A topological insulator is regarded as an ideal candidate for information storage and high-speed lossless electrical transmission devices due to robust topological protected boundary modes. Previous studies revealed that symmetry exerts an unbreakable constraint on the existence, classes, and orders of its boundary modes. It severely limits the controllability and application of a topological insulator. Here, we propose a Floquet-engineering method to break this symmetry-imposed constraint on a topological insulator. By applying periodic driving on a system belonging to a symmetry class that prohibits the existence of first-order topological phases, we find that rich first-order boundary modes are created. Interestingly, exotic hybrid-order topological insulators with coexisting first-order helical boundary modes and second-order corner modes not only in two different quasienergy gaps but also in one single gap are generated easily by periodic driving. Refreshing the prevailing understanding of symmetry constraint on topological phases, our result opens an avenue for the creation of exotic topological insulators without altering symmetries. It greatly expands the scope of the fabricated materials that host topological insulators.

We introduce the concept of antiferron modes in ferroelectric materials as dynamically stabilized collective excitations over inverted polarization states that decrease the system energy. While ferrons represent quantized oscillations around the stable polarization minimum, antiferrons require dynamic stabilization via high-frequency driving. Using a generalized Landau-Ginzburg-Devonshire framework, we derive the effective curvature corrections from external driving, demonstrate the conditions for stabilizing metastable wells, and present the quantized Hamiltonian. Antiferrons could be a promising candidate for developing electrical sensing devices, offering tunable, dynamically controllable excitations with high sensitivity to external electric fields.

Lorentz transmission electron microscopy is widely used for imaging magnetic structures at the nanoscale in real space. However, its interpretation can be complicated by imaging artifacts induced by the defocus distance and specimen tilt. In this work, we systematically examine the origins of such artifacts through experimental and simulated Fresnel defocused Lorentz imaging of Bloch-type skyrmionic spin textures. We analyze the effects from the defocus distance, the magnetic field, and the sample thickness in an individual skyrmion, two neighboring skyrmions, and the skyrmion lattice. We demonstrate that improper defocus distance and specimen tilt may introduce artifacts that are not associated with the actual magnetic configurations. These findings provide a practical framework for Lorentz TEM imaging and highlight the importance of the defocus distance, sample tilt, and theoretical support for reliable interpretations of magnetic textures.

Employing first-principles based calculations, we reexamined the high-pressure phases of the vacancy-ordered iron-selenides, i.e., $A_2{\mathrm{Fe}}_4{\mathrm{Se}}_5$ phase. A magnetic transition from the block-spin antiferromagnetic phase to the Néel-altermagnetism (AM) phase is observed under high pressure when the iron-vacancy order is preserved. Thus, ternary iron-selenides under pressure may be a rare example for coexisting altermagnetism and superconductivity. In particular, an equal-spin triplet pairing would be naturally favored, if the reentrant superconducting phase of ${\mathrm{K}}_y{\mathrm{Fe}}_{2-x}{\mathrm{Se}}_2$ under high pressure emerges from the Néel-AM normal state. In addition, the Néel-AM phase is an intrinsic altermagnetism that does not require ligand atoms nor supercell construction to break the spatial inversion or translational symmetry between the two spin sublattices, with a spin splitting of the band structure as large as 300 meV.

The systems exhibiting coexistence of Kondo coupling and magnetic frustration offer a rich platform for exploring the interplay between these competing effects, which often give rise to exotic quantum phases. Rare-earth-doped metallic pyrochlores with noncoplanar spin configurations, pronounced Ising anisotropy, and strong $f\text{–}d$ exchange coupling, represent an intriguing class of materials for probing the complex interaction between geometrical frustration and potential Kondo interactions. In this study, we investigate the magnetic and electronic transport properties of ${\mathrm{Bi}}_{1.1}{\mathrm{Nd}}_{0.9}{\mathrm{Ru}}_2{\mathrm{O}}_7$ (BNRO), a rare-earth-doped pyrochlore oxide that bridges the nonmagnetic metallic ${\mathrm{Bi}}_2{\mathrm{Ru}}_2{\mathrm{O}}_7$ (BRO) and the weakly frustrated, magnetically insulating ${\mathrm{Nd}}_2{\mathrm{Ru}}_2{\mathrm{O}}_7$ (NRO). From low-temperature magnetic susceptibility measurements, the effective magnetic moment of ${\mathrm{Nd}}^{3+}$ is estimated to be $2.38{\mu }_B/\mathrm{Nd}$, and the isothermal magnetization confirms the presence of Ising anisotropy. A Schottky-like anomaly observed in the low-temperature specific heat data indicates the presence of $f\text{–}d$ exchange coupling between the ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Ru}}^{4+}$ ions. However, this coupling is found to be relatively weak to induce robust spin chirality in the Ru sublattice that could manifest as a geometrical Hall effect (GHE). Indeed, Hall measurements did not reveal any signatures of GHE. The absence of GHE in BNRO is attributed to the underlying Kondo coupling, which weakens the exchange interaction between the ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Ru}}^{4+}$ ions, effectively suppressing the transfer of spin chirality necessary for GHE.

Optical excitation of large-amplitude apical oxygen phonon oscillations has been shown to renormalize the electronic properties of $\mathrm{YB}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6+x}$, inducing a superconducting-like optical response above equilibrium $T_C$. All of the evidence collected so far has been based on the changes of the terahertz frequency $c$-axis response. In these measurements, the capacitive interlayer coupling was seen to transform into a superconducting-like inductive response. This assignment was strengthened by recent measurements of ultrafast magnetic field expulsion. Here, we report an experimental determination of the transient in-plane optical properties, which has so far been elusive due to the high equilibrium reflectivity and the need to evaluate minute changes in the optical response. We report the appearance of a photoinduced in-plane optical gap $2\mathrm{\Delta }\simeq 30\mathrm{c}{\mathrm{m}}^{-1}$ and a divergent imaginary conductivity, both consistent with photoinduced superconductivity. A global fit to these data suggests that in- and out-of-plane electronic properties never completely equilibrate during the dynamics.

A series of ${\mathrm{Mn}}_{100-x}{\mathrm{Rh}}_x$ $(20\le x\le 50)$ thin films were epitaxially grown on the MgO substrate using magnetron sputtering technique, and were systematically investigated by magnetization, longitudinal electrical resistivity, and transverse Hall resistivity. After optimizing the growth conditions, phase-pure ${\mathrm{Mn}}_{100-x}{\mathrm{Rh}}_x$ films with a cubic CsCl-type structure were obtained, and their magnetic phase diagram was built. The manipulation of Rh content leads to a rich magnetic phase diagram, where three different regimes can be identified: for $x<40$, ${\mathrm{Mn}}_{100-x}{\mathrm{Rh}}_x$ films undergo a ferromagnetic (FM) transition below $T_{\mathrm{C}}\approx$ 330–350 K; for $40\le x\le 45$, in addition to the FM transition at $T_{\mathrm{C}}\approx$ 200 K, ${\mathrm{Mn}}_{100-x}{\mathrm{Rh}}_x$ films undergo a FM-to-antiferromagnetic (AFM) transition at $T_{\mathrm{N}}\approx$ 120 K; finally for $x>45$, only one AFM transition at $T_{\mathrm{N}}\approx$ 150 K can be tracked. All the ${\mathrm{Mn}}_{100-x}{\mathrm{Rh}}_x$ films exhibit distinct anomalous Hall effect in their magnetically ordered state, which is most likely due to the intrinsic Berry-curvature mechanism. In addition, all the anomalous Hall transport properties, including the resistivity, conductivity, and angle exhibit a strong correlation with the magnetic properties of ${\mathrm{Mn}}_{100-x}{\mathrm{Rh}}_x$ films, which become most evident for $x$ = 35. Our systematic investigations suggest a strong correlation between magnetic properties and electronic band topology in ${\mathrm{Mn}}_{100-x}{\mathrm{Rh}}_x$ films, highlighting their great potential for AFM spintronics.

We study the distinctive features of the interplay between the interlayer superconductivity and ferroelectricity in van der Waals heterostructures. Corresponding analysis is carried out within the framework of the quasiclassical Eilenberger equations for a tunnel coupled bilayer with inhomogeneous relative shift of the conduction bands between the layers, which describes the net charge transfer in sliding ferroelectrics. It is shown that the critical temperature of the interlayer superconductivity can be significantly enhanced for superconducting nuclei localized in the vicinity of ferroelectric domain walls. We demonstrate that the increase in the tunneling amplitude leads to the decrease (increase) in the difference between the critical temperatures for localized and homogeneous superconducting states for the spin-singlet (spin-triplet) interlayer superconductivity. We also perform an extensive analysis of the effects of the in-plane magnetic field on the interlayer superconductivity. It is shown that the orbital effect can result in the suppression of the spin-singlet interlayer superconductivity and to the enhancement of the spin-triplet one. We find that possible manifestations of the paramagnetic effect include the suppression of the interlayer superconductivity by rather weak Zeeman fields, the two-fold anisotropy of the critical magnetic field for the spin-triplet states, as well as the appearance of reentrant superconducting phases. It is shown that the joint influence of the orbital and paramagnetic mechanisms on the spin-triplet interlayer superconductivity can even lead to a nonmonotonic behavior of the superconducting critical temperature as a function of the external magnetic field. The results are discussed in the context of recent experimental data on van der Waals structures with coexisting superconductivity and sliding ferroelectricity.

Oxygen vacancies are the most common defects in oxide materials. They frequently couple with transition-metal ions to form charge-compensated paramagnetic Me-${\mathrm{V}}_O$ pair centers, which exhibit large zero-field splitting of $2.6-6{\mathrm{cm}}^{-1}$. Such splitting requires the use of high microwave frequencies in electron paramagnetic resonance (EPR) spectroscopy. Using high-frequency EPR (up to 210 GHz), we investigated ${\mathrm{Fe}}^{3+}\text{−}{\mathrm{V}}_O$ centers in the quantum paraelectrics ${\mathrm{SrTiO}}_3$ and ${\mathrm{KTaO}}_3$ over the temperature range 5–296 K. These materials have attracted significant interest due to their unique dielectric properties and recently discovered spin-electric phenomena, including two-dimensional superconductivity and the anomalous Rashba effect in spin-charge conversion. To probe spin-electric coupling, we also performed pulse EPR measurements at 9.79 GHz under applied electric fields. Our results show that the axial crystal-field parameter increases nearly linearly from 13.1 GHz in ${\mathrm{KTaO}}_3$ and 13.55 GHz in ${\mathrm{SrTiO}}_3$ at room temperature to $\simeq 14.6\mathrm{GHz}$ at 20 K, below which it saturates. This temperature dependence is attributed to anomalous displacements of four lateral oxygen ions relative to ${\mathrm{Fe}}^{3+}$, likely governed by the soft optical mode. Application of electric fields up to 30 kV/cm revealed not only splitting of the EPR lines but also redistribution of domain populations, observable at fields as low as 10 kV/cm in the nonpolar tetragonal phase of ${\mathrm{SrTiO}}_3$.

Methylammonium lead iodide ($\mathrm{MAPb}{\mathrm{I}}_3$) is a material of intense topical interest because of its potential applications in highly efficient solar cells, and its phase transitions and dynamical features have fundamental effects on its optoelectronic properties. We present a detailed strain analysis of the cubic-tetragonal-orthorhombic structural transitions in $\mathrm{MAPb}{\mathrm{I}}_3$ using Landau free energy expansions and group theory combined with experimental spontaneous strains and heat capacity data. We find that the cubic-tetragonal transition exhibits the nearly tricritical characteristic with a modest entropy change. In contrast, the tetragonal-orthorhombic transition is strongly first-order, with a much larger entropy change which is a feature of an order-disorder transition associated with the freezing of the $\mathrm{M}{\mathrm{A}}^{+}$ cations. We also observe a pronounced anomaly in the shear strain $e_4$ in the orthorhombic structure near 85 K, indicating a pseudo-Jahn-Teller distortion owing to the formation of Pb $6s^2$ lone-pair states, correlating with electron polaron formation. These findings clarify the interplay of lattice distortion and molecular dynamics in $\mathrm{MAPb}{\mathrm{I}}_3$. By revealing the fundamental strain-mediated mechanisms of these transitions, our work provides insights for strain engineering of hybrid perovskite devices, with implications for their stability and optoelectronic performance.

The square root of the threetangle is calculated for the transverse XY model with an integrability breaking in-plane field component. To be in a regime of quasisolvability of the convex roof, we concentrate on a four-site model Hamiltonian. This leads to a picture of fixed decomposition states through which the optimal decomposition brachiates. In general, the field, and hence, mixing of the odd/even sectors, has a detrimental effect on the threetangle, as expected. Only in a particular spot of models with no or weak inhomogeneity $\gamma$ does a finite plateau of the tangle prevail in a broad maximum region of the field strength $h\approx 0.3\pm 0.1$. There, the threetangle is basically independent of the nonzero angle $\alpha$ of the magnetic field to transversality. This system could be experimentally used as a quasipure source of threetangled states or as an entanglement triggered switch depending on the experimental error in the field orientation.

Recent research on kagome compounds has pointed out their multiple applications in diverse fields. Here, we have reported the physical properties of hexagonal superconductors ${\mathrm{LaIr}}_5, {\mathrm{LaIr}}_3{\mathrm{B}}_2, {\mathrm{LaIr}}_3{\mathrm{Ga}}_2, {\mathrm{LaRh}}_3{\mathrm{B}}_2$, and ${\mathrm{YRu}}_3{\mathrm{B}}_2$, in which transition metal atoms form a kagome lattice. In our ab initio calculations, we have employed the generalized gradient approximation of the density functional theory and the plane-wave ab initio pseudopotential method with and without spin-orbit coupling. Our electronic band structure calculations suggest that the Fermi surface is mostly governed by the $d$ electrons of the transition metal atoms, while the remaining atoms do not play a significant role. Thus, the kagome arrangement of the transition metal atom lattice, which determines the energy and dispersion of the bands from the transition metal atom, has a strong impact effect on the electrons that become superconducting in all the studied kagome superconductors. Furthermore, our phonon and electron-phonon interaction calculations suggest that the propagation of phonons in the kagome lattice formed by transition metal atoms gives rise to superconductivity in all the studied compounds. These results signal that in all the studied compounds, the superconductivity stems from the kagome transition metal lattice and its formation is moderately more impacted with the inclusion of spin-orbit coupling for Ir-rich superconductors than others due to its higher nuclear charge than other transition metal atoms.

We investigate the stability of electron–hole superfluidity in two-dimensional bilayers with unequal and anisotropic effective masses. Using a zero-temperature, self-consistent Hartree–Fock approach, we study two experimentally relevant deviations from the ideal equal-mass isotropic case: (i) isotropic but unequal conduction and valence band masses ($m_c^{*}\ne m_v^{*}$), and (ii) equal average masses with orthogonal in-plane anisotropies $(m_{c,x}^{*},m_{c,y}^{*})=(m_1^{*},m_2^{*})$ and $(m_{v,x}^{*},m_{v,y}^{*})=(m_2^{*},m_1^{*})$. For both scenarios, we compute the order parameter and analyze the BEC–BCS crossover as a function of layer separation and mass ratio. We find that both mass imbalance and mass anisotropy reduce the pairing strength and suppress the inferred critical temperature $T_c$ by breaking perfect Fermi surface nesting and shift the BEC-BCS crossover. Despite these effects, superfluidity remains robust across the full range of densities and interlayer separations considered, with no transition to an unpaired plasma state in the absence of screening. Our results provide a baseline for understanding the interplay of mass mismatch and anisotropy in current and emerging bilayer platforms, including van der Waals heterostructures and anisotropic two-dimensional semiconductors. Our work also establishes that Fermi surface nesting is not a key ingredient for the bilayer superfluidity, which is always the ground state for all electron-hole bilayers, although the resultant $T_c$ depends on the parameter details and may very well be unmeasurably low for large interlayer separations.

We systematically investigate the interplay of disorder and time-homogeneous collisional noise in shaping the transport dynamics of an anisotropic XXZ spin chain. Using stochastic collision models to simulate interaction with the environment, we explore the localization-delocalization transitions across regimes with single and multiple excitations. We find that space-homogeneous and low-rate collisions can shape regions where localization sets in the form of subsequent plateaus. The localization process has universal features for the plateaus duration and the delocalization time. Interactions among the excitations favor this process even for tiniest disorder levels. Our findings can be applied to design stroboscopic protocols where sequences of transport and localization can be tailored. We establish relevant connections to noise-engineering of quantum devices in noisy intermediate-scale quantum simulators platforms, and to realistic biological systems where noise and disorder coexist.

The spontaneous anomalous Hall effect (AHE) has recently been proposed and opens new opportunities in the fields of antiferromagnetic spintronics and quantum devices. Using first-principles calculations, herein we observe the significant nonlinear evolution of anomalous Hall conductivity (AHC) in ${\mathrm{RuO}}_2$ under the influence of Néel vectors and uniaxial strain. By analyzing the magnetic space groups (MSG), it is revealed that the AHE is allowed when the Néel vectors are oriented in the [010] and [110] directions under strain-free or y/z-uniaxial strain, while it is totally prohibited in the [001] direction. The highest AHC of ${\sigma }_{yz}$ in the Néel vectors along [010] direction, and ${\sigma }_{yz}$ and ${\sigma }_{zx}$ in [110] direction, reach up to $41.2{\mathrm{\Omega }}^{-1}\mathrm{c}{\mathrm{m}}^{-1},158.4{\mathrm{\Omega }}^{-1}\mathrm{c}{\mathrm{m}}^{-1}$, and $39.3{\mathrm{\Omega }}^{-1}\mathrm{c}{\mathrm{m}}^{-1}$ at the Fermi level, respectively, corresponding to a 6% $y$-uniaxial compressive strain. Utilizing principal component analysis (PCA) to reduce the dimension of Berry curvatures, we confirm that the variation of AHC under strain is directly correlated with the degree of distortion in Ru–O octahedron. These findings suggest a universal approach to manipulate the anomalous Hall effect in rutilelike unconventional antiferromagnets.

Altermagnets host an array of magnetic multipoles, which are often visualized and studied in reciprocal space. In real space, the relative phase of the multipoles of the spin density around atoms determines whether a system is an altermagnet or a conventional antiferromagnet. In this study, we approach these real space multipoles in altermagnets using a combination of first principles calculations and group theory. We show that, even in collinear magnets, the local spin density is necessarily noncollinear due to spin-orbit coupling. Moreover, the noncollinear contributions often provide a more direct illustration of the magnetic multipolar character of altermagnetism than the collinear contribution, which is dominated by the dipolar term. Our first principles calculations also show that 32-poles, in addition to octupoles, can be visible in the spin density of $d$-wave altermagnets, and they must be taken into account in discussions of the macroscopic response. Finally, we elucidate the interplay between magnetism and subtle crystal structural distortions in perovskite altermagnets, which provide a useful playground for studying phase transitions between antiferromagnetic and altermagnetic phases.

The $R{T}_3{\mathrm{B}}_2$ ($R=\mathrm{Y},\mathrm{Lu}, T=\mathrm{Co},\mathrm{Os}$) family hosts a perfect kagome lattice of $T$ atoms, offering an interesting platform to investigate the interplay of electronic structure, superconductivity, and lattice dynamics. Here, we compare two members of this family, ${\mathrm{LuOs}}_3{\mathrm{B}}_2$ and ${\mathrm{YCo}}_3{\mathrm{B}}_2$, with similar crystallography but differing chemical composition, which results in different electronic structures and correlation signatures, as well as distinct spin-orbit coupling effects. We confirm superconductivity in ${\mathrm{LuOs}}_3{\mathrm{B}}_2$ with $T_c=4.75\mathrm{K}$, while ${\mathrm{YCo}}_3{\mathrm{B}}_2$ remains nonsuperconducting above 1.8 K. Both materials exhibit kagome-derived electronic features, including quasiflat bands, Dirac cones, and van Hove singularities. Fermi surface calculations reveal a highly anisotropic electronic structure in ${\mathrm{YCo}}_3{\mathrm{B}}_2$, establishing a $k_z$-selective metallic behavior and leading to strongly suppressed in-plane conduction, in contrast to the more isotropic fermiology of ${\mathrm{LuOs}}_3{\mathrm{B}}_2$. Phonon calculations for ${\mathrm{LuOs}}_3{\mathrm{B}}_2$ show imaginary modes, indicating potential lattice instabilities. Experimental estimates of the Wilson and Kadowaki-Woods ratios point to significant electronic correlations in both compounds.