]$ play an important role in the adiabatic-connection method of density functional theory. The strictly correlated electron approach can be used to exactly compute these functionals, yet calculations are computationally very expensive even for small electronic systems, and thus semilocal approximations have been proposed. In this work, we develop a meta-generalized gradient approximation (meta-GGA) model for the strong-interaction functionals, named the enhanced point-and-charge (ePC) model, constructed from exact constraints. In particular, the ePC restores the second-order gradient expansion of the PC model, which is relevant for the equilibrium properties of Wigner crystals, and it ensures the non-negativity of $W_{\infty }^{\prime }\left[n\right]$. We assess the ePC model for atoms and various systems: Hooke's atoms, two-electron exponential densities, $s$- and $p$-hydrogenic shells, quasi-two-dimensional infinite barrier model, perturbed uniform electron gas, $H_2$ dissociation, and conventional molecular benchmarks. We prove the good overall accuracy of the ePC model, which achieves a broader applicability than any previous semilocal models.

We study Andreev conversion in clean nanostructures containing an interface between graphene in the quantum Hall (QH) state and a superconductor, focusing on the lowest Landau level. First, several graphene nanostructures formed from zigzag edges with sharp corners are considered using a tight-binding model. We find the scattering state for an electron impinging on the interface from the upstream QH edge state, together with the probability of it exiting as a hole in the downstream QH edge state (Andreev conversion). From these results, we deduce the behavior for edges at an arbitrary angle and for rounded corners. A key issue is whether the graphene-superconductor interface is fully transparent or only partially transparent. For full transparency, we recover previous results. In contrast, interfaces with partial but substantial transparency (well away from the tunneling limit) behave very differently: (i) the hybrid electron-hole interfacial modes are not valley degenerate and (ii) intervalley scattering can occur at the corners, even when rounded. As a result, interference between the two hybrid modes can occur, even in the absence of disorder. Finally, we compare the sensitivity of Andreev conversion to interface transparency in the QH regime to that in the absence of a magnetic field. While the zero-field result closely follows the classic Blonder-Tinkham-Klapwijk relation, Andreev conversion in the QH regime is more robust.

Surface diffusion is typically described using tracer diffusion coefficients $D_s$, which provides a bridge between atomistic dynamics and macroscopic modeling. Here we introduce a new framework to convert helium-3 spin-echo (HeSE) coherent scattering information into tracer diffusion coefficients $D_s$, systematically distinguishing and treating three different diffusion regimes—Brownian, hopping, and correlated—within a single HeSE analysis framework. HeSE resolves adsorbate motion on both $\AA$ length scales and picosecond timescales and yields highly accurate hopping rates and dephasing rates data across a broad range of systems, yet results are seldom reported directly as $D_s$ because a standard conversion from the coherent intermediate scattering function has been lacking. By combining analytical models with molecular dynamics simulations where interadsorbate forces are explicitly included, we establish a unified workflow to extract $D_s$, and produce an initial benchmark library of HeSE-derived $D_s$ for surface-diffusion studies, providing an experimentally derived tracer diffusion coefficients for a set of adsorbate-substrate systems.

Positional polymorphism in solids refers to locally disordered unit cells that, on average, reproduce the high-symmetry structures observed in diffraction experiments. Standard theories of electron-phonon interactions fail to describe the temperature-dependent electronic structure of such polymorphous systems. Hybrid halide perovskites are a prime example, where configurational entropy from both polymorphism and molecular disorder plays a central role. Here we generalize the special displacement method to polymorphous crystals, providing an efficient ab initio framework for electron-phonon couplings without resorting to molecular dynamics. We resolve long-standing discrepancies in hybrid halide perovskite physics, including temperature-dependent anharmonic phonons and band gaps. Our approach provides a practical route to link local disorder, configurational entropy, and electron-phonon interactions, with applicability across diverse material classes, from optoelectronics and ferroelectrics to thermoelectrics.

Graphene is prone to out-of-plane instabilities, with buckling under compression being the most common example. While tensile loading is generally expected to suppress such effects, recent studies on macroscopic elastic sheets have shown that localized tension can induce transverse buckling and giant folding. Whether this mechanism persists in atomically thin materials, however, remains unclear. Here, we demonstrate through molecular-dynamics simulations that when localized tension is applied, graphene develops pronounced out-of-plane folding driven by transverse-compressive stresses. Once folding is initiated, the folding angle follows a robust power-law scaling with the applied strain, enabling quantitative and controllable modulation of the folded morphology. We further demonstrate that the sheet aspect ratio plays a key role in governing the folding response, including the onset of folding and the maximum attainable folding angle. Importantly, this folding behavior and its associated scaling law are found to be robust against moderate thermal fluctuations and low concentrations of lattice defects. These results establish localized tension-induced folding as a robust mechanical instability in graphene and demonstrate that continuum thin-sheet scaling laws remain applicable down to the atomic scale. Our findings provide a framework for tailoring the morphology of graphene and other two-dimensional materials through geometric design and mechanical loading.

We report microwave spectroscopy of ${{}^{167}\mathrm{Er}}^{3+}$ doped in ${\mathrm{CaWO}}_4$, which reveals the hyperfine splitting of the erbium electronic ground state ($Z_1, J_{\mathrm{eff}}=15/2$) induced by the $I=7/2$ nuclear spin. From spectra measured below $\sim 50\mathrm{mK}$ in magnetic fields up to 200 mT, we extract spin-Hamiltonian parameters including the electron $\mathbf{g}$, hyperfine $\mathbf{A}$, and nuclear electric quadrupolar $\mathbf{Q}$ tensors. Crucially, our analysis demonstrates unambiguously that the previously unobserved nuclear electric quadrupolar moment is essential to reproduce the experimental data. With these refined parameters, we identify zero first-order Zeeman (ZEFOZ) transitions at zero magnetic field. Extending the analysis to finite fields, we uncover that ZEFOZ points lie either along the $c$ axis or within the $a\text{−}b$ plane. These results establish ${\mathrm{CaWO}}_4$ as a promising host for long lifetime quantum memories.

We propose a mechanism to control magnetic skyrmion motion by generating a skyrmion number current. This current is produced and controlled via an explicitly time-dependent Hamiltonian containing a Zeeman term arising from the interaction between the spin system and circularly polarized light. We find that skyrmion dynamics exhibit a limit cycle in momentum space, whose properties are determined only by physical parameters: the magnitude of the external magnetic field, the Heisenberg coupling, and the Gilbert damping constant. This method provides a theoretical explanation for the topological origin of optically controlled skyrmion motion, and it opens the possibility for efficient, low-dissipation skyrmion control using skyrmion number currents as an alternative to electric currents.

We probe the first-order hysteretic antiferromagnetic (AFM) to ferromagnetic (FM) phase transition of FeRh in a FeRh/Ta/GaAs stack using surface acoustic waves (SAWs) of three different frequencies up to 889 MHz. A clear signature of the phase transition is observed in the Rayleigh velocity and attenuation variations across the phase coexistence temperature range. The velocity variation closely follows the thermal hysteresis exhibited by the phase transition when probed with magnetometry, thereby enabling the determination of the FM fraction of FeRh versus temperature in the SAW path. The variation of attenuation is modeled under the assumption of strain-induced modulation of magnetic order via the movement of AFM-FM phase domain walls (PDWs) at the SAW frequency. This movement is driven by the strain-dependent difference between the AFM and FM Gibbs free energies, which originates from volume magnetostriction. The measured attenuation and its dependence upon the temperature and SAW frequency can be explained through a dissipative mechanism associated with the PDW oscillation driven by the strain wave. Finally, we demonstrate the drastic changes in the temperature dependence of SAW attenuation caused by the applied magnetic field within the FM-rich phase coexistence range, which arise from SAW-induced ferromagnetic resonance.

We successfully synthesized a verdazyl-based complex, $(p\text{−}\mathrm{Py}\text{−}\mathrm{V}\text{−}2,6\text{−}{\mathrm{F}}_2)\left[\mathrm{Cu}{\left(\mathrm{hfac}\right)}_2\right]$, which forms a spin-$\frac{1}{2}$ extended diamond chain comprising verdazyl radicals and ${\mathrm{Cu}}^{2+}$ ions. The magnetic susceptibility measurements indicate a dominant antiferromagnetic contribution and a singlet ground state. The magnetization curve exhibits a zero-field gap and a $\frac{1}{2}$ plateau. We reproduced these behaviors through numerical analysis based on the extended diamond chain. Furthermore, a perturbative analysis in the high-field region beyond the plateau maps the system onto an effective spin-$\frac{1}{2}$ XY-like chain, thereby demonstrating that the $\frac{1}{2}$ plateau originates from singlet dimer formation in the effective chain. These findings offer a perspective on quantum phases in one-dimensional spin systems and are expected to stimulate further investigations of spin chains with diamond units.

Understanding the relationship between structure and thermal expansion is of great fundamental scientific significance for revealing the nature of thermal expansion and achieving its precise control. This work reports a unique layered open-framework structure with a terminal CN group in $\mathrm{Zn}{\left[\mathrm{B}{\left(\mathrm{CN}\right)}_4\right]}_2$, which displays zero thermal expansion (ZTE) in plane over a wide temperature range (${\alpha }_{\mathrm{a}}=-0.66\times {10}^{-6}{\mathrm{K}}^{-1}$, 100–700 K). A joint study of variable-temperature synchrotron x-ray diffraction, Raman spectroscopy, and first-principles calculations has been performed to investigate the structure, thermal expansion, and mechanism. Our study reveals that the in-plane ZTE originates from two mechanisms: (i) the in-plane tension effect, which gives rise to phonon soft modes with negative Grüneisen parameters, primarily involving the coupled rotations of ${\mathrm{BC}}_4$ tetrahedra and ${\mathrm{ZnN}}_6$ octahedra; and (ii) the elastic effect, where the elastic constants act as a coupling coefficient that enhances the in-plane negative thermal expansion (NTE). This work reveals the origin mechanism of NTE in layered borate systems, emphasizing the synergistic effect between phonon contributions and elastic effects, providing insights into the physical nature of thermal expansion.

We report a computational study of thermal expansion in the hybrid layer structure ${\mathrm{ZnB}}_2{\left(\mathrm{CN}\right)}_8$ using density functional theory (DFT) methods. The crystal structure has a trigonal lattice, with a larger positive thermal expansion in the axial direction ($c$ axis) and a very small negative thermal expansion within the layer normal to the axial axis (the $a\text{−}b$ plane). The results of the DFT calculations for the structure, lattice dynamics and thermal expansion are consistent with experimental data, and, together with a flexibility analysis, it is possible to explain the large difference between axial and area thermal expansivities. We argue from some general features that the difference between the two expansivities is an inevitable consequence of a combination of the elasticity being stiffer within the layers than between the layers, and of the existence of a tension effect operating within the layers, which lowers the values of the area-strain Grüneisen parameters relative to the axial ones. These two factors combine in a way to enhance the axial expansivity but cancel in the calculation of the area expansivity. This is likely to be a general case for any layer structure in which the layers can be described as a partly flexible network.

Point-gap topology, characterized by spectral winding numbers, is crucial to non-Hermitian topological phases and dramatically alters real-time dynamics. In this paper, we study the evolution of quantum particles in dissipative systems with imaginary gap closing, using the saddle-point approximation method. For trivial point-gap systems, imaginary gap-closing points can also be saddle points. This leads to a single power-law decay of the local Green's function, with the asymptotic scaling behavior determined by the order of these saddle points. In contrast, for nontrivial point-gap systems, imaginary gap-closing points do not coincide with saddle points in general. This results in a dynamical behavior characterized by two different scaling laws for distinct time regimes. In the short-time regime, the local Green's function is governed by the dominant saddle points and exhibits an asymptotic exponential decay. In the long-time regime, however, the dynamics is controlled by imaginary gap-closing points, leading to a power-law decay envelope. Our findings advance the understanding of quantum dynamics in dissipative systems and provide predictions testable in future experiments.

Understanding how spin texture formation can be engineered is essential for the design and development of spin-based memory and computing devices. Arrays of interacting nanomagnets called artificial spin ices (ASIs) offer a route towards understanding how dipolar interactions can influence the formation of different spin texture states. Using micromagnetic simulations, we studied $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$-based brickwork ASIs and showed that the formation of single and double vortices, which we collectively term as complex spin textures (CSTs), depends on the magnetization of the nearest-neighboring nanoislands. Micromagnetic simulations of isolated nanoislands reveal that the tips of CST-bearing nanoislands behave as effective dipoles, thus allowing interactions between CSTs and single domains to be interpreted within an Ising dipolar interaction framework. Through an energy analysis of interacting nanoisland sets, we find that the magnetic configuration of nearest-neighboring nanoislands can induce energy splitting between the two chiralities of a single- or double-vortex state. Moreover, we find that this energy splitting can be predicted by comparing the number of attracting dipolar interactions each chiral state produces. These results can allow us to predict the appearance of a CST in an ASI, which can be leveraged towards developing new ASI systems capable of exploiting CST and Ising states.

Vapor deposited two-dimensional ${\mathrm{Cr}}_7{\mathrm{Te}}_8$ displays unusual temperature dependent Hall effect properties, including a room-temperature anomalous Hall effect, sign reversals of the Hall resistivity on cooling, and a peak in the Hall resistivity at low temperatures. The two-dimensional ${\mathrm{Cr}}_7{\mathrm{Te}}_8$ heterostructures that form the basis of these measurements are hexagonal in structure. We study the magnetic and structural properties of bulk ${\mathrm{Cr}}_7{\mathrm{Te}}_8$ synthesized by quenching from $1000{}^{\circ }\mathrm{C}$ with the goal of relating the magnetic, structural, and electronic properties. This quenched phase is metastable, hexagonal, and displays different magnetic properties from the slow-cooled and more thermodynamically stable monoclinic phase. High-resolution x-ray diffraction of the quenched hexagonal phase finds a first-order transition to a lower symmetry monoclinic phase on heating above $\sim 550$ K. Magnetic susceptibility measurements of the quenched hexagonal phase reveal ferromagnetic ordering above room temperature, along with the two distinct transitions at $\sim 220$ K and $\sim 70$ K. Through neutron diffraction studies, we find the $\sim 220$ K anomaly is a spin reorientation transition of the ferromagnetically aligned magnetic moments and the $\sim 70\mathrm{K}$ feature represents a transition from a high-temperature ferromagnet to a low-temperature antiferromagnet. We suggest that these magnetic transitions are related to changes in the unit-cell dimensions and are connected to the temperature-dependent Hall resisitivity studied in two-dimensional heterostructures. This implies a link between structural, magnetic, and electronic properties in the “pseudo” two-dimensional chromium tellurides.

We report the canted antiferromagnetic (AFM) structure together with a spin reorientation in a single chain quasi-one-dimensional (Q-1D) iron chalcogenide ${\mathrm{Ba}}_2{\mathrm{FeSe}}_3$. ${\mathrm{Ba}}_2{\mathrm{FeSe}}_3$ crystallizes in Pnma (No. 62) orthorhombic structure with linear single iron chains consisting of corner-shared distorted ${\mathrm{FeSe}}_4$ tetrahedra along the $b$ axis. ${\mathrm{Ba}}_2{\mathrm{FeSe}}_3$ is a narrow-gap semiconductor and orders AFM below 60 K. Modeling of neutron powder diffraction data reveals a canted AFM ground state of magnetic space group $Pa21/c$ (BNS No. 14.80) with commensurate propagation vector $\mathbf{k}=(0, \frac{1}{2}, 0)$, where the Fe ion spins are AFM aligned with up-down-up-down $(\uparrow \text{−}\downarrow \text{−}\uparrow \text{−}\downarrow )$ sequence along the Q-1D chain direction of the $b$ axis. In the magnetically ordered state, the canting of magnetic moments reorients from the $ac$ plane to the $ab$ plane below 30 K, with a 10° tilting angle toward the $a$ axis, and the magnetic moment does not induce a net moment in either orientation. The density functional theory results indicate that an $\uparrow \text{−}\downarrow \text{−}\uparrow \text{−}\downarrow$ AFM state is stabilized along the chain direction. In this work, we elucidate the unique canted AFM of the iron chalcogenide and pave the way for searching exotic physics in Q-1D ${\mathrm{Ba}}_2{\mathrm{FeSe}}_3$.