We analytically study the orbital response of alternating-twist multilayer graphene to an in-plane magnetic field using the unitary transformation introduced by Khalaf et al. [Phys. Rev. B 100, 085109 (2019)]. This transformation maps an alternating-twist $N$-layer system onto $N/2$ decoupled twisted bilayer graphene (TBG) systems with distinct effective twist angles, together with a single decoupled layer for odd $N$, thereby generating a hierarchy of effective magic angles. For systems with an odd number of layers, we find that the orbital in-plane magnetic response is negligibly small. For even systems, we express the in-plane orbital susceptibility in terms of the corresponding TBG responses in the flat-band regime, which are large compared to the spin susceptibility and even diverge in the clean limit at charge neutrality near the magic angle. For the finite even-layer systems considered in this work, the in-plane magnetic response strongly depends on the effective magic angle within the hierarchy: the larger the twist angle, the smaller the total response. Moreover, we find a general relation between the outermost interlayer and total susceptibilities of the system when the corresponding effective TBG subsystem is in the flat-band regime. We finally introduce the in-plane Maki parameter as the ratio of the difference in orbital susceptibility between the normal and superconducting states to the paramagnetic Pauli susceptibility. For TBG, we find values up to 2 near the magic angle. Our analysis shows that for certain magic angles, the interpretation of Pauli-limit violation in alternating-twist multilayers requires taking into account the orbital contribution to the in-plane magnetic response.

Antichiral surface states, which exhibit unidirectional propagation along parallel surfaces, hold significant promise for classical wave manipulation. However, their physical realization typically relies on complex implementations of a two-dimensional modified Haldane model, limiting practical applications. We propose a simplified approach to achieve such states within the nodal-line semimetal phase of a single-layer honeycomb lattice, where an additional layer degree of freedom emulates the essential physics of the modified Haldane model. We further demonstrate that asymmetric vertical interlayer couplings give rise to valley higher-order topological partial band gaps, which simultaneously support one-dimensional hinge states and gapped antichiral surface states. These results establish a versatile platform in which antichiral surface states coexist with higher-order hinge states, enabling robust topological wave transport.

Quantum groups have a long and fruitful history of applications in integrable systems. Can quantum group symmetries exist in the absence of integrability? We provide an explicit example of a chaotic system with a quantum group global symmetry. The example is a spin chain with a next-to-nearest interaction term. We show the chaotic behavior of the system by studying the Eigenvalue statistics. The spin chain is nonunitary but PT symmetric and, in addition to exhibiting chaos, exhibits an interesting transition after which the eigenvalues become complex.

Recent work [M. Z. Ansari and K. Damle, Phys. Rev. Lett. 132, 226504 (2024)] that analyzed the effect of vacancy disorder on a short-range resonating valence bond spin liquid state of kagome-lattice antiferromagnets argued that such spin liquids are stable to vacancy disorder. The argument relied crucially on a numerical study that identified the following property of the site-diluted kagome lattice: maximum-density dimer packings (maximum matchings) of any connected component of such site-diluted kagome lattices have at most one unmatched vertex that hosts a monomer. Here, we provide an inductive proof of a stronger result that implies this property: If a connected cluster of such a lattice has an odd number of vertices, its Gallai-Edmonds decomposition [L. Lovasz and M. D. Plummer, Matching Theory (North-Holland, Amsterdam, 1986)] has exactly one $\mathcal{R}$-type region that spans the entire connected cluster and hosts a single monomer of any maximum-density dimer packing. If, on the other hand, it has an even number of sites, it admits perfect matchings (fully packed dimer coverings with no monomers) and its Gallai-Edmonds decomposition consists of a single $\mathcal{P}$-type region that spans the entire cluster. Our proof also applies to the site-diluted Archimedean star lattice, the site-diluted pyrochlore lattice (corner-sharing tetrahedra), the site-diluted hyperkagome lattice, and, more generally, to any lattice satisfying a certain local connectivity property. It does not apply to bond-diluted versions of such lattices.

Atomic-scale surface reconstructions critically affect the performance of ${AB\text{O}}_3$ perovskites in catalysis and electronic devices. However, their structural complexity, together with the limited predictive power of existing theoretical models, makes it difficult to determine the true atomic arrangements and therefore hinders rational materials design. Here, using ${\mathrm{SrTiO}}_3\left(001\right)$ [STO(001)] as a model system, we develop a deep potential (DP)-based global optimization framework that efficiently screens candidate reconstructions in large supercells. Within this framework, we identify a series of Sr-adatom-stabilized surface structures for the ($2\times 2$), $c$($4\times 2$), and ($\sqrt{5}\times \sqrt{5}$)$R26.6^{\circ }$ reconstructions, all of which have substantially lower surface energies than conventional models, thereby helping resolve longstanding discrepancies between theory and experiment. We further reveal that Sr adatoms act as structural bridges that interconnect ${\mathrm{TiO}}_5$ units, triggering a pronounced “bonding reinforcement” characterized by enhanced orbital resonance and a significant downward shift of electronic energy levels. To examine the transferability of this $A$-site-adatom stabilization principle, we fine-tune the STO training set to rapidly obtain an accurate DP model for ${\mathrm{BaTiO}}_3\left(001\right)$ [BTO(001)]. Applying the same framework to BTO(001), we predict a previously unreported Ba-adatom ($\sqrt{5}\times \sqrt{5}$)$R26.6^{\circ }$ reconstruction, indicating that the mechanism can be transferred from STO to the related BTO surface. Overall, this work identifies $A$-site adatoms as a stabilizing motif for the related ${AB\text{O}}_3\left(001\right)$ surfaces examined here and provides an extendable, high-accuracy strategy for predicting complex oxide surface and interface structures.

We develop a model to investigate the collective dynamics and coherent interaction of exciton-polaritons and longitudinal acoustic phonons in semiconductor microcavities beyond Fermi's golden rule. Our model predicts temperature-induced dephasing and an energy redshift of exciton-polaritons together with the formation of a reservoir of incoherent excitons with very high in-plane momenta owing to scattering with acoustic phonons. We validate the proposed model by reproducing the temperature-dependent changes of the polariton bistability in coherently driven semiconductor microcavities. The bistability threshold and the extent of the bistable domain are considerably modified by the blueshift induced by the incoherent reservoir. Furthermore, we describe the effect of stimulated backscattering from the reservoir into the coherent polariton state, which occurs at higher reservoir densities.

We demonstrate that structural chirality provides a robust and intrinsic mechanism for controlling Majorana zero modes (MZMs) in chiral nanowires coupled to $s$-wave superconductors. In a tight-binding model of helical nanowires, nanowires with opposite chirality share identical bulk spectra and topological phase boundaries, but their MZMs exhibit opposite spin polarization arising from the chirality-induced reversal of the bond-dependent spin-orbit field. This effect originates from the geometric structure of the nanowire and does not require tuning of other electronic parameters. By analyzing the symmetries connecting opposite-handed nanowires under different Zeeman field directions, we design a quantum-dot-mediated Josephson junction that enables an adiabatic, electrically controlled exchange of MZMs. Numerical simulations confirm the non-Abelian braiding and spin-dependent characteristics of the exchanged modes. These results establish structural chirality as a natural control parameter for the spin and topological properties of MZMs, offering a promising route toward chirality-engineered topological quantum computation.

In this article we analyze the many-body behavior of freestanding doped graphene nanoribbons where the chemical potential lies inside the bulk single-particle bands. We perform an exact mapping from both an extended and an on-site Hubbard model of the ribbons to a Kanamori model, which includes ferromagnetic exchange and pair-hopping interactions. We determine the resulting Coulomb matrix elements analytically, and identify their scaling behavior as a function of ribbon width and length. We propose a low-energy version of the Kanamori Hamiltonian to address the response of the ribbons to external fields, with a view to their use as transport channels in nanoelectronics. We find that the model and the proposed ribbon parameters can produce open-shell, high-spin, many-body states that can lead to shell- and spin-blockade responses.

Nanophotonics enables precise control over light–matter interactions, though most established design frameworks for subwavelength nanoparticles rely on isotropic materials. Uniaxial and biaxial particles—common in natural and engineered systems—introduce new degrees of freedom that couple geometry and material properties, unlocking multispectral and directional response in previously unexplored spectral regions. We present a universal full-wave framework for eigenmodes and resonances in such nanoparticles. Closed-form solutions reveal axial-permittivity sum rules and anisotropy-induced symmetry breaking, producing resonance splitting and novel radiation patterns. Generalizing to ellipsoids enables geometric tuning of multispectral response, while analytic quality factors elucidate mode localization and loss. Full-wave simulations of h-BN and $\alpha$-MoO3 particles confirm the theory. This framework unifies the understanding of anisotropic nanostructures across optics, magnetism, and thermal transport, providing pathways to a new generation of photonic devices with tunable multispectral response and controlled emission with direct applications in sensing and imaging.

We report electron spin resonance (ESR) experiments conducted on oriented powder of the heavy-fermion ferromagnet $\mathrm{Yb}{\left({\mathrm{Rh}}_{0.73}{\mathrm{Co}}_{0.27}\right)}_2{\mathrm{Si}}_2$ in the temperature range 0.75 $\le T\le 4\mathrm{K}$, which includes the transition between the paramagnetic and ferromagnetic ordered phases below the Curie temperature $T_{\mathrm{C}}=1.3\mathrm{K}$. The ESR measurements were performed using a home-built ${}^3\mathrm{He}$ cryostat at $X$-band frequencies. In the ferromagnetic ordered phase the ESR spectra of $\mathrm{Yb}{\left({\mathrm{Rh}}_{0.73}{\mathrm{Co}}_{0.27}\right)}_2{\mathrm{Si}}_2$ are split into two lines. While the resonance in the paramagnetic phase features an easy-plane crystalline electric field induced anisotropy of the $g$ tensor perpendicular to the $c$ axis of the tetragonal crystal structure, the split lines in the ordered phase can be related to ferromagnetic resonance modes with a uniaxial exchange-type anisotropy along the $c$ axis. The corresponding effective anisotropy field can be determined.

Interfacial engineering is an important aspect for the development of high-efficiency photoelectric devices. The microscopic interplay between lattice distortion and carrier transport remains poorly understood. This study utilizes constrained density functional theory (CDFT+$U$) and Marcus theory to bridge this gap, using the anatase (101)/(001) interface as an example to investigate charge separation with a particular focus on the role of polarons. We find that while the interface undergoes distortion of the interfacial structure, both electron and hole polarons strongly localize with trapping energies of −0.48 eV and −0.97 eV, respectively. Quantitative analysis via crystal field theory reveals that the polaron stability is governed by the magnitude of orbital splitting (up to 4.47 eV for electrons and 3.86 eV for holes), which dictates a spatial disparity where both carriers initially favor the (001) side. However, dynamic transport simulations uncover an asymmetric kinetic steering mechanism that overrides these static energy preferences: Electron migration: Electrons exhibit a hierarchical transport pathway, initial intraplane diffusion followed by interface-guided migration, resulting in mobility toward the (101) side that is higher than toward the (001) bulk. Hole migration: Holes generated on the (101) side follow a cascaded mechanism, preferentially penetrating the interface to settle on the (001) side. By demonstrating that efficient charge separation is a product of electronic coupling and reorganization energy rather than mere spatial distribution, this work provides a predictive framework for optimizing photocatalytic efficiency through polaron-aware interface design.

The persistence of ferroelectricity in ultrathin ${\mathrm{HfO}}_2$ films challenges conventional theories, particularly given the paradoxical observation that the out-of-plane lattice spacing increases as the film thickness decreases, an anomalous size effect absent in perovskite ferroelectrics. Here, we resolve this puzzle by revealing that this lattice expansion is counterintuitively coupled to a suppressed out-of-plane polarization. First-principles calculations combined with analytical modeling identify two mechanisms behind this expansion: a negative longitudinal piezoelectric response to the residual depolarization field and a positive surface stress that becomes significant at reduced thickness. Their interplay quantitatively reproduces the experimentally observed lattice expansion. Furthermore, (111)-oriented ${\mathrm{HfO}}_2$ films can support out-of-plane polarization even under open-circuit conditions, in contrast to (001) films that stabilize a nonpolar ground state. This behavior points to the emergence of orientation-induced hyperferroelectricity, an unrecognized mechanism that enables polarization persistence through orientation engineering without electrode screening. We further demonstrate that this principle generalizes to conventional perovskites such as ${\mathrm{PbTiO}}_3$, offering a strategy to eliminate the critical thickness limit by choosing the appropriate film orientation. As a practical pathway to device integration, we also identify the two-dimensional electride ${\mathrm{Ca}}_2\mathrm{N}$ as a near-ideal electrode that fully restores the ferroelectric properties of ${\mathrm{HfO}}_2$ in ultrathin capacitors.

Topologically protected Majorana zero modes (MZMs) have attracted intense interest due to their potential application in fault-tolerant quantum computation (TQC). Graphene nanoribbons, with tunable edge terminations and compatibility with planar device architectures, offer a promising alternative to semiconductor nanowires. Here we present a comprehensive theoretical study of finite graphene strips with armchair, zigzag, and nearly square geometries, proximitized by an s-wave superconductor and subject to Rashba spin-orbit coupling, Zeeman fields, and disorder. Using exact diagonalization of the Bogoliubov-de Gennes tight-binding Hamiltonian, we analyze Majorana polarization, a Pfaffian-based periodic-disorder topological indicator (PDI), low-energy spectra, and real-space wavefunctions to identify the nontrivial topological phases supporting MZMs and distinguish them from partially separated Andreev bound states (psABS) or quasi-Majoranas. We systematically chart the robustness of these modes across geometries and disorder regimes, finding that armchair strips with short zigzag edges provide the most stable platform. Our results unify polarization and PDI diagnostics with spatial wavefunction analysis and disorder effects, yielding concrete design guidelines for graphene-based topological superconductors.

We investigate the nature of quantum phase transitions in a ($1+1$)-dimensional field theory composed of $N$ copies of the Ising conformal field theory interacting via competing relevant perturbations. The field theory governs the competition between a mass term and an interaction involving the product of $N$ order-parameter fields, which is realized, e.g., in coupled Ising chains, two-leg spin ladders, and SO($N$)-symmetric spin chains. By combining a perturbative renormalization-group analysis and large-scale matrix-product state simulations, we systematically determine the nature of the phase transition as a function of $N$. For $N=2$ and 3, we confirm that the transition is continuous, belonging to the Ising and four-state Potts universality classes, respectively. In contrast, for $N\ge 4$, our results provide compelling evidence that the transition becomes first order. We further apply these findings to specific lattice models with SO($N$) symmetry, including spin-$1/2$ and spin-1 two-leg ladders, that realize a direct transition between an SO($N$) symmetry-protected topological (SPT) phase and a trivial phase. Our results refine a recent conjecture regarding the criticality of transitions between SPT phases.

Arranging the stacking orders of $A$-type antiferromagnetic ($A$-AFM) bilayers offers a practical pathway to realizing two-dimensional altermagnets. Previous proposals, however, rely on stringent symmetry constraints, including layer groups and stacking registries. In this work, we demonstrate that circularly polarized light (CPL) irradiation breaks time-reversal symmetry, enabling altermagnetism possessing collinear magnetic moments without these restrictions. Our comprehensive symmetry analysis reveals that inversion-symmetric $A$-AFM bilayer building blocks can host altermagnetism that is robust against stacking slides and variations in illumination direction, with rich and continuously tunable symmetry representations. Using bilayer ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ as a case study, we show that out-of-plane CPL stabilizes distinct $f$-wave or $p$-wave altermagnetic states in forward stacking, while reverse stacking manifests an even-odd parity conversion of altermagnetism based upon specific sliding configurations. These revealments broaden the scope of altermagnet design in inversion-symmetric $A$-AFM bilayers and establish CPL as a versatile control knob for engineering altermagnetic symmetries.