We propose a spin Hall effect (SHE) enhancement mechanism due to Kramers-Weyl point (KWP) alignment in chiral topological semimetals with high Chern numbers. Through model Hamiltonian calculations, we identify enhancements in the intrinsic spin Hall conductivity (SHC) and the spin Hall angle (SHA). Such enhancements, attributed to a unique high Chern number KWP energetic alignment and a high degree of band nesting induced by spin-orbit coupling, strongly depend on orbital-orbital interactions. This represents a mechanism to enhance SHE, differing from the spin-orbit induced anticrossing mechanism in gapped systems. Guided by this principle, we corroborate our results by means of first-principles calculations and reveal multiple realistic materials with large intrinsic SHCs and even larger SHAs than Pt.

Binary nitride semiconductors have important applications in the industrial and technological fields. In this work, based on the recently reported metastable $Pca{2}_1$ phase of SbN, we investigated its structural stability, ferroelectric, dielectric, and piezoelectric properties using first-principles calculations. Our results indicate that the metastable SbN can be stabilized with a small hydrostatic pressure. Furthermore, we theoretically confirmed the presence of ferroelectricity in SbN, driven by stereochemically active ${\mathrm{Sb}}^{3+}5s^2$ lone pair electrons. The estimated polarization value is close to that of traditional ${\mathrm{PbTiO}}_3$. Moreover, SbN exhibits anisotropic dielectric constants, particularly in the ionic contribution part, primarily arising from the distinct mode-effective charges along different directions. In addition, SbN also exhibits a large $d_{33}$ piezoelectric response, which is approximately four times larger than that of wurtzite-type AlN. The large $d_{33}$ value is originated from the enhanced sensitivity of the atomic coordinates to the external strain $\frac{\mathrm{d}{u}_3}{\mathrm{d}{\eta }_3}$ and softening of the elastic constant $C_{33}$. Therefore, our study provides meaningful theoretical guidance for the future experimental synthesis of stable binary nitride semiconductors and their device applications.

We consider a twisted magnetic bilayer subject to the perpendicular electric field. The interplay of induced Dzyaloshinskii-Moriya interaction and spatially varying moiré exchange potential results in complex noncollinear magnetic phases in these structures. We numerically demonstrate the coexistence of intralayer skyrmions and bound interlayer skyrmion pairs and show that they are characterized by distinct dynamics under the action of external in-plane electric field. Specifically, we demonstrate the railing behavior of skyrmions along the domain walls which could find applications in spintronic devices based on van der Waals magnets.

We explore magnetic-field-driven chaos in magnetic skyrmions. Oscillating magnetic fields induce nonlinear dynamics in skyrmions, arising from the coupling of the secondary gyrotropic mode with a nonuniform, breathinglike mode. Through micromagnetic simulations, we observe complex patterns of hypotrochoidal motion in the orbital trajectories of the skyrmions, which are interpreted using bifurcation diagrams and local Lyapunov exponents. Our findings demonstrate that different nonlinear behaviors of skyrmions emerge at distinct temporal stages, depending on the nonlinear dynamic parameters. Investigating the abundant dynamic patterns of skyrmions during the emergence of chaos not only enhances device reliability but also provides useful guidelines for establishing chaos computing based on skyrmion dynamics.

Ferrimagnets possess collinear and noncollinear magnetic phases. Here we identify a crucial influence of the magnetic phase on the excited spin modes. The spin dynamics is launched in a rare-earth iron garnet film by femtosecond laser pulses. The noncollinearity cardinally changes the behavior of spin mode frequencies: the high-frequency one becomes highly sensitive to the external magnetic field while the low-frequency one gets almost field insensitive and even drops with the field growth near the transition to the collinear phase. Near the magnetization compensation point the frequencies of these modes get close to equality.

A giant, reversible magnetoelectric polarization induced under one order of magnitude lower magnetic field was observed in $Y$-type $\mathrm{BaSr}{\mathrm{Co}}_{2-x}{\mathrm{Cu}}_x{\mathrm{Fe}}_{11}{\mathrm{AlO}}_{22}$ $(0<x<1)$ ceramics. When increasing ${\mathrm{Co}}^{2+}$ cations are substituted with ${\mathrm{Cu}}^{2+}$, the saturation magnetization decreases and the flipping electric polarization accompanied with an attenuation feature is gradually frustrated. Samples’ insulation degree and magnetodielectric response together with the superexchange interaction between magnetic moments of $\stackrel{\rightharpoonup }{{\mu }_L}$ and $\stackrel{\rightharpoonup }{{\mu }_S}$ are all enhanced for the moderately doped ${\mathrm{Cu}}^{2+}$ $(x=0.5)$, which contributes to the excellent magnetoelectric coupling performances in $\mathrm{BaSr}{\mathrm{Co}}_{1.5}{\mathrm{Cu}}_{0.5}{\mathrm{Fe}}_{11}{\mathrm{AlO}}_{22}$ with a giant magnetoelectric current of $23\mu \mathrm{A}/{\mathrm{m}}^2$, magnetoelectric polarization of $35\mu \mathrm{C}/{\mathrm{m}}^2$, and huge magnetoelectric coupling coefficients of 4496 ps/m. Furthermore, the magnetoelectric polarization can be tuned by switching angles between the direction of the surfaces of the electrodes and the external magnetic field. Such a giant magnetoelectric polarization under so low magnetic field and reversibility make the multiferroic material system promising in real world applications in conceiving and developing nonvolatile memory and new functional devices.

Kagome metals are important for exploring emergent phenomena due to the interplay between band topology and electron correlation. Motivated by the recent discovery of charge density waves in the kagome lattice antiferromagnet FeGe, we investigate the impact of Sb doping on the structural, charge, and magnetic order of FeGe. The superlattice distortion induced by charge order disappears with only slight Sb doping ($\sim 1.5$%) down to 80 K. The antiferromagnetic ordering temperature gradually shifts to 280 K for ${\mathrm{FeGe}}_{0.7}{\mathrm{Sb}}_{0.3}$. For ${\mathrm{FeGe}}_{1-x}{\mathrm{Sb}}_x$ with $x⩾0.1$, crystal structures with a slightly distorted Fe kagome lattice are formed. A significant change in magnetic anisotropy from easy axis to easy plane with increasing $x$ is identified from magnetization measurements. Interestingly, neutron diffraction reveals noncollinear antiferromagnetic structures widely exist below $T_N$ for all samples with $x⩾0.1$. These noncollinear magnetic orders could possibly be unconventional and result from on-site repulsion and filling conditions of the kagome flat band, as predicted by a recent theoretical work.

Motivated by recent experiments on twisted junctions of cuprate superconductors (SCs), it was proposed [Yuan et al., Inhomogeneity-induced time-reversal symmetry breaking in cuprate twist junctions, Phys. Rev. B 108, L100505 (2023)] that at zero temperature, a random first order Josephson coupling $J_1\left(\mathrm{r}\right)cos\varphi$ generates an effective global second-order coupling, $J_{2}cos\left(2\varphi \right)$, with a sign that favors $\varphi =\pm \pi /2$, i.e., spontaneous breaking of time reversal symmetry (TRS). To obtain a more controlled understanding of the suggested disorder-induced-order mechanism, we construct an exactly solvable lattice mean-field model and prove that when the disorder-average ${\overline{J}}_1=0$, the model exhibits a TRS breaking phase for all temperatures below the SC transition, i.e., $T_c=T_{\mathrm{TRSB}}$, regardless of the specific form of disorder. In the presence of nonzero ${\overline{J}}_1\ne 0$, we show that the two transitions split linearly for small ${\overline{J}}_1\ll \kappa$ (where $\kappa$ is the in-plane SC stiffness), and that $T_{\mathrm{TRSB}}$ vanishes for ${\overline{J}}_1>J_c$ where $J_c=\overline{J_1^2}/\kappa$ in the weak disorder limit.

In a $p$-wave Kitaev model, the nearest-neighbor pairing term results in the formation of the BCS pair in the ground state. In this work, we study the fermionic condensation of real-space pairs in a $p$-wave Kitaev model on a square lattice with a uniform phase gradient pairing term along both directions. The exact solution shows that the ground state can be expressed in a coherent-state-like form, indicating the condensation of a collective pairing mode, which is the superposition of different configurations of pairs in real space. The amplitudes of each configuration depend not only on the size but also on the orientation of the pair. We employ three quantities to characterize the ground state in the thermodynamic limit. (i) A BCS-pair order parameter is introduced to characterize the phase diagram, consisting of gapful and topological gapless phases. (ii) The particle-particle correlation length is obtained to reveal the polarity of the pair condensation. (iii) In addition, a pair-pair correlator is analytically derived to indicate the presence of off-diagonal long-range order. Our work proposes an alternative method for understanding fermionic condensation.

The nature of interstitial hydrogen in ${\mathrm{SnO}}_2$ has been inferred by a combined study of first-principles theory and infrared absorption, near band edge absorption, and photoluminescence spectroscopy. The earlier interpretation of a center with an $\mathrm{O}–\mathrm{H}$ stretch mode at 3156 ${\mathrm{cm}}^{-1}$ as interstitial hydrogen is confirmed. Uniaxial stress experiments on the 3156 ${\mathrm{cm}}^{-1}$ mode reveal that the interstitial hydrogen atom is located in the open $c$ channel of the rutile ${\mathrm{SnO}}_2$ structure. Migration along the $c$ axis of the crystals occurs via low barrier hydrogen jumps of around 0.57 eV to symmetrically equivalent nearest-neighbor positions. Combinational vibrations of the $\mathrm{O}–\mathrm{H}$ stretch mode with the out-of-$ab$-plane and in-$ab$-plane wag modes at about 4014 and 4332 ${\mathrm{cm}}^{-1}$ have been identified. Free carrier absorption and excitonic properties of the defect demonstrate that ${\mathrm{H}}_i$ forms an effective shallow-donor-like state similar to the well-characterized F, Cl, and Sb $n$-type dopants in this material.

Magnetic proximity effects are typically limited to a few nanometers due to the short-range nature of the underlying magnetic interactions. Here, we use off-axis electron holography to reveal an electrostatically induced long-range magnetic proximity effect that extends over a distance of 40 nm at a ferromagnetic/paramagnetic interface in ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$. We show that this behavior results from carrier diffusion and drift across the interface, which changes the ${\mathrm{Mn}}^{3+}/{\mathrm{Mn}}^{4+}$ ratio and hence the local Curie temperature and density of magnetic moments.

We propose a general theory of anisotropic band flattening in moiré systems at the $\mathrm{\Gamma }$ valley. For a two-dimensional semiconductor with a rectangular unit cell of $C_{2z}$ or mirror symmetries, we find that a larger effective mass anisotropy $\eta =m_y/m_x$ of the valence or conduction bands in the monolayer will have a stronger tendency to be further enhanced in its twisted bilayer. This gives rise to strong anisotropic band flattening and correlated physics in one dimension (1D) effectively. We predict twisted bilayer black phosphorus (tBBP) has giant anisotropic flattened moiré bands ($\eta \sim {10}^4$) from ab initio calculations and the continuum model, where the low-energy physics is described by the weakly coupled array of 1D wires. We further calculate the phase diagram based on the sliding Luttinger liquid by including the screened Coulomb interactions in tBBP and find a large parameter space may host the non-Fermi liquid phase. We thus establish tBBP as a promising and experimentally accessible platform for exploring correlated physics in low dimensions.

Nonequilibrium molecular dynamics simulations have been used to investigate phase transformations and plasticity in single-crystal iron from shock compression to dynamic tension and subsequent spall fracture. In consistence with experimental observations, the unloading wave following the compression front is found to evolve into a rarefaction shock at the reverse hexagonal-close-packed to body-centered-cubic (bcc) phase transformation, and a pressure hysteresis between the direct and reverse phase transformations is evidenced. The interaction of this unloading wave with the rarefaction wave reflected from the sample free surface classically induces tension within the crystal, which is found to drive a bcc to face-centered-cubic (fcc) phase transformation in agreement with very recent experimental observation under subnanosecond laser shock loading. At the atomic scale, the mechanism governing this bcc to fcc phase transformation is consistent with a Bain transformation path. The spall fracture process is observed to occur through voids nucleation and growth either at favorable sites (twin boundaries, bcc-fcc grain boundaries after partial transformation) or within the defect-free fcc crystal (after full transformation). Thus, the spall strength increases with the fcc phase fraction near the plane of maximum tension. An amorphous microstructure is observed around the voids, likely due to significant heating upon severe plastic deformation, in consistence with experimental clues from the literature.

The Chern number is a crucial invariant for characterizing topological features of two-dimensional quantum systems. The real-space Chern number allows us to extract topological properties of systems without involving translational symmetry, and hence plays an important role in investigating topological systems with disorder or impurity. On the other hand, the twisted boundary condition (TBC) can also be used to define the Chern number in the absence of translational symmetry. Based on the perturbative nature of the TBC under appropriate gauges, we derive the two real-space formulas of Chern number (namely, the noncommutative Chern number and the Bott index formula), which are numerically confirmed for the Chern insulator and the quantum spin Hall insulator. Our results not only establish the equivalence between the real-space and TBC formulas of the Chern number, but also provide concrete and instructive examples for deriving the real-space topological invariant through the twisted boundary condition.

Dynamical decoupling (DD) is an efficient method to decouple systems from environmental noise and to prolong the coherence time of systems. In contrast to discrete and continuous DD protocols in the presence of bias field, we propose a Floquet DD at zero bias to perfectly suppress both the zeroth and first orders of noises according to the Floquet theory. Specifically, we demonstrate the effectiveness of this Floquet DD protocol in two typical systems including a spinor atomic Bose-Einstein condensate decohered by classical stray magnetic fields and a semiconductor quantum dot electron spin coupled to nuclear spins. Furthermore, our protocol can be used to sense high-frequency noises. The Floquet DD protocol we propose shines light on low-cost and highly portable DD technics without bias field and with low controlling power, which may have wide applications in quantum computing, quantum sensing, nuclear magnetic resonance, and magnetic resonance imaging.

Motivated by frustrated magnets and quasi-one-dimensional magnetic materials, we study the magnetic properties of one-dimensional (1D) Ising chains with nearest-neighbor (NN) and weaker next-to-nearest-neighbor (NNN) interactions in the presence of vacancy defects. The effect of a vacancy on the magnetic susceptibility of a spin chain is twofold: it reduces the length of the chain by an effective “vacancy size” and may also act as a free spin, a “quasispin,” with a Curie-type ${\chi }_{\text{quasi}}=\langle S^2\rangle /T$ contribution to the susceptibility. In chains with antiferromagnetic short-range order, the susceptibility of vacancy-free chains is exponentially suppressed at low temperatures, and quasispins dominate the effect of impurities on the chains' magnetic properties. For chains with antiferromagnetic NN interactions, the quasispin matches the value $\langle S^2\rangle =1$ of the Ising spins in the chain for ferromagnetic NNN interactions and vanishes for antiferromagnetic NNN interactions. For chains with ferromagnetic short-range order, quasispin effects are insignificant due to exponentially large low-temperature susceptibilities, and the dominant effect of a vacancy is effectively changing the length of the chain.

The symmetry of long-range magnetic order in manganese telluride (α-MnTe) is unknown. Likewise, its standing as an altermagnet. To improve the situation, we present symmetry informed Bragg diffraction patterns based on a primary magnetic order parameter for antiferromagnetic alignment between Mn dipoles. It does not break translation symmetry in a centrosymmetric structure, in keeping with an accepted definition of altermagnetism. Four templates serve x-ray diffraction that benefits from signal enhancement using a Mn atomic resonance, and neutron scattering. Even rank multipoles in magnetic neutron diffraction reflect a core requirement of altermagnetism, since they are zero for strong spin-orbit coupling presented by the $j_{\mathrm{eff}}=1/2$ model of an iridate, say. Symmetry in the templates demands that nuclear and magnetic contributions possess the same phase, which enables standard neutron polarization analysis on Bragg spots with overlapping contributions. Identical symmetry demands a ${90}^{\circ }$ phase shift between magnetic (time-odd) and chargelike (time-even, Templeton-Templeton) contributions to x-ray scattering amplitudes, and circular polarization in the primary beam of x-rays is rotated. We illustrate stark differences between our four templates and those of a (PT)-symmetric antiferromagnet (CuMnAs).

We investigate the transport properties of a quantum dot coupled to leads interacting with a multispin system using the generalized master equation within the Coulomb blockade regime. We find that if two states for each scattering region electron manifold are included, several signatures of the interacting spin system appear in steady-state transport properties. We provide a theoretical mapping of differential conductance peak signatures and all spin Hamiltonian parameters related to the inclusion of excited state transitions between uncharged and charged electron manifolds. Our predictions describe a scheme of only using a quantum dot and differential conductance to measure magnetic anisotropy, interspin exchange coupling, exchange coupling between the spin system and itinerant electron, and applied magnetic field response.

Using first-principles quantum-transport calculations, we investigate spin-dependent electronic and transport properties of antiferromagnetic tunnel junctions (AFMTJs) that consist of (110)-oriented antiferromagnetic (AFM) metal $\mathrm{Ru}{\mathrm{O}}_2$ electrodes and an insulating $\mathrm{Ti}{\mathrm{O}}_2$ tunneling barrier. We predict the emergence of a giant tunneling magnetoresistance (TMR) effect in a wide energy window, a series of barrier layer thicknesses, and different interface terminations, indicating the robustness of this effect. We show that the predicted TMR cannot be explained in terms of the global transport spin-polarization of $\mathrm{Ru}{\mathrm{O}}_2$ (110) but is well understood based on matching the momentum-dependent spin-polarized conduction channels of the two $\mathrm{Ru}{\mathrm{O}}_2$ (110) electrodes. We predict oscillations of TMR with increasing barrier thickness, indicating a non-negligible contribution from the perfectly epitaxial interfaces. Our work helps the understanding of the physics of TMR in AFMTJs and aids in realizing efficient AFM spintronic devices.