${\mathrm{YMn}}_6{\mathrm{Sn}}_6$ consists of two types of Mn-based kagome planes stacked along the $c$-axis having a complex magnetic interaction. We report a spin reconstruction in ${\mathrm{YMn}}_6{\mathrm{Sn}}_6$ from ferromagnetic (FM) into a combination of two incommensurate spin spirals (SSs) originating from two different types of Mn kagome planes driven by frustrated magnetic exchanges along the $c$-axis with the inclusion of the Hubbard $U$. The pitch angle and wave vector of the incommensurate SSs are $\sim 89.3^{\circ }$ and $\sim$ (0 0 0.248), respectively, which are in excellent agreement with the experiment. We employ an effective model Hamiltonian constructed out of exchange interactions to capture the experimentally observed nonequivalent nature of the two incommensurate SSs which also explain the FM-SS crossover due to antiferromagntic spin exchange with correlation. We further report the existence of a topological magnon with spin-orbit coupling in the incommensurate SS phase of ${\mathrm{YMn}}_6{\mathrm{Sn}}_6$ by calculating the topological invariants and Berry curvature profile. The location of the Dirac magnon in the energy landscape at 73 meV matches with another experimental report. We demonstrate the accuracy of our results by highlighting the experimental features in ${\mathrm{YMn}}_6{\mathrm{Sn}}_6$.

This paper reports an experimental demonstration of efficient excitation of fundamental dark spin wave solitons on a magnonic active ring below self-oscillation threshold by means of a biharmonic technique. This technique is shown to be especially appropriate for implementing multisoliton regimes otherwise unattainable. Theoretical analysis has revealed a very important role played by the phase relations between individual harmonics generated nonlinearly in the process of the formation of multiple solitons. The proposed ad hoc approach making use of the inverse Fourier transform has allowed us to elucidate the mechanisms underlying the formation of investigated nonlinear waveforms from their power spectra.

The ternary chalcogenide ${\mathrm{Bi}}_2{\mathrm{Rh}}_3{\mathrm{Se}}_2$ was found to be a charge density wave (CDW) superconductor with a $2\times 2$ periodicity. The key questions regarding the underlying mechanism of CDW state and its interplay with lattice and electronic properties remain to be explored. Here, based on the systematic Raman scattering investigations on single-crystalline ${\mathrm{Bi}}_2{\mathrm{Rh}}_3{\mathrm{Se}}_2$, we observed the fingerprinting feature of a CDW state, a collective amplitude mode at $\sim 39{\text{cm}}^{-1}$. The temperature evolution of Raman shift and linewidth for this amplitude mode can be well described by the critical behavior of two-dimensional (2D) Ising model, suggesting the interlayer interactions of ${\mathrm{Bi}}_2{\mathrm{Rh}}_3{\mathrm{Se}}_2$ are negligible when the CDW state is formed, as a consequence, the quantum fluctuations play an important role at low temperature. Moreover, the temperature dependence of Raman shift for the $A_g^9$ mode deviates significantly from the expected anharmonic behavior when approaching the CDW transition temperature $\sim 240\mathrm{K}$, demonstrated that strong electron-phonon coupling plays a key role in the formation of CDW. Our results reveal that ${\mathrm{Bi}}_2{\mathrm{Rh}}_3{\mathrm{Se}}_2$ is an intriguing quasi-2D system to explore the quantum Ising model and modulate the correlations between CDW and superconductivity.

We have studied the Co layer thickness dependences of magnetocrystalline anisotropy (MCA), Dzyaloshinskii-Moriya interaction (DMI), and orbital moment anisotropy (OMA) in W/Co/Pt trilayers, in order to clarify their correlations with each other. We find that the MCA favors magnetization along the film normal and monotonically increases with decreasing effective magnetic layer thickness ($t_{\mathrm{eff}}$). The magnitude of the Dzyaloshinskii-Moriya exchange constant ($\left|D\right|$) increases with decreasing $t_{\mathrm{eff}}$ until $t_{\mathrm{eff}}\sim 1$ nm, below which $\left|D\right|$ decreases. The MCA and $\left|D\right|$ scale with $1/t_{\mathrm{eff}}$ for $t_{\mathrm{eff}}$ larger than $\sim 1$ nm, indicating an interfacial origin. The increase of MCA with decreasing $t_{\mathrm{eff}}$ continues below $t_{\mathrm{eff}}\sim$ 1 nm, but with a slower rate. To clarify the cause of the $t_{\mathrm{eff}}$ dependences of MCA and DMI, the OMA of Co in W/Co/Pt trilayers is studied using x-ray magnetic circular dichroism. We find nonzero OMA when $t_{\mathrm{eff}}$ is smaller than $\sim 0.8$ nm. The OMA increases with decreasing $t_{\mathrm{eff}}$ more rapidly than what is expected from the MCA, indicating that factors other than OMA contribute to the MCA at small $t_{\mathrm{eff}}$. The $t_{\mathrm{eff}}$ dependence of the OMA also suggests that $\left|D\right|$ at $t_{\mathrm{eff}}$ smaller than $\sim 1$ nm is not related to the OMA at the interface. We propose that the growth of Co on W results in a strain and/or texture that reduces the interfacial DMI, and, to some extent, MCA at small $t_{\mathrm{eff}}$.

Quantum magnets based on honeycomb lattices with a low coordination number offer a viable ground to realize exotic emergent quantum excitations and phenomena arising from the interplay between competing magnetic interactions, spin correlations, and spatial anisotropy. However, unlike their low-spin analogs, high-spin honeycomb lattice antiferromagnets have remained comparatively less explored in the context of capturing the classical limits of quantum phenomena. Herein, we report the crystal structure, magnetic susceptibility, specific heat, and electron spin resonance (ESR) measurements, complemented by ab initio density functional theory (DFT) calculations, on polycrystalline samples of ${\mathrm{FeP}}_3{\mathrm{SiO}}_{11}$ in which the ${\mathrm{Fe}}^{3+}$ ions decorate a nearly perfect $S=\frac{5}{2}$ honeycomb lattice without any site disorder between constituent atoms. Above 150 K, an antiferromagnetic Weiss temperature ${\theta }_{\mathrm{CW}}=-12\mathrm{K}$ is observed, consistent with DFT calculations, which suggests the presence of strong intraplanar nearest-neighbor and weaker interplanar further neighbor exchange interactions. An anomaly at $T_N=3.5\mathrm{K}$ in specific heat and magnetic susceptibility reveals the presence of a long-range ordered ground state in zero field. Above $T_N$, ESR evidences short-range spin correlations and unsaturated magnetic entropy, while below $T_N$ unconventional excitations are seen via power-law specific heat. A spin-flop transition is observed at an applied field of ${\mu }_0{H}_{c1}=0.2$ T. At higher applied fields, $T_N$ is gradually suppressed down to zero at ${\mu }_0{H}_{\mathrm{c}2}=5.6\mathrm{T}$. Above ${\mu }_0{H}_{\mathrm{c}2}$, a broad maximum in specific heat due to gapped magnon excitations indicates the emergence of an interesting nearly polarized state dressed by a disordered state in this honeycomb lattice antiferromagnet.

This paper investigates the superconducting properties of a two-dimensional $s$-wave superconductor on a kagome lattice subjected to correlated disorder. Using the Bogoliubov–de Gennes theory, we analyze the impact of disorder correlations on superconducting behavior. Additionally, we derive the stiffness formula for the kagome lattice and calculate its superfluid stiffness. An intriguing finding of our paper is the bimodal characteristic in the probability distribution of the superconducting pairing amplitude at higher disorder correlation strengths for intermediate values of the disordered potential. Our results provide valuable insights into how disorder correlations influence superconductivity and underscore the role of lattice geometry in shaping superconducting properties.

While the conducting ${\mathrm{CuO}}_2$ planes in cuprate superconductors have been widely recognized as a crucial component in producing high superconducting $T_{\text{c}}$, recent experimental and theoretical studies on ${\mathrm{Ba}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_{3+\delta }$ have also drawn much attention to the importance of Cu-O chains in one-dimensional (1D) cuprates. To better understand the cuprates containing Cu-O chains, here we have studied the electronic, magnetic, and phonon properties of ${\mathrm{Sr}}_2{\mathrm{CuO}}_3$ bulk and films based on the spin-polarized density functional theory calculations. We first reproduced the typical Mott insulator feature of the cuprate parent compound for bulk ${\mathrm{Sr}}_2{\mathrm{CuO}}_3$, and then built a ${\mathrm{Sr}}_2{\mathrm{CuO}}_3$ thin film with Cu-O chains exposed on the surface to directly investigate their characteristics. Different from the insulating bulk phase, the ${\mathrm{Sr}}_2{\mathrm{CuO}}_3$ surface shows interesting metallic properties. Further electronic structure calculations reveal the existence of spin-polarized electron gas between surface Sr atoms that strongly depends on the interchain coupling of Cu spins. Moreover, the phonon modes that involve the vibrations of in-chain and out-of-chain O atoms can induce strong charge and spin fluctuations in the surface layer of ${\mathrm{Sr}}_2{\mathrm{CuO}}_3$ film, which suggests significant multiple degree-of-freedom couplings that may be important for the superconductivity in 1D cuprates. Our work provides a comprehensive viewpoint of the properties of Cu-O chains in ${\mathrm{Sr}}_2{\mathrm{CuO}}_3$, facilitating a complete understanding of 1D cuprate superconductors.

Motivated by the recent proposal that the Monte Carlo sign problem might be used as an indicator of quantum phase transitions, we simulate the periodic Anderson model at half-filling with a staggered ionic potential using the determinant quantum Monte Carlo (DQMC) approach. We observe a phase transition from a band insulator to a Kondo insulator as the hybridization increases. At finite temperature, an intermediate metallic region emerges between two insulating phases, which is characterized by a pseudogap in the spectral functions near the boundary of the intermediate region and a quasiparticle peak in the middle. The latter coincides with a crossing point of the $f$-electron occupation on different sublattices as well as the maximum antiferromagnetic (AFM) correlations. The metallic region extrapolates to a single quantum critical point at zero temperature, which may result in exotic quasiparticle excitations associated with the emergent metallic state. The Monte Carlo sign problem is found to be most pronounced in the quantum critical region, implying a close connection between the two phenomena. Our results are qualitatively supported by the Hartree-Fock (HF) mean-field calculations. Our work reveals interesting physics in inhomogeneous Kondo lattice systems that may be worthwhile of more investigations in the future.

Perovskite rare-earth nickelates are a prototypical class of quantum materials that exhibit rich phase-transition physics with promising applications in neuromorphic computing. Although there is existing experimental evidence demonstrating that strain may strongly influence the phase transitions of nickelate thin films, it would be extremely challenging to experimentally construct temperature-strain phase diagrams for different film orientations to guide applications. Here, we use the Ginzburg-Landau theory to formulate the thermodynamics of strained nickelates and calculate temperature-strain phase diagrams of epitaxial ${\mathrm{SmNiO}}_3$ and ${\mathrm{NdNiO}}_3$ thin films with various orientations, which are consistent with the limited existing experimental measurements. We predict that a shear strain can effectively tune the relative magnitude of the magnetic moments on the two nonequivalent Ni sublattices. Our theory provides an efficient theoretical framework for predicting the thermodynamics of strained nickelates, which will provide guidance for engineering their properties through strains.

An electronic topological transition (ETT) in cadmium below 1 GPa is investigated in situ with experimental x-ray absorption spectroscopy and projecting calculated core-valence excitons onto the band structure. These projections are a useful application of the Bethe-Salpeter equation approach that considers many-body effects. The method described herein can be used for systems that are otherwise difficult to probe in situ; therefore, it provides a generalizable approach to identifying and understanding ETTs under high pressure. Although pressure-induced ETTs are often probed using indirect structural responses, our own x-ray diffraction and Raman studies suggest a second-order structural transition around 3 GPa but are largely insensitive to or inconclusive for the previously studied ETT in this region.

The graphenelike form of carbon nitride is known as $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$, a single sheet of which may be composed of an $s$-triazine ($S$-type) or tri-$s$-triazine ($T$-type) periodic lattice with a different size of hole. By employing the first-principles calculation, we find that the difference in the out of plane polarization caused by the symmetry breaking of the $S$-type or $T$-type structure of bilayer $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$ through interlayer sliding may be related to the size of the in-plane hole. The nonpolar bilayer $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$ ($S$- or $T$-type) state needs to slide about two bond lengths before it is electrically driven to the polar state, resulting in ferroelectric structures with opposite polarization directions. It has been confirmed experimentally and theoretically [Zelisko et al., Nat. Commun. 5, 4284 (2014)] that the anomalous piezoelectric properties of $T$-type $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$ monolayer come from their noncentrosymmetric triangular holes. Interestingly, we find here that the $S$-type $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$ exhibits the opposite piezoelectric property to the $T$-type $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$, that is, a negative longitudinal piezoelectricity (NLP). Our computational analysis shows that the superposition of two reversed triangular holes in the $S$-type $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$ plane will result in the emergence of NLP. Hence, the origin of different piezoelectric properties between $S$-type and $T$-type $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$ is comparatively elucidated. These results provide alternative structural manipulation degrees of freedom for the inherent properties of two-dimensional van der Waals layered semiconductor materials, and expand ferroelectric candidate materials for next-generation nanoelectronic devices.

Hexagon-boat-star (HBS) pentagonal tilings often appear in the description of decagonal quasicrystals and their periodic approximants. Being related to the Penrose tiling, they differ from the latter by a significantly higher packing density of vertices, which, in turn, depends on the relative frequency of appearance of the H, B and S tiles. Since boats (also known as “ivy leaves”) have the lowest packing density, reducing their number in the tiling leads to an increase in its packing density. The paper proposes an inflation rule for a chiral tiling, which, in principle, contains no boats and therefore has the highest possible density among HBS tilings. The relationship between the tiling and the real structures of crystal approximants of decagonal quasicrystals is discussed.

In this paper, we propose a concept of bilayer stacking $A$-type altermagnet (BSAA), in which two identical ferromagnetic monolayers are stacked with antiferromagnetic coupling to form a two-dimensional (2D) $A$-type altermagnet. By solving the stacking model, we derive all BSAAs for all layer groups and draw three key conclusions: (i) Only 17 layer groups can realize intrinsic $A$-type altermagnetism. All 2D $A$-type altermagnets must belong to these 17 layer groups, which will be helpful to search for 2D $A$-type altermagnet. (ii) It is impossible to connect the two sublattices of BSAA using $S_{3z}$ or $S_{6z}$, a constraint that is also applicable to all 2D altermagnets. (iii) $C_{2\alpha }$ is a general stacking operation to generate BSAA for an arbitrary monolayer. Our theory not only can explain the previously reported twisted-bilayer altermagnets, but also can provide more possibilities to generate $A$-type altermagnets. Our research has significantly broadened the range of candidate materials for 2D altermagnets. Based on conclusion (i), the bilayer ${\mathrm{NiZrCl}}_6$ is predicted to exhibit intrinsic $A$-type altermagnetism. Additionally, we use twisted-bilayer ${\mathrm{NiCl}}_2$ and CrOCl as supplementary examples of BSAA. Furthermore, utilizing symmetry analysis and first-principles calculation, we scrutinize their spin-momentum locking characteristic to substantiate their altermagnetic properties.

Resonant modes within phononic crystals exhibit remarkable capabilities for the effective control of acoustic waves. In this study, we examine an underwater system comprising bilayer periodic polymethyl methacrylate rods and investigate the behaviors of Fabry-Perot bound states in the continuum (BICs) by adjusting the interlayer spacing parameter and the side length of rectangular rods. Additionally, we demonstrate the evolutionary trajectories of the Fabry-Perot BICs within a two-dimensional parameter space. During the evolution process, we observe fascinating phenomena such as merging, annihilation, and regeneration of BICs. Notably, the merging of BICs enables the achievement of high $Q$ resonance across a broadened range of geometric parameters. The outcomes of this investigation present more opportunities for the design of robust acoustic devices.

Mosaic lattice models have been recently introduced as a special class of disordered systems displaying resonance energies, multiple mobility edges, and anomalous transport properties. In such systems on-site potential disorder, either uncorrelated or incommensurate, is introduced solely at every equally spaced site within the lattice, with a spacing $M\ge 2$. A remarkable property of disordered mosaic lattices is the persistence of extended states at some resonance frequencies that prevent complete Anderson localization, even in the strong disorder regime. Here we introduce a broader class of mosaic lattices and derive general expressions of mobility edges and localization length for incommensurate sinusoidal disorder, which generalize previous results [Y. Wang et al., Phys. Rev. Lett. 125, 196604 (2020).]. For both incommensurate and uncorrelated disorder, we prove that Anderson localization is protected by the open gaps of the disorder-free lattice, and derive some general criteria for complete Anderson localization. The results are illustrated by considering a few models, such as the mosaic Su-Schrieffer-Heeger (SSH) model and the trimer mosaic lattice.