Polar skyrmions and skyrmion lattices (SkX) in ferroelectrics have attracted much attention due to their novel and unique physical properties as quasiparticles. By analogy with conventional lattice crystals, the understanding of lattice defects, particularly grain boundaries, is crucial for elucidation of the unique lattice properties hidden in the polar SkX. The fundamental structure of grain boundaries in polar SkX, however, still remains undeveloped. Here, we show that the grain boundaries in polar SkX not only have a unique lattice structure with giant skyrmion deformation, but also “quasiparticle-based” stabilization in which local lattice mismatch is maintained without relaxation. Our phase-field simulations reveal that skyrmion grain boundaries undergo structural changes accompanied by skyrmion deformation depending on the electric field and temperature conditions. Furthermore, a transition of the stabilization mechanisms occurs, where relaxation due to the movement of skyrmions is replaced by skyrmion deformation, and local giant lattice mismatch is maintained. Our findings provide unique insights into the physical properties and formation processes of polar skyrmion lattices.

We explore the structural and electronic properties of the bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ on ${\mathrm{LaAlO}}_3\left(001\right)$ and ${\mathrm{SrTiO}}_3\left(001\right)$ by using density functional theory including a Coulomb repulsion term. For ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7/{\mathrm{LaAlO}}_3\left(001\right)$, we find that compressive strain and electron doping across the interface result in the unconventional occupation of the antibonding Ni $3d_{z^2}$ states. In sharp contrast, no charge transfer is observed for ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7/{\mathrm{SrTiO}}_3\left(001\right)$. Surprisingly, tensile strain drives a metallization of the bonding Ni $3d_{z^2}$ states, rendering a Fermi surface topology akin to superconducting bulk ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ under high pressure, yet with spin fluctuations enhanced considerably beyond pressure effects. Concomitantly, significant octahedral rotations are retained. We discuss the fundamental differences between hydrostatic pressure versus epitaxial strain and establish that strain provides a much stronger control over the Ni $e_g$ orbital polarization. The results suggest epitaxial ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, particularly under tensile strain, as interesting system to provide novel insights into the physics of bilayer nickelates and possibly induce superconductivity without external pressure.

Conventional second-harmonic generation (SHG) interference, such as nonlinear magneto-optical effects, typically requires magnetism and strong spin-orbit coupling, limiting its occurrence to rare materials, narrow frequency ranges, and restrictive tunability. Challenging this assumption, we demonstrate through symmetry analysis and first-principles calculations that SHG interference can arise purely from crystal symmetry without magnetism or spin-orbit coupling. We show a stable and giant crystal SHG interference occurs universally in $C_{3v}$-symmetric nonmagnetic materials within the broad nonresonant regime. The proposed interference mechanism transcends traditional limitations, offering a transformative potential for distinguishing twinned structures, enabling nonlinear optical diode effects, and advancing electric-field-controlled SHG technologies.

The two-dimensional antiferromagnetic material CrSBr has attracted significant attention due to its unique electrical, optical, and magnetic properties. Previous studies have reported different magnetic resonances in bulk CrSBr samples but left the damping rates of these resonances unexplored, due to the ultraweak nature of the signals. In this study, we optimize the design of a coplanar waveguide and systematically investigate the variation in internal damping rates of magnetic resonances in a CrSBr sample under different magnetization states. Given that CrSBr is sensitive to both temperature and magnetic field, we develop three distinct methods to modify its magnetization: altering the bias magnetic field, varying temperature, and applying a temperature gradient. We find that the internal damping rates of the antiferromagnetic resonance and the ferromagnetic resonance exhibit opposite dependence on either the bias magnetic field or temperature. We attribute these changes to the nonuniform magnetization of the CrSBr sample. To support this hypothesis, we perform an additional experiment applying a temperature gradient to induce nonuniform magnetization. The results confirm our assumption that the temperature gradient enhances the nonuniform magnetization and increases the internal damping rates of the magnetic resonances. Our work reveals the connection between damping and magnetization states in van der Waals magnetic magnets. These findings may contribute to the study of dynamic magnetization properties in van der Waals magnetic materials.

The chiral magnetic soliton, a spiral localized spin texture with quantized topological charges, has garnered significant attention from both scientific and technological perspectives. The Mn-intercalated ${\mathrm{Mn}}_{1/3}{\mathrm{TaS}}_2$ hosts a one-dimensional topological chiral magnetic soliton. This work thoroughly investigates the critical phenomenon of ${\mathrm{Mn}}_{1/3}{\mathrm{TaS}}_2$ single crystals. Fitting the magnetic entropy change yields critical exponents of $\beta =0.268\pm 0.006, \gamma =1.392\pm 0.008$, and $\delta =6.209\pm 0.007$ with a critical temperature $T_C=70.12\pm 0.01$ K. Using these critical exponents, the magnetic entropy change curves are scaled into an independent universal curve, indicating the reliability and convergence of these parameters. The critical exponents of ${\mathrm{Mn}}_{1/3}{\mathrm{TaS}}_2$ are close to those of the two-dimensional (2D) Ising model characterized by a spatial and spin dimensionality of $\{d:n\}=\{2:1\}$, which suggest strong anisotropic spin coupling in this system. Moreover, the spin interaction distance is estimated to decay as $J\left(r\right)\sim r^{-3.37\left(6\right)}$. The $H-T$ phase diagram for $H\perp c$ is constructed, distinguishing the chiral magnetic helimagnetism (CHM), chiral soliton lattice (CSL), forced ferromagnetism (FFM), and paramagnetic (PM) phases. This clarification of the magnetic coupling and phase diagram enhances the understanding of chiral topological magnetism.

We study monitored quantum dynamics of infinite-range interacting bosonic systems in the thermodynamic limit. We show that under semiclassical assumptions, the quantum fluctuations along single monitored trajectories adopt a deterministic limit for both quantum-jump and state-diffusion unravelings, and they can be exactly solved. In particular, the hierarchical structure of the equations of motion explains the coincidence of entanglement criticalities and dissipative phase transitions found in previous finite-size numerical studies. We illustrate the findings on a Bose-Hubbard dimer and a collective spin system.

We introduce a route to Hilbert space fragmentation in high dimensions leveraging the group-word formalism. We show that taking strongly fragmented models in one dimension and “lifting” to higher dimensions using subsystem symmetries can yield strongly fragmented dynamics in higher dimensions, with subdimensional (e.g., lineonic) excitations. This provides a route to higher-dimensional strong fragmentation, and also a route to fractonic behavior. Meanwhile, lifting one-dimensional fragmented models to higher dimensions using higher-form symmetries yields models with topologically robust fragmentation. In three or more spatial dimensions, one can also “mix and match” subsystem and higher-form symmetries, leading to canonical fracton models such as X cube. We speculate that this approach could also yield a route to non-Abelian fractons. These constructions unify a number of phenomena that have been discussed in the literature, as well as furnishing models with unique properties.

We study fermionic quantum spin liquids (QSLs) on the three-dimensional trillium lattice of corner-sharing triangles. We are motivated by recent experimental and theoretical investigations that have explored various classical and quantum spin liquid states on similar networks of triangular motifs with strong geometric frustration. Using the framework of projective symmetry groups (PSG), we obtain a classification of all symmetric ${\mathsf{Z}}_2$ and $\mathsf{U}\left(1\right)$ QSLs on the trillium lattice. We find two ${\mathsf{Z}}_2$ spin-liquids, and a single $\mathsf{U}\left(1\right)$ spin-liquid that is proximate to one of the ${\mathsf{Z}}_2$ states. The small number of solutions reflects the constraints imposed by the nonsymmorphic symmetries in the space group of the trillium lattice. Using self-consistency conditions of the mean-field equations, we obtain the spinon band-structure and spin structure factors corresponding to these states. All three of our spin liquids are gapless at their saddle points: one of the two ${\mathsf{Z}}_2$ QSLs is nodal, while the $\mathsf{U}\left(1\right)$ case hosts a spinon Fermi surface. One of our ${\mathsf{Z}}_2$ spin liquids hosts a stable gapless nodal star that is protected by projective symmetries against additions of further neighbor terms in the mean-field ansatz. We comment on directions for further work.

We present a comprehensive investigation of the synthesis, electrical transport, magnetic, and thermal properties of Ti-doped ${\mathrm{KV}}_3{\mathrm{Sb}}_5$. The parent compound, ${\mathrm{KV}}_3{\mathrm{Sb}}_5$, exhibits a charge-density-wave (CDW) transition at $T_{CDW}=78$ K and superconductivity below a critical temperature ($T_c$) of 0.93 K. Upon light titanium doping, forming ${\mathrm{KTi}}_{0.15}{\mathrm{V}}_{2.85}{\mathrm{Sb}}_5$, the CDW transition is completely suppressed, while superconductivity is significantly enhanced, with $T_c$ increasing to 3.6 K. Bulk superconductivity in the Ti-doped compound is confirmed by resistivity, magnetization, and heat capacity measurements. Anisotropic upper critical fields are observed, with $H_{c2}$ values of 2.12 T (in-plane) and 0.59 T (out-of-plane). To elucidate the origin of enhanced superconductivity, we analyze the electronic density of states (DOS) near the Fermi level. The Sommerfeld coefficient ($\gamma$), extracted from heat capacity data, indicates an increased DOS at the Fermi level, $N\left(E_F\right)$, in the Ti-doped sample, consistent with a BCS framework for superconductivity. Density functional theory calculations further support this enhancement of $N\left(E_F\right)$ and reveal modifications to the Fermi surface topology with Ti doping, suggesting weakened Fermi surface nesting that may be responsible for the suppression of the CDW. These results provide a coherent picture in which chemical doping alters the delicate balance between competing CDW and superconducting phases, demonstrating a viable route to tune superconductivity in kagome lattice materials via chemical pressure.

Intense electrostatic fields, such as those able to break bonds and cause field-ion emission, can fundamentally alter the behavior of atoms at and on the surface. Using density functional theory calculations on the Li (110) surface under high electrostatic fields, we identify a critical field strength at which surface atoms occupying a kink site become thermodynamically unstable against adatom formation. This mechanism leads to the formation of a highly concentrated two-dimensional adatom gas on the surface. Moreover, the applied field reverses the stability of preferred adsorption sites, enabling barrierless diffusion of lithium atoms even well below the threshold required for field evaporation. The here identified mechanisms offer a unified explanation for experimental observations in atom probe tomography and for understanding high electric field phenomena at battery interfaces and electrochemical environments, especially formation of Li rich dendrites.

$\mathrm{NbO}{\mathrm{I}}_2$ exhibits a notable in-plane anisotropic ferroelectric property and a pronounced second-order nonlinear optical response, which has great potential applications in nanoelectronics. However, the collective behavior of lattice dynamics, which represents the atomic origin of emerging novel phenomena, has not been systematically explored, especially in the context of external strain. In this study, we investigate the phonon responses of $\mathrm{NbO}{\mathrm{I}}_2$ under both uniaxial and biaxial tensile strains, applied along two distinct crystallographic orientations. The characteristic P5(LO) Raman mode, which involves in-plane vibrations primarily of Nb-O atoms, demonstrates opposite frequency shifts, with anomalously blue- or redshifts observed when uniaxial tensile strain is applied parallel or perpendicular to the polar axis, respectively. Biaxial strain consistently induced a blueshift in the Raman mode, distinct from that of many conventional two-dimensional materials. These experimental observations are supported by density-functional theory calculations, which reveal the strain-induced deviations in the Nb atomic position-induced pronounced blueshift. This study highlights the distinctive strain sensitivity of $\mathrm{NbO}{\mathrm{I}}_2$, offering a useful feedback mechanism for strain manipulation, and providing insights into the potential of $\mathrm{NbO}{\mathrm{I}}_2$ for applications in flexible optoelectronics and strain sensors.

We investigate the magnetotransport properties of the half-filled antiferromagnetic (AF) one-band Hubbard model under an external magnetic field using the single-site dynamical mean-field theory. Particular attention is paid to the mechanisms driving the magnetoresistivity (MR) behavior. We analyze the dependence of MR on temperature and the strength of the applied magnetic field, providing insights into the interplay between magnetic field–induced fluctuations and transport properties in AF systems.

An emergent numerical approach to solve quantum impurity problems is to encode the impurity path integral as a matrix product state (MPS). For time-dependent problems, the cost of this approach generally scales with the evolution time. Here, we consider a common nonequilibrium scenario where an impurity, initially in equilibrium with a thermal bath, is driven out of equilibrium by a sudden quench of the impurity Hamiltonian. Despite no time-translational invariance in the problem, we show that we could still make full use of the infinite MPS technique, resulting in a method whose cost is essentially independent of the evolution time. We demonstrate the effectiveness of this method in the integrable case against exact diagonalization and against existing calculations on the L-shaped Kadanoff-Baym contour in the general case. Our method could be a very competitive method for studying long-time nonequilibrium quantum dynamics and potentially used as an efficient impurity solver in the nonequilibrium dynamical mean field theory.

Parity-time symmetry and anti-parity-time symmetry are complementary but generally incompatible. In this work, we investigate the coexistence of parity-time symmetry and anti-parity-time symmetry. These symmetries impose intriguing constraints on the spectrum, and the Bloch bands appear in opposite and conjugate tetrads. The bulk states, affected by the non-Hermiticity, are entirely complex; however, the topological edge states, protected by sublattice symmetry, are exactly zero. We demonstrate a two-leg ladder consisting of two Su-Schrieffer-Heeger chains connected by radiative and dissipative cross-couplings. The non-Hermiticity facilitates the formation of a $2\mathbb{Z}$ point gap topology, and the topological zero modes are robust against disorder.

Nonreciprocal magnons, characterized by propagation with differing energies along the $k$ and $-k$ directions, are crucial for modern spintronics applications. However, their realization in van der Waals layered antiferromagnets remains elusive. In this Letter, we report robust nonreciprocal magnon behavior in layered honeycomb antiferromagnets $\text{VP}{X}_3$ ($X=\mathrm{S}$, Se, Te). Our results demonstrate that, in addition to their intrinsic Dzyaloshinsky-Moriya interaction, the nonreciprocity of magnons is strongly influenced by the layer number, interlayer coupling, and magnon-magnon interactions. More importantly, in such layered antiferromagnets, the magnon nonreciprocity exhibits an asymmetric periodic dependence on the Néel vector, offering a novel route for experimentally probing antiferromagnetic order parameters in the two-dimensional limit.

Solid-state refrigeration based on caloric effects presents a sustainable alternative to conventional vapor-compression systems which rely on environmentally harmful refrigerants. Among these, the barocaloric effect (BCE) is particularly promising due to its ability to induce large entropy change through hydrostatic pressure. However, most BCE materials suffer from narrow refrigeration temperature range near their phase transitions and the trade-off between pressure sensitivity ($\mathrm{d}{T}_t/\text{d}P$) and entropy change (Δ$S$), which largely limits their practical application. Here, we report that metal-organic frameworks (MOFs) doped by the C4 group (MOF-5-C4) overcome these challenges by exhibiting colossal BCE (Δ$S$ = $274\mathrm{J}{\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$) with record high pressure sensitivity ($\mathrm{d}{T}_t/\text{d}P=284\mathrm{K}{\mathrm{kbar}}^{-1}$), driven by a frustrated amorphous-crystalline transition that is stabilized by dispersive interactions with adjacent C4 side groups. It achieves a remarkable 30% volume change under moderate pressure, with volume entropy being the dominant contributor, while maintaining efficient cooling across a broad temperature range (290–400 K). Through thermodynamic analysis, we demonstrate that the colossal barocaloric response originates from substantial structural deformations; both molecular vibration and rotation positively contribute to the total entropy change. In our work, we provide atomic-scale insights on the structural and thermodynamic of MOFs with BCE, which is helpful to achieve superior caloric materials for application by molecular designing in the near future.

The development of experimentally feasible two-dimensional (2D) carbon allotropes possessing distinctive properties unattainable by graphene is imperative for the advancement of next-generation carbon-based electronics. Utilizing synthesized polyacetylene and alkane precursors, here we identify a novel 2D tetragonal carbon network, designated as apographene, through a bottom-up strategy. Characterized by an ${\mathrm{sp}}^2/{\mathrm{sp}}^3$ hybridization ratio of 2:1, apographene demonstrates remarkable thermodynamic stability, surpassing that of the experimentally confirmed $\gamma$-graphyne, $\gamma$-graphdiyne, and $\beta$-graphdiyne, and exhibits superior in-plane strength compared to the mechanical robustness of graphene. Our first-principles calculations indicate that apographene functions as an intrinsic Dirac semimetal, encompassing four highly anisotropic Dirac cones with a Fermi velocity ratio of 14.5:1; notably the maximum velocity exceeds that observed in graphene. Interestingly, unconventional Dirac nodal lines, characterized by the coexistence of open and closed configurations, appear within deeper frontier bands, thereby offering electrolyte-gate tunability for topological electronic states. The pronounced anisotropic Dirac dispersion near the Fermi level yields substantial conductivity anisotropy (with a ${\sigma }_{xx}/{\sigma }_{yy}$ ratio reaching up to 31.3), enabling quasi-one-dimensional directional polarization, which serves as a foundation for anisotropic Dirac transport sensors. These findings propose a novel carbon allotrope that integrates structural robustness with exotic quantum states, alongside highlighting a precursor-directed bottom-up approach for the design of unexplored 2D materials.

An analytical model is developed to predict the temporal evolution of the lattice polarization in ferroelectric nanomembranes upon the excitation by a terahertz (THz) electromagnetic pulse of an arbitrary waveform and the concurrent transmission of the THz pulse in both linear and nonlinear regimes. It involves the use of the perturbation method to solve the equation of motion for the lattice polarization in both unclamped and strained ferroelectric nanomembranes within the framework of Landau-Ginzburg-Devonshire theory. The model is applicable to perovskite oxides such as ${\mathrm{BaTiO}}_3$ and ${\mathrm{SrTiO}}_3$, wurtzite ${\mathrm{Al}}_{1-x}{\mathrm{Sc}}_x\mathrm{N}$, and trigonal ${\mathrm{LiNbO}}_3$. Our analytical model provides a theoretical basis for determining the thermodynamic and kinetic parameters of ferroelectric materials through a THz transmission experiment. The calculation results also suggest an approach to reversing the chirality of a circularly polarized THz pulse by harnessing the resonant polarization-photon coupling in ferroelectrics. This capability of chirality reversal, along with the high tunability from a strain applied along any arbitrarily oriented in-plane axis, provides new opportunities for THz wave modulation without relying on complex metasurface designs.